Agreed John Best Regards Charles Grasso Senior Compliance Engineer Echostar Communications Corp. Tel: 303-706-5467 Fax: 303-799-6222 Cell: 303-204-2974 Pager/Short Message: [email protected] Email: [email protected]; Email Alternate: [email protected]
From: [email protected] [mailto:[email protected]] On Behalf Of John Woodgate Sent: Thursday, July 14, 2005 11:19 AM To: [email protected] Subject: Re: EMC Ethics Bob Richards <[email protected]> wrote (in <[email protected]>) about 'EMC Ethics', on Thu, 14 Jul 2005: >There were many instances of an EUT being tested and failed by one >technician, only to be sent back to the lab for another technician to >test it, on a different shift, and it would pass. It may have failed by >2db, then pass by 1db. They always accepted the passing data. What else to do? Many EMC tests are inherently subject to very large uncertainty, more than any 'uncertainty-guru' will admit. There is also 'variability' - a new term coined to cover cases where the test results are **extremely** dependent on the exact test conditions, such as the mains harmonic emissions of single-phase rectifiers. If there is a 3 dB variation between two successive tests, more tests will very likely reveal a 6 dB variation. You don't usually get a *better* answer by repeated testing, you get more variation. OK, if the distribution is roughly symmetrical, you can take an average, but often you get one or two outliers. -- Regards, John Woodgate, OOO - Own Opinions Only. Deadlines are 90% of deadliness. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
