Standards Workshops Introduce
Proficiency Testing

Considering training that started the Thursday before the start of the 2011 IEEE International Symposium on EMC in Long Beach, California, over a half dozen standards committee meetings during the symposium, and finally all the exchanges on the subjects of our standards held during the symposium, we could hardly take a breath!
     As is the case for well over a dozen years, the standards activity started even before the start of the symposium – in fact the Thursday, Friday and Saturday before, August 11–13. Accredited Standards Committee C63® held its usual workshops with a new twist. This year a half day workshop on proficiency testing (PT) for radiated emission measurements was introduced on Thursday. The focus was not only on following the testing protocol, but how to rigorously handle the statistics needed to show trends. On Friday, the workshop on C63.4 which is the FCC referenced emission measurement standard for information technology equipment continued its long run as the most attended workshop on an EMC standard with hundreds of attendees over the many years that it has been presented. On Saturday, the workshop on antenna calibration per ANSI C63.5 and the use of time domain techniques for antenna calibration as well as investigating test site anomalies in the site validation process was held. For more info on C63® visit the web site on www.c63.org.
     The new proficiency testing workshop was presented by Harry Hodes of Acme Testing. The work was part of the PT program that is being used by the American Council of Independent Labs (ACIL). ACIL is a member of C63® where there is a cooperative agreement on sharing information. This was the first time this subject was covered. There were several examples of how to handle the statistics. From the present ACIL PT program, it was found that significant differences in radiated emission measurement results occurred. This of course is what needs to be resolved or at least understood. The attendees then were given a chance to investigate presented PT results.

PHOTOS BY RICHARD GEORGERIAN
Instructor Harry Hodes (standing left) of Acme Testing Company discusses an exercise solution with attendees during the proficiency testing workshop. The ANSI C63® Series Workshop Director Don Heirman of Don HEIRMAN Consultants presents a problem related to C63.4 for the class to solve.

Instructor Bob Hofmann of Hofmann EMC Engineering describes conducted emission testing requirements during the C63.4 workshop. C63.4 workshop student Kermit Phipps of AMS presents a practical problem solution for his team.

 


     The next day, the C63.4 workshop was presented by Don Heirman of Don HEIRMAN Consultants and Bob Hofmann of Hofmann EMC Engineering. It was focused on further describing what is contained in the 2009 edition of the standard. The 2009 edition now has the following:

  • Tables of LISN impedances (in addition to the plots in the 2003 edition) with and without the use of extension cords between the EUT power connection of the LISN and the end of the extension cord where the EUT connects its power plug.
  • Clarifying in Annex B the LISN calibration process.
  • What must appear on video displays during emission testing.
  • Variation in antenna cable loss as a function of significant temperature variation at the test site.
  • Precautions in using spectrum analyzers, which appear in clause 4.2.2 and Annex H.
  • Informative annexes for step-by-step testing procedures have been omitted, because those were mostly duplicative of the normative procedures in the main text.
  • Ensured that the standards not under the control of Accredited Standards Committee (ASC) C63® were dated to guarantee the acceptance of the versions that are referenced, whereas the ASC C63® standards were undated because ASC C63® would be voting their acceptance.
  • Added information on the effects of materials used to construct EUT support tables and antenna masts.
  • Condensed the information about absorbing clamp calibration and use, as well as the artificial hand, as these continue to be in limited use.
  • Retained the Clause 13 requirements for emission measurements of intentional radiators.
  • Introduced site validation specifications above 1 GHz from CISPR 16-1-4:2007, while still allowing use of absorber material on the ground plane for an open-area test site (OATS) and semi-anechoic chambers (in a particular configuration and with particular absorber performance without any further site validation measurements).
  • There was no change in measurement methods above 1 GHz.

     The workshop then presented the proposed changes being considered for the next edition in 2012 which are the following:

  • Removal of measurement methods for intentional radiators (clause 13) since they are now covered by the 2009 edition of C63.10 (measurement of unlicensed transmitters).
  • Revision of the measurement method for emissions above
    1 GHz; this would not be limited to unintentional radiators.
  • Retain the site validation method above 1 GHz contained in CISPR Pub 16-1-4 (so called Site VSWR method).
  • Further described scrolling H pattern requirements for large screen TV receivers as well as those used as computer ­monitors.
  • Add measurement uncertainty similar to that in CISPR 22.
  • Move most antenna calibration requirements to C63.5 (if not picked up in the next edition of C63.5, they will be kept in C63.4 until then).
  • Move site validation requirements to new standard if one is published covering different approaches (potential publication is C63.25).
  • Add information on the various versions of the average detectors and review average measurement method using a reduced VBW.
The C63.4 workshop class poses for a group photo with instructors Harry, Bob and Don (left to right in front row).
Janet O’Neil of ETS-Lindgren, workshop registrar and arrangements facilitator, is shown at far left in the second row.

