Banana skins is a feature in every issue of the EMC & Compliance Journal. If you have any interesting contributions that you would like included please send them to the Editor
This is a compendium of all the “Banana Skins” that have been published up to and including the May 2004 issue of the EMC & Compliance Journal.
“Banana Skins” is a regular feature in the EMC Compliance Journal (published by Nutwood UK Ltd and available on-line at: www.compliance-club.com) and briefly describes reports of electrical/electromagnetic interference.
Some Banana Skin items are personal anecdotes, some come from research, and some are extracted from official documents and reports. Some of these interference incidents had harmless or even amusing results, some lost companies significant amounts of time and/or money, and some resulted (or could have resulted) in injury or death.
I hope that it helps you to identify interference problems that could happen to your designs, so that you deal with them in advance as part of the normal design/development procedure and don’t have the embarrassment and cost of trying to correct poor EMC design after products have been shipped or systems installed. Designing EMC in from the first saves time and cost, reduces customer returns and warranty costs, and reduces the possibility of liability claims.
If you have any suitable anecdotes or know of any relevant research or reports, please tell us about them.
1. To cope with increased North Sea oil production, two new pumping stations with 6 MW adjustable speed induction motor drives were built and installed in Scotland, one in Netherly and one in Balbeggie. Soon after commissioning the local power utility and the telephone company received a flood of complaints. Geographically the complaints came from concentrated pockets spread over an area up to 12.5 miles away from the 33 kV overhead supply lines feeding the drives. A payphone over 4 miles away from the power line was noisy enough to be almost unusable, whereas just across the street a householder's telephone was relatively unaffected. Other symptoms included loss of synchronisation on TV sets (rolling pictures) and ringing on the supply to fluorescent lighting circuits. Although the drives had been designed to, and met the supply industry's G5/3 harmonic limits, the problems turned out to be with higher order harmonics than it covered, up to the 100th in fact (i.e. 5 kHz). The problem became a public relations nightmare for all involved, and culminated in questions being raised at Government level. Remedial EMC work was urgently required and was in fact accomplished, although under extreme difficulties because the cost of any downtime of the oil pumping stations was so high. (From a paper by M J V Wimshurst of Hill Graham Controls, High Wycombe and Allan Ludbrook of Ludbrook and Associates, Ontario, Canada.)
2. A (CE marked) portable PC carried up the stairs in a domestic household whilst operating, reliably caused the "power shower" in the bathroom to turn itself off if it was in use at the time. (Personal communication in 1997)
3. Medical technicians taking a heart-attack victim to the hospital in 1992 attached her to a monitor/defibrillator. Unfortunately, the heart machine shut down every time the technicians turned on their radio transmitter to ask for advice, and as a result the woman died. Analysis showed that the monitor unit had been exposed to exceptionally high fields because the ambulance roof had been changed from metal to fibreglass and fitted with a long-range radio antenna. The reduced shielding from the vehicle combined with the strong radiated signal proved to be too much for the equipment. (An article in the Wall Street Journal reported in Compliance Engineering Magazine's European edition September/October 1994.)
4. Computers used in a room close to a door fitted with a high-technology (magnetic) cat flap caused the latches on the cat flaps to rattle continuously whenever Windows was loaded or a Windows application run. (From the New Scientist magazine, 7th May 1997)
5. The Langley (USA) Air Force Base Rescue Co-ordination Centre reported that its search and rescue satellite was receiving interference on its 121.5 and 243 MHz distress frequencies. The area over which interference was a problem was around 8 square miles, which was significant because normal emergency transmitters on these frequencies can only be detected at ground level for about one mile. The problem was eventually traced to poor connections on an overhead power line. (From an FCC Field Operations Bureau news release, 1994.)
6. An advertisement for engineers for "The HERO Project" quoted Rear Admiral Roland T Guilbalt, Deputy Director, Electronic Warfare Division US Navy as saying that both Desert Shield and Desert Storm suffered from serious and significant EMI problems. We have no more information on this at present, but presume it was due to the very heavy use of high-tech civilian equipment used for the first time in a military situation. (From EMC Technology magazine, 1993.)
7. Excessive mains harmonics in the London area, due mainly to the rapidly increasing use of personal computers, are causing overheating problem in AC power cables (including those that run under the Thames). In the offices where the computers are, it is increasingly common for the power-factor correction capacitors normally fitted to fluorescent lamps to blow (the electricians usually just remove the blown capacitors). Damaged and overheated neutrals, and damaged electrical switchgear is increasingly seen as a result of harmonic mains pollution. In the US, fire insurance companies are being urged not to take on any new policies unless they have had the size of the neutral cables in the company concerned checked for their adequacy for the heating effects of harmonic currents. (Personal communications, January 1998)
8. Hartman Products of Los Angeles, California, has agreed to pay a civil penalty of $60,000 to settle allegations that it failed to file a report regarding a defect in the 1992 Hartman Pro1600 hair dryer. The CPSC (a US consumer safety agency) believes that these hair dryers can turn themselves on even when the on/off switch is in the "off" position. While the dryers' heaters start, their fans do not, potentially causing internal components to overheat and cause fires. (Compliance Engineering May/June 97)
9. The AA and RAC estimate that around 9000 breakdowns they attended in 1996 were the result of remote key fobs being blocked by RFI. An AA spokesman said: "The number of cars being produced with radio-activated keys is standard now. If we're getting 9000 now, what will the problem be like later on?". (Electronics Times 13th Oct. 1997)
10. We recently bought what looked like a fine new idea for an executive toy. It consisted of a very strong magnetic base with lots of ball bearings attracted to it, which it was possible to form into beautiful sculptures. What we did not realise at the time is that magnets and office desks are not cheerful companions. But we soon found this out when the discs with our accounts on them were mysteriously wiped, and the monitor screen went all the colours of the rainbow. It is now only possible to use our office desk toy when not at our desks, and well away from the office. (Letter from Michael Fell in 29 November 97 issue of New Scientist.)
11. Wheelchairs have come in for special scrutiny by the FDA (the US Food and Drug Agency). A few months ago, the agency ordered makers of wheelchairs to shield them and to educate users about the potential hazards of interference. The FDA acted after receiving "many reports of erratic unintentional powered wheelchair movements." These included sudden starts that caused wheelchairs to drive off curbs and piers when nearby police fire of CB transmitters were activated. Miraculously, no fatal injuries have been reported. (But broken limbs have occurred as a result of such interference - editor.) (Compliance Engineering - European Edition September/October 1994)
12. Around 1990 Alan Little leased a derelict arch under the railway line in Camberwell from British Rail. He borrowed money to convert it into a two-level mix of recording and rehearsal studios. The total cost was pushing £50,000. Up until November 1991 it was popular with up-and-coming bands needing somewhere to rehearse and record. Then, one fateful Saturday morning, with three bands booked for the morning and three for the afternoon, disaster struck. All the studio equipment, and the bands' amplifiers, started warbling. The bands and studio crew thought at first that they had an equipment fault. Then other studios in other railway arches in the area began phoning each other. They all had the same problem. Alan Little phoned British Rail and on the Monday morning a BR engineer came round, listened and said the cause was a new signalling system installed by BR.
BR controls its track lights by feeding electric current through its rails. When a train runs over the rails it provides a short-circuit between them, triggering a red light behind the train. Recently BR has begun changing to the use of alternating current. The long rails act as a highly efficient aerial, radiating a powerful AC magnetic field (this was actually around 1 Amp/metre over much of the studio - editor). The AC is at audio frequency, using tones of between 1 kHz and 4 kHz. The tones are complex warbles, to safeguard the system from outside interference.
The effect was heard through the mixing desk, with pick-up from mains and connecting leads. It was even heard through unpowered loudspeakers (even when they were disconnected from their cables and their terminals shorted - editor). It was worst when an electric guitar is plugged into an amplifier. Guitar pick-ups are designed to convert their magnetic fields, modulated by the movement of the steel guitar strings, into sound. They cannot distinguish between magnetic fields from a BR signalling system and those from vibrating strings. (Extracted from an article by Barry Fox in Studio Sound Magazine, June 1992)
13. It was reported in the Sunday Times (15/2/98) and New Scientist (7/3/98) that Sabena Belgian World Airlines had installed magnetic tray tables in its new fleet of A340 Airbuses, to prevent the nuisance of rattling trays on their flights, but that these tray tables were apt to cause loss of data on PC hard disc drives. New Scientist of 28 March reported that the story was untrue, but that tables of this sort had been discovered on a train from Frankfurt to Berlin. The conclusion seems to be that if you intend to use your PC in any kind of vehicle you should always carry a (steel!) paper clip and use it to check for magnetised tables.
14. Quote from an article in the IEE’s Control and Computing Journal, April 1998 (page 52): “High intensity radiated fields (HIRF) guns and electromagnetic pulse transformer (EMPT) bombs are already easy to build from off-the-shelf components. The effects of even hand-built HIRF or EMPT weapons can damage microprocessors at ranges of hundreds of metres. Possibly, in a few years, a van equipped with suitable electronics could cruise down Wall Street (or through Canary Wharf - ed.) and disrupt the information processing capability of thousands of computers without being detected by the local police.”
15. More on radio activated key lock-out problems (banana skin No. 9 from the April issue of EMCJ): a quote from an Electronic Times article (29/9/97) says: “Most radio activated key-entry systems have a manual override. Unlocking the door can be as simple as inserting the mechanical key into the lock and trying the lock according to the instructions printed in the car manual.” The trouble with this advice is that the manual will usually be locked inside the car (or are we supposed to carry it around with us at all times?).
16. More medical incidents:
The magnetic field caused by ground currents in a water pipe system made it impossible to use sensitive electronic instruments in part of a hospital.
A patient-coupled infusion pump was damaged by an electrostatic discharge, but thankfully the alarm system was not affected and a nurse was alerted.
An operation using a plastic welding machine caused interference with a patient monitoring and control system, causing failure to detect that the circulation had stopped in a patient’s arm, which later had to be amputated. (Taken from Compliance Engineering European Edition March/April 1998)
17. At 1:23 pm on Sunday, 24th July 1994 there was an explosion at the Texaco Refinery, Milford Haven. Its force was equivalent to 4 tonnes of high explosive and it started fires that took over two days to put out. Shops in Milford Haven 3km away had their windows blown in. 26 people sustained minor injuries, and the fact that it was Sunday lunchtime and the site was only partially occupied meant it could have been very much worse. Damage to the plant was substantial. Rebuilding costs were estimated at £48 million. There was also a severe loss of production from the plant – enough to significantly affect UK refining capacity. The incident was initiated by an electrical storm between 7:49 and 8:30 am on the Sunday morning, which caused a variety of electrical and other disturbances across the whole site. (IEE Computing and Control Engineering Journal April 1998 pp 57 - 60). There is an HSE report on this incident: “The explosions and fires at Texaco Refinery, Milford Haven, 24th July 1994” HSE Books, May 1997.
Comments: The author has not read the HSE report, but understands from private conversations with HSE experts that the large explosion was caused by the electrical storm giving rise to power surges which tripped out a number of pump motors whilst leaving others running. As there was a great deal of panic and confusion due to the information overload caused by the numerous small fires and equipment outages from the time of the storm, it was not noticed that flammable substances which should have been flared off were accumulating in pipework and vessels. After five hours something ignited the total accumulation, resulting in the large explosion.
The general incidence of surges in the UK’s AC power distribution network is quite low, and this often leads people to believe that qualifying the power surge immunity of their products, systems, or installations is not important. This belief is often supported by the observation that neither of the generic immunity EMC standards included surge testing in their normative sections. But it only takes a single incident such as the above in the lifetime of even a very large plant to make an excellent economic case for a proper preventative strategy. Suitable basic test standards include IEC 61000-4-5 or IEC 61000-4-12 (ring wave), both of which are intended to simulate the indirect effects of electrical storms on power networks.
Engineers are always under pressure to save costs, and the costs of preventative measures are easy to quantify. However, many engineers are uncomfortable with estimating the risks of infrequent and unpredictable events such as thunderstorms so do not effectively communicate the actual risk/cost and safety implications to their managers.
As someone said recently: Doctors kill people in ones, but engineers do it in hundreds. Careers and personal liability are also at stake here too, so it is always best to make an informed cost/risk case and get a written decision from management. There is no shortage of advice and assistance on this sort of thing – sources include:
The Institute of Risk Management:
phone 0171 709 9808, fax 0171 709 0716, or visit IRMG@aol.com
The Hazards Forum:
The Safety and Reliability Society:
The British Safety Council:
Health and Safety Executive:
Infoline: 0541 545 500, fax 0114 289 2333,
or HSE Books:
phone 01787 88 11 65, fax 01787 313 995, or visit www.open.gov.uk/hse/hsehome.htl
The IEE Library:
IEE Publication Sales Helpline:
The Engineering Council:
18. A very powerful ±8,000 Amps DC drive was recently purchased and installed in an industrial plant. It was contractually agreed that it would meet and be declared compliant to the EMC Directive. A control room was also required (like most modern control rooms it was full of PCs and CRT-based VDUs) and the drive manufacturer said that it could be installed near their drive cabinets. When the drive was operated the images on the VDUs were squashed into 50% or less of the screen width. It was possible to tell the direction and loading of the drive directly from the movement of the VDU images, which of course were completely unreadable. The magnetic fields caused by the drive were of the order of 235mT, and most CRT-based VDUs show image movement at greater than 1mT (1mT is approximately equal to 0.8 Amp/metre and to 10 milligauss).
The drive manufacturer claimed that his drive did meet the EMC Directive despite the fact that it caused interference with the control room VDUs. What they in fact meant was that it met the industrial generic standards, which do not include any limits for low frequency magnetic field emissions. They forgot that their EMC Declaration of Conformity binds them to not causing interference of any kind, and that compliance with a harmonised standard only gives a presumption of conformity.
The situation has been remedied by the use of LCD screens, which have only recently been available with a specification suitable for the SCADA system that was used. "Dog kennel" magnetic shields and active field cancellation devices were also investigated. The delay in the use of the control room was several months, and this had an impact on productivity far beyond the cost of the remedial measures.
19. We've learned to live with the condition that if we get up in the middle of the night to use the bathroom, when we turn the light on the fan timer starts. The fan will keep running for twenty minutes, and when it turns off it causes interference that turns on the outside security light (infra-red triggered 500W halogen) which then runs for its time period (15 minutes) whilst shining through the bedroom window.
Now you'll have difficulty believing this bit... Monty Python eat your heart out... before the 500W halogen lamp we had a high pressure sodium lamp with an inductive ballast. When this switched off it would cause interference, which would sometimes start the bedside radio. So the scenario was this...
Get up at 2:00 am, go to bathroom, turn on light, turn off light, go back to bed, and after twenty minutes a bright light would shine through the window and wake you up. If you slept through that (or went back to sleep), fifteen minutes later when the light switched off the radio would start, and then you would wake again.
The moral of this story? If you have bad EMC immunity make sure you use the bathroom before you go to sleep. (From Chris Dupres via email@example.com, 8/7/98)
20. While taking classes in the early 80's, my prof got involved with a terrible incident down in New Jersey. Seems a hospital had a high incidence of infant deaths in the intensive care section of the maternity ward. Late at night, the alarms on the babies' monitors would go off for no apparent reason. Annoyed, the nurses would turn them off and do the rounds on foot.
After some preliminary investigations, my prof found out that a nearby TV transmitter was allowed by their FCC license to increase their output wattage by some enormous amount after say midnight but had to reduce it prior to 6am, or some such arrangement. The cable interconnecting the nurses’ station to the various baby monitors sang like a lark with these frequencies and set off alarms with the induced voltages. Not sure now of all the specifics except what I have related above, nor the name of the hospital, but they lost something like 6 kids before fixing it. (From Doug Mckean, via firstname.lastname@example.org, 29/7/98)
21. Undervoltage AC supplies (brown-outs) are common in underdeveloped countries, or where the AC supply network is incorrectly configured. Parts of Spain are known to experience around 150Vac for lengthy periods during the day, apparently due to network loading, despite an officially specified mains supply of 230Vac ±6%. I had never experienced a brown-out in the UK, except maybe for a second or so prior to a complete supply failure during a thunderstorm, and I used to think that it must not be possible because of the way the supply network is operated here.
On Sunday 26/7/98 around 5pm in Denshaw village the supply dropped to around 140VacRMS (40% below nominal), and stayed at that level for about three hours before shutting down completely as the engineers arrived to fix the problem. We switched off our fridge and other motor-driven appliances, mainly because they were making very strange noises. Our computers kept running, but the CRT screens blanked, making us concerned about what was happening to our data, so we switched them all off as well.
I am aware of electronic control equipment that can misoperate when operated considerably outside its specified AC supply range, and also understand that undervoltages can damage coils and motors. Apparently the motors can stall due to the low voltage, so they don't generate back-emf, so they draw excessive currents and overheat, damaging their insulation and suffering premature failure (if not electric shocks and fires).
Manufacturers of products for the developed world, and their safety test laboratories, usually do not test at supply voltages outside ±10% (sometimes ±15%). Until Sunday 26th July I had not thought this important. So far we have not discovered any damage to appliances or to data. (From Keith Armstrong, Cherry Clough Consultants)
22. There was film footage on TV some years ago of a British in-flight re-fuelling exercise where the tanker aircraft was hit by lightning, but there was no on-going discharge downwards, the implication being that the plane was left charged to 100kV - 1MV or whatever. A few seconds later great balls of glowing gas came off the back of the fuselage and wing tips (where the fuel hose was) into the slip stream, presumably taking away a whole load of surplus electrons, or holes - whatever it was - as "ball lightning". (from Chris Dupres via emc-pstc) Incidentally, New Scientist magazine recently reported that a theoretical basis for ball lightning may have been found.
23. Helicopter blades and bodies tribocharge as they swish through the air, and they don't have a convenient green/yellow wire handy. There are reports of an oil rig computer system crashing whenever a helicopter landed, due to its sudden electrical discharge into the metal decking, and there is a film which shows a crew-member getting an awful shock when he reached up to touch the skids of a hovering helicopter.
Here is another item from Chris Dupres via emc-pstc: A US Coastguard Chief related to me that he had seen "arcs as bright as a welding stick" when an emergency pump was delivered to the deck of a freighter one night. He also told me that the Coast Guards' standards practice calls for NEVER lowering a flotation ring or sling to a person in the water; the person will automatically reach for the line! Instead, they dip the line into the water and drag it to the person.
24. Crane incidents... A new CNC machine being installed in a factory had a spindle controller, which was a small invertor drive in a plastic case. When the spindle was first operated emissions from the invertor caused the overhead travelling crane to start up and drag its chains down the length of the factory. Luckily, the 18 ton casting the chains had been attached to had just that minute been released. (from Phil Hampton)
25. There was the famous case reported by the DTI in the early days of their EMC Awareness Campaign of the guy who was standing under his crane's load using his radio-control pendant when interference caused it to release its load, crushing him to death. Many recent crane incidents are due to the use of radio control, especially where crane radio-control systems share the same frequency bands as amateur radio and/or car radio-keyfobs. The soon-to-be-introduced TETRA system also shares some of these bands, and use 25W transmitters - so expect more wild cranes.
Just to prove that modern technology can't teach old technology any interference lessons, I once worked for a company that I was told had made the controls and drives for the first large-scale hovercraft testing tank in the late 1960's. It was in effect a sophisticated travelling overhead crane, which ran a gantry along overhead rails and towed a hovercraft shape along a large pool of water in an even larger building. In those days they used resistor-transistor logic, which ran on a 40V rail to provide noise immunity. During commissioning the machine suddenly started up by itself and proceeded towards the far end of the pool - it had been set off by "some sort of mains transient". All the personnel on the site were standing by the access ladder to its gantry, but the only emergency stop button was on the gantry - but it and its ladder were moving just faster than running speed and they couldn't get to it. Since it was not operating according to its (hard-wired) programming, the crane ignored its limit switches and crashed clear through the end wall of the building. Luckily nobody was hurt. The next version had E-stops all around the building. (From Keith Armstrong)
26. A foetal heart monitor in a clinic in the UK in June 1998 picked up a cellphone conversation from elsewhere on the premises quite clearly. The visual output of the monitor was unaffected, but the staff tend to use the audio output, and the cellphone conversation was so loud that it swamped the heart signal they were listening for. It must have been an analogue cellphone, and it must have been getting in via the audio stages, or else the visual output would have been distorted. Even slow opamps will demodulate 900MHz signals (as hearing aid wearers are only too aware!). In common with many healthcare promises, the use of cellphones on the premises was banned, but you can't rely on people to read or follow signs. (from Ian Ball)
27. A 40kW RF welder (a dielectric welder for plastic materials) in use in a factory caused a mattress in a bed manufacturer's factory 60 yards away to catch alight. The bed springs must have just been the right length to make an efficient antenna at the frequency the welder was using.
28. GPS is another example of an advanced technology that everyone wants to use, but which has important susceptibility problems. The signals from the GPS satellites are very weak, so the receivers have to be correspondingly sensitive, which means they are readily swamped by interference from industrial sites. Even though they are at microwave frequencies, interference with satellite communications caused by such commonplace things as poor quality power line connections has been observed several times. Added to this, the need to “see” several satellites at once means that GPS is unreliable in the urban canyons of cities.
I was intrigued to see two items on GPS in the New Scientist magazine dated 10th January 1998. The first was an article about the concern of the US military about a Russian GPS jammer. With only 4W of power (about the same as a hand-held CB or security guard walkie-talkie) this device is claimed to prevent GPS systems from working over a 200km radius (yes, 200 kilometres!). Apparently any competent electronic engineer could build such devices from readily available components. The second item in the same issue was an advertisement from BT for their MoBIC mobility system for blind people. This uses a computerised map, speech simulator, and GPS to guide blind people to their destination. Quote: “Getting around the shops is much easier since I started using the US Military’s Satellite Guidance System.”
Designers building GPS into their products, especially where these are used for critical purposes, might like to consider the lack of robustness and ease of jamming of this system. I have visions of hordes of planes, cars, and pedestrians all milling around a factory until a certain machine is switched off, because their satellite navigation systems are blocked by its microwave noise. (From Keith Armstrong of Cherry Clough Consultants)
29. Digital TV is more likely not to deliver a programme to the viewer than the analogue TV services it replaces. It appears that this newer technology is less robust, and that its users will on average suffer a higher loss of service than they may have become used to.
Broadcast digital TV, which can be picked up with existing TV antennae, has a sharper cut-off in performance as signal strength declines. R.S.Sandell, a Fellow of the IEE writing in IEE Review November 98, is concerned that: “Whereas analogue viewers can live reluctantly with a picture that has to be viewed through varying angles of ‘venetian blind’ and alternating densities of ‘boiling porridge’, they can still follow the programme plot for most of the time. This dubious advantage may not be available for some members of the digital generation, who will be confronted by a blank screen. In particularly unfortunate reception location this condition may come and go with time as field strengths vacillate”. Viewers using indoor aerials (the TV with the rabbit ear antenna in the kid’s bedroom?) may find they need to invest in new external aerials or aerial amplifiers and splitters.
Satellite-delivered digital TV is very susceptible to lightning storms, both at the uplink and downlink ends. This leads to the odd situation, when watching digital satellite TV in South Africa during very fine clear weather that thunderstorms near the uplink in Europe can cause all 100 channels (or however many there are) to disappear all together for periods of several minutes. This phenomenon was well understood by the satellite broadcasters, who broadcast a little presentation on this topic every now and again. (From Keith Armstrong of Cherry Clough Consultants)
30. Interference in the Amateur Radio 144MHz band traced to an ultrasonic rodent repeller. (Brad Thomson, Editor of Test and Measurement World, Feb 95)
31. The operation of a domestic appliance used to reset a surround-sound processor, causing a ½ second gap in the audio (From Neil Gardner, Plantronics, August 98)
32. An advanced hi-fi system would change input selection due to taxicab radio transmitters when they called at a public house 100yards away. (From a Technical Director of Lumonics, 1996).
33. A Tissot Two-Timer digital/analogue wrist-watch went into time-travel mode (about x 60) whenever a particular Motorola Micro-Tac portable phone nearby had someone actually speaking into the mouthpiece. (Chris Duprés, 7/7/98. It was his watch!)
34. With over 18 years in EMC I could go on listing interference incidents for a long time. Some examples this year already: My computer (FCC Class B) interferes with my cordless phones, to some degree on all 10 channels. My fax machine (FCC Class B) interferes with my TV and some channels of my cordless phones. My garbage disposal unit interfered with everything! My small personal fan destroys my monitor picture. (From Derek at LF Research, 6th July 98)
35. Domestic microwave ovens can activate the microwave security sensors fitted to some vehicles. (From Terry Beadman, MIRA, 6th November 1998).
36. The Canadian Centre for Marine Communications claim there is evidence that EMI may have contributed to two boat capsizes, via autopilot malfunctions. One was the 16metre fishing vessel the “Dalewood Provider” on August 17 1989, the other was the 64 tons “Martin N” on April 25th 1987. In the latter case three lives were lost. In both cases the concern is that the on-board VHF radiotelephone system interfered with the autopilot sufficiently to turn the rudder hard over. Staff at the Centre report that erratic alterations in a boat’s course when autopilot is engaged and VHF radio used is commonplace, generally due to insufficient EMI suppression at the autopilot’s interface and control cables. (From an article in EMC Technology magazine)
37. The HSE recently prosecuted the supplier of an item of equipment, which led to a release of chlorine in a semiconductor plant. The equipment was not sufficiently immune to mains transients (and proven to be so by our own labs). We prosecuted under section 6 of the Health and Safety at Work Act because the supplier, though aware of the problem, did not inform the users of the equipment. The company pleaded guilty. (From Simon Brown of the HSE, 13th January 1999)
38. The Therapeutic Goods Administration of Australia (TGA) continues to review findings of clinical and laboratory research indicating a potential for temporary interaction or interference between mobile phones and the operation of pacemakers and implantable defibrillators. The findings have indicated that interference may be caused by holding the phone within about 150mm of the implanted device, or in direct contact between the phone antenna and the user's skin. Interference can occur with the phone in standby mode, as well as in use. Some phones incorporate magnets, at least in their loudspeakers, and while held close to the implanted device these can cause them to go into their "magnet" mode, which for a pacemaker is a fixed pace. Based on the most recent testing, simply moving the phone away from the implanted devices will return it to its correct state of operation (editors note: presumably they don't yet use microprocessors in implanted devices). Recommendations for users of implanted pacemakers or defibrillators include: not keeping the phone in a pocket over the site of an implant; using the ear that is furthest away from the site of the implant when using the phone; and not allowing the phone antenna to touch any part of the body. (From Compliance Engineering's European edition Jan/Feb 1998)
39. There is a story of how something was causing havoc with the emergency services two-way radio communications in Nevada, i.e. police, fire, and ambulances. An exhaustive investigation led to one or more really noisy pinball machines at a roadside pub (editors note: I thought they had bars in Nevada instead of pubs). The owner was ordered to get rid of them. He got rid of them and the problem went away. However, it soon reappeared, as another pub owner wound up with the same machines. (From George Alspaugh of Lexmark International, 7th July 1998. )
40. I have a security floodlamp system for my backyard, equipped with a thermal motion sensor. I have found that I have a reliable, though unintentional, remote control capability simply by flicking the kitchen range fan on and off a couple of times. I told my wife that it's a special purpose, hard-wired, digital controller. (From Ed Price of Cubic Defense Systems, San Diego, 8th July 1998.)
41. Eurostar and Railtrack officials admitted this week the threat of EMI causing signal failures is delaying the introduction of European rail services north of London. EMI generated by overhead power lines can affect the trackside signals such that red lights are forced to green. A Eurostar spokesperson said: "In electrical terms, we have found with new trains, such as Eurostar, there tends to be a degree of stray electrical current. This can cause an interference with signalling and effect the integrity cause a signal to go from red to green." Railtrack, responsible for the track and signalling systems, is refusing to allow the trains to run commercially until Eurostar can demonstrate their safety. "We are working hand-in-hand with to solve this problem as quickly as possible," Railtrack said. Eurostar engineers have designed an interference current monitoring unit. When it senses EMI, the motor is stopped and the train coasts to a stop. However, for the highest safety the unit must be set to maximum sensitivity. This could cause the train to stop every few miles. (From Electronics Weekly October 23rd 1996) (Editors note: has anybody seen a Eurostar north of Watford Junction yet? How much has this cost our national economy, especially northern companies? I understand that all Eurostar trains have had TCFs done for them under the EMC Directive and that traditionally both British Rail and Railtrack always imposed stringent EMC immunity standards on their signalling equipment, using the RIA series of standards.)
42. There are a number of railway trains which have been unable to be taken into service because they interfere with signalling. (From Ray Garner of Datel Defence Ltd, November 98, quoting an earlier article in a national newspaper.)
43. A 1.5 MW induction furnace controlled in on/off time-proportioning mode (using large contactors to switch the current) interfered with the computers in a Marks and Spencers store half a mile away. (From Laidler Associates Consulting Services, June 1998)
44. A new large turbogenerator in a UK power station was designed to have its 20kA three-phase output busbars split either side of one of its support pillars, because of a lack of space. The support pillars were steel, part of a steel framework, and created a single-shorted turn around one of the busbars. In operation, the pillar (made of 2 inch thick steel members) got hot enough to blister its paint, and increased in height by 5mm, putting a bearing out of alignment and causing a terrific noise which caused the station workers to run for their lives. (editors note: a large turbogenerator up to speed and adrift from its bearings is a fearsome object!) The cure was another shorted turn, this time around the pillar and made of half inch thick aluminium. (Conversation at Mersey and District Club Europeen, 28th January 1999)
45. Further information on No. 37: The case referred to was the prosecution of Fluid Systems International (t/a Cambridge Fluid Systems) at Swindon Magistrates Court on November 25th 1998. The defendant entered a plea of guilty to a charge brought under S6 (1) (d) of the Health & Safety at work etc. act , 1974. The magistrates imposed a fine of £5,000 and made an order for the defendants to contribute £7,000 towards HSE's costs of £9,482. The case concerned a microprocessor based valve control panel used to control the flows of chlorine and nitrogen in a semiconductor plant. There had been a release of chlorine resulting from all of the valves in the control cabinet being set to an open position. Investigation by the HSE found that the unit was susceptible to conducted transients on the mains supply. There were no precautions against electrical interference in the power supply and the microprocessor watchdog was not effective in ensuring a safe state following detection of a fault. The HSE inspector who dealt with this case was Eifion Davies in our Cardiff office. (From Simon Brown of the HSE, 3rd March 1999)
46. Scenario: Large open-plan office in a publishing company. Lots of eager beavers with 21 inch displays on their MACs, doing all sorts of clever graphics things for page make-up and other arcane processes.
Problem: The displays on only some of the monitors oscillate sideways about 0.5 mm at most, at about 1 Hz.
Diagnosis (partial): The combined magnetic fields of mains cables under the floor and a power transformer on the floor below are sufficient to cause this very small effect. Unfortunately, once you notice it, it keeps catching your eye and it eventually drives you mad! The 1 Hz is due to a beat between the third harmonic of 50 Hz and the second harmonic of the 75 Hz frame rate of the displays.
Solution: Move the transformer. Replace the large feeder cable to it by individual lower-current feeds to the loads served from it, spread out across the void below the office floor.
Continuing problem: Now that the sideways movement has been eliminated, an even more subtle "vertical" movement of the displays is discovered. Again, it's difficult to see, but once you see it, you can't ignore it. This effect is not continuous: it occurs for a few minutes and then disappears for about ten minutes or more.
Diagnosis: An air-conditioning unit is found to have an intermittent fault to earth, resulting in some 3 A flowing in the armour of the cable feeding it. This current is not balanced by currents flowing in the conductors of the cable, and creates a 50 Hz magnetic field with a horizontal component sufficient to cause the effect.
Solution: By turning a monitor through a right-angle, so that the strong horizontal component of the field is parallel to the electron gun axis, the movement disappears. However, it is obviously necessary to correct the potentially hazardous fault in the air-conditioner. The main point here is that the tolerable amount of display movement is "very small indeed" when people are working on complex artworks on large-screen displays. (from John Woodgate, 8th March 1999)
47. "When I was a lad"... reminiscences from Keith Wilson: The relaxed attitudes of those times did not always pay off, however. Slightly later in my career, I moved to a company where engineering standards were, let’s put it politely, a little lacking. For example, interlocking between contactors in reversing pairs was considered an unnecessary expense, and no one would ever consider such niceties as interrupting capacity when selecting a fuse. If the current rating was right, the fuse was good enough for the job. The error of these ways wasn't long in revealing itself, however. In one mechanical handling job, we had around a dozen reversing starters, all protected with totally inadequate fuses. Even worse, the contactors were controlled by some very dodgy solid-state switches, which had been "designed" in-house. Now, in those days, EMC hadn't even been invented. The result was that even the slightest spike on the supply made these solid-state switches turn on - just for an instant - but long enough for all of the contactors to jitter. Frequently, both contactors in a reversing pair would close for an instant, placing a short-circuit across the supply. This meant a mighty bang as the inadequate fuses shattered and spilled their silica contents all over the floor of the enclosure. After a lot of time on site, during which much wiring was re-arranged and many capacitors were added to the system, we managed to get the equipment working after a fashion but, ever since, I've been suspicious of control panels with a layer of silica sand in the bottom! (Taken from Panel Building Magazine, February 1999, page 17)
48. I was testing an item of IT based instrumentation the other day that failed conducted emissions. We replaced its 3 metre long screened 25-way D-type lead, which had been purchased as a "fully screened cable" from a well-known distributor, with my own home-made 15 metre long 25-way D-type lead, which simply used a single braid cable and metallised plastic backshells. The conducted emissions problem (on the mains lead) went away. My customer is now trying to source cables which really are screened. So caveat emptor, even when buying from large distributors. (From Ian Ball of A. D. Compliance Services Ltd, which used to be Dedicated Micros EMC Test Centre.)
