Re: -2dB margin
I read in !emc-pstc that George Stults george.stu...@watchguard.com wrote (in ea1b3684d553cbc96c23d33894bdfe4c3c350...@watchguard.com) about '-2dB margin', on Thu, 3 Jan 2002: After talking with some other folks, I've found that one can concoct a 2 dB margin from CISPR 22 [the section I mentioned below] as follows: Using the formula for statistically assessed compliance Xavg + K*StdDev Limit, assume that the StdDev is 1.0 and that you are initially testing one device as permitted. Then take the value of [K =2.04] for [n=3] and you have a 2.04 dB margin requirement for the initial device. The standard also requires that if you just test one device, that you do subsequent tests from time to time. So in effect, by going with a 2dB margin the first time, you're betting that the statistics will still be in your favor by the time you've tested 3 samples. Does anyone disagree that it could be done this way? It seems a reasonable explanation. An additional question would be, how is from time to time defined. Is it spelled out anywhere? Possibly not, but there is a principle that you can invoke. It was developed in the context of safety testing in service, AFAIK, but it works for other things. What you do is to choose an initial re-test period based on how many units you produce per unit time and how much unit-to-unit variability you expect. If you find that re-testing at this rate throws up failures, re-test more often. If it throws up no failures and not even marginal cases, re-test less often. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: -2dB margin
After talking with some other folks, I've found that one can concoct a 2 dB margin from CISPR 22 [the section I mentioned below] as follows: Using the formula for statistically assessed compliance Xavg + K*StdDev Limit, assume that the StdDev is 1.0 and that you are initially testing one device as permitted. Then take the value of [K =2.04] for [n=3] and you have a 2.04 dB margin requirement for the initial device. The standard also requires that if you just test one device, that you do subsequent tests from time to time. So in effect, by going with a 2dB margin the first time, you're betting that the statistics will still be in your favor by the time you've tested 3 samples. Does anyone disagree that it could be done this way? An additional question would be, how is from time to time defined. Is it spelled out anywhere? George S. -Original Message- From: Pettit, Ghery [mailto:ghery.pet...@intel.com] Sent: Wednesday, January 02, 2002 8:39 AM To: George Stults; 'emc-p...@majordomo.ieee.org' Subject:RE: -2dB margin Just got back from Christmas vacation, but I'll wade in now... There is nothing in CISPR 22 that refers to a 2 dB margin for compliance when a single sample is tested. The only document I ever recall seeing that requirement in is VDE 0871/6.78, paragraph 4.1.3.1. This document was published in 1978 and is long obsolete. I suspect that many people got used to the 2 dB margin requirement from dealing with the VDE in years past and it is now part of the folklore of EMC testing. Ghery S. Pettit Intel -Original Message- From: George Stults [mailto:george.stu...@watchguard.com] Sent: Monday, December 24, 2001 11:43 AM To: 'emc-p...@majordomo.ieee.org' Subject: -2dB margin Hello Group, I've been looking into the 80/80 rule for CISPR 22 compliance for mass produced equipment. I have found a description of the statistics in CISPR 22 :1997 Section 7.1 and 7.2. Its been my understanding that for testing at OATS, if the product has 2dB or less margin, then these statistical methods are required. Is that correct? And, where does the reference to '2dB margin' come from? Thanks in advance George S. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: -2dB margin
Just got back from Christmas vacation, but I'll wade in now... There is nothing in CISPR 22 that refers to a 2 dB margin for compliance when a single sample is tested. The only document I ever recall seeing that requirement in is VDE 0871/6.78, paragraph 4.1.3.1. This document was published in 1978 and is long obsolete. I suspect that many people got used to the 2 dB margin requirement from dealing with the VDE in years past and it is now part of the folklore of EMC testing. Ghery S. Pettit Intel -Original Message- From: George Stults [mailto:george.stu...@watchguard.com] Sent: Monday, December 24, 2001 11:43 AM To: 'emc-p...@majordomo.ieee.org' Subject: -2dB margin Hello Group, I've been looking into the 80/80 rule for CISPR 22 compliance for mass produced equipment. I have found a description of the statistics in CISPR 22 :1997 Section 7.1 and 7.2. Its been my understanding that for testing at OATS, if the product has 2dB or less margin, then these statistical methods are required. Is that correct? And, where does the reference to '2dB margin' come from? Thanks in advance George S. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: -2dB margin
Hi George, I don't think the margin makes any difference in applying the 80/80 rule. If you have a series produced product you must apply the 80/80 rule using a sample size of not less than 5 and not more than 12 pieces. See Clause 11, Assessment of conformity of equipment, of CISPR 11: 1999. Happy New Year to all! Best regards, Jim -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of George Stults Sent: Monday, December 24, 2001 2:43 PM To: 'emc-p...@majordomo.ieee.org' Subject: -2dB margin Hello Group, I've been looking into the 80/80 rule for CISPR 22 compliance for mass produced equipment. I have found a description of the statistics in CISPR 22 :1997 Section 7.1 and 7.2. Its been my understanding that for testing at OATS, if the product has 2dB or less margin, then these statistical methods are required. Is that correct? And, where does the reference to '2dB margin' come from? Thanks in advance George S. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
