No Sleeping in Seattle: A Recap of CISPR Projects from the 74th IEC General Meeting

October 2010 saw the 74^th IEC General meeting in Seattle, Washington, USA. Within the IEC, its special committee CISPR (Comite International Special des Perturbations Radioelectriques –International Special Committee on Radio Interference) came together and this article reviews some of the key projects discussed at that meeting. The activities of IEC TC 77, a parallel committee to CISPR developing the IEC 61000 series and of equal importance, did not meet in Seattle and hence will not be discussed here except for the JTFs (Joint Task Forces) that exist in common with CISPR Subcommittee A, responsible for the basic standard CISPR 16, which will be the main focus of this first part of a two part article. In the second part of the article (to be published in a subsequent edition of this magazine), we will continue with the CISPR product standards and the Joint Task Forces (JTFs) existing between the different subcommittees as well as between CISPR subcommittees and IEC SC 77 B.

CISPR Organization

Before we take a detailed look at the current projects of CISPR, we need to briefly explain the system and the process for those not fully acquainted with it. Standardization can at first appear complicated and it is not unusual to take several years before becoming completely familiar with it. It is a common belief that since the IEC is based in Geneva, Switzerland, CISPR standards are European. However, CISPR standards are in fact applied globally, and are developed by experts from around the world. Participants in standards development need to be technical experts and require being nominated by their respective National Committees (NCs) to particular CISPR subcommittees and working groups based on their expertise or interest. Some experts come from manufacturing companies focusing on the impact of CISPR standards on their products, some from test laboratories monitoring measurement standards, some from regulatory authorities implementing CISPR standards by law, and some from national metrology (testing and calibration) laboratories.

Figure 1: CISPR Organization
Image courtesy of ETS-Lindgren

The committee consists of sub-committees that fulfil both product (vertical) and basic (horizontal) standardization roles:

• CISPR A – Radio-interference measurements and statistical methods
• CISPR B – Interference relating to industrial, scientific and medical radio-frequency apparatus, to other (heavy) industrial equipment, to overhead power lines, to high-voltage equipment and to electrical traction
• CISPR D – Electromagnetic disturbances related to electric/electronic equipment on vehicles and internal combustion engine powered devices
• CISPR F – Interference relating to household appliances, tools, lighting equipment and similar apparatus
• CISPR H –Limits for the protection of radio services
• CISPR I – Electromagnetic compatibility of information technology equipment, multimedia equipment and receivers
• CISPR S – Steering Committee of CISPR that manages its operation

All projects fall into one of two categories: new projects or maintenance of existing standards.

A new standardization project will follow this route:

• NP (New Project)
  • New Projects are generally started after an NP document has been circulated to the National Committees (NCs) and agreed by the simple majority of the permanent members of the Subcommittee (SC). At that time, at least five NCs must each identify one expert to serve on the project for the vote to be successful. A successful NP is then assigned a project number by the IEC Central Office and the subcommittee allocates it to one of its working groups (WGs) with a project leader for action. The project will be given a maximum of five years to publish an international standard. If this is not possible, it can be reset to stage zero (not active).
• 1st CD ( Committee Draft)
  • A CD is produced by a working group within the subcommittee and once ready it is sent out to National Committees for comment. This is a three month process.
• CC Comments
  • The comments of the National Committees are collected and the Working Group is tasked with resolving the comments and then updating the CD accordingly if the comments require changes.
• 2nd CD
  • A second (third or fourth are possible) CD may be produced and commented again or if the working group feels that it is mature enough to go to voting then they can submit a request to the subcommittee to authorize it to go out for vote as a CDV.
• CDV (Committee Draft for Vote)
  • A CDV will be sent out to National Committees for comment and vote.
  • A positive vote can lead to a final draft international standard (FDIS); a negative vote usually sends it back to the WG to produce another CDV taking into account the comments that caused the vote to fail.
• RVC (Result of Voting with Comments)
  • National Committee voting is summarized in this document and the decision on the next stage given. Comments can be attached to the votes by National Committees in which case the document is an RVC.
  • The draft will go directly to publication if the vote on the CDV is 100% approved.
• RVD (Result of Voting )
  • The standard will be published if not more than one quarter of the votes cast are negative.
• FDIS (Final Draft International Standard)
  • The FDIS will be circulated for comment if the CDV had less than 100% approval; this is a two month process.