These four real-life cases all show that a failure to correctly appreciate EMC can lead to serious financial problems. They have been extracted from the paper "The real engineering need for EMC" by John Whaley, General Manager of SGS International Electrical Approvals (UK).
49. Failure to correctly specify EMC performance. A large manufacturer of industrial fasteners, negotiating with a major customer, agreed to install a packaging cell containing an automatic weighing machine, which filled plastic packets with fasteners and an RF welding machine to seal the packets. For cost reasons the two machines were purchased separately. No assessment of the electromagnetic environment took place, and the machine contract specifications included no EMC requirements other than "shall meet all legal requirements".
Both machines were supplied, installed, and tested successfully. Unfortunately when both were operated together the weighing machine suffered >25 % errors due to interference from the RF used by the welder (not an uncommon problem). In an 8 hour shift the cell should have packaged £20,000 of fasteners, but could have given away up to £4,000 of product in incorrect weights.
There was no comeback on the machine suppliers, whose products met specification. Both suppliers appeared willing to help, but when pressed blamed each other. Expert technical assistance was brought in and solved the problem. The fastening manufacturer lost 6 weeks production, suffered additional costs, and lost credibility with their major customer.
50. Over-specification of EMC. A manufacturer of AC inverters won the contract for a large project against stiff competition, but didn't notice that the specification required meeting military EMC standards. Their normal inverter designs failed the EMC tests, and the customer refused them. Not having experience in military EMC, time and effort was wasted only to find that the redesigned inverters would not meet functional specifications.
The inverter manufacturer went out of business, and their customer's production was delayed leading to loss of both revenue and market credibility. The customer should have correctly assessed the electromagnetic environment of his product, when he would have realised that military EMC standards far exceeded what he really needed.
51. A cost reduction exercise that didn't. A manufacturer produced high-quality industrial equipment sold throughout the world. New management thought that poor financial performance was because their products cost too much to make, so began a cost reduction exercise that included employing a production engineer to make design changes.
The designers had been using historically-generated design rules to give their products their famous reliability. These included EMC protection developed over many years of reacting to interference problems in the field. The design departments had no real understanding of EMC, did not realise what protection was lost by the changes, and were unable to suggest cost-effective alternatives.
A number of machines were built to the new design, and with a new price structure sold well in the UK and particularly well in the USA. Unfortunately the product was unreliable due to poor immunity to real-life electromagnetic environments. The consequences included one customer rejecting a product, and the basing of a commissioning engineer in the USA for over one year, as well as loss of product reputation.
Reducing company profitability by employing cost-reduction techniques is not uncommon. Cost-effectiveness techniques should be used instead, taking account of all the consequences of change. In this case the history of the product should have made it clear that EMC expertise was required.
52. Mistakes with a cabling installation. A major manufacturer of automotive parts commissioned a series of robot controlled paint booths with a total project cost of over £2 million, and correctly specified their EMC performance. The successful supplier agreed to meet these EMC requirements, and accepted financial penalties in case of non-delivery. To save costs, it was agreed that the supplier would install his paint booths but the user would arrange for their cabling to be installed by local contractors.
When installed, the paint booths suffered apparently unconnected (and sometimes dangerous) faults and the user would not accept them. Investigations by both the user's and supplier's staff could not identify the problems. The user had problems meeting his production deadlines and had to employ extra painters, while the supplier started to incur financial penalties for late delivery. An independent consultancy quickly identified that the screens of all the interconnecting cables had been terminated in a daisy chain to a local earth (which was not the equipment earth), allowing interference with the control electronics.
The supplier normally used its own trained installation staff to install its products, and had no written instructions on the correct termination of the screened cables. Unfortunately there was no easy answer and 80% of the cables had to be replaced (using the correct
Costs to the Customer
Cost to the Manufacturer
Loss of production
Financial penalties under the contract
Extra painting staff costs
Additional costs of investigation (staff)
Additional costs of investigation (own staff plus independent
Additional re-wiring Costs
Loss of customer’s confidence
The legal arguments about who was at fault continued for some time, but the lack of cable installation instructions from the paint booth supplier was the determining factor. Arguments that his staff normally installed his equipment were discounted, as he had agreed this would not happen on this contract.
This paper was presented at the IEE event "Electromagnetic compatibility in heavy power installations", Teesside, 23rd February 1999. Copies of the digest (ref: 99/066), which contains papers of value to anyone involved with industrial products and installations (not just heavy power), are £20 each (cheque with order) from IEE Sales, phone 01438 313 311, fax 01438 313 465, or e-mail: email@example.com
53. The paper mill at Stanger (South Africa) has a modern electronic variable speed drive system rated at 1MVA. A thyristor-controlled rectifier controls the common DC bus voltage of the individual drives. The motors are independently driven, speed-synchronised units transporting the continuous paper web at high speed. Voltage dips of more than 20%, lasting in the order of 40 ms, are enough to upset the sensitive controls and shut down the drives. This tears the paper web and results in several hours of downtime for cleaning and re-threading. The paper mill used to experience at least one or two such voltage dips a week in its power supply, but since the installation of a superconducting magnetic energy storage system in April 1997, configured as a voltage dip protector, not one shutdown has been caused by voltage dips on the supply from the feeding grid. (Adapted from an article by R Schöttler and R G Coney in the IEE Power Engineering Journal June 1999 special feature on electrical energy storage)
54. Ken Yard of the Radiocommunication Agency described the problems it had recently faced with the introduction of the TETRA services to the UK. Interference to car alarms and immobilisers had caused over 12,000 call-outs on roadside recovery services in the last year alone. He said that the problem was partly caused by TETRA base stations but the main cause was poor quality receivers (in the car system) with insufficient rejection of out-of-band transmitters. He hoped that this situation could be avoided with the new 868MHz band for car keyfobs. (From the article "Compromise on 868 MHz", page 14 of Low Power Radio Association News May 1999, describing a meeting on March 23rd 1999. If your present car keyfob uses 418MHz, you could easily suffer from TETRA during the coming months and afterwards. If it uses 433MHz you may escape - if your receiver is of good quality.)
55. Power quality is especially critical in hospitals, where life sustaining processes demand clean reliable electrical supplies. This was recently highlighted at Glan Clwyd Hospital in North Wales where a problem became apparent on the renal dialysis unit during the testing of emergency generators. The switch from mains power to generator power was causing the newer, computer-controlled dialysis machines to close down and generate an alarm. This caused distress to patients and problems for staff who needed to reset several machines quickly before their blood began to coagulate. Resets were generally successful, though occasionally a unit would not respond so a patient would need to be moved onto a spare machine. The problem was solved with uninterruptible power supplies to provide continuity of operation at the hospital during generator testing. Ten 2.5kVa UPSs are now used in the dialysis unit and one on a treadmill in the cardiovascular unit to safeguard patients from injury should power failure cause the treadmill to stop suddenly. (Extracted from page 121 of IEE Review, May 1999. Take care: not all UPSs appear to be as reliable as we might wish!)
56. Hobart in Tasmania suffered an unusual blight earlier this month. Residents all over town found themselves trapped in their garages when the remote controls that operate the garage doors suddenly failed to function. Roll-a-door companies were flooded with calls from angry garage owners and were at first completely nonplussed by the problem. Then the explanation emerged: the aircraft carrier USS Carl Vinson had just cruised majestically into the town's docks, equipped with navigational radar employing the same frequency as the remote controls for the town's garage doors. According to the local newspaper The Advocate, an apologetic Lieutenant Dave Waterman, the ship's public affairs officer, said that the problem would only occur when the ship was arriving and leaving. (New Scientist, 24th April 1999, page 100)
57. A control cable to the engine management system of a motor car was damaged, and repaired with a terminal block. But the engine ran rough. Wrapping the repair all over with EMC copper tape (conductive adhesive) made the engine run smooth again. (Arthur Harrup, Chief Engineer, William Tatham Ltd, Rochdale, 16th Feb 1999)
58. Some robotic toys interfere with TVs. Some touch-controlled lamps interfere with long-wave radio, even when their light is turned off. An illuminated (battery powered) yo-yo interfered with a Porsche. (Jim Rackham, Principal Trading Standards Officer, 23rd February 1999)
59. During the 1980s we used a French make of chart recorder, which often ran at double speed on Saturdays. This turned out to be due to the increased numbers of TVs and radios in use on a Saturday, whose power supplies injected second harmonic currents into the mains supply. The synchronous motors in the chart recorders were able to latch up to the resulting 100Hz voltage distortion, and consequently ran twice as fast. (Stan Lomax of RTM Group Ltd, Altrincham, March 99)
60. The German economics ministry is considering restricting cable TV networks because of mounting concerns about their possible impact on air traffic safety. Frank Krueger, an economics ministry spokesman, says that the possibility that interference from household cabling will interfere with aircraft navigation and ground communication systems has prompted the government to propose regulations. "It is possible that, in individual cases, certain stations will have to be closed down after a review of the dangers posed by their frequencies." said Krueger. According to the European Cable Communications Association, the discussion about cable broadcasting and air traffic safety is not confined to Germany. Similar safety issues are currently being discussed by the Benelux states and the Nordic countries. The UK Radiocommunications Agency says that, as far as it is concerned, the only debate surrounding clashing transmissions relates to avoiding potential interference with other European broadcasters. (From the lead article on page 1 of Electronics Times, April 1999)
61. The Millennium Wheel on the Embankment in London was supposed to be lifted on September 12th. One of the delays was caused by an EMC problem. The Daily Telegraph, Saturday September 11th (page 6) said: "The operation had fallen victim of the publicity that it had generated because the satellite dishes on the fleet of television vans covering the event interfered with the laser signals monitoring the cables pulling the wheel upright.” The Guardian September 11th said: Work was initially delayed when satellite dishes on media vehicles interfered with electronic equipment used to monitor the lift, and further hampered when a stabilising cable had to be re-routed."
The Engineer, 17th September (page 2) chose to ignore the EMC issues altogether and focused instead on the problems with the stabilising cable and its wheels, brackets, and lateral pins.
62. An engineering company invested heavily in a networked computer-aided design (CAD) system. However, the system's many advantages were overshadowed by the all too regular problems it suffered. The system would crash unexpectedly, sometimes hours of work were lost or corrupted and circuit failures seemed to be almost a monthly event. At first these were assumed to be just "teething troubles" but as time went on, and design work slipped further and further behind schedule, relations with the system's supplier became increasingly difficult. Only when one of the engineering team read an article in a professional journal, did they realise that the problem might not be the system, but the environment. They soon observed that the system's failures coincided with the operation of a large drawing copying machine, which was injecting switching transients onto the ring main. (Furse Electronic Systems Protection Handbook, 1996, page 15)
More on this topic...
Transient faults (in computer systems) are triggered by environmental conditions such as power-line fluctuation, electro-magnetic inter-ference, or radiation. These faults rarely do any lasting damage to the component affected, although they can induce an erroneous state in the system. According to several studies, transient faults occur far more often than permanent ones, and are also harder to detect. ...Curiously, most computer failures are based on either software faults or permanent hardware faults, to the exclusion of the transient and intermittent hardware types. Yet many studies show these types are much more frequent than permanent faults. The problem is that they are much harder to track down. (IEEE Spectrum, August 1999, pages 50 and 51,"Fault injection spot-checks computer system dependability" J V Carriera, D Costa, and J G Silva)
And yet more...
Late last year, lightning struck in the car park area of a UK Building Society's town centre headquarters. Large voltage surges knocked out the security cameras, and were transmitted to other electronic equipment in three buildings via the connecting cables. Once they had entered the building's electrical systems, the voltage surges damaged the security system, fire alarm and distributed computer equipment. Latent damage was also caused to the interface between the fire alarm and the radio tag-operated automatic door system, but this went unnoticed at the time. The problem was identified only when a fire alarm went off some weeks later and staff were unable to exit through the automatic doors. Fortunately it was a false alarm. (Electrical Review, Vol 227 No 12, 10-30 June 94, page 90, "Don't lose your data in a flash" by Tony Harrison)
63. Earlier analogue flight control systems have experienced malfunctions when overflying radio/radar transmitters - the new generation digital systems are very much more robust and can meet the very stringent EMC requirements. (Computing & Control Engineering Journal, IEE, August 1999 page 152, article on "Fly by Wire by Dick Collinson of Marconi Avionics.)
64. Computer manufacturers and others are finding it impossible to meet the EMC Directive because of non-compliant CE marked motherboards and power supplies, according to test house EMC Projects. The company tested 12 different motherboards for a client recently and found that every one of them failed to meet EN55022 limits, according to the company's MD Mike Wood. Failures ranged from a few dB to 20dB over the limit line. None was accompanied by instructions about how the boards should be installed to meet EMC regulations. "I feel very sorry for companies trying to meet standards when they use these boards," Wood said. "It is almost impossible for them to comply." He pointed out that any manufacturer relying on CE marked components to justify compliance without testing is likely to have severe problems. (Approval, Jan/Feb 99, page 5)
Talking to a representative of Intel Corporation (UK) of Swindon about this general issue in 1998, he said that they always tested their motherboards to make sure they were EMC compliant in a variety of different manufacturers' PC enclosures, and that this took approximately two weeks. He claimed that this was one reason why none of the "hottest" machines reviewed in the computer trade press used Intel motherboards - given the fast pace of the computer industry, taking the time to properly qualify a motherboard meant taking second place in the performance stakes to those who were less careful of their legal and ethical obligations. (Keith Armstrong, Cherry Clough Consultants, October 1999)
65. According to the Cellular Tele-communications Industry Association's web site www.wow-com.com: researchers have found that analogue phones have no effect on pacemakers, although some digital phones do. Already, doctors advice pacemaker wearers to exercise caution around electromagnetic devices such as MRI machines. Digital phones should be approached in the same way. Wireless Technology Research Ltd conducted tests involving over a thousand pacemaker patients. They found no clinically significant interactions with the phone in the normal position at the ear. Some interference was noted in 20% of the tests with the phone 6 inches from the pacemaker. But even then, only 6% were clinically significant. Regular operation resumed once the phone was removed. The Food and Drug Administration (USA) believes pacemaker wearers should avoid placing phones next to the implant, as in shirt or jacket pockets. When using the phone, patients should hold it to the ear opposite to the side of the body where the pacemaker is located.
Other cardiac patients use implanted cardiovascular defibrillators (ICDs). The University of Oklahoma's Wireless EMC Centre investigated the effects of all the analogue and digital wireless phone technologies operating in the US and Europe on ICDs from four manufacturers. No interactions were found between phones that operate in the 1800 and 1900MHz bands. Only one unnamed company's ICDs were affected, and these effects were only caused by TDMA-11 Hz which is only used in specialised operations, and even then no permanent ICD reprogramming occurred. Still, doctors say that additional research is necessary, and researchers say that ICD patients should follow the same guidelines as pacemaker wearers. (Extracted from Electronic Design magazine, October 18th 1999, page 32H)
66. During the past decade, the U.S. Food and Drug Administration (FDA) has received more than 28 medical device reporting incidents of adverse interactions between medical devices and electronic article surveillance (EAS) systems, metal detectors, and security systems. Several case reports and four peer-reviewed studies document adverse reactions between EAS systems and implanted pacemakers, implanted automatic cardiac defibrillators, implanted neurostimulators, and other ambulatory medical devices. Anecdotal reports and newspaper articles suggest that many more device interactions have occurred and gone unreported. Each year millions of people enter establishments protected by EAS systems. Because more people are using electronic implants and ambulatory medical devices, adverse interactions with EAS systems are of increasing concern. (Extracted from an article in Compliance Engineering magazine's European Edition, September/October 1999, Page 32. The article does not draw any conclusions for wearers of implanted devices in the way that item 65) above does.)
(Editor's Note: The number and variety of implanted medical electronics devices is rapidly increasing. Stevie Wonder (the musician) is apparently soon to receive an artificial retina chip. Some very serious people are talking about implanted personal enhancements which are not for medical purposes. EMC takes on a whole new dimension when parts of your body or mind can suffer interference from common electronic technologies.)
67. The Critical Care Telemetry Group submitted a petition document (to the USA's FCC), ET Docket 95-177, 10/97 covering new channels from 470 to 668 MHz for powers of 200,000 mV/m at 3m at the same time as the digital TV group submission. This resulted in some confusion and a case where in March 1998 at Baylor University Hospital some medical devices failed due to the DTV broadcast. The FCC and the FDA produced a fact sheet stating that the DTV operators must co-ordinate with the regional hospitals before broadcasting. (Details can be found on the FCC web pages, http://www.fcc.gov. (Extracted from ERA Technology's Safety and EMC Newsletter, Supplement to Issue 47, October 1999, page 12, reporting on a paper by Art Wall of the FCC which he presented at the IEEE's EMC Symposium in Seattle, August 1999)
68. In early February a DC-10 was entering its final landing approach at New York's JFK airport when it suddenly banked sharply to the left, nearly causing a crash. NASA and FAA experts concluded that the plane's flight controls were upset when someone in first class turned on his portable CD player. Apparently, newer planes are more heavily computerised and vulnerable to interference. Of particular concern is interference to frequencies used by the VOR (Visual Omni-Range) network, because flight control systems use these navigation beacons for autopilot operation and instrument landing. (Taken from Compliance Engineering Spring 1993, page 92, itself commenting on an article in Time, Feb 22, 1993)
69. With reference to Lufthansa's "weird" ban on CD-ROM drives (Letters, 28 March, p.64), the airline is probably extending an existing ban on personal CD players to computers. In the only documented case of interference from personal electronic equipment that I am aware of, an early CD player jammed the instrument landing system on an airliner in the mid-1980s. Because CD players are optical devices, some of the cheaper models did not include any shielding against radio-frequency (RF) interference from the logic devices in their controllers and were therefore quite noisy in the RF bands. (Allan Gibson)
In the feature "do portable electronics endanger flight?" in IEEE Spectrum (September 1996), the reason given for the ban on equipment containing CD players is that "portable compact disc players have an internal clock of 28MHz", which "produces harmonics at 56, 84, and 112MHz - and 112MHz is a VHF aircraft navigation channel" for aircraft. (Kevin Connolly)
(These two items both appeared on the same page (56) in New Scientist 25 April 1998)
70. Earlier this year, at Paddington railway station in London, I saw this sign on the door of the airlines' check-in area (operated by BA, American Airlines and British Midland) for customers travelling by rail (Heathrow Express) to the airport: "Please do not use mobile telephones in the area as it interferes with the equipment." (I'd love to know more. I'd speculated -- wild guess!-- that it was US-built check-in equipment that had not been tested for immunity to GSM phones...) (from Glyn Garside, Director, Engineering Services, Adept Technology Inc., San Jose, California.)
Reply from Jim Rackham of Warwickshire Trading Standards (one of Trading Standards' four EMC Specialists): If the use of a mobile phone is likely to cause any risk to Health and Safety, then the business would have a duty to warn anyone entering the premises not to use it. On a more general note as shops are usually on 'private property' then the owners would have the right to lay down reasonable conditions on what actions were acceptable within the premises. If in certain circumstances mobile phones could interfere with equipment then it might be reasonable for them not to be used - some equipment could still predate the regulations. However, as installations should comply with the protection requirements and if it is reasonable that mobile phones could be used in the vicinity of CE marked equipment, that equipment should be reasonably immune from their interference.
(From Keith Armstrong of Cherry Clough Consultants): An EMC specialist from a major IT company told me that their computer systems only achieve 1V/m immunity although built from equipment that individually meets 3V/m. 1V/m is equivalent to a GSM hand-portable at around 5 metres, in a strong signal area without reflections from nearby metal structures. In weak signal areas (or standby mode) with no reflections, this would instead be around 7 metres. For this reason they generally ban the use of cellphones and walkie-talkies in the computer rooms they build.
71. The robots used on the Robot Wars TV show apparently suffer terribly from interference. They are radio-controlled (R/C), often using hobbyist gear. Here are some comments extracted from the "Robot Wars: Tip Swap: weapons idea centre", soon after a robot ran amok and injured someone. The 'failsafes' they are talking about are supposed to shut down all robot activity except when valid R/C is established. (From Bill Armstrong of PC Help.)
(Saturday, January 8, 2000).... Despite what the Reg's state hardly any of the failsafes on the robots were in a working condition. Remember that an awful lot of robots were suffering from radio interference problems, this I find odd, as personally all the robots that have been built here in my workshops ....have never had a problem. ....As for the question of failsafes, most of them are definitely not failsafes and don't work. ....one common problem on lots of commercial units is because the unit tries to detect an output pulse from the receiver, this works well in a normal environment but in studio conditions this is not the case, interference can (and will) cause 'spikes' on the output and it will assume that is the correct signal and fail to shut it down. Some of the more expensive models actually measure the pulse width and if it falls outside the normal pulse width they then fail safe. .... (Sunday, January 9) In my opinion, the biggest safety problem is with the failsafe system. Having run 27MHz R/C cars for years, I am used to how easily control is lost even in friendly RFI/EMI conditions. Most people use commercial RC aircraft failsafes (the little orange thing), which is fine when you are flying a plane outside, in friendly EMI conditions, and signal is completely lost (e.g. transmitter battery fails).... They are not meant to deal with conditions of huge RFI/EMI interference present at Robot Wars - indeed our electronics guy laughed at the simplicity of the circuit when he took apart the failsafe we bought. It would bypass the majority of interference, and render the robot uncontrollable (and unpredictable). .... Also I have to suspect the method of testing at the auditions. According to .... the test is simply to switch off the transmitter - and if nothing happens, then the robot passes. But aren't the auditions held in a quiet warehouse, with friendly RF (i.e. little interference), making them totally unrealistic? .... (Sunday, January 9)...the only problem is that a failsafe on some robots may be irrelevant. There are plenty of home-made speed controllers out there with home-rolled micros running the show that could go rogue regardless of whether they have an input at all. Even if PCM is used (for the R/C), there are some being controlled with relays and home made interface circuits that are not too stable irrespective of input. It certainly needs a more technical look at the way people are controlling their motors and weapons.... (Monday, January 10) ....The lack of failsafes on weapons channels scares me - I've been near a couple of robots when the weapons channel has fired for no reason.... (Wednesday, January 12) ....Just a quick note on the orange failsafes mentioned further back on this thread, I've done some investigating, they come in two varieties. The FS-1 (the one with undervoltage monitoring) works beautifully, the other, the FS-2 is not suitable for use on robots. As mentioned further back, it lets through most interference. There is no external difference in appearance between the two units, other than the number printed on the label.... (Wednesday January 12)...The problem we have is when the receiver loses its signal, it holds its last state for 1.5 seconds before it fails safe i.e. the robot does the last thing it was doing for 1.5 seconds after its signal was lost.
72. The Helsinki City Transport (HKL) rolling stock is ageing fast. The most recent trams were built 20 years ago. Hitherto, all auxiliary equipment, such as ventilator fan motors were DC and the maintenance of these units was becoming something of a nightmare. Spares were costly and it was a very labour intensive process keeping them in service.
In each HKL tram there were six ventilation fans with DC motors cooling the passenger compartment, brake resistor, and traction motor. The thinking was that one big inverter supplying six AC motors was going to be cheaper than several smaller inverters supplying one motor each, so a 15kW unit was mounted in the main electrical panel of one of the trams. The existing cabling was retained because of cost considerations and this connected the various motors in parallel. EMC problems very quickly surfaced. Not only was the vehicle's own radio system badly affected, but -crucially - third party electrical equipment also suffered interference, including that of a hospital on the tram's route.
The problem was solved in the end by siting individual inverters close to the motors they controlled. (From an article by Les Hunt in dpa Magazine, March 99, Drives Supplement page 29.)
73. Every 11 years violent storms on the surface of the Sun cause massive amounts of energy - in the form of protons and electrons - to be thrown out into space. After a few days, this energy reaches Earth, interferes with the planet's magnetic field and generates huge currents - particularly in the polar regions. These induced currents can subsequently induce massive surges in (power distribution) transmission lines, damaging transformers and causing high-amplitude harmonics. In the space of just 2 minutes in March 1989, six million people in Quebec, Canada, suffered a complete blackout because of a severe storm from space. In the UK the problems were less severe, but some were experienced (see Electrical Review, 20 July 1999).
The first space weather prediction system for electric power grids has been completed in the UK. The main problem for networks is losing control of voltage regulation, but with the new system certain regions can be highlighted as being particularly at risk and necessary precautions taken. So far in Solar Cycle 23 - the name for the current bout of activity - longer-term forecasts have given two clear warnings of potential disruption. (From Electrical Review, Vol. 233 No 5 p 10.)
74. There was a minor collision between a supply vessel servicing a semi-submersible offshore oil and gas installation. The vessel experienced a sudden power increase brought on because of interaction between radio signals from a portable VHF radio and the joystick control. This caused the joystick to execute commands not requested by the operator and resulted in contact between the vessel and the installation. The interaction caused minor damage (though it could have been far worse).
The incident occurred outside UK waters and was reported in a safety notice issued by an offshore operator. The safety notice was seen by an HSE inspector on a bulletin board on an offshore installation, dated 30 September 1999, which referred to the incident as having happened 'recently'. (from Simon Brown of the HSE, 14th and 15th February 2000)
75. Extract from IMO Resolution A.813 (19):1995, General Requirements for EMC for all Electrical and Electronic Ship's Equipment: "NOTING the growing number of problems experienced with equipment that is susceptible to electromagnetic interference, which can result in dangerous situations,..."
76. National Semiconductor plans to begin shipments of Class-D audio amplifier ics before Christmas. The delay of the launch, which was first reported by NE in June this year, has been attributed to the design of the development board. Class-D amplifiers, while efficient, require careful layout to prevent EMC problems from the internal 50kHz oscillator. (From New Electronics magazine, 14th December 1999, p 8.)
77. Faulty thermostats can cause annoying interference to radio and TV broadcast reception. They cause short bursts of interference, which may recur at intervals. Thermostats in central heating systems, fridges or freezers switching on and off have all caused interference problems. Our experience shows that the thermostat found in the central heating system is most often the source of the interference. Often the offending thermostat is found in the house receiving the interference, although the agency is aware of cases where the source of the interference was some distance away. (From the Radiocommunication Agency's publication RA 272 (Rev3) May 1999.)
78. Millions of motorists are risking their lives every time they use mobile phones while driving. New research has revealed (that) signals sent from mobiles can disrupt sophisticated electronic control units fitted in most modern cars. And it is feared that in some instances this could scupper vehicles' braking and engine systems. One major manufacturer has also warned that the transmissions from mobiles could trigger air bags fitted to the car.
The alert over making calls in the car was given by the AA following research into the problem. The motoring organisation is now urging drivers to ensure they stop their cars before making any calls. Last night an AA spokesman said: "It is the same as aircraft operators asking people to switch off their mobiles while on a plane. The mobile is transmitting all the time and there is the possibility of interference with electronics in the car. You might get a misfire or your braking system might not operate. The answer is to only use the phone when you are stationary or to install an outside aerial." (From an article by Bill Caven in the Daily Record, 10th Jan 2000, p 23. Also see an article by Ian Fletcher in the Sunday Mirror 9th Jan 2000, p 9. Both were sent in by Dai Davis, Head of IT, Communications and New Media Group at Nabarro Nathanson.)
Items 79 through 83 below are taken from comments by Art Wall (Associate Chief of the Policy and Rules Division of the USA's Federal Communications Commission) during an EMCTLA seminar on FCC requirements on the 18th May 2000.
79. Radio remote controlled garage door openers are short-range devices which use a part of the spectrum also used by the military. People got fed up with their garage doors opening every time a military jet flew over, so the manufacturers added coding to their signals.
80. Retail shops use anti-pilferage devices (the hoops that are to either side of their doors) which operate in the USA between 510 and 1705 kHz. The goods to be protected have a small label stuck on them that resonates at the appropriate frequency and disturbs the field produced by the hoops, allowing detection. It was found that heart pacemakers were susceptible to the anti-pilferage fields, so pacemaker manufacturers had to improve their designs to make them less susceptible.
81. There used to be a lot of problems with light dimmers interfering with AM broadcasts. The manufacturers added suppression to their products to satisfy customers and maintain sales levels (and not because of any regulations or standards).
82. A plywood laminating machine in Kentucky used 1.6 MW at 6 MHz to speed up the drying of the laminating glue. Operators removed a door, which had a perforated metal screen so that they could see the inside of the machine better - subjecting themselves to hazardous levels of RF field. (Incidentally, Art claimed that more RF energy is used world-wide in manufacturing, for processing materials, than is used in broadcasting.)
83. Diathermic knives are electro-surgical units used by surgeons to cut tissue whilst sealing blood vessels using RF energy. Although they pass the FCC limits of 10 mV/m at 1 mile distance, they can generate 1000 V/m at the surgeons head.
84. Mobile phones can cause interference to aircraft electronics according to tests by the UK's Civil Aviation Authority (CAA) safety regulation group. Evidence of interference to aircraft had been anecdotal, with many reports by pilots suggesting that mobile phones were the source of the problem. Tests were conducted on the ground on a Virgin Atlantic 747 and a British Airways 737. The conclusion was that "transmissions made in the cabin from portable telephones can produce interference levels that exceed demonstrated susceptibility levels for aircraft equipment approved against earlier standards." Faults attributed to mobiles included noise of the flight crew headsets and false triggering of warning signals, which could have a 'cry wolf' effect meaning crews might ignore a real warning. (Electronics Weekly, May 31 2000, page 2)
85. In recent radio interference case, a cable television (CATV) system was found to be causing radio interference. Upon investigation it was found that this was due to the CATV system picking up the interference from a buried cable in a parallel duct (and re-radiating it). (Peter Kerry, "EMC in the New Millennium" IEE Electronics and Communications Engineering Journal, April 2000, Page 47)
86. People have learned to live with problems such as their mobile phone not working near the fluorescent light. (Peter Kerry, as 85 above)
87. I was intrigued by the article by Prof. Yacamini et al. Relating to overvoltages at the terminals of downhole pumps supplied by variable speed drives (February 2000 PEJ, p.29). In the 1960s there was a series of faults on a group of cross-bonded 132 kV cables in the London area which were never satisfactorily explained, despite extensive on-site measurements using foils embedded in the joints, the last fault occurring shortly after the measuring instruments had been disconnected. These faults were located in joints at about one-quarter or half-way along the routes, successive faults occurring at the same joints, despite very careful repair by an experienced cable jointer. No serious overvoltages were measured. Much investigation into surge voltages on cables and overhead lines has shown how steep-fronted waves can impose overvoltages, particularly at discontinuities such as exist at motor terminals. The continual overstressing of insulation by the spikes every half-cycle can lead to progressive failure, even if the overvoltage is not sufficient to cause immediate breakdown. (H. J. Langley, Letters to the Editor, IEE Power Engineering Journal, April 2000, page 48)
88. Working for Ferranti in the mid 1970s, we had a problem with the power metering in a power station near Loch Lomond. Every now and again (once every few weeks) we got totally ridiculous readings. Neither the readings nor their occurrence was predictable or consistent. We tried various earthing schemes and surge suppression, but then discovered that there was an aluminium smelter close by - and its huge power cables ran 3 feet underground the power station's control room. The fields from these cables were powerful enough to magnetise wristwatches. The problem was solved by filtering the electronics of the kWh meters. (Dave Dunn, Senior Applications Engineer, IMI Norgren, Manchester)
89. In 1994, studies revealed that the total cost of computer downtime to U.S. businesses had climbed to an all-time high of over $3 billion. "Power-related problems" was the number one cause of computer downtime, amounting to over 45% of occurrences and resulting in losses of $1.5 billion. Many of the power-related problems could be traced to the most basic element of the computer network: the wiring and grounding of the host building. (From "Networking Equipment and Downtime: Caught in the Middle" by Tony DeSpirito, Electronic Design magazine, April 1997, pp 42-48. We wonder what the 1999 figures were.)
90. Recent developments in broadband data access methods over existing telephone or mains wiring will cause unintentional RF emissions which may adversely affect the established radio noise floor. (From a report produced by York EMC Services for the Radiocommunications Agency on the effects of ADSL, VDSL, and power line technology such as HomeLAN. The report is downloadable from http://www.radio.gov.uk/busunit/research/ay3525/intro.htm. Many other interesting documents may be found by hunting around the RA's website http://www.radio.gov.uk for their research.)
US readers: we understand that xDSL technologies are more heavily used in the US than in Europe. Has anybody noticed a significant increase in the radio noise floor over the last couple of years? If so please contact the Editor at firstname.lastname@example.org with your experiences.