 

     The next day Don, Zhong Chen of ETS-Lindgren, Dennis Camell of NIST, and Greg Kiemel of Northwest EMC presented what is covered in C63.5 on antenna calibration, proposed changes for a 2012 edition and then the use of Time Domain techniques to determine antenna calibration as well as test site validation, especially above 1 GHz.
     Items included in the C63.5 portion of the day included:

  • General test conditions for calibrating an antenna.
  • Standards site method (SSM) also known as the three antenna method.
  • Reference antenna method where specific construction techniques give predictable antenna factors.
  • Calibration geometry specifics that differ for antennas calibrated for use in compliance testing and those used in test site validation.
  • Specific biconical antenna calibration and the differences in those with 50 or 200 ohm baluns.
  • Determining the measurement uncertainty for the various antenna calibration methods in the standard.
C63.4 workshop students Dan Sigouin of Industry Canada,
Harry Hodes, and Victor Kuczynski of Vican Electronics
(from left) discuss a challenging problem.
Team 1 discusses solution to a measurement problem related to C63.4.
Site of C63.5 workshop at Northwest EMC in Irvine, California, just south of Long Beach where the IEEE
EMC Symposium was held.
Don Heirman introduces the topic and the agenda for the C63.5
and time domain workshop.

 

     Also indicated were the areas being investigated for the next edition of the standard expected to be published by mid 2012. Here is a sample of those considerations presented:

  • Clarify text as needed in annex H in section 5.1 on the use of free space antenna factor (FSAF) and near-FSAF in section 5 and annex G.
  • New text covering standard gain horns above 1 GHz which either use the physical dimensions for reference with some S11 electrical check to assure working horn or incorporate what cal labs use for horns above 1 GHz (extrapolation, etc).
  • Add free space corrections for dipoles similar to the Japan Voluntary Control for Interference (VCCI) and the International Electrotechnical Commission (IEC).
  • Add vertical Ed_max to annex A.
  • Add limits to vertical vs. horizontal 1m ratio for hybrid antennas.
  • Add minimum frequency resolution for calibrations.
  • Re-instate sentence on biconicals – “Antenna factors obtained for biconical dipole antennas using the SSM that are used for either product testing or NSA testing shall be corrected to free space values using the correction factors provided in Annex G” as in the 2004 edition.
  • Develop text for complex fit of log periodic antennas.
  • Develop text for time-domain gating for free-space AFs (i.e. reduction of reflections).
  • Measurement uncertainty estimates (either this document or in the uncertainty document).
  • Expand reference antenna options.

The time domain method portion of the workshop focused on site validation in addition to antenna calibration. Note that the site validation work is now part of the standards work on the subject given in the draft of C63.25. In advance of publication, the following information was presented to show the usefulness of this technique.

  • Measurements can be done with a swept frequency vector network analyzer.
  • Converting from frequency to time domain using the inverse Fourier transform is extremely easy and fast with modern computational hardware and software.
  • Conversions are done “on the fly” using time domain reflectometry (TDR) equipped Vector Network Analyzers (VNAs).
  • Procedure is basically analogous to testing of products:
    – Place a transmitting antenna on the turntable with a receiving antenna at the 3-meter measurement location
    – Measure the response (voltage and phase converted to voltage and time) every 6 degrees of turntable azimuth
  • The proposed TDR method is similar to taking a radar measurement of your site.
  • The results are the amplitude, distance and angle of any reflections.
  • The amplitude of the reflections is measured relative to the direct path thus making them a direct measurement of error introduced by the site!
Dennis Camell of NIST, lead instructor for the C63.5 workshop,
presents general antenna calibration test conditions.
Zhong Chen of ETS-Lindgren discusses the modeling of biconical antennas during the C63.5 workshop.
Jeff Poole of Agilent Technologies discusses the use of a vector
network analyzer (VNA) used in the time domain process.
Greg Kiemel of Northwest EMC shows comparison between site validation using CISPR and that using time domain techniques during the C63.5 workshop.
C63.5 workshop attendees view the time domain site validation process in
Northwest EMC’s 10 meter semi-anechoic chamber.
Zhong Chen points out the VNA display that shows how to pick out site irregularities.

 

     The workshop then concluded with the following:

  • The same test site will have the same performance when measured with TDR and the IEC/CISPR Site VSWR (SVSWR) technique in CISPR 16-1-4 if the SVSWR measurement is done with continuous antenna movement (not in specific increments now in the SVSWR procedure).
  • The TDR method will be faster and will yield diagnostic information (frequency, azimuth and distance to reflections – and hence show where the test site has to be improved to meet the validation specification) that SVSWR does not.

     These workshops are planned for the week before the 2012 IEEE International Symposium on EMC in Pittsburgh, Pennsylvania. The venue will be either at the convention center or at the host hotel. For more information, please contact Janet O’Neil at j.n.oneil@ieee.org.                    EMC

Please check the C63® website – www.C63.org – after January 2012 for more information about scheduled ANSI C63® workshops in 2012.

 

 

 



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