Once a standard is published, it is said to be in its stability period and amendments can be published after this period expires. Maintenance will take place on the standard automatically after three years, although it can be started earlier or later but not more than five years. After two amendments, if a third amendment is produced, then all amendments will be combined together and a new edition of the standard will be published.

Basic Standards

CISPR SC/A provides basic standards to CISPR product committees as well as to other IEC technical committees for use in determining conformity to limits.

Standard: CISPR 16

Specification for radio disturbance and immunity measuring apparatus and methods.

Working Groups

• WG 1 – EMC instrumentation specifications
• WG 2 – EMC measurement techniques, statistical methods and uncertainty

Joint Task Forces with other CISPR SCs developing standards

• SC A/D/ -SITE-VAL – Chamber validation methods
• SC A/F – CDN measurement method of radio frequency disturbances for lighting equipment in the frequency range 30 MHz to 300 MHz
• SC A/H – Maintenance of CISPR 16-4-5 on conditions for the use of alternative test methods
• SC A/I – Placing testing and instrumentation from CISPR 13 and 22 into Pub 16 and referencing Pub 16 without repeating it in SC I documents

Joint Task Forces with TC 77 SC77B

• TC 77/SC 77B/JTF REV on Reverberation Chambers
• TC 77/SC 77B/JTF TEM on TEM Waveguides
• TC 77/SC 77B/JTF FAR on Fully Absorber-lined Rooms (FARs)

Table 1 shows how the CISPR 16 standard is structured.

Table 1: CISPR 16 Publication Structure

CISPR 16-1

CISPR 16-1-1 Ed 3.0 Measuring Apparatus

Use of Spectrum Analyzers

CISPR 16-1-1 has been revised and has added the use of spectrum analyzers without pre-selection for compliance measurements. The RMS/Average detector has been introduced and is of interest particularly for the protection of digital radio services.
Status: Published January 2010

Inclusion of FFT-based Test Instrumentation

The addition of Fast Fourier Transform (FFT)-based measuring instrumentation brings the possibility of reducing test time for emission measurements. This is done by taking the time domain emission response, use of the FFT and then comparing the amplitudes to the limits which are in the frequency domain. In particular, there will be significant advantages for pre-scan due to better coverage of maximization procedures, turntable and antenna height scan, better probability of intercept, and where non Quasi-Peak measurements are allowed. Final measurements, however, will probably better be left to conventional methods where true Quasi-Peak compliance can be obtained.
Status: Published January 2010

CISPR 16-1-2 Ed 3.0 Ancillary Equipment – Conducted Disturbances

JTF CIS/A -I; Transfer of AAN (Asymmetric Artificial Network) characteristics from CISPR 22

The JTF CIS/A-/F was established in 2008, tasked with transferring the CDN (Coupling Decoupling Network) method of emission measurement in the frequency range 30 MHz to 300 MHz, currently limited to lighting equipment in CISPR 15, to CISPR 16 with the goal of applying the methods to other types of equipment.

The JTF has developed specifications and measurement methods for a CDNE (“E” stands for a CDN for Emission testing), the CDN for Emission measurement. A draft will introduce and define the CDNE in CISPR 16-1-2. Subsequent drafts will follow for the measurement method in CISPR 16‑2-1 and measurement uncertainty in CISPR 16-4-2.
Status: Being discussed within WG1

CISPR 16-1-4

Specification for radio disturbance and immunity measuring apparatus and methods – part 1-4: radio disturbance and immunity measuring apparatus – Antennas and test sites for radiated disturbance measurement. Ed. 3 – 2010.

Evaluation of Setup Table

The impact of the setup table on EUT emissions can be measured and included in the uncertainty budget, also now above 1 GHz in CISPR 16-1-4 Ed 3.0. The move above 1 GHz now requires more focus on the materials used for these tables and as a result, the use of lower permittivity materials is needed if the test shows a significant effect of the table top material. (See Figure 2.)
Status: Published April 2010

CISPR 16-1-4 Reference Site Method

CISPR 16-1-4 (and also 16-1-5) will be amended for the introduction of the Reference Site Method which offers an improvement on the method of validation of compliance test sites through the use of the AAPR Antenna Pair Reference. A few definitions before we explain Antenna Pair Reference.