91. It sounds like the perfect weapon. Without fracturing a single brick or spilling a drop of blood, it could bring a city to its knees. The few scientists who are prepared to talk about it speak of a sea change in how wars will be fought. Even in peacetime, the same technology could bring mayhem to our daily lives. This weapon is so simple to make, it wouldn't take a criminal genius to put one together and wreak havoc. Some believe attacks have started already, but because the weapon leaves no trace it's a suspicion that's hard to prove. The perfect weapon is the electromagnetic bomb. The idea behind it is simple. Produce a high-power flash of radio waves or microwaves and it will fry any circuitry it hits. At lower powers, the effects are more subtle: it can throw electronic systems into chaos, often making them crash. In an age when electronics finds its way into everything bar food and bicycles, it is a sure way to cause mass disruption. (From "Just a normal town..." the cover story in New Scientist's July 1st 2000 issue, pp 20-24. The article goes on to quote a researcher who claims that modern computers and their systems are easier to crash with EM weapons than older models. For more on this see Banana Skins no. 14, June 98, available from the archives at http://www.compliance-club.com)
Items 92 to 98 below are all taken from "Study to predict the electromagnetic interference for a typical house in 2010" by Anita Woogara, 17 September 1999, downloadable via the RA's website http://www.radio.gov.uk as mentioned above.
92. Hearing aids operate between 200 - 4000Hz. Manufacturers have to comply with the Medical Devices Directive and the IEC118-13 'Immunity of hearing aids from interference with cellular phones'. However, due to the interference experienced, it is not felt that these are adequate for those (hearing aid) users who also wish to use items such as mobile phones.
93. Mobile phones and passing taxi radios have been known to interfere with Anti-skid Braking Systems (ABS) and airbags, causing drivers to lose control of the car.
94. Railways cover most of the country and can pass quite close to residential buildings and hence affect the equipment inside them. Additional immunity constraints are placed on the users of information technology equipment in the near vicinity. However, it is unclear how suppliers know that their users will be situated near railway systems. (The study makes similar comments about tram systems.)
95. Mobile phones are becoming so popular that in America it is difficult for people to have a phone call without being cut off due to interference. This is leading to people suing mobile phone companies for not providing the advertised service.
96. Cochlea implants are small electronic devices placed under the skin to assist hearing. Unfortunately, they are prone to interference, such as the security checks at shop entrances and airline security, which can damage an implant. People with cochlea implants have also been told not to use mobile phones.
97. The (UK) government is trying to encourage people to use public transport. An incentive to use public transport would be punctuality. BT is investigating an idea, which would enable the time of arrival of the bus to be checked by using either the web or a mobile phone or pager. The bus would be fitted with a GPS tracker so that its position could be monitored. This technology would be useful but in large cities GPS on buses might not be that reliable, due to the interference.
98. Electronic tagging takes the form of a small bracelet worn around the wrist or ankle. Presently the (UK) Home Office is the main user of electronic tagging, keeping track of prisoners in the community. Children could be fitted with a tagging bracelet before setting off to walk to school and parents could be notified if the child wanders off the route, via mobile phone or pager. The problem with this would be when the GPS signal was interfered with and incorrectly showed that the child was off the route. This interference is likely to take place in cities. These problems already occur with prisoner tagging. (For more on GPS problems see Banana Skins no. 28 in the December 1998 issue, available from the archives at http://www.compliance-club.com).
99. Elaine Scarry has found some common threads in the crashes of TWA 800, Swissair 111, and Egyptair 990, that indicate a significant possibility that they were brought down by electromagnetic interference from military aircraft or ships on exercise. This possibility does not appear to be under consideration by the accident investigators for these incidents. Read her articles in the New York Review of Books by going to http://www.nybooks.com and then searching their archives using the author's name: Scarry.
100. My neighbour has had a new heart pacemaker fitted. Every time he makes love my garage doors open. (Attributed to Bob Hope, 1975, and celebrating our 100th Banana Skin.)
101. Poor power quality costs businesses in Europe €13-20billion a year, the European Copper Development Association estimates. This is the first attempt to pin down the cost in Europe of voltage deviations, transients, interruptions, and harmonics, says the organisation. These problems are increasing because of the growing use of equipment such as switch-mode power supplies, variable-speed drives, and high-frequency lighting, it adds. The use of such polluting equipment means that 70-80% of power quality problems are caused by operations on sites, rather than by external effects, says the institute. Problems produced by poor-quality power include glitches in computers, burnt-out motors, failed transformers and fires caused by high neutral currents. (From Electrical Review, 4th July 2000, page 3.)
102. In the lighting industry, simple switch-mode power supplies with AC outputs, often called "electronic transformers", are used increasingly to operate 12 volt lamps from the mains supply. In a retail store 50-100 of these units each rated around 50W would not be uncommon.
Most of these devices claim to meet the EMC Directive individually and are CE marked. However if a number of these devices are operating in one location, then their total emissions can be shown to exceed the limits for both RF and harmonics, sometimes by a large margin. There are already instances of other equipment malfunctioning, and of sine wave distortion causing conventional transformers to overheat (due to enhanced core losses). I have experience of a building, which had recently been fitted with about 50 off 50W "electronic transformers", the harmonic emissions from which so distorted the mains supply waveform that conventional transformers powered from the same mains distribution overheated.
Clearly, this is not just an EMC issue, but a significant safety concern. But my experience so far is that lighting equipment manufacturers, on the whole, don't seem to understand this significance of this problem, and that installers could not care less. (From Fane Murray, 4th September 2000.)
103. Another common problem is that of knowledge of Directives. Some contenders appear to have a hazy understanding of the EMC and LV Directives for example. (Stuart Wetherall, Publisher, writing about the 'Panel Builder of the Year Awards in Panel Building Magazine, September 2000 pages 12 to 20.)
104. Just a note of thanks for your illuminating series in EMC journal. As an electrical layman I found them helpful when trying to analyse my 10 year dissatisfaction with the Israeli brand of mains, which seems to contain harmonics from 9th upwards (scope trace attached).
Not only does the mains supply show obvious clipping, ringing, crest flattening and zerovolt crossover distortion, but the thick line (represented by my crude felt-tip trace) resolves itself into stable "carrier wave" oscillations at 10kc to 10 MC (which is why my AM radio gives off sounds like a buzz-saw at BBC World and other frequencies). "What in the developed world would constitute a road-hazard, in the developing world often has to serve as the road". (From Nick Maroudas PhD (ChemEng) DIC, 2nd October 2000)
105. Video cameras in racing cars provide exciting live pictures for TV, but the image is often spoilt by interference. (From New Scientist, 30th September 2000)
106. In the lead-up to the 1998 Grand Prix, electrical storms caused a spike in the power supply which sent major ripples across the facility's feed lines - crashing all race control computers. After the ensuing chaos, the problem was rectified and the race proceeded as scheduled but the experience left the Silverstone management adamant that this type of disturbance would not be repeated at future events. (From "Grand Prix UPS weathers the storms", Electrical Products September 2000 page 34.)
107. Twinkling antennas are a recent innovation in the mobile phone market. They incorporate one or more Light Emitting Diodes (LEDs), which are intended to illuminate when the mobile phone is transmitting. Reports from Mobile Phone companies using the 1800 MHz band have highlighted cases of interference from 900 MHz GSM mobiles. It has been suggested that the non-linear characteristics of the LEDs will cause a transmitting twinkling antenna to radiate harmonics. (Tests carried out by the Radiocommunications agency on two 900 MHz cellphones fitted with twinkling antennas showed that...) the ERP of the second harmonic...exceeded the ETS 300 577 maximum. (From EMC Matters, published by Brian Jones: email@example.com. The full report of Project 564 is available on the RA website http://www.radio.gov.uk)
108. In the UK 886 to 906MHz has been allocated as a band suitable for the operation of Industrial Scientific and Medical (ISM) equipment. ISM machines are at present allowed to emit 120dB V/m (i.e. 1Volt/metre) measured at 30 metres from the wall of the building housing the equipment over this frequency range. This presents a problem as it occupies part of the band allocated to mobile phone operators.
The main users of the ISM band are organisations operating industrial microwave ovens. The ovens are used in food production although other uses such as vulcanising rubber are also on record. High power magnetrons are used as the source of microwave energy, the magnetrons are designed to operate at 896MHz. For process purposes the ovens are normally conveyor fed. Consequently depending on the size of product being treated a large aperture exists at each end of the oven allowing relatively high levels of microwave energy to be emitted. The channel 30 mobile to base-station frequency coincides with the magnetron centre frequency. ... The second oven at Griffith laboratories is of particular interest as the emissions are known to disturb the operation of a base station located in the vicinity. (Dr D Welsh: "Industrial Microwave Oven (ISM) Emissions and Mitigation Techniques",, Proceedings of EMC York 2000, 10-11 July 2000.)
109. The current Australian regime (for EMC compliance) only covers emissions requirements, but there has been extensive discussion about whether immunity should also be made mandatory. ...a submission from a major telecommunications network company (Telstra) outlined difficulties it has experienced in dealing with customer equipment susceptible to interference. The ACA mandates interoperability, safety, and emissions standards but telecoms carriers have little control over the EMC quality of equipment connected to their network. (Chris Zombolas of EMC Technologies Pty Ltd: "Australian framework comes under review", Approval, Sep/Oct 2000 pp7-8.)
110. When Ford began the development of an electronic anti-lock braking system in 1982, their engineers noted certain "concerns" about its behaviour when subjected to high levels of interference. (Ed: Such as those created by mobile radio transmitters of around 100W, either on-board or mounted on nearby vehicles.) Not only was it liable to fail, bad enough if a driver had come to rely on it, but it could do so in a particularly nasty manner, deactivating the system. (Tom Shelley: "Screening protects anti-skid brakes", Eureka May 1987, pp36-37.)
111. Fields in and around vehicles with onboard transmitters (at the maximum legal power of 110W) range mostly between 10 and 300 V/m, with some exceptions. Field strengths in and around vehicles adjacent to vehicles with transmitters range mostly between 5 and 100 V/m. ("How does EMI affect automotive electronics?" Microwaves, April 1980, pp 96.)
112. I'm tempted to think your article about mobile phones on aeroplanes was itself a flight from reality (19 August, p 18). The problem with cellphones is that they radiate at moderate powers which are capable of upsetting the operation of any of the semiconductors in any of the electronic systems in the aircraft. Try this little experiment: phone a friend using your POT (plain old telephone landline) and then phone someone else using your cellphone. Hold the cellphone at various distances from the POT handset and its cables and see how far away it has to be before you can't hear the "blippety-blip" noises on the POT. According to the reported statements in the article, the possibility of interference in these little experiments would be "very low" when in fact it almost always occurs. (Keith Armstrong: "Mobile menace", letters, New Scientist, 9 September 2000.)
113. As a captain of a brand new Boeing 737 aircraft, I can assure readers that the effects of mobile phones are very noticeable on the flightdeck. The chief problem is a series of rapid beeps from the handset when it "checks in" with a base-station. The handset does not need to be making or finishing a call to perform this function, it only needs to be switched on. The interference manifests itself as a loud and annoying interference, but since some of our navigation equipment works on the same frequencies, interference with navigational capabilities cannot be ruled out. Another more worrying source of cellphone interference was not even mentioned in your report - mobile phones in air-traffic control centres. We had a case the other week on a Spanish sector where a mobile phone in the air-traffic control centre was continuously trying to check in with its base station and the interference was totally blocking the frequency. Mobile telephones are an airborne menace, but you have to ask why aircraft systems are not better protected against interference in the first place. Thunderstorms can saturate our old-fashioned (but new) AM radios with static, and the ADF navigation equipment will direct the aircraft straight towards the nearest thunderstorm instead of the airfield. Is this really the high-tech field of aviation? (Ralph Ellis: "Mobile menace", letters, New Scientist, 9 September 2000.)
114. In general, an above ground pool is 6 to 12 times more hazardous than an in ground pool. Of the cases investigated, the majority of hazardous situations associated with pools were found to be above ground pools in close proximity to transmission line towers. It was recommended that all pools of the above ground type in close proximity to transmission lines be removed immediately. (D.J.Woodhouse, K.D Newland, W.D. Carman, all from Energy Australia: "Development of a risk management policy for transmission line easements", ERA's Earthing 2000 conference, 21-22 June 2000, pp 6.7.7)
115. A European train operator had a problem on a section of track near a radio transmitting station. When a certain type of locomotive was passing by the radio station its main circuit breaker would open, causing it to brake. It was found out that the temperature sensors within the traction motors picked up the radio signal. The cables to these sensors weren't screened. A modification to this would have been very expensive as the sensors are mounted within the winding of the motors.
The solution chosen was to increase the time window for the signal to be above a certain limit before the control would take action. Due to the long time constant of the thermal behaviour of the system, this solution was acceptable and sufficient. (Jennifer Cortese, Melbourne Australia, December 2000)
116. I was lying on my back underneath a diesel engine (part the emergency power generator of a hospital) with the sump off, doing some work on the bearings. There was not a lot of room between the engine and the floor. The diesel generator was turned off, that is to say the OFF pushbutton on the control panel had been pressed and the controlling PLC’s display showed the OFF condition.
Suddenly, the diesel’s starter motor operated and the engine began to run, with the crankshaft whirling around a couple of inches above my nose. Very cautiously, I slid out from underneath. I discovered that a ‘bush taxi’ that called at the hospital was responsible. These bush taxis had extra powerful radio transmitters fitted, so they could stay in touch with their base when very far away in the bush. Keying the powerful transmitter at the hospital entrance created enough interference for the generator’s controlling PLC to think it had received the start command. (Attendee at an EMC seminar in Sydney, November 2000.)
117. We were close to finishing the construction of an eight-million-dollar mining machine in a cavern in Australia. The operators of the mine had a central control room from which they wished to be able to exert manual control over any machine in the mine, even though the machines were automatic or had local control. Accordingly, the mine operators ran their own cables from their control room and connected them to spare inputs and outputs on the PLC for each new machine, also making the necessary software modifications themselves.
Suddenly, while we were standing by the machine, it started up of its own accord. Luckily, no-one was working on it at the time, although they could have been, but it was still a very serious issue as the machine had not yet been filled with lubricant and could easily have been wrecked. It turned out that no special precautions had been taken with the cables from the control room to the PLC, or with the software changes, and a transient interference with the new cables had caused our machine to start up unexpectedly. (A different attendee at an EMC seminar in Sydney, November 2000.)
118. I was visiting a company that made cutting machinery for carpet manufacturers. These machines had blades 5 metres wide, and very sharp. Adjusting the blades to get a good cut over the whole 5 metre width involved careful adjustments, and I noticed that some of the engineers would lie under the blade while making these adjustments. I also noticed that the control panel (which used low-cost PLCs and not safety-critical types) was in ‘single step mode’ during these adjustments. I asked the Chief Engineer if they had ever had one of these machines start up on its own, and he said that it had been known to happen. (Keith Armstrong, February 2001)
119. I just had to write to you about the [November] editorial “Whose spectrum?”. It is right on the mark. However, I would like to point out that there is another crucial difference between UWB devices and hair dryers in addition to the list that Charlie Trimble so appropriately collected; if you choose to shield the hair dryer or otherwise filter its electromagnetic emissions, it still functions as a hair dryer!
If in the future, UWB is (heaven help us) given the desired rulemaking, becomes as pervasive as that industry dreams it will, and then is found to jam GPS at large distances, there will be no technical remedy, just a face-off between two competing industries. To follow the thread of your editorial, if we must grant UWB an FCC Part 15 exclusion just because we have a precedent with other emitters in the band, then we are truly facing a spectral “tragedy of the commons”. (Stephen Lazar of The Aerospace Corporation, writing to the editor of GPS World magazine, Page 6 of their January 2001 edition)
(Editor’s note: ‘ultra-wideband’ radio communications devices use a train of very brief pulses occupying many MHz, even GHz of spectrum simultaneously, using time-domain techniques to distinguish one transmission from another unlike traditional radio that uses frequency domain techniques. Their transmitted spectra look like wideband white noise at relatively low power, and the effect of large numbers of them is to raise the noise floor considerably, to the point where the weak signals from GPS could be jammed. Also see Banana Skins December 1998 issue. The same technology is also capable of being used as a ‘personal radar’ useful for all sorts of things, such as checking someone’s heartbeat without contact, or detecting people through walls. We will no doubt be hearing a lot more about UWB in the future.)
120. How EMC saved hundreds of millions of dollars. The new series of Australian banknotes have a plastic film embedded in them, RF welded into place. When the new bank note production line was first used, the emissions from the RF welder upset other printing machines and ruined large numbers of banknotes. They called me in and I fixed the problem, improving their productivity and saving them from burning hundreds of millions of misprinted dollars! (From Chris Zombolas, EMC Technologies Pty Ltd, Melbourne, Australia)
121. Police Frequency Freaks Hospital. Further to confirmation that mobile ’phones can indeed interfere with the navigation systems and electronics on board aircraft, news arrives that the UK’s new £2.5 billion national police radio network is being urgently tested amid fears that it will interfere with vital hospital equipment and breath-test and radar speed machines. Until it is checked, police have been told to turn their new radios off in hospitals and near other vital equipment. There could also be problems at airports, ports and even in police control rooms.
The network uses a digital radio system called TETRA, or Terrestrial Trunk Radio. The handsets send out pulses at frequent intervals to the nearest masts, identifying their presence, but the pulses can affect the electronics of some types of equipment. The alarm was raised when Jersey police, who are already using Tetra, reported possible problems with their speed and drink-drive equipment. Scientists at the Defence Evaluation and Research Agency (DERA) have been commissioned to discover the level of interference and what else the radios could affect. (Source: The Times, January 2001, sent in by Harold Smart who saw it in the Royal Institute of Navigation Journal, January/February 2000 issue.)
122. Interference clouds future of multi-billion police radio project. Police from the channel island of Jersey, which is going through pre-implementation testing of the TETRA technology, is advising its officers to be much more careful about using the equipment than was the case with previous kit. Because of fears of interfering with hospital equipment, the States of Jersey police have imposed tough rules on using equipment and ordered the lowest powered handset available.
The testing also threw up concerns that, according to a statement issued by the Jersey Police, “if a speed detection device suffered external radio inter-ference, it was rendered inoperative”. There are also concerns about breath testing devices. According to reports police are being advised that they can only do breath tests 10m from handsets or 35m from more powerful car transmitters. This has raised concerns that the system, the price of which has already been a source of discontent with the old bill, will be turned off in many situations.
The Police Federation has raised concerns that operational effectiveness and even police safety will be damaged, and not improved, by the introduction of the technology. A spokeswoman for the suppliers of the technology, BT Quadrant, said that the equipment used complied with international standards. She compared the equipment to GSM phones which also have to be turned off in hospitals.
(Extracted from an article posted in The Register on 22nd Jan 01 by John Leyden, http://www.theregister.co.uk/content/5/16266.html, sent in by Graham Eckersall, G4HFG.)
123. Police radios can trigger positive breath test. If you’re ever asked to do a breath test by the police you might do well to insist that they turn off their radios before you blow into their breathalyser. The advice comes from an ex-copper who wrote to us after we printed a story about police concerns about interference from next-generation handsets (see above – editor). He writes: “When at the Metropolitan Police training school, it was taught that PCs should not press the PTT (push to talk) button on the personal radio whilst waiting the requisite forty seconds for the lights to (hopefully) go red. Never. “Oh, no - indeed. Definitely not. Especially if the subject was being ‘griefy’. Honest.”
He adds that the idea that that a PC might surreptitiously give a quick burst of transmit on his radio whilst his partner was administering the breath test to an uncooperative suspect, was similarly frowned upon. Its worth noting here that, at least in Britain, the actual charging and conviction of drink driver suspects relies on a different test which is administered at police station. Our correspondent explains the technique was used to annoy awkward customers. “This merely gave the opportunity to cause inconvenience, spend time filling out the forms, apologise profusely and sincerely (again, honest) afterwards, give the driver back the keys to his car and advise him where he might find a cab to drive him back to it. At four in the morning. “Oh dear. Terribly sorry, but we are not insured to give you a lift if you are not a prisoner anymore. Sir. No cash on you, then it’s a long walk back, in the rain,” he added.
Another reader, who worked for the St. John Ambulance, a first-aid volunteer service, recounts a time on duty when he saw a policeman using his radio to trigger a positive result on a breath test. Apparently it was all a bit of innocent fun and the guy was using the trick in a rather strange attempt to chat up a woman he fancied. Our man in the St. John’s Ambulance service says that ambulance radios can have the same effects on breathalysers. It’s not that we condone drink drivers, but if you’re ever pulled up (and assuming you’re not too drunk in the first place) now you know what to look out for. Lets be careful out there. (Article by John Leyden in the Register, http://www.theregister.co.uk/content/archive/16413.html, posted on the 26th January 01, sent in by Graham Eckersall, G4HFG.)
124. Pacemaker users get digital radio warning. A reader was taken aback when he took delivery of digital radio handset from Motorola that contained a series of warnings for pacemaker users. The Motorola d700 handsets, which will be used in a Terrestrial Trunk Radio (TETRA) digital communications project, contain recommendations from the Health Industry Manufacturers Association which advise a minimum separation of 15cm between a handset and a pacemaker.
This advice, albeit well intentioned, leads to a number of surprising tips. Pacemaker users should not keep handsets in their breast pockets and furthermore should “use the ear opposite the pacemaker to minimise the potential for interference”. It goes on: “if you have any reason to suspect that interference is taking place” with a pacemaker you should “turn the handset OFF immediately” — that’s if you’ve not been hit by shortness of breath, of course. We gather there’s also warnings about hearing aids, “other medical devices”, explosives, and a range of other things, which leads our reader to conclude that “it’s hardly surprising people are scared of these things”.
A health and safety expert at Motorola confirmed the information and pointed out, quite reasonably, that the instructions are part of the training it provides its users to make sure its equipment is used safely. He said that “similar power levels” were used by Tetra and GSM equipment, which means that interference levels were “not horrifically different”, though higher, than older analogue technologies commonly in use today by emergency services, the chief market for Tetra.
So, should pacemaker users avoid mobile phones? Well the issue seems to have more to do with the electrical immunity, or lack of it, associated with a particular pacemaker — whose manufacturers ought to provide concerned users with all the information they need. It makes you think though. (Article by John Leyden in The Register, http://www.theregister.co.uk/content/2/17357.html, posted on 5th March 01, sent in by Graham Eckersall, G4HFG.)
125. People around the globe are fascinated with Bremerton’s tale of a bizarre electronic failure. The widespread failure of keyless remote entries on vehicles around Bremerton last week has sparked interest far beyond the local community - thanks to the ubiquity of the World Wide Web and nationally syndicated talk radio. Since the story first ran Saturday in The Sun, it has been broadcast by two nationwide radio programs that focus on bizarre phenomena - “Coast to Coast with Art Bell” and “The Jeff Rense Show.” It also has been posted on numerous Web sites, including The Sun’s (www.thesunlink.com), and reprinted in other newspapers.
The widespread posting has fueled a flood of responses from all over the country — and even from as far away as Russia and Croatia. Meanwhile, the strange incident remains a hot topic in West Sound as residents try to solve the mystery and add to the list of impacts beyond the mass failure of remote entry devices. The outage, which went from about 4 p.m. March 21 until about 6:30 a.m. Monday, apparently was caused by interference with the short-range UHF radio signals transmitted by small hand-held keyless remote devices to an unlocking receiver in the vehicle.
The source of that interference remains a mystery, however. The Federal Communication Commission believes the local military presence is “very possibly” the source of the disruption, said a government official familiar with the agency’s investigation into the outage. Although Navy officials still insist they can find no link between the interference and USS Carl Vinson’s recent return to Bremerton, most responses sent to The Sun reflect a widespread belief that the military presence is to blame for the disruption. They also question whether the interference might have caused other problems — and that still might be occurring.
Some samples of responses:
• An ex-Navy technician wrote: “You know as well as I do that an active electronic countermeasures (ECM) was inadvertently left aboard a ship docked at the shipyard, causing remote car lock devices to be inoperative. That’s what ‘jammers’ are supposed to do. It is not a coincidence that the effect occurred when (USS) Carl Vinson arrived, and then when the sailors went back to the ship Monday and took a good look around, they turned it off.”
• A computer buff in Izakovic, Croatia, wrote that electromagnetic emissions from U.S. Navy warships fry his Internet modem whenever they pull into the local harbor. He now is on his fourth modem and suspects that similar emissions caused the interference in the Bremerton area. “Bremerton mystery is not a mystery at all. U.S. Navy has in operation VTRPE radar and IR/visual/radar satellite detection shielding technology (which causes the problem).”
• Two Bremerton readers reported that something has been interfering periodically with the radio signal that controls their household atomic clocks. The clocks display the exact time, as broadcast continually over several radio frequencies between 2.5 and 20 MHz from a transmitter in Colorado that is linked to the U.S. Naval Observatory’s atomic clock. One clock owner said the problem has persisted intermittently even after the keyless remotes began working again Monday.
Other readers reported problems with TV reception, car alarms and computer microchips in Bremerton and Port Orchard last week during the period of disruption.
• Employees of state and local government agencies reported that their radio systems experience periodic failures in the Bremerton and Bangor areas. “We’ve called (PSNS), and they won’t tell us one way or the other,” one respondent wrote via e-mail. “If we knew when they were testing it would help.”
• A respondent who identified himself as a “Russian geophysicist” sent an e-mail from Moscow suggesting other possible sources of the disruption, such as rogue TV signals or police communications gear.
(Article by Lloyd A. Pritchett, The SUN newspaper of Bremerton, Washington, USA, March 2001, ttp://www.thesunlink.com/news/2001/march/03302mystery.html, sent in by Graham Eckersall, G4HFG, who saw it referred to in the ARRL news (US ham radio organisation) in April 01.)
126. In the corner of the town square, four GIs huddle behind a wall. Someone yells: “Incoming!” A huge explosion lifts the ground, raining down heavy clods or earth that hurt if you don’t turn your back. “Glad I moved you up?” smirks the director, Tony To, having advised a more sheltered vantage point than that previously adopted. The crew set up for the next shot. A warning: mobile phones off. Incoming calls can trigger remote-controlled explosives. (Extracted from an article by Jeff Dawson, in the Sunday Times TV and Radio Guide, 13th May 01, page 4. Jeff was watching a programme about the second world war being made.)
127. After a lightning strike to a factory, a servo-operated packaging machine was found to be operating backwards. It continued to operate at full speed even when its guards were opened, despite supposedly having a hard-wired safety system. (Contributor wishes to remain anonymous, May 01.)
128. The indications are that lightning strikes are on the rise in Europe and it can be expected that damage from these strikes will also be on the rise. (Taken from “Markets for Power Line Surge Suppressors in Europe” by Christopher Lanfear, PCIM Europe, Nov 2000, Page 34.)
129. Today we can easily find examples of more or less serious electromagnetic problems:
nThe magnetic field caused by ground currents in the water pipe system makes it impossible to use sensitive electronic instruments in part of a hospital building.
n A patient-coupled infusion pump is damaged by electro-static discharge, but thankfully the alarm system is not affected, and a nurse is alerted.
n An operation using a plastic welding machine cause interference with a patient monitoring and control system; the monitor fails to detect that circulation has stopped in the patient’s arm, which later has to be amputated.
n A wheelchair carrying a handicapped man goes out of control when it comes close to a radio station antenna mast, and eventually the occupant is ejected into the street.
n A robot starts running amok due to a radio control transmitter, smashing all equipment within its reach. (Editor’s note: always make sure the mains isolation switch for a robot is outside its possible reach!)
n Interference from a passing truck with a radio transmitter causes a crane to drop its load on a person.
n A passenger’s laptop causes a plane’s navigation system to malfunction, causing the aircraft to go off course.
(Taken from “Immunity testing: Examining requirements and test methods” by Dag Björklöf, Compliance Engineering European Edition’s 1999 Annual Reference Guide, page 51.)
130. RA officials obtained convictions against truck drivers for using illegal citizens band (CB) radios. The convictions came as a result of an official stake out of two truck stops on the M4 highway in Wiltshire last October. (Taken from: “Enforcement Efforts Around the World” Conformity 2001, page 209.) (Editor’s note: Almost certainly these truckers were using illegal high-power boosters, capable of creating very high field strengths over large distances. Not a good idea when incidents such as described in the 6th bullet of item 129 above can occur.)
131. The co-existence of Bluetooth and Wi-Fi in the 2.4GHz Industrial Scientific and Medical (ISM) band was discussed at the recent Wireless Symposium in San Jose. Because the simultaneous operation of these two systems can interfere with each other, the search is on for ways to improve their performance when they are in proximity. As explained by Jim Lansford of Mobilian Corp. (Hillsboro, OR), these two technologies (known as WPAN and WLAN) are headed for significant growth. “Co-existence has become a significant topic of analysis and discussion throughout the industry”, says Lansford. “With both of them expecting rapid growth, co-location of Bluetooth and Wi-Fi devices will become increasingly likely.” “They create in-band coloured noise for one another. Neither was designed with specific mechanisms to combat the interference from the other. Bluetooth assumes it will hop away from bad channels. WLAN (802.11b) assumes that if it fails, two Wi-Fi stations tried to transmit at the same time.” (Extracted from “Living in a Wireless World” by Sherrie Steward, Compliance Engineering, March/April 2001, page 10.)
132. Any time you have more sources of RF energy, the EMC design must accommodate with greater immunity. One area of growth is the use of the 2.45GHz band, where such activity as Bluetooth, cordless phones, HomeRF, new RF lighting, and other systems are all vying for use and must work with each other’s ambients. There have been claims of interference, but this situation is still coming to a boil. It is only a matter of time before products with lesser immunity in this band will not work together at all user locations. (Taken from “EMC in a High-Frequency World” by Donald N. Heirman, Compliance Engineering, Jan/Feb 2001, page 30.)
133. For example, 15 percent of all computer server crashes can be attributed to electromagnetic interference. (Taken from “The EMC Building: design and construction strategies” by Jose M Rio, ITEM Update 2000, page 28.)
134 It can clearly be seen from table 1 that GPS receivers are very sensitive compared to the others (GSM and Bluetooth) and not surprisingly, this means they are more prone to interference. For military applications this problem is largely solved by the use of controlled reception pattern antennas which electronically ‘point’ the antenna at the satellite, boosting the signal to interference ration by typically 30dB. GPS signals can be interfered with by harmonic interference from commercial TV stations and mobile telephone base-stations. In some countries, including Germany, Austria and Hungary the GPS frequency band is also shared by local fixed radio services and GPS reception is impossible in some (small) areas of Hungary for this reason. (Taken from “GSM, GPS and Bluetooth in an Automotive Environment” by Dr Peter Miller, Euro-EMC’s EMC seminars 3-5 April 01.)
135 In spite of using coaxial cables in cable TV distribution systems there is a lot of shield leakage, based on technical imperfections and ageing. Catastrophic emissions in the aeronautical security bands are jamming Germany. LANs ands WANs are growing increasingly, adding to this critical situation. (Taken from Megabits Per Second on 50Hz Power Lines” by Diethard Hansen, IEEE EMC Society Newsletter, January 01.)
136 According to her study (Kate Harris, International Switching Symposium 2000, Birmingham, UK) measured ADSL data rates suffer as much as a 2000-b/sec drop when exposed to RFI, which can occur in the bands where DSL networks and AM broadcast share the same spectrum. In North America, this sharing occurs at the medium-wave AM broadcast band. The downstream bands of ADSL and ADSL.lite intersect with AM radio broadcasts in the 535-1104 khz and 535 – 552 kHz ranges, respectively. There is no overlap between their upstream bands and AM radio broadcast. In fact, the narrow overlap of ADSL.lite and AM radio enables minimum capacity loss in ADSL.lite services when combined with low-pass filtering and modern RFI immunity.
In Europe, however, the upstream band of symmetric high-bit-rate DSL (SHDSL) does share spectrum with AM radio, at the long-wave AM band. And the downstream bands of ADSL and ADSL.lite overlap the long-wave AM band in addition to the medium-wave AM band. Therefore, DSL networks in Europe must contend with a broader RFI threat.
According to Eckert, regulatory agencies are more concerned about egress (interference with AM radio caused by the DSL systems) rather than ingress (interference experienced by the DSL system from AM radio transmissions). But because DSL services are ‘white’ and not concentrated in a carrier, interference produced by these services sounds like white noise, making it difficult for AM radio users to identify the problems as interference. Complaints received by a regulatory body would not necessarily pin-point the origin of the interference or the use of a DSL product as the culprit. So regulatory bodies have been slow to act, which has in turn slowed standards work. (Taken from “Addressing the Risk of RFI to and from DSL Networks” in Compliance Engineering Jan/Feb 2001, pages 12 and 14.)
137 Additional areas being investigated by the FDA include electronic article surveillance (EAS) machines and their impact on implantable medical devices. The EAS machines are utilised as anti-theft devices in the exits of many retail stores. There have been instances caused by the interaction of these electromagnetic machines and implanted medical products. (Taken from “Update on Medical Devices and EMC” by Daniel D Hoolihan, ITEM 2000, page 84.)
