Hi all, I agree that witnessing the lab test is valuable. I had a recent experience highlighting that issue.
A long-time customer of one of our power supplies reported that an IEC61000-4-5 line surge test on a new version of their system showed it failing at 240Vac, but passing at 120Vac. When we inquired about the changes making up the new version, they replied that a new circuit board had been added, but that could not possibly be the source of the failure. We enumerated & justified all recent changes to the power supply, including questions concerning whether we had incorporated new lead-free parts. They returned the power supplies for testing, and no failures were observed, even when tested with two different models of line surge generators. The customer then sent the failing system to us for testing. No failures were observed. We provided logging files created during our tests, calibration information on the surge generators, and answered questions whether we were using the proper revision of the test standard. At that point, I took their system to their test lab to see the testing performed. The first thing I noticed was that the system EMI filter was rewired between tests at 120Vac and tests at 240Vac. That detail was never communicated to us. I did indeed see system failures when the system EMI filter was rewired. I then asked that the new circuit board be removed, reverting the system to the previous 'known good' version. The system then passed, and the customer acknowledged the issue was now in their hands. Lessons learned: - Know exactly how the test is performed. It may require witnessing the test. - If failures happened after a change has been made, test a previously 'known good' version. Pat Lawler EMC Engineer Condor DC Power Supplies "Anchondo, Dan" <[email protected]> Sent by: [email protected] 12/09/2005 11:46 AM To: <[email protected]> cc: Subject: RE: Problems with surge testing John The variability is something I had forgotten. You can't exactly repeat any test but you can come reasonably close. If I have a failure I generally grab a spec, confirm set up and witness the test again (if I can). I'm not against questioning a lab's result but the set up confirmation takes the guesswork out. A lab result that is other than pass means I have to fix it no matter what varies but I get your point. Merry Christmas to all. Regards' Dan Anchondo From: [email protected] [mailto:[email protected]] On Behalf Of John Woodgate Sent: Friday, December 09, 2005 10:14 AM To: [email protected] Subject: Re: Problems with surge testing "Anchondo, Dan" <[email protected]> wrote (in <[email protected]>) about 'Problems with surge testing', on Fri, 9 Dec 2005: >I would suggest you fix the problem that was indicated by the lab test >results. All the differences between your set up and the test lab are >factors but at some point the test lab?s result needs to be reckoned >with. Failure or not. Maybe you didn't see other messages on this subject. EMC test results vary a lot, for reasons well understood, without anything being actually 'wrong'. And test labs sometimes make mistakes. -- 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. 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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/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: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