Three methods of site validation and the antennas used to show validation are described in CISPR 16-1-4:

• Tuned dipoles – Normalized Site Attenuation Method (NSA) up to 1 GHz
• Broadband antennas – Normalized Site Attenuation Method (NSA) up to 1 GHz
• Broadband antennas – Reference Site Method (RSM) up to 1 GHz

Table 2 identifies the site validation methods that are applicable for specific test sites.

There is currently a joint amendment of CISPR 16-1-5 with the RSM project defining the following sites:

• An OATS is an open area test site with a metallic ground plane. (See Figure 3.)
• A CALTS is an antenna calibration test site using an open area test site (OATS) with a metallic ground plane and a tightly specified SA (Site Attenuation) performance in horizontal electric field polarisation only. A CALTS can be used to determine the FSAF (Free Space Antenna Factor) of an antenna.
• A REFTS – Reference Test Site – is defined by
• CISPR 16-1-5 as an OATS with a metallic ground plane and a tightly specified SA performance in horizontal and vertical electric field polarizations.
• A COMTS is defined as a compliance test site which is used for the demonstration of compliance to radiated emission limits.

The antenna pair reference site attenuation A_APR is a set of site attenuation measurement results for both vertical and horizontal polarizations that uses a pair of antennas separated by a defined distance on a REFTS, with one antenna at a specified fixed height above the ground plane and the other antenna scanned over a specified height range, over which the minimum insertion loss (maximum received signal from the transmitting antenna) is recorded.

The advantage of the A_APR is that it includes the antenna factors as well as the coupling of each antenna to the ground plane and the coupling between the antennas. In addition, the radiation patterns of the antennas are included as
compared to the NSA method where the radiation patterns are approximated Hertzian dipoles.

Assuming the reader is familiar with the NSA approach, there are two different ways of obtaining the antenna pair reference site attenuation as shown below:

1. REFTS
   Use a REFTS according to CISPR 16-1-5 (see next section). Identical positions on the REFTS should be used for A_APR determination as were used for the REFTS validation according to CISPR 16-1-5.
2. Averaging Technique
   On a large OATS, deviations of the site attenuation from the ideal behavior are caused by the limited area and flatness of the ground plane and reflections from objects in the near vicinity such as buildings and trees. The OATS must meet 16-1-5 construction conditions, in which the recommended ground plane is of minimum size 20 m by 15 m and flatness less than +/-10 mm.

   A sinusoidal ripple is created in the measured site attenuation, mainly in vertical polarization due to reflections from the edges of the ground plane. The magnitude and the location of the ripple will also change if the location of the antennas on the ground plane is changed.

   The site attenuation is measured at several locations to minimize these effects and an average value is calculated. This average value will converge to the site attenuation of an ideal site.

   Measurements are carried out at multiple locations, in a form of a mapping, around the prospective reference site at 3 and/or 10m and the standard deviation between the measurements sets is compared. (See Figure 4.) If the standard deviation of the results in both horizontal and vertical polarizations is below the stated limit, then the site can be used as a reference site.

   Round robin tests have already given valuable input and several papers presented in the last CISPR A meeting show good correlation between the RSM and NSA methods.

The method has been published in both standards as an amendment at the end of 2010.

Status: CISPR 16-1-4 amd1 Ed. 3.0 Publication December 2010
Status: CISPR 16-1-5 amd1 Ed. 1.0 Publication December 2010

CISPR 16-1-4 Radiated Emission Methods above 1 GHz

Very recently, some concerns have been raised about the problems of performing chamber validations according to CISPR 16-1-4 and radiated emission product tests according to CISPR 16-2-3 for large equipment above 1 GHz. Issues highlighted include the significant quantities of floor absorber required at distances greater than 3 m (Figure 5), the enormous logistics of such a configuration that can mean raising large and heavy equipment off of the floor and the fact that no product standard currently has emission limits other than at 3 m above 1 GHz. The current generic standards IEC 61000-6-3 and IEC 61000-6-4 include emission limits from 1 to 6 GHz at 3 m, but state that emissions may be measured at greater distances with the limits decreased by 20dB/decade (relative to distance) with SAC and OATS facilities requiring absorber to achieve free space conditions as defined in CISPR 16-1-4. The basic standard CISPR 16-1-4 does not specify a test distance for the chamber validation test, nor emission limits, naturally leaving this to the product standards. The basic standard CISPR 16-2-3, clause 7.6, states a preferred distance of 3 m and allows for other distances between 1 and 10 m with the requirement that the antenna beam-width encompasses the EUT. Significant detail is given on the definition of the RX characteristics [1] which may or may not now be included in CISPR 16-1-4. While there is adequate detail on the setting up of EUTs below 1 GHz, there is less detail and guidance concerning EUT setup above 1 GHz. Some of the product standards, such as CISPR 22, specify measurements above 1 GHz with limits between 1 and 6 GHz for 3 m only, but since they now refer back to CISPR 16-1-4 and CISPR 16-2-3 the same problems apply as just mentioned.
Status: A pre-project to discuss the above issues was initiated at the Seattle meeting.