138 Two unusual forms of ESD, internal chair discharges and metal-to-metal discharges from “jingling change” have cause severe field problems in electronic equipment. These forms of ESD are not covered by any current standard.
n When a person rises from a chair, charges are generated on both the surface of the chair seat and internally that can cause ESD events to occur inside of the chair. These discharges are between metal parts of the chair that are not electrically connected to each other. The discharges cause intense electromagnetic fields to be radiated from the metal parts of the chair, usually the legs. This radiation has been shown to be capable of disrupting the operation of nearby electronic equipment. This effect was first reported in 1993 by Honda and Smith. Most chairs I have observed with this effect produce about a dozen discharges over the first 10 to 15 seconds after a person rises from the chair. However, some office chairs are capable of producing several hundreds of discharges over as much as a minute. Just purchasing “ESD safe” chairs alone will not eliminate the problem. I have personally observed an “ESD safe” chair in a factory emitting this type of interference. Since 1993, many types of equipment have been affected by this phenomenon, including communications equipment, computer equipment, even critical equipment in the field of aviation.
n When small pieces of metal, such a pocket change, move around inside of an insulating pouch such a pocket or plastic bag, they generate different charges. When they touch, small ESD events are generated, for the most part too small to be seen. I have measured risetimes of the fields to be smaller than 100 picoseconds, with sub-nanosecond pulse widths. With the increasing speed of electronic circuits, many types of circuits have become susceptible to this form of interference. I have caused upset by shaking a plastic sandwich bag with a handful of pocket change near communications equipment, a 100MHz PC, and some consumer electronics. In one case, shaking a bag of coins 3 feet from a rack of equipment caused dozens of red LEDs to light! (Taken from “Unusual Forms of ESD and Their Effects” by Doug Smith, Conformity 2001, page 203. The article originally appeared in the 1999 EOS/ESD Symposium Handbook.)
139 You might be interested to note that it is possible to intercept VDU emanations at 1km for monochrome and more for RGB. Both figures are likely to be greater using sophisticated technical means. (Taken from a discussion about TV detector vans and TEMPEST in The Register, www.theregister.co.uk, 4th March 2001 by Andrew Orlowksi, sent in by Graham Eckersall.)
140 In a newly-constructed financial dealing room, the earthing was done as per IEE Protective Earthing (BS7671). After 2 weeks the US made computer equipment failed. US engineers said it was due to leakage currents from their ITE. Protective bonding for safety is only concerned with 50Hz currents, and is not adequate for modern computers which need a lower earth impedance at higher frequencies because of earth leakage from their mains filters. In a large computer installation earth leakages (alone) of 70A have been measured at the main earthing terminal, and they are rarely less than 10A. (Sent in by Keith Armstrong, reporting on the presentation by Peter Smith of his paper “Protective or Clean Earthing – a Potential Difference” at ERA’s Earthing 2000 conference 2000, Solihull, 21/22 June 2000.)
141 We have a product used in-vehicle for vehicle handling testing (see the SR30 robot stuff on our website if you're interested). One version has a control box that incorporates the closed-loop position controller, servo-amp, interlocks etc and communicates with a remote lap-top, usually part of the end-users data capture system to select the test type and set-up and to upload any test information captured in the controller card.
Early experience suggested that separating the ground references of the remote equipment (normally cigarette-lighter powered) and our control system (direct battery powered; it takes up to 100A instantaneously but has a tare drain of 5A) were a good idea, to prevent the inevitable fighting over the apparent vehicle chassis '0V’ reference. We therefore installed the proprietary opto-isolated serial comm’s card supplied by the controller manufacturer and used a shielded comm’s lead (RS232) with the shield connected at one end only – our end in fact.
Six of these units had performed quite happily in the field (and flew through the fairly arduous 30V/m tests used in automotive EMC testing) but the seventh seemed to be very sensitive to the particular laptop/power unit combination used. Very regularly the serial comm’s would lock up when the PWM servo amp was enabled.
With the unit back at our base the symptoms were all too readily reproduced on the end user’s laptop (but not with the newish Dell used in all our testing). Looking at the serial comm’s lead I noticed something different about the 9-pin D-type connector at our end; it had been fitted with a flexible push-in capacitive filter 'thingy', of the type available from RS and used on some of our equipment.
As this was not (and had not been) part of the standard assembly I removed it, and the serial comm’s problem was instantly solved!
I can only imagine that this 'thingy' was not acting as a filter but was acting as a convenient means for noise to be injected onto the cores of the serial comm’s lead. The connections entering our control case are on the isolated side of the opto card, referenced to the 0V potential of the remote laptop. The connector shell is referenced to our case and its control 0V potential, therefore if our case potential moves relative to the RS232 cores (as I can only imagine it must be when the amplifier is enabled) the capacitors in the filter will act as convenient low impedances directly injecting noise onto the cores.
Fitting the filter 'thingy' at the laptop end is, of course, the thing to do ...... and moving the shield connection to that end should also help, otherwise the transfer capacitance twixt shield and cores could also be a problem in much the same way as the capacitive filter! (from Dave Bethell, Anthony Best Dynamics Ltd, 25th June 01)
142 We have news from down-under
about things that bump and grind in the night...
Australia's ABC TV and Sydney's new FM radio station 'Nova 96.9' have unwittingly joined forces to meddle with automatic garage doors. VK2WI reports that hundreds of radio-controlled garage doors across Sydney have been overloaded by the ABC and Nova transmissions and some are refusing to open and close. In several cases the doors have developed a life of their own, randomly opening and closing at all hours. The reason is that Nova broadcasts on 96.9MHz and the ABC TV sound signal is on 69.75MHz.
When the two signals mix in an overloaded door receiver, the result is a 27.15MHz signal, which passes straight through most door receivers which are tuned to 27.145MHz, only 5kHz different. This causes erratic behaviour, dependent upon signal content, and the doors open and close in sympathy. Perhaps the designer has sleepless nights, too! (from Graham Eckersall G4HFG / W4HFG 6th July 01, who got it from the ‘News’ section of the RSGB website.)
143 Subject: Bizarre Solution... What you describe is a common problem to commercial-radio technical folk. Proximity to active radio-transmitting antennas can cause really wild things to happen to electronic circuits such as the metering portions of your 645 Pro. (It's interesting to note that even some very well-designed and expensive electronic test equipment can be rendered essentially useless by these strong radio-frequency fields.) The wiring within your camera (it may be nothing more than a centimetre or so of printed-circuit land on a fiberglass circuit board) acts as an antenna. The signal it picks up can then be rectified (changed from a radio signal to a small D.C. voltage) and this voltage can, in turn, add to or subtract from the small voltage generated or controlled by the light-sensing elements in your camera metering system. I would guess that if it adds, you get underexposure; if it subtracts, you get overexposure. It will depend upon exactly how the rectification occurs in the camera circuit. A parallel case of this type of interference occurs when an automobile with a radio-controlled door lock is located near a high-powered radio or television transmitting tower. Often, it's impossible to unlock the car using the small, keychain-type device because of the same type of effect. In some cases, a particular program signal will trigger the car alarm! The tops of some of those California hills are loaded with radio transmitters and can contain very strong radio-frequency (RF) fields. It would be my guess that the metal housings of some cameras would shield the internal electronics from RF effects. Of course, a plastic housing offers little such shielding. At best, even a metal-bodied camera would be subject to "radio interference." It can be pretty squirrely stuff! Radio signals and light are both forms of electromagnetic radiation and the inverse square law works for both. The best cure, therefore, is increasing the distance between your camera and the transmitters. As a radio engineer, I've learned long ago that you just can't do certain things close in. Hope this simple explanation helps. (David Mehall, 22 Aug 1996, from a thread on photography)
144 Gun Wharf, a leisure centre in Portsmouth, opened in Easter 2001. It had an underground car park, and the car park had a video surveillance system. It seems that electromagnetic emissions from the video system would often interfere with car central-locking and security systems – locking the cars as soon as they were unlocked, or just not allowing them to be unlocked at all. Many people had to leave their cars in the car park and take taxis home. (From Anne Cameron, Alenia Marconi Systems, 6th July 01)
145 A relatively recent (1997) definition of Information Warfare given by the Ministry of Defence is: “The deliberate and systematic attack on critical information activities to exploit information, deny services to the authorised user, modify and corrupt data.” The issues involved reach well beyond the realm of military warfare, extending to e-business, e-commerce, e-finance and e-government. The power, water and food distribution systems, the emergency services, air traffic control systems, the banking sector and the financial markets, to name but a few, are all dependant on networked digital systems for effective communication and control. It is a sobering reflection that ‘the most advances society in the world is really only four meals away from anarchy, and if you could attack a society through its computers to cause the breakdown of the mechanisms, the infrastructure, which cause it to run, you will bring about mass deaths.’4
Line of sight devices. Two distinct classes of line-of-sight devices have been described. The first is a form of low-energy radio-frequency (LERF) jammer, which can be used to temporarily disrupt digital electronic circuits at close range (of the order of metres). Since any cable or circuit component in an electronic system is in principle an unintended antenna, capable of both transmitting and receiving at its characteristic frequency, a low-energy wide spectrum RF field will contain with high probability frequencies matching the resonant frequencies of critical circuit components. If this is the case then the system would go into ‘random output mode’; its behaviour would be impossible to predict, but could range from single recoverable processing error to total loss of the RAM contents.15 A parts list and circuit design for such a low-tech device was posted on an Internet bulletin board in 1995 and described at InfoWarCon in 1996. The device was subsequently built and tested in the UK to check the veracity of its design.10
The second class of device is the high-energy radio-frequency (HERF) gun or non-nuclear electromagnetic pulse (NN-EMP) cannon, which can permanently damage digital circuits at longer ranges (or the order of a kilometre) by blasting them with a pulse of microwave energy in the gigahertz frequency range. The MOS chips are effectively ‘fried’ by this process. HERF technology is high-tech and remains the subject of classified military research. However, the unclassified technology had been reviewed and discussed in detail.16 In order to protect (or ‘harden’) systems against RF attack they need to be entirely enclosed in a Faraday cage, ideally including the electrical power feeds and communications links, since these can act as antennas for the RF field or EM transients.
Eavesdropping and surveillance. Since a cable or circuit component can act as a transmitting antenna, unshielded computers and networks are liable to leak compromising RF emanations that are a potential source of intelligence. Passive intelligence gathering from unshielded systems (ElInt) has been given the name TEMPEST (transient electromagnetic pulse emanation standard, see Reference 16, note 3) while emanations specifically arising from the CRT screens of VDUs are known as van Eck radiation after the scientist who was able to demonstrate remote reconstruction of the screen contents using low-tech equipment.17 It has been pointed out that malicious software could be used to infiltrate a target system, obtain critical information, and encode it in the system’s Tempest emanations in order to broadcast it back to the attacker.18
Summary and prospects. The threats to, vulnerabilities of, and impacts on critical national infrastructures (CNI) are real and capable of assessment, although in practice this is a complex and challenging task, the more so since information warfare possesses several characteristics of that are not shared by conventional warfare: it is global (there are no borders); it is precise (surgical strikes are possible); it is un-proportionate (the cost of attack is much less than the cost of defence).19
Some of the accounts of information warfare carried by the media have been exaggerated or are inaccurate, but this must not deflect us from addressing the crucial issues of defining, developing, and deploying critical infrastructure protection (CIP) policies and strategies. (Extracted from “Information Warfare: battles in cyberspace”, by Richard E Overill, IEE Computing and Control Engineering Journal, June 2001, pp125 – 128. There was a lot about hackers and such which has been omitted from this extract.)
146 Case #22804: Lead boxes – Good for Kryptonite, bad for CRT monitors.
A prestigious New York Hotel had upgraded their check-in and reservation computers to modern PCs with colour CRT monitors. One unit’s screen, in the managers office, was nearly impossible to read due to a wavy image. Magnetic fields at up to 60 milligauss were found at the monitor location and were coming from a power company electrical vault under the sidewalk outside. Some monitors can be disturbed by as little as 10 milligauss. Due to some bad advice, the hotel had an aluminium box built (didn’t work), then a lead box (didn’t work either but at least now the monitor was protected from Superman’s X-ray vision). Eventually they came to us and our standard five-sided ImageGuard CRT monitor enclosure did the trick. (from the Journal of Magnetic Shield Case Studies, an in-house advertising medium published by the Magnetic Shield Corporation.)
147 Silicon Film Technologies, the firm developing a digital ‘film’ that fits in a standard SLR camera body, has suspended operations because of failure to meet EMC standards. “The failure of certification tests in the summer delayed Silicon Film’s anticipated revenues, but development expenses continued,” said Robert Richards, president and CEO of Irvine Sensors, the firm’s largest creditor. Last week Silicon Film said it had met the FCC emissions requirements but could not conform to the stricter European standards. “We believe at least some of those stricter standards must be met for a successful product launch,” added Richards. If alternative finance is not found, the firm – 51 per cent owned by Irvine Sensors – will go onto liquidation. (From Electronics Weekly, 19th September 2001.)
148 A particular make of 30mA RCD units fitted in plastic consumer units in site contractor’s portable cabins would trip when the walkie-talkies used by the contractors were keyed within 1 metre distance. Replacing them with a different make of RCD solved the problem. (From Chris Byrne of CB Electrical Engineers Ltd.)
149 The penetration of high-intensity radiated fields (HIRF) into conducting enclosures via apertures is an EMI issue that is relevant to all aviation. The stories are numerous, of disrupted communications, disabled navigation equipment, etc., due to the effects of sources external to the aircraft. (Extracted from “HIRF penetration through apertures: FDTD versus measurements” by Stavros V Georgakopoulos, Craig R Bircher and Constantine A Balanis, IEEE Transactions on EMC, Vol. 43 No. 3 August 2001 page 282.)
150 It should be emphasised that changing heat-sink gasket material as an EMI mitigation strategy is limited to cases in which the heat-sink patch resonance constitutes a significant part of the overall coupling mechanism. Even then, it is necessary to ensure that the shifted patch-resonance does not coincide with a clock harmonic. Despite these limitations, there are at least two commercial products in which the substitution of one electrically insulating heat sink gasket for another (of the same size but different composition) has resulted in significantly reduced EMI at certain troublesome frequencies. In one of these cases, this reduction was sufficient to allow the product to meet FCC requirements. (Extracted from “EMI considerations in selecting heat-sink thermal gasket materials”, Huang et al., IEEE Transactions on EMC, Vol. 43 No. 3 August 2001 page 259.)
151 Each year the size of transistors shrinks, thereby improving performance (but not EMC performance! – Editor). Yet, according to Technology Review, transistors must be big enough for electrons to pass through. Preparing for an inevitable impasse, Toshiba has demonstrated a transistor that can turn on and off based on the movement of a single electron. Unlike other quantum-level transistors, the device operates at room temperature. It’s also the first successful hybrid circuit, mixing single-electron transistors with traditional metal-oxide transistors, which are required to boost the weak quantum-level signal. Chips based on the circuit should offer blazing performance and low power consumption. Before building a full-fledged processor, researchers face challenges such as finding a way to protect the chips from the disrupting effects of stray electromagnetic fields, electrical discharges, and physical movement. Hybrid chips should be available for use by 2010. (From Electromagnetic News Report, July/August 2001, Pages 11-12.)
152 50 years ago…The Postmaster General’s Advisory Committee on Wireless Interference from Ignition Systems has now presented its report. The Committee devoted its attention in the main to the abatement of interference with the television services of the BBC from ignition systems, including those used in motor vehicles, motor boats, fixed or portable stationary engines, motor mowers, tractors, etc. The Committee’s recommendations are based on the assumption that all reasonable measures will be taken to reduce the susceptibility to interference of receiving installations. They recommend that ignition equipment, when installed as intended, should not radiated an interference-producing field which exceeds 50 microvolts per metre in the 40-70 megacycles per second frequency band, measured on specified equipment at a point not less than ten metres distant. The committee advise that suppression to this amount can be achieved with negligible effect on the mechanical performance of the engine. In the case of about 60 per cent of existing motor cars the Committee think that the required degree of suppression can be achieved by fitting a single resistor costing about 2s 6d. (From: Council Notices, The Journal of the IEE, September 1951.) (Editor’s note: 2s 6d is equivalent to 12.5p now, or about 18 cents US. Of course in 1951 this amount of money was worth a lot more than it is now.)
153 An early set-top box was found to interfere with the picture of the TV it was placed on top of, but only after 2 to 5 minutes. The designers had spent months making sure that the emissions from the product were very low. Then they found that the product caused the same interference when no cables were plugged into it, and then even when it was switched off!
It turned out to be due to the magnetic fields from the stereo speakers in the TV. Placing any metal object on top of the TV caused similar interference problems, after a few minutes. (From the “War Stories” forum held on the 17th August 2001 at the IEEE’s International EMC Symposium in Montreal, Canada.)
154 A particular computer manufacturer had a software lab that checked the compatibility of their new products with a number of applications. With one new product the evaluation systems shut down when the testing staff left the room. The new product at that time consisted of a motherboard and HDD with no enclosure, plus the usual keyboard, monitor and mouse.
It turned out to be caused by the induction field developed by the static charge between the staff and their furniture when they stood up (not a spark, just a changing ‘static’ field). This field interfered with sensitive circuits on the exposed motherboard and caused the shutdown. (From the “War Stories” forum, 17th August 2001, IEEE International EMC Symposium, Montreal, Canada.)
155 Testing the shielding effectiveness (SE) of an aircraft on an OATS (Open Area Test Site). The engineers had shielded a wheel well using aluminium foil and a ground strap and were confused by random variations in the SE of up to 20dB. These variations were eventually noticed to correlate with the clouds passing in the sky, but at night there were no variations in the measured SE.
The problem was eventually found to be caused by corrosion between the grounding surfaces. Heating and cooling of the aircraft’s metalwork due to the sunlight and shade caused by the clouds caused the quality of the electrical bond at the corroded grounding surfaces to vary, causing corresponding variations in the SE of the wheel well. It proved possible to simulate the problem by banging the aircraft with a length of 2x4. (From the “War Stories” forum, 17th August 2001, IEEE International EMC Symposium, Montreal, Canada.)
156 A new non-invasive blood pressure monitor was an electronic version of the old ‘cuff’ method. While testing it for RF immunity it would fail to measure at all between 950 and 1000MHz. It was found that its pressure sensor was outputting misleading signals during the test, despite being a standard part that had been used for many years without problems (or so claimed its salesperson). The pressure sensor had a 6-pin package, with 2 unused pins marked “do not connect”. Copper tape over the transducer and its pins made the problem go away. The problem was then isolated to just three of its pins, one of which was a compensation capacitor for the sensor’s internal amplifier. An engineer working for the Japanese company that made the sensor said that he had seen the problem before in an automotive application.
The N/C pins were connected to the inputs of the internal amplifier and used for performance checks during production testing. The pins were acting as antennas, picking-up the external RF field and injecting it into the internal amplifier at its most sensitive point, where it would be inevitably rectified (demodulated) by the semiconductor junctions in the amplifier’s IC and cause major shifts in DC operating points. Even with these pins cut off from the package the problem still remained – the amplifier was so sensitive that the internal leads and the bond wires to the IC still made effective antenna at 950MHz.
Eventually the sensor was modified by the manufacturer so that it did not have this problem. In the meantime one year’s worth of production of the new product suffered the additional cost of $20 per unit for a shielding can and its fitting. (From the “War Stories” forum, 17th August 2001, IEEE International EMC Symposium, Montreal, Canada.)
157 We put a tape recorder into a drone aircraft used for surveillance. When the tape recorder came on, the drone nose-dived. The 10kHz bias oscillator for the tape recorder was exactly the same frequency as was used by the aircraft’s control system, and this caused the problem. The moral of this story is to avoid using standard frequencies. (From the “War Stories” forum, 17th August 2001, IEEE International EMC Symposium, Montreal, Canada.)
158 How many EMC engineers does it take to change a light bulb? No. 1.
A 20 Amp 20 Volt power supply for a medical xenon lamp had to meet EU emissions standards. The PSU was to be fitted in various boxes, some of which could be plastic, so needed not to have to rely on any shielding from its enclosure. The output of the PSU had a 50 microHenry choke in series, to generate the high voltage which would ‘kick-start’ the discharge in the xenon lamp. Unfortunately, 20mA of RF common-mode current was measured the lamp cable!
After a lot of work on the power supply, to no avail, someone tried a different type of lamp and found that the RF noise was 40dB less. Three other types of lamp were also found to be 40dB less noisy. Then other xenon lamps of the same type as the original noisy one were tried and found to be 40dB quieter too. So it seems that all xenon lamps are not created equal.
By the way, the answer was: four engineers. (From the “War Stories” forum, 17th August 2001, IEEE International EMC Symposium, Montreal, Canada.)
159 How many EMC engineers does it take to change a light bulb? No. 2.
We had designed a shoe repair kit for use by the US army. The only electrical item in it was a standard domestic-type incandescent filament lamp that ran from 110V 60Hz, so the squaddies could repair their shoes at night. Unfortunately, our regular contact with the military was on an assignment elsewhere and we had to deal with a novice who didn’t understand EMC at all and insisted that we had to fully test the shoe repair kit to MIL-STD-461, the US military’s EMC standard. He would not be moved by our arguments that the testing was a waste of time. He was following the procedure and it was more than his job’s worth to believe us when we said that it didn’t need testing as it was bound to pass. So we had to do the tests.
Imagine our surprise when our shoe repair kit failed its emissions test by a significant amount at 45MHz! We soon discovered, of course, that this was due to the light bulb. When we contacted Sylvania, its manufacturers, we eventually discovered that around 1% of all incandescent light bulbs (not just Sylvania types) had VHF oscillations, typically occurring between 28 and 45MHz and caused by a ‘monode’ gas plasma oscillator occurring in the very hot gas close to the coiled filament. The emission frequency could not be predicted because there was no configuration control during manufacture for the aspect of the filament construction that caused the VHF oscillation. As far as we know, this 1% problem with incandescent filament light bulbs is still around.
We don’t remember what the answer was in number of engineers, but it was quite a few. (From the “War Stories” forum, 17th August 2001, IEEE International EMC Symposium in Montreal, Canada.)
160 This is a supplement to Banana Skin no 153 in Issue 37. The stereo speakers on our television had been making rude reverberating noises for some time, particularly so when the sound was moderately loud in the bass. On reading in Banana Skin 153 about the metal chassis of an early set-top box causing picture interference, I removed the old set-top box, which we never use, from our T.V. and the sound is now OK. So it seems that interference from a metal plate above the television set can affect the sound as well as the picture.
161 In the mid 1960s, a London bank was experiencing malfunctions in its new mainframe computer. On the assumption that the cause was mains-borne interference from extraneous sources, a motor alternator set had been installed at the bank to isolate the computer from the mains. That done, the malfunctions continued. So they asked Eric Langham for help. He found radio frequency ringing on the mains input to the computer, triggered by abrupt changes in alternator volt drop apparently brought about by sudden changes in load current during operation. The addition of R-C snubbers across the three phase input to the computer eliminated the RF ringing and cured the problem. (Verbal from Eric Langham, Chartered Electrical Engineer.)
162 Small amplitude hunting of the speed of the DC thyristor drive of a 250 hp extraction fan was largely unaffected by experimenting with the values of the R-C stabilising circuit around its speed error amplifier. Then, quite suddenly, the hunting stopped - coincidentally, it transpired, with the chief electrician switching on the automatic power factor correction system in the electrical sub station as the factory load increased. With hindsight, it is apparent now that cyclic voltage dips in the electric mains originating from commutation in other phase angle controlled thyristor power equipment had been delaying the latching of the thyristors in the fan drive (which were fired by trains of short pulses) until the introduction of the power factor correction capacitors reduced the amplitude of the dips. (From when I was Senior Systems Engineer for E M Langham, Chartered Electrical Engineer, 1962-79.)
163 Various guillotines cutting material to length were frequently making double strokes. The source of the trouble was found to be RFI generated when the output contact of the length counter switched the initiating relay in the guillotine control. The contact had originally been suppressed by an R-C snubber comprising 100 ohms in series with 0.1 microfarads connected across it inside the counter. In some counters these components had blown up and were open circuit! Bench testing of the several types of relay used in the guillotines showed that the original capacitor was too small, in some cases, to limit the peak voltage transient to within its own voltage rating. The shortcoming was cured by connecting appropriate R-C snubbers in parallel with the coils of the guillotine relays. (Yet another from when I was with E M Langham, Chartered Electrical Engineer.)
164 In the early 1980s, an electronically controlled flying saw occasionally (perhaps once or twice during an eight hour run) switched itself off whilst cutting slowly moving heavy density material into short lengths. Each event cost some £1000 in lost output whilst the scrap material was cleared and production restored. At the end of an all-night vigil, the user’s systems control manager traced the cause to be the false triggering of an integrated circuit monostable in the 24 volt DC control sequencing logic, coincident with a brief period of heavy regeneration of the thyristor controlled main DC drive during its operating cycle.
Bursts of thyristor commutation current generated disturbances which caused radio frequency ringing at the output of an autotransformer which had been installed to match the 430 volt factory supply to the 380 volt rated German electrics. RFI was breaking through into the 24 volt DC supply because a small capacitor, shown on the circuit diagram, had been omitted by the manufacturer. Critically damping the autotransformer output leakage inductance by R-C snubbers and installing the missing capacitor effected a complete cure. (From when I was Systems Control Manager at the Cape Insulation Rocksil Works in Stirling, 1979 to 1987.)
165 Variations in the analogue output signal of a flue gas oxygen monitor operating from a probe in the waste gas duct of a glassmaker’s furnace were traced to common mode interference from the furnace heating phase angle controlled electric boost. The coupling was found to be directly conductive and its effect dependent upon probe temperature. Operation adequate for using the probe signal to control the combustion air/oil ratio was achieved by re-siting the probe further away from the furnace and its boost electrodes in a less hot part of the flue. (Another from the Cape Insulation Rocksil Works.)
166 The cause of sporadic false firing of its thyristors which, when it occurred, switched the output of a single phase heating controller to full power was under investigation. Then the problem suddenly ceased when the firm’s electrical engineer, acting quite independently, discovered and disabled a defective electrical contactor in the mains power factor control system. (Another from Cape Insulation Rocksil Works.)
167 The output thyristors in photocell detectors in the rolling unit of a multi-section pipe making machine were failing to latch on immediately and delaying the response of the control system. Cure was effected by re-routing their screened cables directly back to the control cubicle through dedicated individual steel conduits. Then the same defect was found elsewhere on the machine. Detailed investigation revealed that the manufacturer’s technician had installed and earthed all the screened cabling in a manner contravening his firm’s explicit documented instructions. So, during a fortnight’s shutdown brought about by the need to carry out other remedial work, the user’s electricians revamped the screened cable terminations and cured all the associated malfunctions. (Yet another from the Cape Insulation Rocksil Works.)
168 The inverter powering the hoist drive of an overhead travelling crane frequently tripped during long travel, coincidentally with the operation of a limit switch which directly switched a tungsten filament indicator bulb in the driver’s cabin. RFI from the switch was found to be injecting a false motor speed feedback pulse train into the control system and transiently grossly mismatching the inverter voltage and frequency output to the needs of the motor. The malfunction was cured by removing the lamp bulb as the crane driver did not need the indication. (From David Blake BSc CEng MIEE, Managing Director of Electronic Design Solutions Ltd, describing events from when he was Managing Director of Pace (Stirling) Ltd - consulting engineers – from 1987 to 1998.)
169 When checking the calibration of load cell equipment in the hoist mechanism of an overhead travelling crane, it was found that its electronic signal converter could be made to give any value of analogue output voltage between zero and full scale (10 volts) dependent upon the proximity and orientation of the tester’s walkie-talkie radio. No remedial investigation was undertaken because no personnel would be on the crane during normal operations and maintenance staff now knew not to use a walkie-talkie there. Possible effects from other sources of RFI, such as inverter drives, were not looked for because the equipment performed reasonably enough in normal circumstances. (From David Blake, details as for 168 above.)
170 Personally, I could list a ton of stuff that would instil fear and loathing amongst the faintest of EMC hearts. Sitting in a jet airliner at the end of the runway readying for take-off and watching the cabin lights dim slightly in sync with the sweep of the main radar dish just a couple of hundred yards away. ESD events in the kitchen area of the airliner causing the phone in the cockpit at the other end of the plane to ring making the pilot pickup to answer. ESD events in the control tower of an airport causing the computer and other essential equipment to crash. Enough spurious radiation events to require laptops and cell phones to be turned off upon takeoff or landing. Why am I and hundreds of others trusting out lives on something so ... sensitive? But we think nothing of dialling up the cell phone inside a car packed with digital controls for things like the brakes, the accelerator, gas control ... The automobile industry does its best to test for the severest of electrical events with lightning simulations. But what about internal to the car less than a meter away? And by the way, do they allow cell phones and laptops in that airport control tower? Do they have conductive floors and require people to wear ESD proof shoes? Define safety related issues? Does it necessarily have to do with physical safety? How about the spurious radiation from an ATM being decoded by someone nearby to gain access to your bank account to drain it? (Posted by Doug McKean on emc-pstc, 2nd Jan 2002)
171 EMC? Ha! I’ve replaced the incandescent lamp on my bedside table with a new energy-saving compact fluorescent lamp. With the lamp on, I cannot listen to even the strongest AM radio station on my clock radio (on the same bedside table) due to the lamp interference. This must not be the usage contemplated by EMC requirements. My TV and stereo are more-or-less integrated (they are in close proximity). On New Year’s Day, I wanted to listen to the radio version of the football game description while watching the TV. With the TV on, I cannot listen to even the strongest AM radio station due to the TV interference. This must not be the usage contemplated by EMC requirements. I take my Grundig portable radio with me when I travel. Most hotels have sufficient interference sources that I cannot listen to AM radio, and sometimes not even FM radio (with lights and TV off!). This must not be the usage contemplated by EMC requirements. EMC? Ha!(Posted by Rich Nute on emc-pstc, 3rd Jan 2002. Rich is based in the USA.)
I have it from a message on the RFI@contesting.com list that Phillips bulbs produce less RF noise than others. I can’t vouch for that, however. (One of the replies to the above, from Cortland Richmond, 3rd Jan 02)
172 The Sound Dept. was asked to design sound effects for a fairly standard play. To deliver the sound effects, sixteen amplifier/loudspeaker positions were required, six of them on stage. All went well during the rehearsals and during the first day of production. The sound designer seemed to have done a good job, so I went back to my office to plan a touring season. But on the second day of production, I was summoned to the stage by the director of the play. His artists could not concentrate on what they were doing because of loud clicks coming from the on-stage loudspeakers. Sure enough, every time someone used the lift to and from the fly floor, a loud noise could be heard in every loudspeaker on the stage. The problem was traced to the input cables for the amplifiers. The input cables were neatly taped to the floor, following the line of the set. Unfortunately, the cables ran parallel with the lift power wiring, which was under the stage and out of sight. On inspection it was found that the input cables to the amplifiers ran parallel with the lift wiring for at least seven meters. Every time the lift was used, the magnetic field generated by the switching current, coupled with the amplifier cable shields and the switching noise was injected into the input circuit of each amplifier. When the input cables were re-routed, the noise was reduced, but did not totally disappear.
Some years later I found out why. In each case, the cable shield was only connected to ground at one end. This is still the most common method used for trying to control low frequency noise, such as hum or buzz, for equipment that connects the cable shield to the internal circuit 0V conductor (this is now known as “the pin 1 problem” because the three-pin XLR style connectors used in pro-audio connect the cable screen to pin 1). Each cable shield was thus an excellent receiving antenna for frequencies whose wavelengths were a small fraction of the cable length. The switching noise was duly induced in the cable shields and the noise currents delivered to the output connectors of the mixing console (the cable shields being disconnected at the amplifier ends), where the noise was injected into the mixing console ground conductors. Thus the switching noise was added to the signals delivered from the mixer to all sixteen power amplifiers. (From Tony Waldron, Technical Manager of Cadac Electronics Ltd, recalling an incident when he was Head of Sound at the Royal National Theatre in 1986.)
173 Today I heard about a case where an ISDN terminal was susceptible to a DECT phone next to it while a 900 MHz GSM did not cause anything. This was in the field, not in test lab. In test lab my experience is that if it passes below 1 G it also passes above it. (Posting from Ari Honkala to emc-pstc, 10th Jan 02)
Try putting a mobile phone next to your computer mouse! Even more fun if the computer has speakers! (One of the replies to the above, from Peter Flowerdew, 10th Jan 02. We recommend making sure all data is backed up on removable media before trying this or other interference experiments on PCs, MACs, or other computers.)
