RE: Distance of Measurements, 55011
Eric, You are correct in your evaluation of EN 55011 (Cispr 11). Keep in mind that the situation of not allowing distance correction is only found in Cispr 11, NOT Cispr 22. In reference to this specification, I had the opportunity to converse with several Competent Bodies in reference to Cispr 11 Class A test distance requirements. All three of the Competent Bodies I spoke to confirmed that they will accept extrapolated Cispr 11 data measured at 10 meters. They all cited that the specification is being re-vamped, and the 30 meter distance requirement is expected to be changed. Eric brought up a good point, and I would be interested to hear if anyone has run into problems due to this 10m/30m CISPR 11 situation. Sincerely, Randy Flinders EMC Test Engineer Emulex Network Systems * opinions expressed are completely personal, and do not reflect the position of Emulex Corporation. -- From: Eric Lifsey To: emc-pstc; treg Subject: Distance of Measurements, 55011 List-Post: emc-pstc@listserv.ieee.org Date: Monday, June 16, 1997 9:36AM Shall I muddy the issue further...let me address an interesting section of EN 55011:1991. But first; for reference; Clause 5 of EN 55011 lists the limits and measuring distance for Class B at 10 meters, Class A at 30 meters. Section 8.1.3 entitled Radiation Measurements (9 kHz to GHz) speaks to the issue of high ambients and moving to a shorter distance to take measurements. However, the wording (IMO) indicates that the 20* Log(D/d) correction is not allowed. Let me quote: Note - Due to the unpredictability of the relationship between the measured values of the electromagnetic radiation disturbance and the distance from the equipment under test no correction is allowed for in the limits when measurements are made at a closer distance. no correction The key implication (IMO again) is that running Class A measurements at 10 meters must meet the limits specified at 30 meters! Please correct me (pun) if I'm wrong! To my knowledge, many labs are doing Class A measurements at 10 meters. (IMO, 10 meters is better because most sites need an additional RF preamp for 30 meter sensitivity; if not handled carefully, measurement uncertainty is worsened. Of course, EUT size and other factors exist.) CISPR-11 is due for an overhaul (and for other interesting problems too) and I hope they fix this one while they're at it. Regards, Eric Lifsey National Instruments
RE: Distance of Measurements, 55011
Eric, You are right and this muddy point hopefully will be cleared. CISPR SC B Interference from Industrial, Scientific and Medical Radio Frequency Apparatus is preparing Annex to CISPR 11 which will allow testing class A equipment at 10 meters and class B at 3 meters with 20*Log(D/d) limit relaxation as in CISPR 22. In a case of dispute measurements at 30 meters will take precedence. Preliminary discussions took place in Mandelieu-La-Napoule, France in October 1996 during regular CISPR meeting. Further discussions on the subject are expected in November 1997 during CISPR meeting in Japan. If agreement is reached, schedule of events could be: DEC 97 - JAN 98 DIS issued 6 months - Voting 6 months - for CISPR Secretariat in Geneva to translate it into French, prepare and print Annex DEC 98 - Annex available. CENELEC might move faster after NOV 97 and significantly sooner publish Annex to EN 55011. Mirko Matejic Member of CISPR SC B -- From: eric.lif...@natinst.com To: emc-p...@ieee.org; t...@world.std.com Subject: Distance of Measurements, 55011 List-Post: emc-pstc@listserv.ieee.org Date: Monday, June 16, 1997 10:36AM Shall I muddy the issue further...let me address an interesting section of EN 55011:1991. But first; for reference; Clause 5 of EN 55011 lists the limits and measuring distance for Class B at 10 meters, Class A at 30 meters. Section 8.1.3 entitled Radiation Measurements (9 kHz to GHz) speaks to the issue of high ambients and moving to a shorter distance to take measurements. However, the wording (IMO) indicates that the 20* Log(D/d) correction is not allowed. Let me quote: Note - Due to the unpredictability of the relationship between the measured values of the electromagnetic radiation disturbance and the distance from the equipment under test no correction is allowed for in the limits when measurements are made at a closer distance. no correction The key implication (IMO again) is that running Class A measurements at 10 meters must meet the limits specified at 30 meters! Please correct me (pun) if I'm wrong! To my knowledge, many labs are doing Class A measurements at 10 meters. (IMO, 10 meters is better because most sites need an additional RF preamp for 30 meter sensitivity; if not handled carefully, measurement uncertainty is worsened. Of course, EUT size and other factors exist.) CISPR-11 is due for an overhaul (and for other interesting problems too) and I hope they fix this one while they're at it. Regards, Eric Lifsey National Instruments