Chamber Validation above 1 GHz: TDR

In a separate discussion on the chamber validation methods above 1 GHz, there has been some effort in the USA to challenge the sVSWR chamber validation method described in 16-1-4 by proposing an alternative Time Domain Reflectometry (TDR) method [2]. The proposal first challenges the sVSWR method’s sampling of a standing wave at six positions and recommends measuring along the same distance continuously – the error between the two measurements being not insignificant. The TDR method proposed avoids the under-sampling and reduces the number of test positions and therefore claims to be more accurate and faster. It is not currently clear how this idea will progress or not, but it will most likely be taken up within the US National Committee and the ANSI C63 committee before any attempt at introducing any changes to CISPR 16-1-4 take place.
Status: No action currently

CISPR 16-1-5

Specification for radio disturbance and immunity measuring apparatus and methods – Part 1-5: Radio disturbance and immunity measuring apparatus – Antenna calibration test sites from 30 MHz to 1000 MHz

As a result of the New Work Item of CIS/A/822/NP and CIS/A/847 RVN of March 2009, it was decided to split CISPR 16-1-5 and CISPR 16-1-6 into two parts with the site validation methods now to be described in CISPR 16-1-5 corresponding to the antenna factor measurement methods being developed in CISPR 16-1-6.

Originally, it was planned that antenna calibration methods would be included in CISPR 16-1-5, but as that standard expanded on the subject of site validation, it soon became obvious that a separate document was needed in order to focus on current methods of antenna calibration and to also provide a collecting document for Antenna Factors for measurements at 1 m distance as in CISPR 25. CISPR 16-1-6 will be a horizontal and basic EMC standard that will specify the antenna calibration methods for the accurate free-space antenna factor required for radiated disturbance measurements.

The main purpose of this maintenance action is to add site validation methods for the other calibration sites in CISPR 16-1-6. Some methods do not require a ground plane reflection and in that case, the aim is to remove the influence of the ground.

The proposed antenna calibration methods in draft CISPR 16-1-6 Ed. 1.0 (CISPR/A/905/CD) are listed in Table 3.

For each method there is a corresponding method of site validation added to CISPR 16-1-5. The current CD includes methods of site validation that do not involve comparison with a theoretical value, such as used in the NSA of CISPR 16-1-4
or the CALTS of CISPR 16-1-5. They are more like the SVSWR method of CISPR 16-1-4 in which the acceptance criterion is based on a maximum allowed variation of E-field magnitude. In addition, a site is considered validated for a given pair of antennas if it gives the same value for antenna factor as obtained on a site that has been validated by a separate validation process.

At the recent meeting of CISPR, the National Physics Lab (NPL), in the UK presented the case for not validating sites using two horn antennas because of the large standing wave that exists between the horn antenna pair, and that the site should be calibrated using double-ridged horn and log periodic antennas. Examples are shown in Figures 6 – 8.
Status: Currently CC on 2nd CD (CIS A 907 CD) available

CISPR 16-1-6

Specification for radio disturbance and immunity measuring apparatus and methods

Part 1-6: Radio disturbance and immunity measuring apparatus – EMC-antenna calibration

The proposed new standard, CISPR 16-1-6 is currently at 2nd CD stage and provides procedures and information on the calibration of antennas for determining antenna factors. It is intended to be used by those antenna calibration laboratories and not for end-user test laboratories performing radiated emission measurements. Multiple calibration methods are specified that can be applied to antennas intended for use in radiated emission measurements according to CISPR 16-2-3 and CISPR-based product standards, in the frequency range of 30 MHz to 18 GHz. Guidance on uncertainties inherent in the calibration measurements and the associated instrumentation will be included. CISPR 16-1-6 will later include loop antenna calibration as required by CISPR 11 and 1 m AF as required by CISPR 25 in the future.