174 The Japanese Ministry of Health, Labour and Welfare announced that there was a case where the operation of a heart pacemaker was influenced by the electromagnetic field from an anti-pilferage device when the patient walked through the exit of a library. Fortunately, the effect was to reset the personalised parameters in the pacemaker to the initial (non-personalised) settings, and the patient didn’t feel discomfort with that. The ministry believes that risk of hazard caused by electromagnetic interference between pacemakers and anti-pilferage devices is low, and a recommendation to the patients was not to stay long time near anti-pilferage devices. The information source was: articles on newspapers (Asahi, Yomiuri, Mainichi, etc.) at 17 January 2002, and Pharmaceuticals and Medical Devices Safety Information No.173 (January 2002) from the ministry. (From: Tom Sato, 19th Jan 02)
175 Scientific studies have reported increased interference effects in pacemakers caused by digital phones that did not occur with the older analog technology. Cell phones have decreased in size so that they are often carried in a shirt pocket directly adjacent to an implanted medical device. There are a number of wireless technologies in use today which involve different combinations of power levels and modulation schemes. (From “Immunity testing for Active Implantable Cardiovascular Devices” by Daniel D. Hoolihan of Hoolihan EMC Consulting, ITEM 2001, p45)
176 The inability to trade can result in large losses that far exceed the cost of the operation. In a recent example a claim for £10m compensation was made as a result of a 20 minute power interruption. (From “Introduction to power quality” by David Chapman of the Copper development Association, March 200, page 1)
177 It is estimated that power quality problems cost industry and commerce in the EU about €10 billion per annum while expenditure on preventative measures is less than 5% of this. (From “The cost of poor power quality” by David Chapman of the Copper development Association, March 200, page 1)
178 There are no official statistics on the severity and distribution of voltage dips but some medium scale measurements are now in progress and can be expected to yield valuable information in due course. One study, carried out by a major generator, measured voltage disturbances at 12 sites with demand between 5 and 30MVA. In a ten-month period 858 disturbances were logged, 42 of which resulted in disruption and manufacturing loss. Although all 12 sites were low technology manufacturing operations making low added value products the financial loss totalled €600,000 (average €14,300 per event or €50,000 per site), with the highest individual loss of €165,000. The table below gives some typical values:
Industry Typical financial loss per event
Semiconductor production €3,800,000
Financial trading €6,000,000 per hour
Computer centre €750,000
Telecommunication centre €30,000 per minute
Steel works €350,000
Glass industry €250,000
(From “The cost of poor power quality” by David Chapman of the Copper development Association, March 200, pages 3 and 4)
179 In the USA, many of the emergency services (fire, police, ambulance, etc.) use a radio system which operates at 800MHz. The base-stations for these systems are often quite widely spread, to reduce the cost to the public purse. These systems are known to suffer from ‘adjacent-channel’ interference, which seems to be on the increase due to crowding of the spectrum. The interference has resulted in documented cases where officers or other have been put at risk. The main problem appears to be intermodulation in the RF front-ends of the handsets, caused by out-of-band signals from other licensed transmitters. It is often forgotten that most radio receivers achieved their narrow channel bandwidths in the intermediate frequency processing stages, and that the bandwidth of the earlier stages is much wider, making them prone to interference from powerful signals at nearby frequencies. Refer to “Interference to Public Safety 800MHz Radio Systems, Interim Report to the FCC, Dec 24, 2001” which can be downloaded from: http://www.apco911.org/afc/project_39/interim_report.pdf (From Keith Armstrong, Feb 02)
180 When my BMW 330Ci is locked, it causes interference to my digital TV service - despite being parked about 30ft from the dish. My wife's Mercedes-Benz doesn't cause this, no matter where it is parked. I was thinking of swapping her Merc for an X5, but two BMWs parked on the drive at once might limit my evening's entertainment to Scrabble. I'm sure I could get the dish moved, at a cost, but I shouldn't need to do that. I.B., via email. Reply: There is an EC directive about electronic interference that came into force several years ago. Either your car's alarm immobiliser system or the dish/TV receiver does not conform to it. (Honest John's Agony column, Daily Telegraph Motoring Section, Saturday 30/03/2002, page 10)
181 Two navy warships nearly collided when the radar beams of one disabled the steering of another. The minehunter HMAS Huon went out of control and veered across the bow of the frigate HMAS Anzac. Huon – the first of six state-of-the-art coastal minehunters – lost its steering as a result of electromagnetic interference (EMI) from Anzac and passed ahead of the frigate “at close range” according to an Auditor-General’s report last week. The previously unreported incident occurred in June 2000 while the warships were sailing to Singapore.
The near-collision was used in the Australian National Audit Office report to highlight shortcomings in the testing and evaluation of new defence equipment, especially in the navy, leading to the installation of only partially tested systems. “The incident prompts questions concerning the adequacy of EMI testing during developmental testing and evaluation and whether the services should complete more extensive operational testing and evaluation before integrating new platforms into defence exercises,” the report stated. The ANAO report rejected Defence Department claims that such testing was expensive and not necessarily cost-effective and said that T&E (testing and evaluation) should be conducted as early as possible in order that risks could be reduced before they became dangerous. “In extreme cases, inadequate T&E could have tragic consequences,” the report said. (Extracted from “Loose radar blips nearly sink ships” by Wayne Smith, Friday February 1st 2002, sent in by Chris Zombolas of EMC Technologies Pty Ltd, Melbourne, Australia, March 2002.)
182 Currently, appliances in the U.S. do not need to meet any EMC compliance standards. Since U.S. appliance manufacturers can (and do) produce domestically used products without any regard for EMI suppression, how serious is the EMC problem in the U.S.? It’s difficult to know the entire scope of the problem, but a few examples have come to our attention. For example, the new 2.4GHz portable phones will not function near laundry rooms when certain models of washing machines are running. This problem is easily overcome by not using these portables near these washers. A little inconvenient, but not intolerable.
In another case, a company that imports and distributes microwave ovens asked us to investigate complaints that some of their microwave ovens were turning on by themselves. The cause was a surge on the power line, probably caused by the air conditioning system turning on. The solution was not simple and required units to be recalled and fitted with a hardware and software modification. The costly remedy was necessary because, in this case, the susceptibility of the appliance electronics created a safety hazard.
In Europe, EMC issues will continue to be managed through the existing EMC Directive, so European manufacturers will remain quite familiar with designing and developing next-generation products that are EMC complaint. Without such a directive here, U.S. manufacturers will need to institute good EMC practices to ensure a more EMC friendly environment for smart, networked appliances. (Extracted from “Smart Appliances and EMC – Good EMC practices necessary to prevent smart homes from being chaotic homes” by Nissen Isakov, president of LCR Electronics, Norristown, Pa. USA, writing in Appliance Manufacturer magazine, March 2002 issue, pages 16-17.)
183 More electronics means more risk from externally generated electromagnetic interference (EMI) and from EMI generated by systems in the vehicle that are adjacent or interconnected. The effects can be quite serious: on certain highway overpasses in Europe, the engines of some vehicles have been shut off when their control units encountered high EMI levels from, among other things, high-voltage lines beneath the roadway, reported David Ladd. He is communications manager at Siemens VDO Automotive (Auburn Hills, Mich., USA), which operates an electromagnetic compliance testing lab. “These problems must be identified and corrected before the vehicle goes into production,” he emphasized. Because of these risks, the auto industry is re-evaluating its requirements and testing for new sources of EMI. Suppliers are increasingly relied upon to develop expertise in managing potential risks during the early stages of engine control unit development, noted Ladd. And the growing use of optical-fibre databuses is eliminating one possible source of EMI problems. (Extracted from “Can you trust your car?” by Ivan Berger, Contributing Editor, IEEE Spectrum, April 2002, pp41-45.)
184 It reminds me of a weakness of the original Bosch "Jetronic" electronic injection system as used as OEM equipment on various European cars in the late 1960s to mid 1970s (this was at a time when the good ol' carburetted American V8 was still the norm here). A common stunt was that people with (illegal) 50 Watt transmitter boosters attached to their CB radio, would drive up beside a Bosch-injected VW or Volvo or whatever, toot the horn to get the driver's attention, then hold up the CB's microphone for the guy to see, and (with a flourish) key the transmitter. The injection system in the "victim's" car would immediately stop and his car would die until the transmitter was keyed off! Now, THAT'S EMI susceptibility! (Extracted from a posting on emc-pstc in the thread: “RE: Automotive standards” by Bob Wilson of Vancouver on 5th April 2002.)
185 Take a large poorly built transformer or solenoid and push the core hard up against the equipment housing and you could well exceed 0.7mT nearby. Several metres from a train (0.7mT) is less likely but not impossible. These figures should be borne in mind the next time you read about the dangers of the magnetic fields from overhead power lines. I have several times seen building site welders sitting on their transformers with their testicles dangling over the gap and I haven’t seen welders dropping like flies. (Extracted from a posting on emc-pstc in the thread: RE: Teslars?? By Nick Rouse on the 8th February 2002).
186 NASA runs an Aviation Safety Reporting System (ASRS) to which pilots and other aircrew can voluntarily report incidents. On 1st May they released a report of 50 incidents taken from the ASRS which involve the use of Passenger Electronic Devices (PEDs), but not all of the reported incidents concern electromagnetic interference. This report is very useful when you need to show people that some PEDs can interfere with some aircraft systems and communications. You can download it from: http://asrs.arc.nasa.gov/report_sets/ped.pdf. (From Gary Fenical of Laird Technologies, USA)
One of the incidents reported in the NASA ASRS PED report (see item 186 above)…
Aircraft: DC9. While at cruise FLT FL3100 we noted the onset of multiple anomalies with independent and interrelated onboard electronic systems. The radar altimeter began flagging and sweeping, the GPWS and TASCII annunciated ‘FAIL’, the VORS flagged, despite good idents and, by and large, rational signals. Tests of the equip were otherwise satisfactory so we made announcements requesting that certain PEDs (cellphones, pagers, TVs and radios) be verified in a depowered condition, and the flight attendants did a ‘PED Walk’ in the cabin. The problems initially vanished but then reappeared, and we repeated the process this time requesting that all PEDs be depowered. The 3rd and final PED walk revealed that several pagers had to be depowered by battery removal, and there was a computer in use with an external battery pack. (No incoming calls to pagers were admitted to.) After this, the anomalous indication vanished for good and all systems operated normally (including the GND VOT signals).
Another incident taken from the NASA ASRS PED report (see item 186 above)…
Aircraft: DC9. During CLBOUT from BDL, the captain’s radar altimeter flagged and the TCASII and GPWS subsequently annunciated ‘FAIL’. The problem continued throughout the CLB to FL350 whereupon I had time to ask a flight attendant to do a PAX electronic device walk. She discovered that a Sony Video Walkman was in use in seat XX. After the Sony was shut off, the problems cleared up. The item was a Sony GVA-500 Video Walkman.
Just one more incident taken from the NASA ASRS PED report (see item 186
Aircraft: Brasilia EMB120. I experienced interference with VOR navigation reception. We found a PAX in seat XA operating a 300MHz Toshiba Protégé Laptop computer. We had her discontinue the use of the computer and normal reception was restored. I have had previous problems with Toshiba computers that are used in row X. I will not limit the use of PAX electronic devices yet, however I now immediately check to se if a laptop is on when experiencing navigation problems. Callback conversation with RPTR revealed the following info: the RPTR stated that the same exact incident happened on a different EMB120 at row X and with a Toshiba laptop computer. That time, they were at McAllister VOR, when the needles on the MFD (Multifunction display) went crazy and were spinning in circles. In both cases, it was spinning in circles on both NAV1 and NAV2. The RPTR guessed it was a laptop computer causing it and had the flight attendant check it out and had the person turn it back on to see what would happen, and the instruments resumed almost a normal position, but it was 40 degrees off from ATC. He said row X is the first row behind the trailing edge of the wing. With this particular incident, he is 90 percent sure that the PAX did turn her computer back on afterwards, but they were almost on top of the new VOR, so he believes that’s why it didn’t interfere again with the navigation. The RPTR speculates that perhaps the Toshiba laptop computer and the VOR had the same or similar frequencies.
190 Villagers in Dorset were baffled when their pop-up toasters began to speak Russian. Phones and other electrical appliances in Hooke also chatter away in foreign languages and play music. The phenomenon has been blamed on a powerful radio transmitter in nearby Rampisham that transmits BBC World Service. John Dalton, chairman of the parish council, says: “I’ve heard foreign voices through an electric organ. And I was amazed when I got the World Service signature tune through a toaster”. (From “Weirdness of the week” in the Sunday Times’ ‘News Review’, 12th May 2002, page 4.12)
191 “The basic problem was that the black boxes didn’t work. The signal was weak because civil servants were frightened to interfere with signals for conventional television and mobile phones. So screens would go fuzzy during a drama’s crucial kiss or freeze just before the winning goal.” Green groans. “This is not an excuse but if I did it again, I would check all the technology worked first. We were promised extensive coverage but it was like Swiss cheese. One side of the street would receive a signal but not the other. It made marketing hopeless. When I went into my local Dixons in the country, they said that I couldn’t get digital but my box worked fine. Its remarkable we got 1.2 million viewers, it was such a farce.” Didn’t he try to get the signal turned up? “There is no question but that this Government was useless. I went so many times to Chris Smith, Tessa Jowell, and Tony Blair, saying: ‘We’re losing £1 million a day, please turn up the signal. You never told us it wouldn’t work: it’s softer than an electric razor.’ The Government shouldn’t have to interfere but they sold us a dud product.” (From “Is ITV Digital a mess? Yes. Did we make mistakes? Definitely”, an interview with Michael Green, chairman of Carlton Communications in The Daily Telegraph, Saturday May 4th 2002, Page 10. This was just after ITV Digital closed down with a financial loss of about £600 million and 1700 people losing their jobs.)
192 The main problem with ITV Digital is that its technology did not work. It was inferior to rival offerings from satellite and cable. The signal had to be transmitted at low strength, otherwise it interfered with mobile phones and even French television. The result was only half the country was covered, and the service was unreliable.
The Government failed to sort out the different regulators, such as the Radio Authority and the Radio Communications Agency, which dragged their feet in allowing ITV Digital to turn up its signal. (Two extracts from “How the digital dream became a nightmare”, The Daily Telegraph, Saturday May 4th 2002, page 11.)
193 A portable gas detector failed without the operator noticing when used near a handheld radio transmitter. The equipment was being used to protect people involved with sewer repair work from the effects of toxic gases. The electric field strength from the transmitter may locally have exceeded the proposed (at that time - Editor) industrial generic immunity level of 10 V/m. This is an example where equipment, which may have conformed to a standard, was apparently not immune to interference in use. It was subsequently modified to include an additional screen. (From “Dangers of Interference, EMC and Safety” by Simon Brown of the UK’s Health and Safety Executive, in the IEE Review’s EMC Supplement July 1994 page S-11)
194 A pilot complained about navigation and communication equipment on his plane becoming inoperable when flying through rain. Studies have shown that when an aircraft flies through rain, static electricity on the aircraft skin can exceed 100,000 volts. In the hanger, testers simulated this situation by isolating the aircraft from ground. Using a high voltage power supply they charged the aircraft to approximately 100,000 volts. A portable RF receiver was used to locate the source of broadband RF noise. It turned out to be arcing between poorly bonded aircraft surfaces. (From “The case for combining EMC and environmental testing”, by W H Parker W Tustin and T Masone, ITEM 2002, pages 54-60.)
195 Author Masone recalls a flight test to document a similar problem. The test involved flying EMI specialists into a storm. Immediately upon entering the storm, Masone heard a high-pitched squealing sound form the pilot’s headset. Its intensity was such that the pilot had to remove his headset. The navigation display then went black. All navigation and communication equipment was inoperable in a whiteout condition with freezing rain and snow! Fortunately, the pilot was experienced, and there were no other aircraft in the flight path. Upon exiting the storm, all navigation and communication functions returned to normal operation. Back at the hangar, high voltage testing led to the discovery of a poor bond between two surfaces on the horizontal stabilizer. (From “The case for combining EMC and environmental testing”, by W H Parker W Tustin and T Masone, ITEM 2002, pages 54-60.)
196 The system is also immune to electromagnetic interference, unlike other methods of computer control. Flying to close to civilian radio masts, for instance, has in the past brought down military aircraft. (From “Fibre optics to aid helicopter safety” by Rob Coppinger, The Engineer, 19 April 2002, page 11.)
197 The Pacemaker Committee of Japan issued the following guidelines at March 1996…Keep handy cellphones (and PHS, cordless phones, etc.) away at least 22cm from the implanted pacemakers. When using such devices, patient should use the ear at the opposite side of his pacemaker. Stay at least 30cm from antennas of land mobile radiotelephones and shoulder radiotelephones. Patients shouldn't use other radio transmitters such as amateur radios, walkie-talkies (excluding that with extra-low power), etc. This committee is a conference group in Japan Association of Medical Equipment Industries (JAMEI). The criteria was also referred in a guideline issued by the Electromagnetic Compatibility Conference Japan. I found the Japanese text of the guideline on the Internet, at http://www.medtronic.co.jp/ja/misc/keitai.html (it seems JAMEI itself doesn't publish any information on the Internet), but I couldn't find the English version of the guideline. (From Tom Sato, Jun 02)
198 Was just at a cheesy hotel with the replacement circular fluorescent lamps directly above (2 feet) the hotel-provided radio (less cheesy than most). Turning on the light completely destroyed the signal. AM and FM and all channels. Turn it off and the radio was nice and clear. Wanted to steal the bulb to measure later - decided on the towels instead. Not only should these bulbs have not been CE marked, they should have had a label for use only inside microwave ovens or something. (From Gary McInturff, 24th April 02, in a thread on “CE for Fluorescent Lamps” on the IEEE’s emc-pstc discussion list.)
199 Well, I've stumbled over one of my pet peeves again. We had a combination keyboard/touchpad (CE marked) which failed ESD testing a couple of months ago. It would either give false inputs or become unresponsive when 8KV air discharges were made to the touchpad. I tried ferrites at both ends of the cable...no luck. Since we don't make the keyboard, I can't open it up and make changes (although I would like to open it up with a sledgehammer...that would make some changes). So, we bought another brand. This one has a keyboard and trackball. Our hope was that the trackball would be more zap-proof than the touch pad....No dice...snap, crackle, pop it fails too. Oh, by the way, this keyboard was prominently CE marked as well. (From Chris Maxwell, 19th April 2002, in a thread on “Suitable CDN for IEC61000-4-6 ethernet 10/100” on the IEEE’s emc-pstc discussion list.)
200 The most spectacular ‘banana skin’ of all times! In 1899 (!) in Colorado Springs Nikola Tesla himself tested his tesla coil. He did not use filters, the harmonics burned out the wiring in the power company in Colorado Springs. (From Geert Starre, 14th May 02)
201 Please could you help with a project I have, investigating potential safety implications of mobile phones and aircraft. Three potential hazards come to mind.
1). While using mobile phones on the ground, whilst refuelling the aircraft, the displacement of air at a rate of approx. 1500 lt. per minute out of the tanks as vapour spill from vents at the wing tips. They are not intrinsically safe, so what energy is required to ignite fuel vapour? (I have personal experience of seeing the results of a person with a mobile phone strapped to his belt while filling his petrol tank. The mobile rang, igniting the vapour, and causing a jet bast from the tank which unfortunately took all the skin off from his wrist to his elbow).
2). Batteries should one become damaged and or shorted causing a fire what would be the possible fire hazard and what extinguishant should be used?
3). Potentially the worst case scenario RF break through from the mobile into the systems. They often can be heard over radios when transmitting in the vicinity of the receiver, a unwanted signal in my view, therefore what could happen if the signal is induced into and reacted upon in one of the many other systems? Again personal experience has shown of signals in an industrial process line where a 3 watt transceiver was being used some 15 meters from a large electronic motor control center, which sent motors into random speeds simultaneously causing major stoppages for the process line and months of these random transients to get solved. From an aircraft's point of view I have experienced transmitting from the aircraft's fitted VHF Transmitter on a particular frequency and the aircraft pitching nose down some 20deg while the autopilot was being used.
(A query made by Paul Barnes to an IIE Special Interest Group on the 2nd February 2002)
202 One of my first business trips after I got out of college was going to Chemical Bank in New York City, because one of the Sycor 250 terminals (for which I had written the firmware) would lock up every night. The hardware designer and I installed some hardware and software monitors on this unit, and left for the evening. Next morning we returned, and discovered that it had died shortly after 11pm-- the very time that the cleaning people were making their rounds! We discovered that the cleaning people were plugging their industrial vacuum cleaners into the same wall outlet as our terminal because it was convenient. I think that the bank changed to a simplex wall outlet there, and that solved the problem. (John Barnes, dBi Corporation, from a thread entitled Re: Voltage Spikes on Power Lines etc on emc-pstc on 14/03/02 23:14:43)
203 I discuss problems with powerline-spikes in chapter 8, Designing Power Supplies, of my book Electronic System Design: Interference and Noise Control Techniques (Prentice-Hall, 1987, now out of print). For equipment that will be used indoors, you should try to design your equipment to be immune to 6kV spikes. That is approximately the voltage at which our wall outlets arc over. (John Barnes, from the same thread as above)
204 The Enforcement Bureau of the FCC is taking strong action against retailers who are illegally marketing non-compliant equipment, specifically long-range cordless telephones. The Commission has initiated action against New Image Electronics (NIE), a Miami, Florida electronics store, for selling long-range cordless phones designed to operate on civil aviation frequencies.
The agency's action followed a six month investigation that began in February, 2001 when the FCC's Enforcement Bureau received reports from the Federal Aviation Administration (FAA) of sporadic, but potentially harmful, interference to aviation frequencies in the Miami area. FCC agents traced the interference to NIE, and investigators visited the store on at least two separate occasions, actually purchasing a long-range cordless telephone during its second visit. Not surprisingly, the purchased phone possessed none of the labeling or FCC authorization required for marketing the device in the United States. In its response to the Commission, NIE did not deny that it had sold the phone to the FCC's agents, but claimed in its defense that their clerk had mistakenly believed that the phone was being sold for export when one of the agents gave his address as "Puerto Rico." In its forfeiture decision, the FCC noted that Puerto Rico is part of the United States.
The Federal Communications Commission (FCC) has also taken action against two other Miami-based retailers for illegally selling long-distance cordless telephones. The Commission has issued monetary forfeitures to Electronics Unlimited and Lightning Electronics for the illegal marketing of non-compliant, high-powered cordless phones. (From Curtis-Straus update for April 2002, via Conformity Magazine).
205 I was asked to do EMC tests on a multi-channel digital location recorder designed and built by the R&D department of a well-known record manufacturer. The recorder was housed in a 19" rack unit and controlled by software running on a laptop computer, via RS 422. The audio results were said to be excellent, but they invariably had problems with the control functions. On the last recording session, the machine went into record mode as requested, but during the session, control of the recorder was lost. No command would allow the engineers to stop the machine or come out of record mode. The whole system had to be re-booted before they got control back. This was a classical orchestral session with 80 musicians, so the problem could have been expensive.
I placed the recorder unit in the EMC test chamber, connecting the system up normally, but with the laptop computer outside in the control area. This was to isolate the two different parts of the system. The recorder unit passed the basic emission tests when running in record or playback mode on its own. But when the RS 422 line was connected between the laptop computer and the recorder rack, the system failed the radiated emission test by a wide margin.
If the RS 422 cable radiated interference, it was very likely that the same cable would receive interference. I set up for the conducted immunity test. The cable, carrying signal or control data, is bombarded with a known level of RF from a computer-controlled oscillator/power amplifier, with the generated RF modulated by a 1kHz sine wave. The equipment under test is monitored to check if interference to the wanted signal can be detected in the main signal path or on the control data. Since the problems with the recorder involved the control data, we decided to test the RS 422 cable first.
The RF oscillator automatically sweeps through the test frequency range under computer control. Any problem that occurs is picked up by a volt meter/detector and logged in the test file. If necessary, fault events can be manually entered via the computer keyboard. The recorder unit was put into record mode and I started the test. At first all went well. But, as the modulated frequency approached 8 MHz, the time code display on the laptop screen stopped. All other controls seemed still to be working. However, at about 16 MHz, a second event was detected, and the laptop had lost control of the recorder unit. The recorder was permanently in record mode! I put the EMC test system in pause, and rebooted the recorder and laptop. Restarting the test at 18 MHz, everything was working properly until the modulated RF approached 33MHz (the bus/processor frequency of the recorder electronics). Multiple events were detected and control of the recorder system was lost once more and the laptop crashed. To cut a long series of tests short (similar problems were encountered on the other side of the recorder’s processor/bus frequency) - the problem was obviously interference on the RS 422 data communication circuit. But how could this be the case? RS 422 is a balanced transmission system and the cable was shielded.
An inspection of the RS 422 connectors at each end of the circuit revealed the following:
i. The connector at the laptop end had the cable shield correctly bonded to the chassis.
ii. The connector at the recorder unit end was an insulated component. The cable shield connection was wired directly to the logic 0V track on the printed circuit board (the digital version of the pin 1 problem).
iii. The custom made RS 422 cable had the cable shield connected to the recorder unit end only. The cable was constructed in this way, because the engineers had found that hum was introduced into the recorder when the RS422 cable was connected to the standard desktop PC used during the design phase of the project.
Thus, any interference current induced into the cable shield of the RS 422 data communication circuit was injected directly into the recorder unit’s ground conductor, allowing interference currents to flow in the RS 422 I/O electronics, resulting in poor or bad data on the RS 422 communications circuit. The laptop (or any other) computer, and the recorder was, at the very least compromised, by any interference induced on the RS 422 cable shield. (From Tony Waldron, 8th Jan 02)
206 Dear Ann Landers. I've always had trouble with peripherals. Keyboards and mice that were CE marked and looked like such good prospects have mostly turned out to be fickle. Well, I've been involved with a touchpad for about five months now. When I first bought it, we were so happy. Whenever we were together it, it could read my mind. A tap of my finger and it knew just what to do. And then this ESD gun comes along. One zap and BOOM! The touchpad turns its back on me. It won't respond at all! I tried talking to it...but it just gave me the cold shoulder. I suggested counseling...still no response. I threatened to go and get a mouse...no response. Well, I finally had to just take a deep breath and go through with it. I cycled power. Well it now responds to me... but I don't know if I'll ever trust it around an ESD gun again. I don't know if our relationship will ever be the same. Signed "Out of touch in New York"
OK, OK, the real question is... does anybody have some words of advice regarding touchpads. I am testing a unit which consists of a keyboard/touchpad combination. The touchpad is approx 1.5" x 1.5" and is able to sense a sliding or tapping finger. The touchpad is used to perform all of the functions that a mouse typically performs. I am assuming that it has some sort of capacitive sense circuit which can tell when your finger slides across the pad or taps on the pad. I have one that gets all out of whack with 8KV ESD. i.e. the touchpad becomes unresponsive and it stops software execution in our host system. Unfortunately, this is one of those instances where we don't build the keyboard/touchpad; so my bag of fix tricks is limited. Probably limited to seeing if another manufacturer produces a keyboard/touchpad with better performance. Or, am I slamming my head against the wall on this one? The keyboard/touchpad is already CE marked by its manufacturer. Is his typical? Are all touchpads (even CE marked ones) ESD sensitive? Do I just live with it? Am I over-testing this touchpad? Overall... I have had REALLY bad experiences with CE marked keyboards and mouses. Now I have trouble with our first touchpad. We typically use a capacitive filter on our inputs and we typically put a ferrite on the cable...yet still trouble. Is this typical of what others see? (From Chris Maxwell 02/01/02 21:56:34 via emc-pstc. Note: Ann Landers is a magazine’s “Agony Aunt” in the USA.)
207 Over the past couple of years, there has been extensive discussions of the potential interference that ultra-wideband (UWB) radio signals might cause to GPS once UWB devices proliferate across the planet. But GPS is also susceptible to interference from more conventional transmissions both accidental and intentional (jamming). For example, a particular directional television receiving antenna widely available in the consumer market contains an amplifier which can emit spurious radiation in the GPS L1 frequency band with sufficient power to interfere with GPS reception at distances of 200 meters or more. Harmonic emissions from high-power television transmitters might also be a threat to GPS. Furthermore, the GPS L2 frequency is susceptible to interference from out-of-band signals from transmitters operating in the lower part of the 1240 to 1300 MHz band which is shared by terrestrial radiolocation services and amateur radio operators. As for intentional interference, the weak GPS signals can be readily jammed either by hostile forces during conflicts or by hackers who could easily construct a GPS jammer from a surplus home-satellite receiver.
I have experienced the effects if RFI on GPS in Germany and some neighbouring countries since 1995. During this time I only experienced RFI to the GPS L1 frequency twice. In 1997 near the Swiss airport of Lugano, signals emitted from a permanent transmitter operated by the Italian military were detected (see Figure 3). In February 2002, for 20 to 30 seconds an unknown interfering signal with a frequency of 1570.96 MHz disturbed the reception of L1 at Frankfurt Airport and surrounding areas up to a distance of 150 kilometres (see Figure 4). While Geodetic receivers exhibited a loss-of-lock, a certified aviation receiver merely experienced a degradation of the S/N. Dual-frequency GPS users routinely detect interference to the GPS L2 frequency in Germany, Switzerland, and The Netherlands. In all cases the sources are amateur packet radio transmitters in the frequency band between 1240 and 1243.25 MHz. Such transmitters are called “digipeaters” (short for digital repeaters or relays). They are part of a Europe-wide network of a kind of wireless Internet operated by radio amateurs (see Figure 5). They cause interference to dual-frequency GPS receivers operated by researchers at several universities as well as by geodesists and surveyors. Figure 6 shows a comparison of the spectrum of such signals with a susceptibility curve representing the interference power required to degrade the S/N by 10dB. (Two extracts from the text of: “A Growing Concern – Radiofrequency Interference and GPS” by Dr-Ing Felix Butsch of Deutsche Flugsicherung GmbH (DFS) in GPS World, October 2002, pages 40 - 50.)
208 Early field trials in UK, Germany and Switzerland showed excessive radiated emissions (up to 40dB) above NB30 RegTP limits, which are about 20dB more relaxed over the 4/2000 RA version of UK MPT 1570 in the short wave spectrum. Broadcast, military, commercial as well as licensed amateur radio services started seriously objecting to a nationwide implementation of PLC. (PLC = Power Line Communications, basically sending telephone or Internet data over existing mains wiring and cables – Editor)
Far field effects and underestimated PLC system antenna factors  lead to short wave signal mirroring at the ionosphere. That is today not at all taken into account by officials in the ministry of economy in Berlin, which supervises the RegTP agency, the equivalent to the FCC US. These sky wave propagation effects might lead to background noise increase  also outside Europe. Sensitive receiving sites in Germany may experience, based on first simulations, degradations of 10 to 40dB! This is unacceptable for security agencies in the present political scenario.
The introduction of power reduction in broadcasting, due to digital technologies, reducing transmit power and therefore lowering electromagnetic pollution or heath hazards, become useless if at the same time the signal noise ratio will be PLC degraded.
Reports on publicly available, new measurements data from PLC modems/systems (e.g. ASCOM). Some indicating serious legal and technical trouble in wide spread PLC field trails systems.
Suspicion arouses, due to questionable promoter companies, seemingly forcing contracts with non-discloser agreements to be signed by their clients. This could hamper independent measurements.
Everybody is fighting physics. Due to Shannon, signal to noise ratio (typ. 15dB) is EMI relevant. PLC signal level, modulation and existing line noise are important to bridge the distance without costly repeaters. The PLC community is therefore fighting for “better”? less stringent regulations and want new EMC standards.
Little attention was formerly given to commercial System EMC; box testing was rather dominant. Finally, the commercial EMC community is forced into System Thinking! Cable TV systems started interfering with air traffic control over major German cities.
Typical test problems are identifying PLC Interference in bands <30 MHz, receiver jamming, time variant EMI. It takes wireless experts to be sure it is PLC and not other EMI. Normally at CW, AM, SSB, the whole receive spectrum is experiencing a massive noise floor increase (sounds like an old steam locomotive sometimes), resulting in total blocking. The sensitivity is wiped out.
Generally speaking there is very little willingness of the PLC people to talk technical even today.
On the official side, however, 100 serious, professional NB30 objections, some demanding even lower limits, filed to RegTP, were politically ignored by the ministry of economic affairs last year when NB30 came out. Reliable sources indicate, Federal Cabinet Minister Mueller (Economy) – originating from RWE (a company which is active in the PLC business – Editor) – before entering his political career in the SPD government – wants to return to his old company!
(A number of extracts from: “Update on Power Line Telecommunication (PLT) Activities in Europe” by Diethard Hansen of Euro EMC Services (EES) www.euro-emc-service.co.de, chairman of ATRT WG PLC, RegTP, Germany, presented at the IEEE’s International EMC Symposium held in Minneapolis, Minnesota, August 19-23 2002, and published in the Symposium Record on pages 17 - 22.)
209 Array-pattern nulling effects have become an important field of study recently due to the increased pollution of electromagnetic (EM) environments. These techniques reduce degradation of signal-to-noise ratio (SNR) performance due to undesired interference in radar, sonar, and communications systems. (Taken from “Reduce SNR Degradation in EM Environments Using a Nulling Technique” on page 56 of Microwaves and RF Journal, September 2002.)
210 EMI and RFI are not new phenomena. They are problems that have been around for years. When I was a small boy (which is longer ago than I will admit), I grew up across the street from a ham radio enthusiast named Bob Beebe, W71GM.
Bob had a powerful one-kilowatt linear amplifier for his ham rig, and a rotating beam antenna on his roof that covered more area than his roof did. We could hear him on every electrical appliance we owned. His calls are indelibly etched on my memory: “Hello, CQ, CQ, C. Hello CQ, CQ, CQ. This is W71GM, I Got Manilla.” (Manilla was the name of his wife!) Every time we got a new radio, we’d have to call Bob to come over and wrap it in copper or place ground wires all around it in order to shield out his emissions.
In another life I ran a company that made weighing systems for industrial trucks – i.e., scales to make sure trucks were within legal limits. They were portable, could be towed behind a police car on a small trailer, and used portable electronics that plugged into the car’s cigarette lighter. They ran off the same electrical system the police radio did, and the indicators were often placed right next to the radio or on the car roof, right next to the antenna. Immunity to RFI was a significant design requirement.
