The new CISPR 16, its Structure and Contents and the Current Projects of CISPR Subcommittee A
By Manfred Stecher, Rohde and Schwarz, Munich, Germany
CISPR Publication 16 is the basic standard for the measurement of radio disturbance in the frequency range of 9 kHz to 18 GHz. The immunity measurement section is relatively small and is limited to the immunity of sound and TV broadcast receivers. Whereas the second edition (1987) had a volume of 228 pages, the next edition already needed a reorganisation. CISPR 16 was divided in three parts: 16-1:1993 with 220 pages, 16-2:1996 with 151 pages and 16-3:2000 with 239 pages. Before the revision (Nov. 03), the whole standard consisted of 4 parts with 1015 pages. Under the overall title “Specification for radio disturbance and immunity measuring apparatus and methods”, the individual titles were:
CISPR 16-1: Radio disturbance and immunity measuring apparatus (Engl./French)
CISPR 16-2: Method of measurement of disturbances and immunity (Engl./French)
CISPR 16-3: Reports and recommendations of CISPR (English only)
CISPR 16-4: Uncertainty in EMC measurements (Engl./French)
Due to the many projects currently running in CISPR Subcommittee A, further growth is expected. Until the revision, some of the parts were impractically thick; part 16-1 had e.g. 407 pages, it contained all information from the measuring receiver to the antenna calibration test site. If a user needed information about artificial mains networks for the measurements of conducted emissions, he had to acquire the whole standard. The IEC rule, which requires a new edition with the publication of a third amendment, would lead to many expensive new editions due to the old structure and the numerous projects. In addition, part 16-3 was called a technical report, even though it contained normative material.
From the above mentioned reasons, a reorganisation was undertaken with the following guidelines: to create smaller, subject-related publications so that the user finds all that is needed for a certain subject. All material in the new publications was to be taken from the existing publications and newly voted amendments to avoid re-balloting and thus allowing a short time for the reorganisation. Therefore the former basic structure (4 parts) was kept and the new parts were designated 16-1-x, 16-2-x, 16-3 and 16-4-x, where the x-values can range from 1 to 5. 16-3 was determined to contain technical reports only, 16-4 was to be normative with informative background annexes (except 16-4-1, which was to be a technical report). Material on compliance and measurement uncertainty was combined in 16-4. Statistics and limit rationale material was moved from 16-3 into 16-4. Each new publication has a new table of contents and an introduction that describes the changes and sources of material.
Fig 1: New vs. old structure of CISPR 16
In order to organise the many individual projects, they are arranged in groups (tables) for the purpose of this paper. All documents released by the committee are designated as “publication”: Committee Draft (CD), Committee Draft for Vote (CDV), and Amendments (e.g. A1 of 16-1). In cases of finished projects the publication is printed in bold characters.
3.1 Group on reproducibility of emission measurements
The length of the following table shows the importance of reproducibility of measurement for CISPR/A. The table contains the last publication as “No. of Publ.” distributed on “Date of Publ.“ and the part of the reorganised CISPR 16, where the result of the work will finally go as “New Publ.“ (designations in the table head).
1. Instrumentation uncertainty. The measurement uncertainty caused by the influence factors effective in conducted and radiated emission measurements and in measurements using the absorbing clamp are described in CISPR 16-4-2. This also accounts for the uncertainties when determining compliance with an emission limit.
2. 3, 4 and 5 Compliance uncertainty. Measurement procedures in EMC have limited reproducibility since uncertainties due to the instrumentation, the test methods and the EUT characteristics are to be considered in the compliance test (see Fig 2). The documents are analysing these uncertainty sources and are defining the EMC relevant terms in analogy to the ISO Guide on Uncertainty in Measurement.
Fig 2 Compliance uncertainty applied by manufacturer and market supervision
6. Amendment of V-AMN specification. Projects 1 and 3 resulted in findings which entailed the need to amend the specification of the artificial mains V-network (AMN). In addition to the impedance magnitude, also the phase is going to be specified as well as the isolation between mains port and EUT port. A 10-dB attenuator on the receiver port shall guarantee the agreement with the impedance tolerance.
7. Amendment of the conducted emission measurement method. The findings in the project on compliance uncertainty (3) made clear that the specification of the test method had to be improved in order to avoid/reduce measurement errors and uncertainty: by minimising the influence of ground loops as well as magnetic fields in test setups with AMNs as well as voltage probes and by improving the test setups so, that the desired specifications of the AMN (impedance and isolation) are preserved.
8. Errors and imperfections of the chapter on the discontinuous disturbance analyser have been amended.
9. Amendment of the specifications of the devices (ISN) for the measurement on signal (especially on unshielded telecommunication) lines. Now it contains a methods of longitudinal conversion loss (LCL) and voltage division factor measurement.
10. The capacitive voltage probe is a new device for measuring the common-mode voltage on signal and telecommunication lines with more than 4 pairs. It can be attached to the lines, while keeping the influence on the source small using a low coupling capacitance (C < 10 pF).
11. An improvement of the Absorbing clamp calibration procedure became urgent, as differences of the interpretation of the existing calibration procedure in CISPR 16-1 were reported. The need to validate the absorbing clamp test site resulted from investigations on test sites, for which the OATS serves as a reference.
12. The amendment of the absorbing clamp test method includes the validated absorbing clamp test site and an improved VSWR of the clamp by use of a 6-dB attenuator on the receiver port of the clamp and many details for good reproducibility.
Fig 3. Validation of absorbing clamp test site
13. Antenna calibration and site validation (of the OATS). CISPR/A firstly agreed to define an antenna calibration test site (CALTS), which can be found in CISPR 16-1-5. Further topics are progressing slowly. There is agreement on using free-space antenna factors. For future site validation methods, there is a chance of using the reference test site (REFTS) procedure in order to minimize the uncertainties of present procedure.