The proposed calibration methods are listed in Table 4.

Status CC on 2nd CD available, target date 2012-02

CISPR 16-2 Methods of Measurement of Disturbances and Immunity

• CISPR 16-2-1 Amd. 2 to Ed. 2.0: Conducted disturbance measurements

  Inclusion of key test methods from CISPR 13 and CISPR 22

  (JTF CIS/A-/I – Joint Task Force between CISPR/A and CISPR/I)

  Note that CISPR requires technical committees to provide justification for product standards that set different requirements than the generic standards and that use different test methods than those given in CISPR 16. The aim is to determine both differences and places where information contained within the basic standards is repeated in the product standard with the intention of providing an opportunity to justify or re-align and simplify these documents. First up was CISPR 22 largely because some of the work had already been completed in the JTF CIS/A-I.
  Status: CDV 2011-03

• CISPR 16-2-2 Ed. 2.0

  Inclusion of FFT-based test instrumentation
  Status: Published

• CISPR 16-2-3 Radiated disturbance measurements

  Inclusion of key test method from CISPR 13 and CISPR 22
  Status: 1st CD 2010-11

  Addition of the measurand for the radiated emission measurement method less than 1 GHz
  Status: Published

  Application of CMADs
  Much debated within CISPR A in the last five years, CMADs (Common Mode Absorbing Device) are ferrite clamps used during testing as cable termination on all cables leaving a test setup. In 2009, a Round Robin Test organized by CISPR/A/WG2 demonstrated that the CMAD could reduce uncertainty in radiated measurements. This first CD proposes its introduction into CISPR 16-2-3.
  Status: 1st CD 2010-12

CISPR 16-4 Uncertainty in EMC Measurements

• CISPR 16-4-2 Ed. 2.0: Uncertainty in EMC measurements
  Status: CDV approved – FDIS 2011-03

CISPR – CISPR JTF Work

CISPR has set up a number of internal joint task forces (JTFs) or cross sub-committee groups in order to facilitate better application of test methods (using the output of SC A) and better use of the interference model (provided by SC H).

JTF CISPR SC/A & SC/D on FFT-based test instrumentation

• Inclusion of FFT (Fast Fourier Transform) based instrumentation in CISPR 16 to make use of new time domain based technology
• Status: All CDVs 100% approved; standards published and JTF disbanded

JTF CISPR SC/A & SC/F on CDN test method

• CDNE measurement. The task is to transfer the methods for measuring conducted emissions from luminaries from CISPR 15 into CISPR 16.
• Status: CD in preparation

JTF CISPR SC/A & SC/I on updating CISPR 16-1-2, 16-2-1, 16-2-3 and 16-3

• Common measurement methods so that the SC I standards using SC A basic measurement techniques simply reference them in the product standard; also to suggest that techniques used in SC I and not in CISPR 16 be added to CISPR 16 so that they can be removed from SC I publications and simply refer to the CISPR 16 documents

• Status: CD in preparation

In Closing

This concludes part one of this update of CISPR activity from the October 2010 IEC General Meeting in Seattle. In the second part of this article – to be published in the following issue of this magazine – we will continue with the CISPR product standards and the Joint Task Forces (JTFs) existing between the different subcommittees as well as between CISPR subcommittees and IEC SC 77 B. For more information, please consult the IEC website www.iec.ch or contact your National Committee. 

Acknowledgements

The author wishes to acknowledge and thank Don Heirman, CISPR Chairman, and Manfred Stecher, Chairman of CISPR SC/A, for their invaluable review of and contributions to this article. They can be contacted at d.heirman@ieee.org and manfred.stecher@rohde-schwarz.com, respectively.

About the Author

Martin Wiles BSc, MSc, MIET is a Senior RF Engineer at ETS-Lindgren, in Stevenage, England. He represents the UK as a member of CISPR A. He can be reached by e-mail at martin.wiles@ets-lindgren.com.

References

1. Riedelsheimer, Trautnitz, “Influence of Antenna Pattern on Site Validation above 1 GHz for Site VSWR measurements,” 2010 Asia Pacific Symposium on EMC, April 12-16 2010, Beijing, China.
2. Windler, Michael J., “Site Qualification above 1 GHz and SVSWR Systemic Errors,” 2010 Asia Pacific Symposium on EMC, April 12-16 2010, Beijing, China.