We had just finished a complete redesign of our indicator family. We had access to a screen room facility and a technician through another company, so we went there to do the EMI/RFI testing. During the very first test, however, the indicator went totally off-scale! No matter what we did we could not quiet down the indicator. After two hours of tweaking we got some improvements and then hit a plateau. No matter what we did we could not quiet down the indicator. The screen room technician finally spoke up and asked us what the input circuit looked like. We told him it was a high-gain differential amplifier, which then fed an A/D converter. He asked us what part number the amplifier was. We told him. It was a commonly available amplifier made by at least four or five manufacturers. He then asked us who manufactured the part. We told him. He then told us that particular manufacturers often had RFI problems with its parts and why didn’t we buy the same part from a different vendor. We did, and the RFI problems almost totally went away. It took us only a few more hours to achieve the RFI objective and the product then successfully went into production.
There was no clue in any of the published specification from any of the manufacturers of this part number that there would be differences in RFI sensitivity between product offerings. We had no reason whatsoever to suspect that part. We might have struggled with that design for months if that technician had not put us on the right path. There are two morals to this story:
l A good technician with experience can be more valuable than someone else with all the university degrees in the world.
l There can be subtle differences inside IC packages in otherwise identical parts that may only be determined by laboratory testing or trial.
More than one engineer has been ‘burned’ by a part that behaved unexpectedly. Sometimes, as in this case, there are simply differences in design or manufacture or otherwise “identical” parts. Sometimes a supplier changes a manufacturing process without telling anyone. Often this involves the implementation of an improved process, which coincidentally may offer faster rise times. Perhaps the manufacturer thinks that the change or improvement will have no particular consequence for anyone, and treats it as simply an in-line adjustment. But sometimes the faster rise-time results in timing or EMI problems that didn’t exist in the user’s design before. These can be particularly difficult to trouble-shoot, because people rarely equate the problems with a device, particularly a device that used to work just fine. (Extracts from “Lessons Learned the Wrong Way” by Douglas Brooks, President of UltraCAD Design Inc., www.ultracad.com, published in Printed Circuit Design magazine, September 2002, pages 30 and 39.)
211 Its an all too familiar scenario. You’re on the phone to an important customer, and – far from being able to hear whether he’s about to place the biggest order of the year – all you hear is an irritating crackling on the line.
Well, if its any comfort at all, you are not alone. Every year, thousands of users report that their critical business calls have suffered, for some inexplicable reason, from intermittent hissing, buzzing, crackling, and general interference. And when the phone companies investigate the phenomenon, they find nothing wrong. It’s a phenomenon that frustrates IT departments, telecoms engineers, sales managers, directors, in fact anyone that has to use a phone for business.
But this understandable annoyance that many of our industries suffer as a result of poor quality voice communications is nothing compared to the potential loss of revenue that can arise if their data systems suffer the same fate. And yes, you’d better believe that this is exactly what too many businesses are experiencing at this very moment.
I’m not suggesting that spikes and surges in the power supply are at the root of each and every problem, there is little doubt that they contribute to a significant number of these anomalies and aberrations. In fact, no lesser source than IBM’s Systems Development Division comments that “More than 80% of mains power problems are transient and noise related.” (Extracts from from “Communication problems – can tvss provide the answer?” by Mike Burgoyne of Advance Galatrek, in Components in Electronics magazine, September 2002, page 28.)
212 Two individuals have filed a petition with the FCC for reconsideration of a proposal that would require all electronic equipment to be shielded against electromagnetic pulse (EMP). With the prospect of future terrorist attacks clearly on their mind, the petitioners wrote that there is “the need for mandatory shielding to protect vital civilian equipment from the possible hostile use of an Electromagnetic Pulse (EMP)”. (Conformity, October 2002, page 46)
213 Every time the passenger ferry passed a certain point leaving the harbor, the automatic logging system was reset to its default settings. This always happened late in the evening, around 23:00. Strangely enough, this problem never occurred when the ferry was arriving at the harbor. After a thorough investigation, it was found that at 23:00 the stoves and ovens in the kitchens were switched off for the night. The transient overvoltages from the switch-off found their way to the bridge via the signal and power cables on board. The investigations also showed that no cable screens at all were correctly grounded.
The problem with the log was solved by introducing cable feedthroughs with electromagnetic disturbance protection, and by adding transient filters. (From Roxtec Ltd, page 23 of its booklet on ‘Cable and pipe transits for EMC’, December 2002, www.roxtec.co.uk)
214 Offshore oil and gas production platforms present an extremely difficult electromagnetic environment due to the amount of electrical and electronic devices crammed into a small space. In this case, a platform was anchored to the sea bottom, but its exact position was adjusted by thrusters, i.e. large electric motors driving propellers. The position of the platform was controlled by a computer system. The power and control cables, all screened, were routed from the control room on the bridge at the top of the platform, all the way down to the engine rooms far below. However, the cable feedthroughs were not protected against electromagnetic disturbances. Com radios were used both on board the platform and for communication with land.
When a technician tried to use his com radio in the engine room, the connection was continually bad. By letting the radio antenna touch a cable harness, the connection became much better. By feeding its electromagnetic energy into the cable screens, the radio got a much improved “antenna”. Unfortunately, the energy in the cable screens also went elsewhere. It went via the cable screens to the thruster control equipment, which interpreted the energy as a signal for adjusting the position of the platform. (From Roxtec Ltd, page 22 of its booklet on ‘Cable and pipe transits for EMC’, December 2002, www.roxtec.co.uk)
215 Bad EMC design caused operating problems in a quality control system in a foundry. The quality control system consisted of two subsystems, a robot subsystem and a measurement subsystem. An industrial robot picked up the heavy metal pieces and placed them at the measurement system. The measurement system checked for the presence of cracks in the metal. The electromagnetic environment was tough, with motor drives, arc-welding equipment and electric forklifts nearby. The problem was intermittent malfunctions in the entire system.
An investigation showed that the two subsystems interfered with each other. The industrial robot subsystem was carefully designed and installed with respect to EMC. The measurement subsystem, however, was not designed or installed with respect to EMC. The industrial robot subsystem was designed in a series of zones, where each zone was screened and equipped with Roxtec EMC cable feedthroughs.
The measurement subsystem was not divided in electromagnetic disturbance protected zones at all. Some of the cables were screened, while others were not. The screened cables entered the control cabinet via a large opening in the cabinet floor. The internal layout of the control cabinet was not done according to EMC principles. By redesigning parts of the measurement subsystem installation, it was possible to bring the operating problems down to an acceptable level. (From Roxtec Ltd, pages 24-25 of its booklet on ‘Cable and pipe transits for EMC’, December 2002, www.roxtec.co.uk)
216 A system to combat satellite interference, which costs operators millions each year in lost bandwidth, has been developed in the UK. Qinetiq’s satID system is designed to pinpoint ground bases inadvertently transmitting to an operator’s satellite, and using up some of their expensive bandwidth. The introduction of satellite services, the growth of personal satellite communications technology and congestion of the geostationary arc are increasing these interference problems, said Dr Rob Rideout, senior scientist for geolocation at Qinetiq.
“Satellites suffer a lot from interference, and as satellite transponder bandwidth is an expensive resource, to have that tied up is a big commercial problem for operators. The cost could run into many millions.” The vast majority of satellite interference is not malicious, but results from equipment failure of operator error. “Someone could be operating at the wrong frequency due to an equipment malfunction, or an operator could be pointing at the wrong satellite.” (Taken from an item by Helen Knight in The Engineer, 22 Nov - 5 Dec 2002, Page 11)
217 I was very interested in Rob Coppinger’s article ‘Jaguar tests cars for radiation’ (News, 1 March) which reported on Volvo’s decision to make adjustments to three of its models after they were found to generate a high level of electromagnetic radiation (EMR). I purchased a new VW Golf – which in common with all modern cars is full of high-tech gadgetry – and found that the electromagnetic fields were some 100–200 times greater than they had been in my old Peugeot. (Taken from a letter by Andrew Collett, Letters, page 36 of The Engineer, 22 Nov - 5 Dec 2002)
218 Allen Brown (Letters, September) asks whether there is any explanation as to why electric light bulbs sometimes ‘sing’ just before they fail. If a lamp filament fails during use and the break is not sufficient to interrupt the current, an arc will form across the break. Arcs formed in this way can be surprisingly long if the ends of the filament move. The singing is the sound of the this discharge, possibly acoustically modified by the thin glass envelope. Therefore filament lamps start to sing when they fail and not before. On a safety note, as this discharge is a UV source it is not advisable to look at a ‘singing lamp’ in view of the chance of ‘arc eye’, but to switch it off. If the singing was due to arcing across a break, the lamp will of course not light again.
I first met the ‘singing light bulb’ effect as a very junior technical assistant in a lampworks in the mid-1930s. Part of my job was to inspect the life-test racks twice daily, perform the BSI 161-1936 specified interruptions in supply, and record failures. Out of several hundred lamps on test, it was not uncommon to find one ‘singing’. The explanation is, of course, that the tungsten coil, having suffered long, has now parted at its weakest point and is now arcing using the remains of the tungsten coil as ballast. Left undisturbed it may run for some hours, depending largely upon the pressure and purity of the gas filling.
(These two contributions are from Alan Vicary and William J Chapman respectively, published in the Letters page of the IEE Review November 2002, page 25. We wonder whether any RF emissions measurements have ever been made on a ‘singing’ light bulb – we would expect there to be a significant emissions of broadband disturbances, probably modulated at the audible ‘singing’ frequency, peaking at the resonant frequencies of the mains wires. Filament light bulbs are often held up as an example of a “passive EM” device, i.e. one causing no electromagnetic emissions and unaffected by electromagnetic disturbances. But ‘singing’ light bulbs not too uncommon, and it seems that about 1% of ordinary coiled filament light bulbs are VHF transmitters at between 28 and 45MHz – see Banana Skin No. 159.)
219 The Food and Drug Administration (FDA) is aware of a safety issue that affects users of all electrical products. Specifically, electromagnetic interference is resulting in hazards to users and operators. Our purpose in writing to you is threefold: 1) to inform you of our involvement, 2) to encourage interchanges between professional and trade associations (medical and non-medical) to develop solutions, 3) to ask you to re-assess your product designs.
We are concerned about the response of electrically-powered products exposed to various electromagnetic environments and the consequences of that response. CDRH has received reports of malfunctions of medical devices and radiation-emitting electronic products due to electromagnetic interference (EMI), including radiated emissions, conducted emissions, and electrostatic discharges. Sometimes, the consequences were severe even though emissions were within currently accepted limits; for example:
· monitor failed to detect a patient’s critical condition,
· defibrillator failed to resuscitate a patient,
· wheelchair suddenly moved towards street traffic,
· laser beam went into the audience area of a light show,
· radiation beam shutter did not close.
Electrically powered products can be sources of EMI, or unintentional receivers of electromagnetic fields, or both. The increasing use of electronics, proliferation of electromagnetic sources, and lack of electromagnetic compatibility (EMC) testing for many products has led CDRH to begin developing a strategy for EMC. (Taken from “A Letter to Industry” – an open letter from the FDA’s CDRH (Center for Devices and Radiological Health) to registered medical device manufacturers, firms filing electronic product radiation reports, and related trade and professional associations, on September 18th 1996. The full text of this letter is at http://www.fda.gov/cdrh/emc/letter.html)
220 This is to let you know that laboratory tests performed by the Food and Drug Administration (FDA) showed that radio waves can cause unintended motion of powered wheelchairs and motorized scooters. …. The following information summarises what you should know about EMI. You may use this information to minimize the risk that EMI will affect your powered wheelchair or motorized scooter.
…. If my wheelchair or motorized scooter is affected by EMI, what kind of motion should I expect? This is hard to predict. It would depend on an number of factors, including: the intensity of the radio waves, the construction of the powered wheelchair or motorized scooter, whether it is on level ground or on a slope, and whether it is in motion or still. The motion can be erratic, with the powered wheelchair or motorized scooter moving by itself or coming to a sudden stop. Further, it is possible for EMI to unexpectedly release the brakes on a powered wheelchair or cause it to go in unintended directions. Some intense sources of EMI can even damage the control system of the powered wheelchair or motorized scooter.
.… What can I do to reduce the risk that my powered wheelchair or motorized scooter could be affected by EMI? Here are some precautions that you can take:
1) Do not turn ON or use hand-held personal communication devices, such as citizens band (CB) radios and cellular phones, while the powered wheelchair or motorized scooter is ON.
2) Be aware of nearby transmitters, such as radio or TV stations and aware of hand-held or mobile two-way radios, and try to avoid coming close to them. For example, a powered wheelchair or motorized scooter with an immunity level of 20 V/m should stay at least three feet from a hand-held two-way radio and ten feet from a mobile two-way radio.
3) Be aware that adding accessories or components, or modifying the powered wheelchair or motorized scooter, may make it more susceptible to interference from radio wave sources. (Note, there is no easy way to evaluate their effect on the overall immunity of the powered wheelchair or motorized scooter.)
(Taken from “Radio waves may interfere with control of powered wheelchairs and motorized scooters”, published by the Department of Health and Human Services of the FDA on September 20, 1994. Available as a download from the FDH’s website at http://www.fda.gov)
221 NASA Reference Publication 1374 (RP-1374), “Electronic Systems Failures and Anomalies Attributed to Electromagnetic Interference”, can be downloaded in PDF format from the NASA Archive website at: http://trs.nis.nasa.gov/archive/00000296. Although it includes many case studies relating to the space program (some of which were very costly), it also includes cases from the marine, aircraft, automotive and medical industries. This publication is of great interest for electronics in general as it does not cover incidents relating to spacecraft charging from natural space plasma, which is of course peculiar to the space environment. (Many thanks to Władysław Moroń, Adviser to the President, Office of Telecommunications and Post Regulations, Republic of Poland for drawing RP-1374 to our attention.)
222 For months, the elusive culprit had jammed GPS signals in Moss Landing Harbor, Monterey California. The team of engineers roamed the waterfront with a spectrum analyser and receiver. They identified not one but two culprits, and unearthed evidence of a third, all of them readily available, commercial-grade television antenna boosters.
In April 2001 the captain of the research vessel PT SUR, based in Moss Landing, California, made a radio telephone call at-sea to one of the authors, stating that signal reception of GPS in the whole of Moss Landing Harbor was jammed. He was advised to contact the U.S. Coastguard (USCG) and the Federal Communication Commission (FCC). When the problem persisted for another month, we launched an effort at the local level to determine the cause of the jamming.
One of the major ships in the harbor paid for a technician and new equipment to fix the problem, but finally had to turn off GPS in the harbor area, give the alarm that GPS was off line, and use radar only for harbor entrances in bad weather.
We began our search for the source of jamming radiation in May 2001, spending several days looking for it. Two factors complicated the effort: the large number of metal objects that reflected the energy, and the shifting of the frequency of the emitter.
Only by turning off shore power to individual boats could we determine the actual emitter location. We contacted the boat owner and gained access, quickly determining that the emitter was a commercially available VHF/UHF television antenna with built-in preamplifier. The preamplifier was powered all the time, even when the TV was not on. In fact, the TV was seldom on, and most of the time the TV antenna was in a paint locker inside the locked boat. From this interior. Its emissions jammed all of Moss Landing Harbour and an area at least 1 kilometer out to sea.
A few days after Source-1 was removed, there were still long periods when our MBARI GPS receiver was tracking few or no satellites. The MBARI GPS receiver was being jammed during most nights. We conjectured that the jamming’s diurnal pattern derived from the temperature sensitivity of the second jammer’s center frequency. This turned out to be correct. This told us that we would have to search for the second jammer at night and early morning. Again the hunt was not easy. (They abandoned the search for Source-2 and instead went hunting for yet another jammer they had discovered, Source-3.) In the end, it turned out to be another commercially-available VHF/UHF television antenna on a boat, one dock over from Source-1.
The FCC has determined that the preamplifiers in Source-1 and Source-3 came from the same factory, which sold units to at least four well-known U.S. brand names of consumer electronics equipment. The bad units apparently began with a design change in late 2000; the number of units sold is not known to the authors.
The FCC made a few more attempts to locate Source-2 during the summer. In the fall of 2001, the FCC succeeded in locating Source-2. It again turned out to be a VHF/UHF television antenna with preamplifier.
Source-1 had the highest level at -96 dBm. Its location is known to have been 325 meters from the MBARI antenna. It was at an elevation angle of -2.5 degrees. While the beam pattern of Source-1 is unknown, if it were omni-directional, it would exceed the FAA specification for aircraft GPS receivers for GPS landing systems at a range of 50 kilometers or more. It is known to have caused marine GPS receivers to lose lock out to 3 kilometers.
Conclusion: In one small California harbor, at least three emitters capable of jamming commercial GPS receivers were present. Locating these sources proved difficult. The existence of the jamming was well-known in Moss Landing Harbor, and reported at least once to the appropriate agencies. However, the problem persisted until local engineers and scientists hunted down the worst offender.
(The above was extracted from “System Challenge – The Hunt for RFI – Unjamming a Coast Harbor” by James R Clynch, Andrew A Parker, Richard W Adler and Wilbut R Vincent of the Naval Postgraduate School, and Paul McGill and George Badger of the Monterey Bay Aquarium Research Institute, GPS World January 2003 edition, pages 16 - 22, www.gpsworld.com. Note how much time and effort it took to identify the low-cost culprits.)
223 In July 2001, the Subcommittee on Safety of Navigation of the International Maritime Organisation (IMO) approved the draft revision of IMO Resolution A.815(19) World Wide Radionavigation system. Of particular interest in the Resolution is the requirement of signal availability of at least 99.8 percent over a 2-year period and continuity of service of at least 99.97 percent over a period of 3 hours for navigation on those harbor entrances, harbor approaches and coastal waters with a high volume of traffic and/or a significant degree of risk.
On most modern ships, (D)GPS is the only source of position information to the electronic chart (ECDIS) and to the mandatory onboard transponder of the Automatic Identification System (AIS). Especially on high-speed craft and on one-man bridges there is little time to cross-check navigation accuracy with other available information, such as radar. False position information to the AIS could even lead to “AIS-assisted collisions”.
The Volpe report on GPS vulnerability recommends that public policy must ensure, primarily, that safety is maintained even in the event of loss of GPS. The reasons for possible loss of GPS are well described in the Volpe report and in other publications. However, IMO or other maritime bodies do not address solutions for the case of loss of GPS (yet). The future of the Northwest European Loran-C system is unsure after the end of the agreement between the participating countries in 2005; many world-wide maritime areas are not covered by Loran-C. Other terrestrial navigation systems for maritime application have been phased out. The combination of GPS and Galileo will increase the availability of signals and the possibility of Receiver Autonomous Monitoring (RAIM) but Galileo is also vulnerable to interference or jamming.
(Extracted from the contribution by Jac Spaans, Professor Emeritus, President of the Netherlands Institute of Navigation, to the review entitled “Directions 2003” in GPS World, January 2003, pages 28 and 30, www.gpsworld.com. We note that GPS systems are cheap to implement because the U.S Military pays for the satellite system. No doubt this is why so many people want to use them, even for safety-related or safety-critical functions, despite their obvious shortcomings. The “Volpe” report can be downloaded via http://www.navcen.uscg.gov/gps/geninfo/pressrelease.htm or direct from http://www.navcen.uscg.gov/archive/2001/Oct/FinalReport-v4.6.pdf.)
224 Electronic signal jamming devices that can be purchased through the Internet for less than $40 could play a decisive role in the effectiveness of possible U.S. air strikes against Iraq. According to recent report in the Wall Street Journal, U.S. congressional and military leaders are becoming increasingly concerned that widely available and relatively inexpensive devices that jam signals from GPS satellites could hamper efforts to effectively target high precision bombs in densely populated areas (such as Baghdad). Such munitions are now largely dependant on signals from GPS to deliver their warheads within 10 to 30 feet of their intended target.
Even the smallest of jamming devices can be remarkably effective at scrambling signals from GPS satellites. A 19 pound device demonstrated at the Paris Air Show in 1999 by a Russian company claimed effective jamming of GPS signals for more than 100 miles. The device boasted a puny 4 watts of power.
(From “GPS Jammers Could Hinder Attack on Iraq”, in the “Newsbreaks” section of Conformity, November 2002, page 8, www.conformity.com. The Wall Street Journal Article referred to in the above was “US Bombs May Not Find Targets In Iraq Due to Satellite ‘Jammers’”, Tuesday, September 24, 2002, www.wsj.com.)
225 A well-known make of wireless baby alarm is known to cause occasional interference with aircraft communication as the planes approach some airports in the UK. It is not the wireless technology in the baby alarm that is the problem, it is their plug-top power supply, which uses a switch-mode converter. A faulty batch of power supplies was shipped with the baby alarms, and although they function well enough they emit powerfully on VHF radio channels used by National Air Traffic Services Ltd. (NATS).
The interference is particularly difficult to detect on the ground but when NATS is informed of problems of this sort, they are able to overfly the troubled area with a specially equipped aircraft, partly funded by the Radiocommunications Agency (RA). When the aircraft has located the source of the interference, NATS will send in a specially equipped road vehicle which identifies the house concerned.
Officers from the RA then exchange the faulty plug-top power supply and send it back to the baby alarm manufacturer, who ship a (non-VHF-transmitting) replacement. It is a lot of trouble to go to for a low-cost electronic item, but flight safety requires us to do it. (From Tom Perry, UK Civil Aviation Authority.)
226 Mass deployment of ADSL systems in Greater London has the potential to exceed the ITU noise floor. In addition, the emission level is predicted to exceed the maximum co-channel interference level of an airborne ADF (Automatic Direction Finding) receiver by up to 15 dB over the centre of the city, reducing to 2 dB at the edge of the city.
Mass deployment of VDSL systems has the potential to increase the noise floor by up to 18 dB at 10MHz at a height over central London of 100m. At the centre of London, the cumulative emissions level exceeds the ITU noise floor at all heights up to 20 km. At the edge of the city, an increase in the noise floor of between 5 dB – 8 dB is anticipated at a height of between 5 km – 10 km.
(Extracts from: “Prediction of interference due to telecommunication drop wires in the ADSL and VDSL bands” by A R Bullivant or W S Atkins Singapore Pte Ltd and A J Maddocks, ERA Technology Ltd, presented by Tony Maddocks at the IEE Seminar “EMC – It’s nearly all about the cabling” at Savoy Place, London, January 22nd 2003. ADSL and VDSL are the technologies used for delivering ‘broadband internet access’ over ordinary telephone wires.)
227 The U.S. Department of Defense will use in-theatre jamming of the L1 signal to deny its adversaries the use of GPS. While jamming GPS signals has always been a military option, its use became a necessity following deactivation of Selective Availability. In addition to such military procedures, terrorists might try to jam the GPS signals using easily constructed equipment. GPS signals are also susceptible to unintentional jamming.
The civil GPS community got an eye-opener in 1997 as well. First, the Russian company Aviconversias announced in September that it could deliver a commercial GPS/GLONASS jammer capable of blocking civil GPS receivers within a radius of 200 kilometers. Then military GPS testing in the New York area in December caused a number of GPS receivers in civil aircraft to lose track of GPS signals during approach to Newark International Airport. Thus it was confirmed that civil receivers were vulnerable to jamming, and at the same time, that jamming equipment was commercially available.
One of the most important studies in this field, and – coincidentally – with very good timing (released one day before the 9/11 attacks on the World Trade Centre – Editor), was the so-called Volpe report on the vulnerability of GPS which concluded that, like other radionavigation systems, GPS is vulnerable to jamming, and that jamming of GPS could jeopardize safety and have serious environmental and economic consequences. The report also concluded that increased use of GPS in civil infrastructure makes it an increasingly attractive target for hostile activities by individuals, groups and states. At the same time, the analyses underlined the commercial availability of equipment for jamming purposes.
(Extracts from “Jamming GPS – Susceptibility of Some Civil GPS Receivers”, by Börje Forssell and Trond Birger Olsen, in GPSworld, January 2003, pages 54 - 58, www.gpsworld.com.)
228 In looking to the future, with GPS playing an increasingly important role in our daily lives, we must ensure that we maintain that reliability. With safety and security as its top priorities, the department has developed a 14-point action plan to mitigate any potential vulnerability. We are working closely with the Department of Defense in their GPS modernization efforts, redoubling our efforts to protect critical spectrum resources, and developing capabilities to locate sources of interference quickly. (An extract from an article by Jeffrey N. Shane, Associate Deputy Secretary, U.S. Department of Transportation, in “Directions 2003” in GPSworld, December 2002, Page 24, www.gpsworld.com. Forgive us for being critical, but it seems to us that the vulnerability of GPS is actual, not potential; and that sources of interference need to be located considerably more quickly than the several months reported in item 222.)
229 The FCC published a rulemaking authorizing unlicensed ultra-wideband (UWB) signal emissions. Many believe these have the potential for interference to GPS and to raise the noise floor.
The GPS signal reception environment will be more challenging in the future – the UWB rulemaking is a bellwether event. There is incredible demand for wireless capability, which will only grow in the future. At the same time, dependence on GPS-based POITIME is increasing in military systems, in “safety-of-life” navigation systems, and in essential transportation, communications, financial, timing and other infrastructures.
(Extracts from an article by Jim Doherty, Senior Analyst, Institute for Defense Analyses; member, Independent GPS Assessment Team, in “Directions 2003” in GPSworld, December 2002, page 26, www.gpsworld.com. Note that the GPS satellite signals are so weak that they are already below the ambient noise floor even in the quietest locations on the earth’s surface. Software algorithms are used to make them readable. UWB is bound to be widely adopted because of its low cost. )
230 The DOT/Volpe study on the vulnerability of GPS concluded that interference – either intentional or unintentional – could deny GPS access for critical infrastructure applications. It also concluded that, for safety-of-life applications, back-up systems to GPS would have to remain in place. Lacking other qualifiers in the summary text, one assumes that the back-ups are intended to remain in place indefinitely. (From an article by Terry McGurn, former senior analyst, Central Intelligence Agency, in “Directions 2003” in GPSworld, December 2002, page 33, www.gpsworld.com.)
231 The perception of the vulnerability of satellite navigation signals by both Europe and the United States seems to have changed 180 degree over the last ten years. In the 1990s, Europe was cautious about transitioning to GPS aviation landing systems, and it was Europe that pushed for the introduction of microwave landing systems (MLS) as a replacement for instrument landing systems (ILS). The key reason stated was the weakness of the signal delivered from space. The U.S. on the other hand, championed the benefits of GPS and declared that by the end of the 1990s, Wide Area Augmentation System (WAAS) and Local Area Augmentation System (LAAS) would be operational and ILS (and other navaids) a technology of the past.
Over the last year the U.S. has acknowledges that GPS is a vulnerable system, particularly to intentional and nonintentional interference, and has concluded that backup systems and techniques to find intentional interference will be required for critical infrastructure. On the other hand, Europe seems unworried by the situation and declares that Galileo (which will use the same technology as GPS) has a very good backup – called GPS.
Some also believe that the applications suggested for Galileo, such as road tolling, will promote widespread jamming by the public – with major implications for other users. (Extracts from an article by Alan Shuster Bruce, Manager GNSS Programs, Thales Avionics UK, in GPSworld, December 2002, pages 33 and 34, www.gpsworld.com.)
232 Just recently, the U.S Coast Guard and FCC confirmed that certain consumer VHF/UHF marine television antennas cause inaccurate position information or a complete loss of GPS receiver acquisition and tracking ability. On a broader scale, the FAA has acknowledged interference sources to be commercial and civilian aviation such as broadcast television, personal electronic devices, Mobile Satellite Service (MSS) communications systems, and ultra-wideband (UWB) radar and communication systems. The busier the airwaves become, the more susceptible GPS is to interference.
With electronics schematics obtained from the internet, you can go to an electronics supply store, spend about $500 and get the parts you need to build a GPS jammer that can disable the commercial use of GPS out to 100 to 125 kilometers – line of sight.
One long-term solution would be to increase satellite signal power. But those large improvements are not scheduled for another 10 years! You can now use an appliqué or antenna and electronics add-on package which removes the interference before it gets to the GPS receiver. This is what ERI provides. (Extracts from an ‘advertorial’ by Mario M. Casabona, President and CEO of Electro-Radiation Inc. (ERI), in “Showcase” in GPSworld December 2002, page 21, www.gspworld.com.)
233 ADSL and VDSL (broadband internet over ordinary telephone wires), low voltage lighting using ‘transformerless’ power supplies, plug-top switch-mode power supplies, variable-speed motor drives used in domestic appliances to save energy, power line telecommunications (PLT), ultra-wideband (UWB) radar and radiocommunications – are examples of the kinds of ‘noisy’ low-cost electronic devices and systems likely to enjoy wide adoption over the next few years. If present trends continue (as they seem likely to) – in the not-so-distant future interference with radio communications (including safety-critical avionics systems) will no longer be identifiable or preventable as it will arise from ‘ensembles’ of many thousands of such cheap and cheerful interference sources, even if they all actually complied with the relevant emissions standards prevailing at the time they were taken into service and none were faulty. (From “Future Trends in EMC” presented by Keith Armstrong at the Flomerics seminar “Introduction to EMC” in Taipei, Taiwan, September 17 - 18 2002, www.flomerics.com.)
234 The environment in which we live is becoming richer with man-made electromagnetic energy and at the same time the susceptibility threshold of electronic technology is decreasing. (From Maqsood Mohd, Chairman of the IEEE EMC Society Education and Student Activities Committee (EASC), writing in the IEEE EMC Society Newsletter, January 2003, www.ieee.org)
235 President Bush's son of star wars has neutralised its first targets in Yorkshire even before the British government has given the formal go-ahead for the RAF Fylingdales base on the moors to be used for the project. The upgrading of the security and surveillance systems at the base, in preparation for an onslaught of peace protesters objecting to the scheme, is knocking out the electrical systems of expensive cars.
Visitors to the beauty spot of Goathland, where the TV series Heartbeat is filmed to portray an idyllic 1960s rural life, have found themselves trapped among its charms. High power radar pulses trigger the immobilising devices of many makes of cars and motorcycles - BMW, Mercedes and Jeep among them. Many have had to be towed out of range of the base before they can be restarted.
The RAF admits it is a problem but says it is down to the car manufacturers to change their frequencies. However, Jeep claims this is not possible because of government restrictions.
Either way the locals are not amused. Frank Doyle, who owns a shop called Bazaar in Whitby, makes regular deliveries to the Goathland area in his Mercedes Vito van. He said: "I have got stuck three times in less than two weeks and have to keep calling breakdown services to get out of the place. "I am very fed up with it. It's not just the inconvenience - it messes up the business and my social life. Now when I'm on deliveries I keep the engine running, but still can't visit friends who live near Fylingdales."
Goathland resident Jackie Fearnley said: "I know that car alarms do go off, but this is getting ridiculous. It is disturbing all the villagers - and I don't think it is going to help tourism here either. Someone has got to sort this out."
North York Moors National Park car park attendant Bill Peirson said that Jeep Cherokees, Mercedes cars and vans, and BMWs seemed to be worst affected by the radar. "As soon as the alarms go off, I go over to the owners and explain it's probably the Fylingdales radar that's caused it.
"Motorbikes are the worst. There was a bike alarm screaming all afternoon recently and the rider didn't have any breakdown cover. I asked a friend in the village with a trailer to tow him away, and as soon as they were out of Fylingdales' range, it stopped."
Wing Commander Chris Knapman, of RAF Fylingdales, said it was not up to the base to resolve the problem. "We have had the frequencies we use for a very long time," he said. "They are allocated to commercial, military and government users, and the allocation is very tightly controlled. As far as we are concerned, the radars are working on frequencies which are well known, and most car manufacturers take that into account."
A spokesman for Jeep said: "The problem is that the government gives manufacturers such a narrow band to operate in - so the radio wave we use for our key fob is severely restricted." (“Son of star wars leaves drivers stranded” by Paul Brown and Nigel Burnham, Wednesday December 18 2002, The Guardian Copyright, Guardian Newspapers Limited. Mike Feeney of Freeman Hospital, Newcastle on Tyne, spotted this on the Guardian Unlimited site. To see this story with its related links, go to http://www.guardian.co.uk.)
236 These devices (active television antenna profiled in January 2003 GPS World article) can also interfere with specialized mobile radio (SMR) systems. We have a cell site near Mission Bay in San Diego. A few months ago we started getting interference on several of the channels in this site. The interference was centred around 815MHz and was about 2MHz wide.
Two days of sniffing it out with a spectrum analyzer was required. The boat owner was on an extended trip but allowed us to disconnect the offending antenna. (Rich Reinhofer, Supervisor RF Operations, Nextel, San Diego, writing in GPS World, March 2003, page 8, www.gpsworld.com. The article he is referring to was summarised in the last issue’s Banana Skins as No. 222.)
237 I’ve also been involved in hunting down interference caused by active television antennas. In my case, the interference was to a cellular telephone system and the TV antennas were mounted atop RVs (Recreational Vehicles – Editor) at mobile home parks. The unit(s) causing interference were in some cases more than two miles from the cellular phone site that was receiving interference.