14. Calibration and characteristics of monopole (rod) antennas. In order to guarantee reproducibility when making measurements acc. to CISPR 25 and possibly acc. to a future version of CISPR 12, CISPR/A has agreed on a calibration procedure with a dummy antenna.
15. Resonant loop antenna. In order to show compliance with very low limits for telecommunication network radiated emissions, a high sensitivity was needed, which can be achieved with tuned loop antennas mentioned now in CISPR 16-1-4.
16. Requirements on balun imbalance and cross-polar performance of antennas including measurement procedures have been defined in CISPR 16-1-4.
17. Influence of setup tables and antenna towers on radiated emission measurement results depending on the material have been shown in various papers. In order to quantify the uncertainty contribution of setup tables and antenna towers to the radiated disturbance measurement, test procedures are going to be defined.
18. Validation of common mode absorbing devices (CMAD). CMADs are proposed to be used on EUT cables in order to improve the reproducibility of radiated emission measurements. Impedances and dissipative attenuation will be the main parameters to be defined and measured.
19. The measurement of emission in the presence of ambients is a problem on OATS and with in-situ measurements. Solutions are not available for every case, but the publication provides help for many conditions.
20. In-situ measurements are to be used in cases of an actual interference situation or if a product standard calls out. Since the standard distance between EUT (or building) and antenna cannot be applied in many cases, the publication gives guidelines on inter- or extrapolation procedures.
21. Measurement times and scan rates and automated measurements of emissions. This addition to CISPR 16-2-1 (-2 and -3) gives guidance on how to avoid errors due to emissions varying with time (broadband and pulse-modulated narrowband emissions) when using modern automated test equipment. Hints are given how to find the minimum measurement times as well as how to reduce the overall measurement time by using a prescan, data reduction and final measurement sequence.
22. Amendments of the 80/80 rule: The comparison of any emission frequency of mass-produced equipment for the application of the 80/80 rule causes erroneous judgements. Frequency sub ranges have been introduced as a solution. Further guidance is given for the use of a reduced number of samples.
23. Scan rates with the average detector: In analogy to the existing annex on the use of spectrum analysers and scanning receivers, a new annex will give guidance on the proper use of averaging filters depending on the signal type to be measured.
3.2 Group on test equipment and methods above 1 GHz
1. Measuring receivers for 1 to 18 GHz will be integrated in the existing clauses on measuring receivers with various detectors instead of a separate clause on spectrum analysers above 1 GHz. In this frequency range the requirements for VSWR, IF bandwidth and the detectors will be defined more precisely.
2. Site validation > 1 GHz. Instead of the NSA, a so-called VSWR method will be applied, in which the variation of the attenuation between two broadband antennas in various positions of the room shall not exceed a certain value.
3. Measurement method > 1 GHz. The preferred measurement distance is 3 m. Antenna height variations are only needed if the area defined by the antenna beam width exceeds the EUT surface.
4/5. Measuring receivers with an RMS/Average weighting detector. All digital radiocommunication services use coding with error correction, which results in a corner of the weighting curve. This can be approximated by a combination of RMS and linear average detection (see Fig. 4).
Fig 4 Weighting curves of the RMS/AV detector; corner frequency 1KHz
6/7/8. Measuring receivers with amplitude probability distribution (APD) display function are proposed for the measurement of emissions from microwave ovens to replace the existing methods in CISPR 11. This will allow the definition of limits for various probability classes (e.g. 10-6, 10-3).
3.3 Group on new test sites and methods
1. The application of TEM Waveguides for EMC tests is described in IEC 61000-4-20, which was drafted in a joint task force (JTF) consisting of members from CISPR/A, SC77B and others (e.g. SC77C immunity to HEMP). It contains general requirements and application criteria for emission and immunity tests.
2. The application of the reverberation chamber or mode-stirred chamber is described in IEC 61000-4-21, which was also developed in a JTF between CISPR/A and SC77B. Besides general information, it describes the use of the stirred and tuned modes for emission and immunity measurements. In addition, measurements of shielding effectiveness are described.
3. Characteristics and validation of fully anechoic rooms (FARs) for emission tests. Radiated emission tests in FARs do not require antenna height variation. Their application is mainly limited to measurement distances of 3 and 5 m, due to the feasibility difficulties for greater distances. For site validation a reference site method is described with an acceptability criterion of ± 4 dB.
4. Emission measurement method in a FAR. Test setups for tabletop and floor-standing equipment are defined (see Fig 5).
Fig 5 Test setup in a fully anechoic room
5. Application of the FAR for EMC measurements. In another JTF a procedure to determine the uncertainty contribution of the FAR for emission and immunity measurements is going to be determined.
6. Uniform arrangements for radiated emission and immunity measurements for time-saving purposes are going to be defined in another JTF. The only necessary measure between an emission and immunity test will be the introduction of absorber material on the floor between antenna and EUT.
7. Conditions for the use of alternative test methods. The increasing number of available test methods replacing the test in 30 to 1000 MHz on an OATS or in a SAC (e.g. FAR, TEMwaveguide or reverberation chamber) requires criteria for correlating measurement data of an established method with those of the alternative method.
3.4 Group on limit modelling
1. The amendment of the CISPR 16-4-4 section on a model for the calculation of CISPR limits serves for telecommunication networks.
The reorganisation of CISPR 16 into 14 parts is justified by its continuous growth. In addition it has been shown into which direction CISPR Subcommittee A is moving. The improvement of the reproducibility of emission measurements, the extension of the frequency range to 18 GHz and the development of new measurement methods are the main activities of the subcommittee.
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