good point, but more than margin, is consistency, I'd rather have a solid -3 db 100% of the time than -6 db one day and -1 the next and so on, and moving lab to lab would affect that.
From: [email protected] [mailto:[email protected]]On Behalf Of Robert A. Macy Sent: Monday, July 18, 2005 9:04 PM To: [email protected] Subject: Re: EMC Ethics John et group, One of my EX-Clients rather than fixing the problem would "shop" test labs. The client compared results from each lab and found a "dead" test lab and used it to get passing data. I've always told my clients that not passing with good margin merely points out that the design is "out of control". Geesh! If you can't even control a smple thing like emissions and susceptibility what's the warrantee costs and marginal performance going to be like? - Robert - > -----Original Message----- > 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