If what you were tracking (see Banana Skin 222 – Editor) was the second harmonic of the signal from the oscillating amplifier, the signal only has to drift a small amount for the fundamental signal to cause interference to the base station receivers of cellular telephone, public safety, and business radio systems operating in the 806-849 MHz band.
IS-95 CDMA cellular telephone systems are extremely sensitive to this type of interference. In my company’s case, finding the offending devices and getting them turned off is worth a nearly unlimited effort.
Author’s reply: The emissions from the antenna we studied in detail had a fundamental frequency near 1575 MHz. This was not a harmonic. Its precise frequency depended upon temperature and other environmental variables. The other two antennas also had temperature-dependant frequencies near to the GPS L1 frequency, but we did not study them in a laboratory environment. We do not know that this was the fundamental frequency for the other two RFI sources, but that is likely. Jim Clynch
(Eric Lawson, Senior Engineer, Alltel Communications, writing in GPS World, March 2003, with reply, Page 8, www.gpsworld.com. Note that in the USA all the personal cellphones operate around 1.9GHz, but they have a number of other specialised cell-based telecommunication networks operating in the 800-850 MHz region, including a country-wide system for use by police and other emergency services, see Banana Skin No 179.)
238 We are currently looking at numerous applications for GPS on board locomotives. I was quite interested in the recent article “The Hunt for RFI” but was quite disappointed that it did not list the model or manufacturer’s name of the offending pre-amplifiers as we may want to put out a bulletin to determine if any of these devices are installed in our railroad yards or office cars. Is this information available? (Gary G Wilson, RF Systems Engineer)
I have been involved with tracking similar problems with interference to radio systems here in Indianapolis, Indiana area. The cause of the interference has been traced to defective manufactured RV television antennas. The article did not mention the manufacturer of the antenna. Could you pass along my query about the manufacturer? (Bill Atkin)
Names of the equipment jamming GPS were not published in the January article for liability reasons. The U.S. Coast Guard now has a safety notice at www.uscg.mil/hq/gm/moa/docs/11-02.htm, listing brands and model numbers of know emitters. You can reach this site via www.navcen.uscg.gov by going to GPS, Notes, and Information. The list may not be complete, however. The model traced by Bill Atkin is not on it. The FCC tracked the preamplifiers in three jamming antennas to an overseas factory owned by a subsidiary of a U.S. company. It is believed that the bad units began with a design change in late 2000. The number of units sold is not known, but they went to at least five different companies producing consumer goods.
(Two letters published in GPS World, March 2003, page 8, with a reply from that publication’s editor, www.gpsworld.com)
239 The following jurisprudence shows how negligence can be interpreted. In the Netherlands a recent lawsuit came up about a wheelchair. This chair unintentionally drove off a subway-platform. The driver was badly injured and her insurance company started an investigation with help of an EMC laboratory. They found out that the chair was activated by a field of only a few Volts/meter at a frequency of 1.89 GHz. The manufacturer of the chair did not accept his responsibility by arguing that his chair did meet the relevant product standard for wheelchairs. The radiated susceptibility test in this standard however did not go beyond 1 GHz. The judge decided that the manufacturer could have known that 1.89 GHz was a commonly applied frequency for the digital telephone network. The manufacturer was sentenced because he had put an unsafe product on the market. It should be noted that this example is about Product Liability and not about EMC. We also learn from this case that the application of a standard is not a guarantee for being safeguarded from lawsuits. (From Dick Groot Boerle, Teamleader EMC Laboratory for Thales Nederland B.V., from his paper “EMC and Functional Safety, Impact of IEC 61000-1-2”, the IEEE International EMC Symposium, Minneapolis, August 2002.)
240 Electromagnetic effects can cause impressive disasters which urge us to control the problem. One example is the catastrophe with H.M.S. Sheffield during the Falkland crisis. An Exocet missile hit this frigate because its search radar was switched off (so its anti-missile guns couldn’t be used – Editor) It was switched off because it was known that the satellite communication system was interfered with by this radar.
At the time of the disaster some officers used this communication link to talk with their prime minister…The ‘disaster philosophy’ is already known to many EMC-engineers who every now and then make use of a disaster to get new budgets. (Also from Dick Groot Boerle, as above.)
241 The case in the Rotterdam harbour is an 'old case' of about 15 years ago: we have installed X-band (1 kW) radars for Vessel Traffic Control and due to one of these transmitters the steering machine of a small towing ship was influenced in such a way that the ship hit the quay. (Also from Dick Groot Boerle, private correspondence, June 2002.)
242 In the late 1960s and early 1970s the International Research and Development Company Ltd (IRD) of Newcastle upon Tyne were engaged in the building of prototype superconducting DC machines. These were of the homopolar type, in which a conducting disc armature with brushes near the shaft and at the perimeter rotates in the axial field with a maximum field strength of several Tesla produced by a large superconducting coil.
The field coil had to be cooled to 4.2 degrees Kelvin and one of the most difficult aspects of the design was to minimise heat conduction to the coil via the current leads. The solution was to weld a long tube to the top of the cryostat through which long current leads were taken and to suspend the coil from the top of the tube by means of thin high tensile wires in a bifilar suspension. The coil was in essence freely hanging.
Now in a normal DC machine there will be a torque reaction on the field winding structure when delivering power, but a feature of the disc type homopolar machine is that the conductors feeding current to and from the armature brushes take the reaction and not the field coil. Thus it was that the 50 HP prototype with its freely suspended field coil was tested in the laboratory satisfactorily. IRD then scaled up the 50 HP motor to a 3.25 MW boiler feedpump motor that, after much tribulation, was finally installed at Fawley Power Station.
The great moment came when the refrigeration systems were finally working and after about a week the coil resistance had reached zero. The field power supply was gradually switched on and then suddenly there was an almighty clunk as the massive field coil in its wrapping of mylar superinsulation banged against the cryostat walls. This was not supposed to happen and the structure was not designed for this eventuality!
What everyone had forgotten was that there would be massive amounts of steel in a power station and it was to this steel that the energised coil was attracted. Much time was then spent positioning additional steel masses in appropriate positions around the power station to neutralise the attractive forces. These masses had to be strongly bolted down, otherwise they would have taken off and crashed into the cryostat. (From Dr Antony Anderson, 25 Oct 03)
243 Two Norwegian computer users have found that wireless keyboards may be a security risk, after they accidentally transmitted their typed words to each others computers 150 metres away. (“60 Seconds Technology”, page 6 of New Scientist 16 Nov 2002.)
244 Since the 1960s, there have been reports  that electromagnetic interference (EMI) can cause critical-care medical devices to malfunction. Such malfunctions have caused inappropriate therapy, patient injury, mortality, or have had the potential to do so. Fortunately, such incidents are rare, and the incidence of such malfunctions appears to be declining with time. However, vigilance is still required because (1) the electromagnetic compatibility (EMC) of many new radio-frequency (RF) sources and new medical devices being introduced into healthcare is unknown, and (2) there will be a substantial increase in usage of wireless information technology needed by healthcare but the EMC of such technology is unknown.
The latter need has been highlighted by reports that perhaps 1 out of every 200 patients admitted to US hospitals die due to medical errors, an annual rate exceeding that due to automobile accidents or due to heart disease. In the vast majority of cases, excellent physicians and medical staff make such errors because they do not have access to appropriate information (e.g., medication errors; current information unavailable). At least some of these deaths would be preventable if wireless information technology were widely used. However, the associated increased RF emissions may cause increased medical-device malfunctions. (Taken from: “Risk of patient injury due to electromagnetic interference malfunctions: Estimation and minimization” by B.Segal et al, IEEE International EMC Symposium, Montreal, August 13-17 2001, page 1308 in the Symposium Record.)
245 Whilst the number of EMI-related incidents documented during the 1990s was quite small, government statistics do establish that patient morbidity and mortality did result from the ensuing electromagnetic interference from EMES (electromagnetic energy sources) and medical devices, including medical device to medical device interference.
It is submitted that the new millennium will pose greater EMI challenges for healthcare professionals due to two emerging phenomena. The first is the integration of wireless technology into many medical devices for monitoring control and intercommunication purposes. Thus with the addition of digital and wireless technologies, many therapeutic devices will have tripartite functionality. The second important phenomenon will be the integration of wireless technology into the physical infrastructure of hospitals (smart building concepts) for monitoring, control, tracking, record-keeping and intercommunication (of equipment and personnel purposes).
At present, a small number of hospitals are integrating the operation of the cellular telephones of their healthcare staff into the hospital PBX system, but ‘digital hospitals’ concepts are emerging which will integrate which will integrate fully both wireline and wireless communications into the physical infrastructure of the healthcare facility. Obviously, these phenomena have the potential to increase the ambient level of electromagnetic energy within hospitals and they call for comprehensive EMI strategies. (Taken from: “Risk analysis and EMI Risk Abatement Strategies for Hospitals: Scientific and Legal Approaches” by David A Townsend, Faculty of Law, University of New Brunswick, Canada, IEEE International EMC Symposium, Montreal, August 132-17 2001, page 1304 in the Symposium Record.)
246 FDA has evaluated reports of medical device malfunctions caused by electromagnetic interference (EMI), performed device testing, and developed standardized test procedures. Over 500 incident reports are suspected to be attributable to EMI affecting cardiac pacemakers. More than 80 of these reports involve cardiac and other medical device interactions with electronic security systems. EMI presents a risk to patient safety and medical device effectiveness that is likely to continue as the use of electromagnetic energy in the medical device environment increases (e.g. cell phones, security systems). (Taken from: “Medical Device EMI: FDA Analysis of Incident Reports, and Recent Concerns for Security Systems and Wireless Medical Telemetry” by Donald Witters et al, of the Center for Devices and Radiological Health (CDRH), Food and Drug Administration (FDA) Rockville, USA, IEEE International EMC Symposium, Montreal, August 13-17 2001, page 1289 in the Symposium Record.)
247 Electromagnetic interference (EMI) has been responsible for many medical device malfunctions, raising concerns about the safety of patients who depend on these devices. However, the incidence of unreported EMI malfunctions is unknown. Between 1984 and 2000, Health Canada’s Medical Devices Bureau received thirty-six reports of medical device malfunction attributed to EMI. These included 4 reports of medical device malfunctions caused by wireless cellular phones, two cases of EMI interference from electronic article surveillance (EAS) systems on implantable cardiac pacemakers and possibly one case of premature failure of a pacemaker.
The Bureau also investigated reports of interference from other radiofrequency sources. These included (1) Interference of an electrosurgical device with the electrocardiogram signals displayed on the monitor of an automated defibrillator; (2) Complete inhibition of the pacing signal of a pacemaker by a pulsating magnetic field from a video display terminal; (3) Failure of the R-wave detection circuitry of a cardiac defibrillator in the presence of a simulated muscle artifact signal from an electrocardiogram simulator; and (4) Interference of the line isolation system in an intensive care unit with the performance of a defibrillator. These reports highlighted the need for guidelines on the management of EMI within hospitals, especially in critical-care areas. (Taken from: “Electromagnetic Interference in Medical Devices: Health Canada’s Past and Current Perspectives and Activities” by Kok-Swang Tan et al, Medical Devices Bureau, Therapeutic Products Directorate, Health Canada, IEEE International EMC Symposium, Montreal, August 13-17 2001, page 1283 in the Symposium Record.)
248 The problem — electromagnetic interference (EMI) from electrosurgery units transmitting noise onto real-time video images from an endoscope being used during the operation. (A real-life problem discussed in a paper given by Nigel Beaumont-Rydings of the Royal Oldham Hospital at a meeting of the “CE North West” club on 30th March 1998.)
249 Steve Juett provided the first “War Story” on the EMC challenges facing biomedical instrumentation in hospitals. He presented very straightforward slides illustrating the situation. The FDA has no immunity requirements for biomedical instrumentation. Not surprisingly, the myriad of telemetry links and proliferation of personal computing devices and cellphones present challenges to medical equipment used to save lives, the sensitivities of which can be in microvolts!
Finally, Steve Juett provided another story from the biomedical arena – tracing down the source of an interference problem at the hospital to a local TV station trying out its HDTV band. It took some effort to get in touch with the right individual at the TV station to resolve the problem! (Taken from a report on the May 2001meeting of the IEEE EMC Society Dallas USA Chapter, in the IEEE EMC Society Newsletter Issue 92, pages 8-9. Steve Juett is the Director of Biomedical Engineering at Baylor Hospital in Dallas.)
250 I do a lot of work with shielding for MRI scanners. RF interference can ruin the images, which are time-consuming and expensive so all MRI scanners are installed in rooms with some degree of shielding. One hospital I visited the trace an interference problem was the quickest job I ever had. The hospital had “Switch off your cellphone” warning signs all over it – and a plainly visible cellphone basestation on its roof. When they got the basestation switched off, their interference problems ceased. (Gary Fenical of Laird Technologies, private conversation 23rd May 2002.)
251 A number of medical interference incidents listed in Don White’s 1998 EMC Encyclopaedia:
· Apnea monitors susceptible to FM transmissions: The US FDA has reported cases where susceptible apnea monitors used to monitor the breathing of newborns during sleep have been affected by EMI from RF broadcast sources. The apnea monitor is designed to alarm when the newborn stop breathing. External interference has been demonstrated to mimic the rhythmic breathing patterns when the interference modulation is demodulated by an audio rectification mechanism. The effect is to fool the apnea monitor and not alarm properly.
· Patient monitoring system picked up EMI causing alarms not to sound. Two patients died when system failed to detect arrhythmia.
· Paramedics could not sense heart rhythm due to excessive artifact on CRT monitor. Patient not resuscitated.
· External defibrillator/pacemaker stopped pacing when ambulance attendant used hand-held transmitter too close to patient.
· Battery charger cycling at 1-Hz rate in respiration monitor, coupled to respiration circuit. Patient died with no alarm.
· Erroneous displays and latch-up of anesthesia gas monitor during electrosurgery.
· Intro-Aortic balloon pump stopped pumping when system printer was turned on.
· Pacemaker ceased function during ambulance radio transmission.
· Ventilator - cessation of ventilation, inoperative monitoring, error messages.
· ESD Disabled apnea monitors without activating an alarm.
· Radiation therapy device - ESD caused source to turn on, display to blank, unintended gantry movement, timer failures.
· Severe interference with heart rate and graphs of ICU patient monitor when blood-pressure monitor in use.
· Infusion pump caused interference with patient monitors.
· Movement of chiropractic table caused by muscle stimulator.
· Microsurgical drill began to run when electrosurgery unit was activated.
· Erroneous displays and latch-up of anesthesia gas monitor during electrosurgery.
· Intro-Aortic balloon pump stopped pumping when system printer was turned on.
· Neonatal monitors were interfered with when placed close to similar models.
· Respiration rate controller ceased to function when oxygen analyzer was placed on top.
· Cellular phones interfered with incubators, infusion pumps, dialysis equipment, defibrillators. They are banned from some hospitals in Europe.
· Reading of invasive blood pressure monitors jumped 3 to 10 mm Hg when paging transmitter on hospital roof was activated.
· Displays of telemetry patient monitor would “flat-line” when paging company transmitted digital control information to remote sites.
· ECG monitor in defibrillator was interfered with when emergency crew transmitted with antenna inside station wagon with defibrillator.
· Pulse oximeter displayed saturation of 100% and pulse rate of 60 on a patient who had expired. Telemetry transceiver, part of the system, too close to oximeter.
252 TETRA: The risk to medical devices from the use of TETRA handsets is comparable to that from GSM cellular phones. All personnel using TETRA handsets on hospital premises should therefore be made aware of, and follow, the local policy guidelines applicable for cellular phone systems. In the case of emergency services dealing with an on site incident, the risk of interference should be treated as secondary to the risks associated with managing the incident. Staff responsible for Trust radio communication policy should liase with local representatives of the emergency services to agree and formulate local working practices.
Outside Media Broadcasts: Ensure that a hospital representative such as the Risk, Safety Communications Manger is available to assist Media personnel with the location and operation of equipment. Media personnel using radio handsets (radio-talkback system) on hospital premises should be made aware of the hospital policy on use two-way radios for all locations in which they will be working. Ensure that any outside broadcast vehicles equipped with radio-talkback and microwave link transmitters are parked as far away as practicable from patient treatment areas or wards. (Extracted from Medical Devices Agency Safety Notice SN 2001 (06) downloaded from www.medical-devices.gov.uk on January 2nd 2003. The full notice gives information on the technical basis for these warnings.)
253 The Food and Drug Administration (FDA) received over 90 problem reports of medical device malfunctions related to EMI from magnetic field emitting security devices since 1998. The malfunctions were judged serious enough by the reporters (clinical users of these devices) to potentially cause patient injuries. Examples of malfunctions with implanted devices ranged from disturbances in the cardiac sensing operation of pacemakers, unintended firing of implanted cardiac defibrillators (ICDs), changes in drug delivery rates of infusion pumps, and over-stimulation of patients with neurostimulators resulting in severe pain or falls.
As a result, the FDA undertook a study of the EM fields emitted from the security screening systems to determine the nature of the EM fields seen by electronic medical devices worn by, or implanted in, patients passing near these screening systems. Measurements of the magnetic field emissions from security devices reveal that some security screening devices can emit fields at strengths that exceed the test level specified in some medical device standards. The FDA took action to alert users and manufacturers of active medical devices and security screening devices of the potential for interactions. (Taken from: “Comparison of Magnetic Fields Emitted from Security Screening Devices with Magnetic Field Immunity Standards” by Jon P Casamento of the FDA’s Centre for Devices and Radiological Health (CDRH), presented at the IEEE 2002 International EMC Symposium, Minneapolis, August 19-23, pages 937-940 in the Symposium Record.)
(Editor's note: the standards referred to in Jon's paper were CENELEC draft standards prEN 45502, Part 2-1 for cardiac pacemakers and Part 2-2 for implantable defibrillators. The 2002 version of EN 60601-1-2 (the EMC safety standard for medical devices) includes a magnetic field immunity test of 3A/m but only at 50Hz, whereas the security screening devices he tested could emit fields of up to 1000A/m at frequencies between 200Hz and 100kHz and 3A/m up to 10MHz.)
Items 254 - 258 are taken from the IPEM conference “Practical Methods for Mitigation of EMI and EMF Hazards within Hospitals”, York, 28th January 2003. IPEM = Institute of Physics and Engineering in Medicine, http://www.ipem.org.uk.
254 Medical diathermy is used for physiotherapy, to heat tissues throughout their volume. 27MHz continuous ‘short-wave’ diathermy can use RF powers of up to 400W, but is becoming unfashionable. 27MHz pulsed short-wave diathermy is just coming into fashion and uses average RF powers of around 40W. 2.45GHz microwave diathermy is out of fashion, people being scared off by the idea of ‘microwave cooking’. There is also a technique known as Interferential Therapy which operates at 4kHz.
Electrosurgery equipment typically uses 500kHz. ‘Cutting’ typically uses 1200V and 400W, ‘Point Coagulation’ typically uses 2000V and 150W, ‘Spray Coagulation’ uses 380V and 80W, and ‘Blend’ uses 1800V and 300W (the high frequency prevents the patient from receiving a fatal shock - Editor).
There are significant levels of emissions from the diathermy and electrosurgery leads, and most theatre equipment is now designed to avoid interference from this source. ‘Bipolar’ diathermy technology reduces the interference caused; and most modern equipment uses sinusoids, which reduces the potential of harmonic emissions to cause interference problems.
A traction machine in a physiotherapy department has been seen to malfunction when a 27MHz diathermy system was switched on in the next room. The long leads associated with pacemakers make good antennas and can download large currents at 27MHz directly into the heart, damaging it. External pacemakers used during surgical operations have much longer leads than implanted pacemakers, and are a nightmare. Diathermy has also caused certain defibrillators to charge up and some pulse oximeters to give wrong readings. (Taken from: “Surveying a hospital for electromagnetic interference” by Lindsay Grant, Consultant Clinical Engineer, Royal United Hospital, Bath, U.K. Diathermy and electrosurgery are well-known by surgeons as causes of interference problems. For more examples see Banana Skins 83, 247, 248, 251, 257, 258 and 261.)
255 Medical device interference from mobile phones. Actual reports of serious problems are hard to come by. However, in-house tests at the University of York, and field-test studies such as that commissioned by the Medical Devices Agency have shown that many types of hospital equipment are susceptible to RF radiation, although generally only at distances of less than 2m. Victims of EMI from mobile transmitters typically include diagnostic equipment such as ECGs, EEGs, pulse oximeters and other physiological monitoring equipment; plus therapeutic equipment such as infusion pumps, ventilators and defibrillators. Physiological monitoring has a bandwidth of around 100Hz and is very sensitive – so very susceptible. For example the sensitivity of an ECG is 1mV and of an EEG is 100µV, whereas ‘Evoked potential’ monitors can be sensitive to as low as 1µV.
The type of modulation employed by the mobile transmitter can be significant. For example, an external pacemaker we tested withstood a GSM modulated signal at 30V/m field strength, but TETRA modulation caused interference at 3V/m. GSM modulates its signal at 217Hz, whereas TETRA uses 17Hz which has a greater probability of lying within the pass-band of medical equipment.
We found that a distance of 1.2 metres was required for the medical equipment we tested to be safe. For comparison: Rice and Smith (Canada) found that 10 out of 14 devices failed with a 0.6W mobile phone at distances of under 500mm; Irnich and Tobisch (Germany) tested 224 devices and recommended a safe distance of at least 1 metre; The U.K.’s Medical Devices Agency tested 178 devices and found that 4% exhibited effects with mobile transmitters at 1 metre, although only 0.1% of them had serious effects at that distance (Bulletin BD 9702). (Taken from “Mobile communication systems and medical equipment”, by M P Robinson, I D Flintoff and A C Marvin, York Electromagnetics, University of York.)
(Also see: M P Robinson, I D Flintoft and A C Marvin, ‘Interference to medical equipment from mobile phones’, J. Med. Eng. Technol. vol. 21, p. 141, 1997. M L Rice and J M Smith, ‘Study of electromagnetic interference between portable cellular phones and medical equipment’, Proc. Canadian Med. Biol. Eng. Conf. p330, 1993. Steve Smye, ‘Assessing the risk to medical equipment of interference from mobile phones’, EMC York ‘98 Conf. Proc., July 1998, “Electromagnetic compatibility of medical devices with mobile communications”, Bulletin MDA DB 9702 March 1997 from the U.K. Medical Devices Agency, http://www.medical-devices.gov.uk, “Safety Notice SN 2001 (06)”, the U.K. Medical Devices Agency, www.medical-devices.gov.uk)
256 Magnetic Resonance Imaging (MRI) uses very powerful static magnetic fields, up to 3 Tesla in the U.K., but systems with up to 8 Tesla are available and there is a trend towards using more powerful fields. This magnetic field can accelerate ferromagnetic objects with serious consequences. A patient was struck by an oxygen bottle while being placed in the magnet bore. Parts of a fork lift truck weighing 800 pounds were accelerated by the magnet, striking a technician and resulting in serious injury. A pair of scissors was pulled out of a nurse’s hand as she entered the magnet room, hit a patient, causing a head wound. Dislodgement of an iron filing in a patient’s eye during an MRI exam resulted in vision loss in that eye.
Implantable medial devices such as stents, clips, prostheses, pacemakers and neuro-stimulators are all potential hazards in an MRI scan, and devices should be tested for MR compatibility. It is known that pacemakers can be very sensitive to static magnetic fields of the order of 1 milliTesla. Monitoring equipment such as ECG, heart-rate, blood pressure, blood oxygen monitors are also of concern. MRI scanners also use intense RF fields, with most U.K. systems operating at 42.6, 63.9 or 127.8MHz. (Taken from: “Electromagnetic fields in the hospital environment”, by Jeff W. Hand, Director, Radiological Sciences Unit, Hammersmith Hospitals NHS Trust, London.)
257 E-M fields in hospitals. Broadband RF field measurements in the hospital environment have found that E fields can be up to 30V/m. The strongest sources included electrosurgical units, hand-held radios and VDUs. Power frequency magnetic field measurements in the hospital environment have found H fields up to 5A/m. The strongest sources included power lines and supplies, patient monitoring equipment, VDUs and electrosurgical units. 63% of all E-field measurements and 7% of all H-field measurements made in the hospital environment exceeded proposed IEC immunity requirements for medical devices. (Also taken from: “Electromagnetic fields in the hospital environment”, by Jeff W. Hand, Director, Radiological Sciences Unit, Hammersmith Hospitals NHS Trust, London.)
258 Pacemakers have always been designed with interference in mind. When they sense signals outside of the normal signal range of 10 to 300 beats per minute they go into an ‘interference mode’ and pace in a backup safety mode. This will keep the patient alive but will make them feel very unwell. All modern pacemakers have bi-directional radio telemetry systems that allow the cardiology technician to send instructions to the pacemaker. The digital coding is robust, but it is an obvious point of entry for interference signals.
In general mains signals do not cause problems with pacemakers. Surgical diathermy can be a problem. There have been some reports of pacemakers being damaged and some currents being conducted down the lead and causing myocardial tissue fibrosis, with consequent loss of pacing function, but these are extremely rare. Arc welding has long been known to be contraindicated for patients who have pacemakers. The problem is mainly with spot welding as the interference generated can appear at roughly cardiac frequencies. There have been isolated reported cases of ventricular standstill when a therapeutic ultrasound unit’s lithtripter is synchronised to the P wave of the ECG. RF physiotherapy equipment using pulsed and CW at 27MHz can cause interference problems – care needs to be taken and an expert involved in any discussion about patient treatment.
GSM mobile phones can be a problem when held very close to the pacemaker site. This is due to the 2.2Hz bursts of 900MHz signal at switch on and switch off, and 8.3Hz bursts during the ring phase. Patients are told to use the phone with the ear opposite the pacemaker site and not to keep it in their breast pocket. Otherwise there are no problems. Transcutaneous nerve stimulators (TENS) (such as are used in slimming and muscle toning devices – Editor), are common sources of interference. They can cause complete inhibition of pacing and potential death. Patients who require TENS above the waist should be individually evaluated by the pacemaker clinic and safe levels of operation established.
A number of recent reports have indicated that Electronic Article Surveillance (EAS) systems in shops can be a problem. These normally only occur when pacemaker patients linger close to the security gates. Under some extreme circumstances the field can be sufficient to cause the pacemaker to revert to its emergency reset conditions. This is not life-threatening but can make the patient feel very unwell.
External pacemakers are particularly prone to interference because they have a much longer lead and the system is not entirely screened within the body Such systems carry a high risk in the hospital environment and patients need to be kept well away from physiotherapy departments which have potentially life threatening sources of interference. Mobile phones and hospital radios can also cause problems that may initiate dangerous cardiac arrhythmias. (Taken from “Electromagnetic interference and cardiac pacemakers”, by Lindsay Grant, Medical Physics Department, Royal United Hospital, Bath.)
259 It is quite staggering to discover that over 90% of medical electrical devices that we have tested have failed to comply with the standards applied for on the first attempt.
(Taken from: “Why 90% of medical devices fail conformity assessment the first time around”, by Donald J. Sherratt, Medical Stream Director, Intertek Testing Services, IEEE 2002 International EMC Symposium, Minneapolis August 19-23 2002, Workshops and Tutorial Sessions. Note that his graphs show 97% failing EMC tests to IEC 60601-1-2:1993 – which is easier to meet than the current versions of the generics – and 90% failing safety standards.)
260 Healthcare need wireless informatics to reduce the numbers of patients dying from medical errors (such as lack of patient medical records). The electromagnetic environment in a hospital is very low, if no portable radio-frequency sources are near by. But the EMI patient-injury risk is hard to calculate because the immunity of medical devices is largely unknown. The potential for EMI malfunction is very high, but these don’t necessarily injure patients. Even though the patient-injury risk is small, it needs minimisation. Soon, wireless usage in top hospitals will not be optional, it will be essential. EMC efforts are needed to make it happen. (Taken from “Wireless Healthcare: Making it work” by Bernard Segal, McGill University, SMBD Jewish Hospital, Montreal, speaking in the “Current EMC issues in healthcare” workshop session of the IEEE 2002 International EMC Symposium, Minneapolis, August 19-23 2002.)
261 In the USA, the Food and Drug Administration (FDA) collects reports of medical equipment failure. Jeffrey Silberberg of the FDA’s Centre for Devices and Radiological Health (CDRH) states that between 1979 and 1993 there were over 100 reports attributed to EMI. These include interference to a wide range of devices, including ECG, ventilators, infusion pumps and apnoea monitors, from a variety of sources including electrosurgery, fluorescent lights and radio transmitters. The EMI reports form only a small portion of the 95,000 incidents reported to the FDA each year, but Silberberg and others believe there is widespread under-reporting of EMI incidents. (Taken from “EMC of Medical Equipment”, Dr Martin P Robinson, University of York, N. J. Wainwright York EMC Services Ltd., EMV’99 Dusseldorf, Germany. Also, see – “Performance degradation of electronic medical devices due to electromagnetic interference”, Jeffrey L Silberberg, Compliance Engineering vol. 10 p. 25 1993. An updated version was published in Compliance Engineering’s European Edition’s 1995 Annual Reference Guide as: “Electronic medical devices and EMI”, pages F-10 - F-15.)
Editor’s note: Other useful sources of information on medical EMC issues include the IPEM seminar mentioned at the top of this article, plus: “Electromagnetic compatibility for medical devices: Issues and solutions”, FDA/AAMI Conference 1995, conference report edited by Stephen Sykes of the U.S. Food and Drug Administration, 1996, ISBN 1-57020-054-8, published by the Association for the Advancement of Medical Instrumentation, http://www.aami.org.
“Electromagnetic compatibility / electromagnetic interference: Solutions for medical devices”, FDA/AAMI Conference 1997. Conference report published by the Association for the Advancement of Medical Instrumentation, http://www.aami.org.
“Technical Information Report TIR-18 – 1997: Guidance on electromagnetic compatibility of medical devices for clinical/biomedical engineers – Part 1: Radiated radio-frequency electromagnetic energy”, AAMI, http://www.aami.org.
For FDA’s Centre for Devices and Radiological Health (CDRH) “Safety Alerts”, public health Advisories and Notices, go to: www.fda.gov/cdrh/safety.html. For the FDA’s “Med Watch” safety information and adverse event reporting program, go to: www.fda.gov/medwatch.
262 Tilting train interference problems. The high-speed tilting train project on the West Coast Main Line has been hit by more problems after tests revealed it can interfere with signals. The hitch was discovered during a non-passenger run of the Virgin Trains Pendolino train between Crewe and Liverpool. It was discovered that electromagnetic interference from the controls driving the motors on the trains can change the lights on the signals. The roll-out of the service, which is planned to run between London and Scotland, has already been subject to delays. Network Rail – the company that has taken over from the Railtrack – said it was now discussing the problem with Virgin, the Strategic Rail Authority and the Alstom company, which is building the Pendolinos. There is speculation that train’s traction motors might have to be redesigned and that special filters will need to be fitted to the signals.
But a Virgin spokesman insisted on Friday that the company did not anticipate having to put back the autumn 2004 date for the Pendolinos to switch from 110mph to a full tilting mode of 125mph.
The trains were due to be introduced in full 125mph tilt mode on the West Coast line in May 2002. But a series of delays have seen the cost of the West Coast upgrade reach £9.8bn and have meant the Pendolino project timetable has slipped. Virgin has so far received 15 of its 53 Pendolinos. But they are only running at 110mph in non-tilt mode and only on Tuesdays between London and Wolverhampton and on Wednesdays and Thursdays between London and Manchester. Virgin hopes to run Pendolinos on five days a week by the end of the summer and, by 2006, reduce journey times between London and Scotland by about an hour to four hours 33 minutes.
(BBC News World Edition, Friday 2 May 2003 10:13 GMT, from http://news.bbc.co.uk/2/hi/uk_news/england/2995355.stm. A similar item appears on Erik’s Rail News for May 2003, at http://www.eriksrailnews.com/archive/may03.php, and we understand that another report on this interference problem appeared in the Daily Mail around the same time.)
A rail industry insider, who wishes to remain anonymous, brought the above news item to our attention – and adds the following comments…
The fact that interference is taking place at a number of different sites raises the issue of general safety procedures associated with the installation of new equipment within the railway.
It is likely that the interference is probably due to the introduction of new rolling stock using motor drive systems based upon fast switching power converters (refer to Tim Williams’ article “EMC Threat to Broadcast Bands”, Approval, Nov/Dec 2001, pages 26-30).
As well as the threat to radiocommunications at 150kHz and above, interference is produced by these switching converters in the frequency range 10kHz to 150kHz. Unfortunately, this is outside the range covered by the present family of railway EMC standards, EN 50121-1 to -5.
However EN 50121 (and the Protection Requirements of the EMC Directive) does require that all EMC phenomena be addressed in the EMC control process, i.e. all interference sources and levels are to be identified and only equipment with sufficient immunity to them should be installed.
In new railway projects this process works well with equipment being designed installed and tested to the requirements of meeting the emission and immunity requirements of the EN 50121 family of standards.
The problem is that much of the equipment installed in the UK railway is based upon so called ‘grandfather rights’, meaning that equipment that has been in use within the railway for many years with no EMC problems being reported, can be used in new projects without having to meet EN 50121.
Clearly, if the electromagnetic environment of the railway network remains the same, the use of ‘grandfather rights’ is justifiable. But if the EM environment is significantly changed by the introduction of a new major source of interference (such as the Pendolino? or the Eurostar – see Banana Skin No. 41) the use of the ‘grandfather rights’ approach must be questionable in any part of the railway where the new interference source is to be employed.
From the office of the Rail Regulator:
“Grand Father Rights” refers to the fact that standards can evolve and change over time, but it is sometimes necessary to replace/repair equipment to an old (or out of date) standard in order that it will work satisfactorily. It may not be possible or cost effective to replace all equipment with the latest current standards.
263 Railtrack did not know the electromagnetic susceptibility of much of its rail network. The following excerpts are taken from a hearing into complaints from rolling stock suppliers Adtranz and Alstom against the infrastructure operator (Railtrack) – regarding the inability of Railtrack to provide technical data (including EMC data) for acceptance of new rolling stock onto the UK rail network.
Adtranz/Alstom: Railtrack still does not know where its infrastructure is or how it performs. Nor does Railtrack know where its own infrastructure is non compliant with its own norms. The result has been that Railway Group Standards fail to define in key respects, mainly electromagnetic interference and gauging, the actual requirements that Railtrack will demand compliance to when trains are presented for approval.
Railtrack’s fundamental failure to know where its infrastructure is, how it performs and the condition that it is in, continues to produce extraordinary turbulence in the requirements for safety acceptance.
We have £500 million vehicles parked in the sidings. All those vehicles are built within existing gauges. They are built with lower interference levels than any of the vehicles in service and we are trying to get those vehicles approved against criteria which are spiralling towards the impossible and left to individuals and subjective appraisal.
Railtrack: Railtrack’s inherited infrastructure is 57,000 track circuits of a variety of different types. Many of them have been introduced over a number of years, tens of years, thirty years plus. Many of those track circuits were never designed for the concept of modern traction packages that we currently have being used today.
Most of them were originally designed for something like very statically controlled EMUs etc. A lot of those track circuits are susceptible to certain generated interferences that will come off these new trains. It is an inherent factor of the new train design. The track circuits which were installed and in many cases installed by BR do not necessarily meet today’s standards.
Certainly the manufacturing requirement from Westinghouse or Alstom or previous companies that designed these track circuits would have designed it for work at a certain length. For reasons of fitting it to the infrastructure, the infrastructure will sometimes be of varying lengths, sometimes they are much longer in length because clearly if you could just increase it by 50% you can reduce the number of track circuits being fitted to the railway, has a nasty effect of making it far more susceptible to the EMC.
At the time the BR engineers did that, there was perfectly reasonable reason for doing it. They could make the track circuits work, they could make them reliable to operate the railway in a safe manner to detect trains. Unfortunately that same design criteria has made them more susceptible to the design of traction packages today.
Chairman: Sitting where we are if 15 years ago the British Railways Board had mandated that track circuit design ought to be a fairly limited range of track circuits that appeared to be roughly right in terms of emerging traction packages for the next ten years then we might not be sitting here now talking about electromagnetic interference.
(Taken from “Hearing RE Adtranz/Alstom complaint about vehicle and route acceptance”, held on Tuesday 9th May 2000 at the Office of the Rail Regulator, London. Document reference 14419 Version 2 - Final. From: http://www.rail-reg.gov.uk/filestore/docs/adtranz-alstom.pdf or else go to the Rail Regulator’s home page at http://www.rail-reg.gov.uk and enter 14419 into the search window.
Note that the Eurostar trains are still not permitted to travel north of London because they can interfere with track circuits. This problem became public in 1996 – see Banana Skin No. 41 at http://www.compliance-club.com/archive1/Bananaskins.htm – but seven years later the problem still has not been fixed.
Other examples of railway interference problems can be found in the “Banana Skins compendium” via a link from www.compliance-club.com or at: http://www.compliance-club.com/archive1/Bananaskins.htm, especially (at the time of writing) numbers: 12, 42, 94 and 115.)
264 Potential for interference from railways. A report from York EMC Services for the RA has looked at the potential for interference from the various parts of the railway system. The following quotes summarise their conclusions:
“It is well known that the railway electromagnetic environment is much more severe than that found in most commercial and domestic premises. However, in many instances the railway runs very close to such premises. In fact, in the example of an inner city light rail scheme the railway effectively runs along public roads, which brings it into close proximity to non-railway premises and potential victim systems.
There are concerns about radio frequency emissions from railways and their potential to interfere with the operation of commercial radio services and other equipment, such as information technology equipment.
There is concern amongst CISPR and the radio community that the emission levels and measurement techniques set out in EN 50121 [the railways emissions standard] do not provide adequate protection to radio services.… Some evidence has been found showing that such emissions are capable of interfering with electrical or electronic equipment and radio services operating adjacent to the railway lines… The findings of this study have implications for planned or existing buildings in which IT equipment will be used, where the buildings are situated very close (i.e. less than 10m) to electrified railway lines. There is a significant probability that the passing trains will interfere with PC monitors that are only a few metres away from the lines.”
(Taken from the Radiocommunication Agency’s new web-based training course on EMC at http://www.radio.gov.uk/topics/research/RAwebPages/Radiocomms/index.htm from its
Interference in Railway Systems page.)
265 Radar detectors interfere with SKY TV. Radar detectors that warn drivers they are approaching a police speed trap can emit signals that cause interference to SKY digital television (and numerous other microwave communications systems).
Although it is suspected that this type of interference is widespread, only a small number of cases have been reported. This is because most people would attribute the freezing or break-up of their digital TV picture to a glitch in their equipment, or SKY’s transmission, rather than interference. Relatively few people notice if this type of interference always occurs when a particular vehicle (fitted with a radar detector) passes their property.
The European Commission’s Directorate on General Enterprise have been made aware that equipment approved to their Automotive EMC Directive 95/54/EC has been found to interfere with radio systems operating in the 10-20GHz frequency range. It used to be considered that products that came under the 95/54/EC and were ‘e’ marked were excluded from being covered by the EMC Directive 89/336/EEC and so did not require CE marking.
However, it is now the Directorate’s opinion that 89/336/EEC applies to all of the EMC aspects that are not covered by 95/54/EC. Since 95/54/EC only covers emissions up to 1GHz, 89/336/EEC covers emissions from automotive equipment from 1GHz to 400GHz. Sadly, most of the applicable test standards under 89/336/EEC only test emissions to 1GHz, but at least the Protection Requirements of 89/336/EEC require that no interference is caused regardless of the frequency.
In the USA, where satellite TV is not very common, significant interference has occurred to satellite terminals used to link retail establishments with remote computers for verifying credit card transactions. Accordingly, the Federal Communications Commission (FCC) has announced that from August 2002 all radar detectors manufactured or imported in the USA must meet the Part 15 emissions limits in the 11.7-12.2GHz band.
(“Proposed changes in the Guidance to the Automotive EMC Directive 95/54/EC and the EMC Directive 89/336/EEC to jointly impose both “e Marking” and “CE Marking” on vehicles and vehicle equipment”, ERA Technology Ltd, Safety and EMC Newsletter, Number 68, April 2003, page 7. Also see: “FCC stiffens rules for radar detectors”, Conformity, September 2002, page 8. http://www.conformity.com. And: “All radar detectors marketed must be FCC approved effective October 27, 2002”, DA 02-2852 October 28 2002,
When comparing the phenomena regulated by both Directives it becomes apparent that harmonised standards under 89/336/EEC cover a wider range of phenomena than regulated by 95/54/EEC. The latter Directive limits itself to regulating radiated emissions below 1 GHz and for safety critical components regulates higher levels of immunity. This thus implies that it doesn’t harmonise all the protection requirements specified in Directive 89/336/EEC, reason for which it is incorrect to argue that Directive 89/336/EEC doesn’t apply to such products at all. A logical line of thought is that it only ceases to apply for the phenomena, which are regulated by the automotive EMC Directive and thus continues to apply for all other phenomena.
(Taken from: “Guidance in the EMC guide on the relation of the EMC and Automotive EMC Directive” Brussels, 15 January, 2003, Ref: 07-28 EMC-AUTOMOTIVE, DG ENTR/G/3, which is available from the EMCTLA who may be contacted via http://www.emctla.co.uk. Does this mean that motor cars should be CE marked, with a Declaration of Conformity to the EMC Directive, after all?)
266 Examples of interference with satellites. The wake shield experiment was launched in February 1994, but the small satellite used could not be deployed due to EMI with its attitude control system. This was caused by inductive coupling (crosstalk) between the unshielded attitude control sensor cable and the power bus of the spacecraft. This was an unpleasant lesson learned at the cost of a failed experiment.
The Gamma Ray Observatory satellite experiment launched in 1991 experienced a transponder lockup that prevented the spacecraft from receiving control commands. EMI from a ground source (plus design problems) was the cause.
The NOAA-11 weather satellite was launched in 1988. In September 1991 a series of phantom commands were observed and determined to be caused by EMI due to a noisy VHF (Very High Frequency) environment.
The NOAA-12 weather satellite was launched in 1991. In September 1991 it experienced phantom commands when it flew over Europe, due to the heavy commercial VHF environment over Europe.
(The above incidents are items 2.2.2, 2.2.4, 2.2.5, and 2.2.6 in NASA Reference Publication 1374: “Electronic systems failures and anomalies attributed to electromagnetic interference” published in July 1995. Download it from:http://trs.nis.nasa.gov/archive/00000296/01/rp1374.pdf.)
267 Saturn Launch Vehicle interference. During on-pad checkout at the Kennedy Space Centre prior to one of the early development test flights of the Saturn launch vehicle, the range safety receivers detected an extraneous signal. Because these receivers processed commands for engine cut-off, arm and destruct, a thorough investigation was conducted.
The spurious signals were caused by the multitude of telemetry transmitters located on board to collect test data, however, none of these were operating near the range safety receiver frequency.
Further investigation determined that the various RF signals were ‘mixing’ and producing intermodulation products in a non-linear circuit created by metalwork that was not properly bonded, namely the hinged cable tray covers and chain handrails on the gantry.
(The above incident is item 2.1.1 in NASA Reference Publication 1374: “Electronic systems failures and anomalies attributed to electromagnetic interference” published in July 1995. Download it from: http://trs.nis.nasa.gov/archive/00000296/01/rp1374.pdf.)
268 Safety-critical residual current detector (RCD) tripped by mobile phone. The ‘incident’, which occurred at a site handling radioactive material in 1996(?) was as follows: It was noticed that use of a mobile phone within approx. 1.5m of a portable RCD caused the RCD to trip. The RCD was connected in the supply to a monitor for ‘in air’ alpha particles. The concern was that such monitors connected via RCDs could be inadvertently tripped without being noticed. This could result in a failure to detect hazardous radiation levels. Although, as far as I am aware, there was no such failure in this case. Portable radios caused the same effect up to 2.5m from the RCD. This illustrates a general principle that where electronic devices are employed for ‘passive’ monitoring to reduce risks to health or safety, steps should be taken to avoid such false tripping resulting from EMI, and regular tests carried out to verify the operation of the monitor. Hopefully, the immunity of RCD’s has improved since the time of this incident, but the general principle remains. (From Simon Brown of the UK’s Health and Safety Executive, 19th June 2003.)
269 USS Forrestal disaster. With the war in Southeast Asia providing experience for all phases of naval operations, several carriers which normally belong to the Atlantic Fleet were occasionally routed to WESTPAC duty, and thus it was that on June 6, 1967, Forrestal left Norfolk, Virginia, for what was to be her first combat deployment.
Carrying Air Wing 17, Forrestal was the first U.S. carrier to be built from the keel up with an angled deck. She carried East Coast squadrons, two F-4B squadrons squadrons; VFs 11 and 74; VAs 106 and 46, flying A-4Es; RVAH-11, with RA-5C Vigilantes, for which the big carrier had undergone major modification for the IOIC reconnaissance intelligence system; the KA-3Bs of VAH-10; and VAW-123, flying E-2As.
Forrestal arrived on Yankee Station on July 25 and immediately began combat operations, her aircraft flying 150 sorties during the next 4 days, without the loss of a single aircraft. At 10:52 A.M. on July 29, the second launch was being readied when a Zuni rocket accidentally fired from an F-4 Phantom parked on the starboard side of the flight deck aft of the island. The missile streaked across the deck into a 400 gallon belly fuel tank on a parked A-4D Skyhawk. The ruptured tank spew highly flammable JP-5 fuel onto the deck which ignited spreading flames over the flight deck under other fully loaded aircraft ready for launch. The ensuing fire caused ordinance to explode and other rockets to ignite. Spread by the wind, the flames engulfed the aft end of the stricken ship turning the flight deck into a blazing inferno.. Berthing spaces immediately below the flight deck became death traps for fifty men, while other crewmen were blown overboard by the explosion.
Nearby ships hastened to the Forrestal’s aid. The Oriskany, herself a victim of a tragic fire in October 1966, stood by to offer fire-fighting and medical aid to the larger carrier. Nearby escort vessels sprayed water on the burning Forrestal and within an hour the fire on the flight deck was under control. But secondary fires below deck took another 12 hours to contain. The damage and loss of life was catastrophic.
The four-and-a-half-acre flight deck was littered with pieces of aircraft, as men struggled to clear away bombs and ammunition, throwing the ordnance over the side. One young 130-pound lieutenant found the strength to heave a 250-pound bomb overboard.
The Zuni rocket that was accidentally fired from an F-4 Phantom and started the fire is believed to have been triggered by a combination of the powerful fields at deck level from the ship’s radar and an incorrectly fitted shielded cable connector. (From http://forrestal.org/fidfacts/page13.htm)
270 Government admits radio towers, units were too close. Eastern Creek has emerged as a possible site for Sydney’s five commercial AM radio transmitters as the NSW Government admitted yesterday it approved residential development too close to the Homebush Bay towers. The Opposition has said the 1998 decision to allow Payce Constructions to build a 1200-unit residential development within 200 metres of the tower used by 2SM and 2UE was “a first-class bungle”. But the Minister for Planning, Andrew Refshauge, said his department had acted with the best evidence before it and that no one had raised the issue of electromagnetic radiation from the towers when the masterplan was advertised in 1998. “There was no information to suggest radio broadcasts would cause any problem despite the fact the proposal was advertised widely. There was no submission made that would suggest that there was any problem.”
The Herald reported yesterday that the Australian Communications Authority had warned PlanningNSW 14 months ago that there were concerns about electromagnetic radiation from the tower, which could cause serious interference with electrical and electronic equipment. The authority also raised potential health risks associated with exposure to high-powered electro-magnetic radiation. Waterside, being built in Bennelong Road, is so close to the tower used by 2UE and 2SM that it is within the “drop zone” - the area usually kept clear in case a tower falls. This occurred recently in Brisbane, when DMG’s tower was sabotaged and toppled, putting the station off air for several days.
The Opposition spokesman on planning, Andrew Humpherson, yesterday accused the Government of trying to cover up the debacle which he said had exposed taxpayers to substantial costs and claims for compensation, not just from the radio stations, but also from the developer and people who had bought the units. “We need answers. Just what was the Government aware of in 1998?” Mr Humpherson said. Dr Refshauge’s office said yesterday that there had been no submission from the broadcasters when the 1998 plan for residential development was exhibited. But the chief executive of Commercial Radio Australia, Joan Warner, said the industry had commented on the plan.
PlanningNSW, the Sydney Olympic Park Authority, broadcasters and the Australian Communications Authority are studying Eastern Creek as a relocation option. (By Anne Davies, Urban Affairs Editor, Sydney Morning Herald, February 18 2003,
http://www.smh.com.au/articles/2003/02/16/1045330466812.html, sent in by Chris Zombolas of EMC Technologies Pty Ltd.)
271 Bulb Manufacturer Lights Up Spectrum Wars. A Maryland company will soon be manufacturing energy-saving light bulbs that almost never wear out. But a host of satellite radio broadcasters are crying interference.
According to a recent article in the Wall Street Journal, Fusion Lighting, Inc., of Rockville, MD, the manufacturer of the microwave powered bulbs, is drawing fire from Sirius Satellite Radio, Inc. and XM Satellite Radio Holdings, Inc. because the bulbs emit radio waves that directly interfere with satellite radio broadcasts. The year-long battle has seen the combatants engage in debate before the Federal Communications Commission (FCC), a private testing laboratory in Columbia, MD, and, in the near future, it appears, in courtrooms in Texas and Maryland.
Fusion began manufacturing specialty light bulbs in the 1970s, when its microwave powered ultraviolet bulbs were used in ink drying equipment in specialty industrial applications. The bulbs operated in frequency bands reserved for industrial, scientific and medical equipment.
When the company sold the ultraviolet business in 1994, Fusion’s investors looked for broader applications for the light bulb technology, and hit on the idea of marketing the microwave bulb’s energy efficiency and long life for broader commercial applications. Fusion says that it’s now about a year away from commercial sales of the bulbs for use in lighting applications as diverse as gas stations and airport runways.
Trouble is that the lights make real the prospect of highways being lit up at night by hundreds of microwave bulbs that could, calim some, silence the satellite broadcasts. Understandably, the satellite broadcasters aren’t standing for it, each having paid the government more than $80 million dollars for the right to broadcast on the contested frequencies.
Last year, the FCC attempted to broker a compromise between the parties, with Fusion eventually agreeing to reduce emissions from its bulbs by 95% by putting a metal casing around the microwave generator, using a metal reflector and coating the glass over the light. Not good enough, said the satellite broadcasters, who insisted on an emissions reduction of 99.9%. The FCC says that it’s still months away from reaching a decision on the matter.
Meanwhile, Sirius has brought suit against Fusion, charging that Fusion executives “charged Sirius with securities fraud and dishonesty” in that company’s efforts to raise additional capital. In its prospectus, Sirius mentions that “new devices may interfere with our service,” but makes no mention of light bulbs. The CEO of Fusion reportedly raised the issue of Sirius’ limited disclosure with a friend at Lehman Brothers Holdings, which was offering the Sirius shares, and the concern was eventually escalated to the underwriters handling the offering. Fusion has filed a countersuit against Sirius alleging defamation. (From Conformity, Vol. 6 No. 10, October 2001. Go to www.conformity.com and click on the ‘News Breaks’ button.)
272 Power Line Communication can interfere with radio astronomy. Power line communication (PLC) system which extends the available frequency bandwidth up to 30 MHz has been proposed in Japan. The electromagnetic interference problems on PLC had been investigated by the PLC study group organized by the Ministry of Public Management Home Affairs, Post and Telecommunications (MPHPT). The study group held collaborated field experiments of the PLC facility and we measured interferences caused by the PLC facility in the HF and UHF bands in order to evaluate the influences of the expansion of PLC bandwidth on radio astronomical observations.
In the field experiment, two sets of PLC modems (SS and OFDM) were tested as an access system. During the PLC modems were on, the HF spectra observed showed strong increase of the noise-floor level, and it was found that the PLC noise exceeded the level of galactic noise by more than 30 dB. In UHF band, spurious emission around 327 MHz was identified. In both HF and UHF band, the interferences exceeded the limit of harmful interference level for radio astronomical observation which is given in Recommendation ITU-R TA769-1. Safety distances where the Recommendation was satisfied are estimated to be 219 km and 12 km at 9.2 MHz and 327 MHz, respectively. PLC seems to be a harmful interference source for the radio astronomical observation in both HF and UHF bands. (From: “Interference measurements in HF and UHF bands caused by extension of power line communication bandwidth for astronomical purpose”,
http://www.qsl.net/jh5esm/PLC/isplc2003/isplc2003a7-1.pdf. This item was found at: http://www.arrl.org/tis/info/HTML/plc, which has 24 pages of information and links on PLC/PLT.)
273 Interference with ABS and Airbags. Early ABS systems on both aircraft and automobiles were susceptible to EMI. Accidents occurred when the brakes functioned improperly because EMI disrupted the ABS control system. For aircraft, the initial solution was to provide a manual switch to lock out the ABS function when it was inoperable due to EMI and to use the normal braking system. Later, the solution was to qualify the ABS system prior to flight, based in the expected electromagnetic environment they would be exposed to.
For automobile systems, the solution was to ensure, if EMI occurs, that the ABS system degrade gracefully to normal braking – essentially an automatic version of the aircraft manual switch. Eventually, automobile ABS was qualified by EMI testing before procurement.
During the early years of ABS, a particular make of automobile equipped with ABS had severe braking problems along a certain stretch of the German Autobahn. The brakes were affected by a nearby radio transmitter as drivers applied them on a curved section of highway. The near-term solution was to erect a mesh screen along the highway to attenuate the EMI.
Mobile phones and passing taxi radios have been known to interfere with Anti-skid Braking Systems (ABS) and airbags, causing drivers to lose control of the car.
(The above examples include items 22.214.171.124 and 126.96.36.199 from NASA Reference Publication 1374 (RP-1374), “Electronic Systems Failures and Anomalies Attributed to Electromagnetic Interference”, which can be downloaded from: http://trs.nis.nasa.gov/archive/00000296/01/rp1374.pdf. They also include examples taken from “Study to predict the electromagnetic interference for a typical house in 2010” by Anita Woogara, Bristol University, & Smith Group, 17 September 1999, available via http://www.radio.gov.uk/topics/research/topics.htm#emc.”
274 The RSGB EMC Committee receives many enquiries from members about interference to reception of amateur radio signals. Accordingly, the RSGB (Radio Society of Great Britain) has produced a leaflet that gives advice about identifying and locating sources of Radio Frequency Interference (RFI, also called electromagnetic interference or EMI). Issues covered include…
● TVs, set-top boxes, Cable TV
● Switch-mode power supplies (e.g. ‘lump in a cord’ or ‘plug-top’ devices)
● Electric motors
● Intruder alarm systems
● Telephones and fax machines
(Taken from the Radiocommunication Agency’s new web-based training course on EMC at http://www.ofcom.org.uk/static/archive/ra/topics/research/RAwebPages/Radiocomms/index.htm, from its “Interference” section on: “Household Appliances and Electronic Equipment”. This course is also available on this magazine’s website at http://www.compliance-club.com – scroll down the homepage until you find it.)
(Note that since the RA was subsumed into OFCOM, www.ofcom.org.uk, in December 2003, all the old RA webpages are running in the ‘legacy’ section OFCOM’s website. The RA’s site, of course, contains a great deal of valuable research that they had done into EMC, and this is also on OFCOM’s legacy site as part of the original RA website. How long this valuable resource will be maintained by OFCOM is unknown. It is also not known if OFCOM are going to continue the RA’s valuable research on EMC, more important in these days of increasing spectrum use and more novel sources of interference, than ever before. If any OFCOM representatives would like to comment on these issues, we will be pleased to print their letters.)
275 Europe’s Smart-1 spacecraft, which is en route to the moon, has an engine problem that could leave the vehicle stranded in space. Engineers at the European Space Agency are hard at work on software they hope will rescue the probe, and plan to transmit it to the spacecraft next week. Smart-1 is powered by an ion thruster, which produces thrust in one direction by accelerating xenon ions in an electric field in the other direction. Although this creates only about the same thrust as the weight of a postcard, the engine works continuously, gradually increasing the size of the spacecraft’s elliptical orbit until it is captured by the moon’s gravitational field, a process that takes 15 months.
Soon after the spacecraft was launched, the engine started switching off repeatedly. The spacecraft’s circuitry is sensitive to high-energy protons from the sun, which generate rogue voltage spikes. Engineers routinely build capacitors into circuits to mop up any voltage induced in this way. But after launch, the team found to its dismay that the mopping up feature had been omitted from some key circuits. Each time a high-energy proton hits a particular optical sensor, it generates a spike that causes the on-board computer to switch off the engine, called a “flameout”. (Taken from the “This Week” section of the New Scientist, 31 January 2004, page 14)
276 In 1994 the Federal Communications Commission (FCC) in the U.S.A. was receiving about 25,000 complaints per year from people unable to use their telephones because of interference from nearby radio stations. It is believed that this number represents only a tiny fraction of the actual instances of this type of interference.
The FCC’s Field Operations Bureau (FOB) conducted a study, which found that although most residential telephones are susceptible to receiving interference, manufacturers can design telephones to be interference-free.
The transmitting stations most likely to be involved in interference complaints are citizens band (CB), broadcast, and amateurs. Transmitted power was not a significant factor: one-third of the transmitters used under ten watts. The study also found that filters cannot be relied upon to eliminate telephone interference. In two out of three cases in which they were tried during the study, they did not work.
(Taken from: “Interference Free Telephones”, FCC (Federal Communications Commission, Washington D.C., U.S.A., News media information 202/632-5050, May 4, 1994, indexed at: http://www.fcc.gov/Bureaus/Common_Carrier/News_Releases/1994/index3.html, download from: http://www.fcc.gov/Bureaus/Common_Carrier/News_Releases/1994/nrcc4019.txt)
277 In October 2002, a set of avionic equipment was tested under controlled conditions in a test chamber for susceptibility to cellphone interference. General aviation avionic equipment, representative of earlier analogue and digital technologies, was used. The equipment, comprising a VHF communication transceiver, a VOR/ILS navigation receiver and associated indicators, together with a gyro-stabilised remote reading compass system, was assembled to create an integrated system.
The tests covered the cellphone transmission frequencies of 412MHz (Tetra), 940MHz (GSM900) and 1719MHz (GSM1800), including simultaneous exposure to 940 and 1719MHz. The applied interference field strengths were up to 50 volts/metre for a single frequency, and 35 volts/metre for dual frequencies.
The following anomalies were seen at interference levels above 30 volts/metre, a level that can be produced by a cellphone operating at maximum power and located 30cms from the victim equipment or its wiring harness.
● Compass froze or overshot actual magnetic bearing.
● Instability of indicators.
● Digital VOR navigation bearing display errors up to 5 degrees.
● VOR navigation To/From indicator reversal.
● VOR and ILS course deviation indicator errors with and without a failure flag.
● Reduced sensitivity of the ILS Localiser receiver.
● Background noise on audio outputs.
Most anomalies were observed at 1719MHz.
The results of the tests endorse current policy that restricts the use of cellphones in aircraft.
The CAA will remind operators about the specific risk from cellphone usage on the flight deck, and recommend that confirmation be obtained from passengers at check-in that cellphones in their luggage have been switched off.
(Taken from the Radiocommunication Agency’s new web-based training course on EMC at http://www.ofcom.org.uk/static/archive/ra/topics/research/RAwebPages/Radiocomms/index.htm, from its “Interference” section on: “Aviation/Aerospace”. This course is also available on this magazine’s website at http://www.compliance-club.com – scroll down the homepage until you find it.)
278 The experiences of the crew of the research vessel (R/V) Deep Scan, a privately owned research and recovery ship, offer some insight into the complexities of integrating commercial off-the-shelf (COTS) computing equipment into a shipboard electromagnetic environment.
R/V Deep Scan is constructed as a commercial vessel with many of the electrical characteristics of military mine-clearing ships. Its hull and deck structures are constructed from wood, closed cell foam and fibreglass, and it shares EMI/EMC problems common to non-metallic ships.
Computing equipment on board is said to be compliant with FCC Part 15 for radiated emissions. A commercial workstation processes sonar and navigation track data from multiple transducers. A 386 PC processes both electromagnetic survey data from multiple detection transducers and data for navigation. Navigation data is provided by COTS GPS (Global Positioning System) and LORAN-C receiver systems. Depth information is provided by COTS depth sounding equipment. Heading data is provided by a COTS fluxgate compass.
Operating the marine VHF transmitter at more than 1W begins to corrupt collected data, and any use of HF SSB transmission causes the COTS computing equipment used for magnetic data collection and navigation to enter states that challenge rational explanation.
FCC rules limit the levels of unintentional electromagnetic radiation, but the close proximity of COTS computing equipment (the vessel is under 60 feet long) to the antennas used for data collection and communications is largely responsible for disruption of operations due to the EMI the COTS equipment generates.
EMI generated by the switching power supplies in the COTS equipment slightly degrades the LORAN-C signal-to-noise ratio through radiated coupling. COTS computing equipment generates sufficient radiated interference on the HF bands to render HF communications impractical. Broadband interference and harmonics from COTS computing equipment interfere with communications reception on selected VHF channels, in some cases enough to prevent useful communications.
Daily operations on board R/V Deep Scan are influenced by the EMI and susceptibility problems associated with the use of COTS computing equipment. Responding to a call on the VHF radio presently requires the crew to wait for a logical break in survey operations, or requires termination of survey operations. During survey operations, monitoring some VHF channels is not possible, HF transmission is impossible and HF reception is seriously degraded.
(Taken from the Radiocommunication Agency’s new web-based training course on EMC at http://www.ofcom.org.uk/static/archive/ra/topics/research/RAwebPages/Radiocomms/index.htm, from its “Interference” section on: “Marine”. This course is also available on this magazine’s website at http://www.compliance-club.com – scroll down the homepage until you find it.)
279 Problems associated with electrical noise have been solved at Northumbrian Water Broken Scar water treatment works in Darlington, County Durham. Such problems are an inevitable element of major pump installations, especially where large inverter drives are involved. This is sometimes a major problem for instrumentation, which generally involves cables carrying a smaller signal between a sensor and a control and analysis unit.
At Broken Scar, a large inverter drive meant that there was very high electrical noise. The ultrasonic level measurement unit that was originally installed, which used a coaxial cable to carry a signal, was swamped and unable to provide a reliable measurement. The solution was a Pulsar ultrasonic level measurement system …. performing an initial (digital) conversion on the signal at the transducer head, communicating digital information to the signal analysis. Despite the noise still being present, the system can discriminate between noise and the “true” signal to give a reliable measurement. (Adapted from an advertisement for Pulsar Process Measurement Ltd, in Plant and Control Engineering Magazine, Oct/Nov 2003, page 11.)
280 We have seen an increase in AC mains supply dips from typically seven per year to eighteen, which is causing increased losses in production. (A comment by a representative from a major steel manufacturing company at the IEE’s Wales South-East & Wales South-West Power Specialist section’s “Power Quality Seminar”, held at the University of Wales Swansea on Wednesday 12th November 2003.)
281 Signals from wireless communications transmitters are continuing to create significant interference issues for public safety officials, according to a recent report in the Washington Post. The interference problems reportedly stem from the close proximity of spectrum allocations for public safety communications and some older style wireless telecommunications technologies, which operate in the 800 Megahertz band. As we’ve previously reported (see Conformity, August 2002), more than 70 government agencies in 27 states have reported interference problems with wireless communications services used by public safety officials.
According to the Post article, communications problems most often arise when a public safety official (such as a police officer) is far from a transmitter that carries emergency radio signals but close to a transmitter for a wireless system carrier. In these cases, the signal from the wireless system overwhelms the weaker emergency signals, effectively blocking emergency communications.
The communications system operated by Nextel Communications appears to remain the principal source of most of the interference complaints. The Nextel network was originally cobbled together in the 1980s from underutilized portions of spectrum allocated for limited specialty uses. However, as the Nextel network has grown, its use of spectrum has begun to overlap with the frequencies used by public safety agencies.
State and municipal public safety authorities are responding in various ways to the continuing problem. Some jurisdictions are attempting to upgrade the communications infrastructure to provide stronger signals to radios operating on public safety bands. Still others are attempting to pass ordinances that require wireless carriers to certify that their signals do not interfere with public safety communications. Meanwhile, some police officers have reportedly found a simpler solution to interference with public safety communications bands, They carry their own cell phones! (From: “Wireless Interference with Public Safety Communications Growing”, Conformity, November 2003, pages 8 and 10, http://www.conformity.com.)
282 Historically, EMC issues on railways have been dominated by the possibility of interference from high power electric traction supplies, particularly DC, affecting safety-critical low power train detection equipment. The introduction of switched traction controllers raised further concerns and early variable frequency chopper drives have caused incidents, leading to the adoption of fixed frequency choppers for DC traction drives. By the time traction inverter drives for AC traction became commercially attractive, due to the introduction of GTO thyristors and subsequently IGBTs, the potential risk was well understood and care has been taken to design traction drives to be compatible with train detection systems, either by design or high-integrity monitoring.
Now, probably the greatest threat to train detection is to older track circuits operating on the same frequency as the AC utility used to produce the DC traction supply and older trains without power electronic traction controllers. In a recent incident on the UK network, a failure on the rectifier of a DC traction supply was detected by a number of new power electronic trains being brought to a halt by their interference current monitoring units even though each train was perfectly healthy. (From: “GM/RT8015 and Safety” by Jeff Allen and David Bulgin of the Rail Safety and Standards Board, presented at the IEE Seminar “EMC Assurance in a Railway Environment”,9th September 2003.)
283 As part of the development of this directive (Automotive EMC – Ed.), it has become evident that many aftermarket devices can be found to be susceptible to the many switching events on a vehicle. This can be simply audio clicks or, worst case, result in hardware failure of the component resulting in damage to the vehicle itself. For this reason, and following lobbying by the vehicle manufacturers, the committees responsible for the directive have included in this latest draft requirements for all ESAs (electronic sub-assemblies – Ed.) to be immune from a series of transient events.
(From: “Transient Test Requirements for “e”-Marking – Necessity or Bureaucracy?”, by James Gordon-Colebrook and Alex Mackay of 3C Test Ltd, presented at the Automotive EMC 2003 Conference, 6th November 2003, http://www.AutoEMC.net.)