hi All, I just glanced at this thread, so please excuse if out of context.
I see this fairly simply: if you pass at 8kV ( the requirement ) then it's irrelevant that you crash and burn at 9kV. If the standard of 8 kV is not sufficient, raise the level. As a test lab, I do what my clients ask. If my name is attached to something then I make sure it's accurately documented as to why things were done. The concept of thresolding has no use in commercial compliance work, it passes or it doesn't. For diagnostic work it maybe useful, but that's it. If you are trying to stake a clim for safety margin, on a sample of one, I would think that's rather silly. To assure you manufacturing process builds a particular product consistantly, you are better testing several models in an engineering test and submitting the lowest performing one for a compliance test. If your product performance is all over the place, you should worry about that before sending for a compliance test. Just my 10 cents worth. Happy snow days, Derek Walton L F Research On 1/6/2010 9:02 PM, Doug Smith wrote: > Hi All, > > Not testing to failure can lead to real legal problems. The ESD > testing that is done is nowhere near what many products will face and > not knowing the result of failure is in my opinion gross negligence > for many products. What if a product passed at 8 kV air but became > dangerous at 9 kV. That difference is likely less than the uncertainty > of an air discharge test. What if it simply failed at 9 kV. A > company's profit could be wiped out by returns in the Winter. > > What should be done is first test for compliance. Then test to failure > (most likely a soft one, but damage cannot be ruled out) to determine > margin and consequences of failure. From that, one can make a decision > if anything needs to be done for reliability in the likely > environment. Most times nothing need be done but if you start seeing > field returns that match the failure mode, you know what is happening > and can respond much more quickly to the original bad decision. > > It does not mater if doing the complies with ISO, IEC, or any other > body. If a company is interested in quality, they will do this. > > Doug > > On 1/6/10 11:48 AM, John Davies, Blackwood Labs wrote: >> >> -----Original Message----- >> From: John Davies, Blackwood Labs [mailto:jdav...@blackwood-labs.co.uk] >> Sent: 06 January 2010 19:33 >> To: 'Ken Wyatt'; 'd...@dsmith.org' >> Cc: 'EMC-PSTC@LISTSERV.IEEE.ORG' >> Subject: RE: [PSES] ESD Test Failure of Stainless USB Mouse >> >> Why test to failure? There's absolutely no point in doing this >> unless you >> want to fully understand a products extreme performance! >> >> I run a test lab and if any one of my engineers test to higher levels >> than >> the test standard requires (or as started in the established test >> plan) then >> I would drag them over the coals for doing so. It wastes time, it costs >> money, it goes against ISO 17025 and our internal procedures, and, most >> importantly of all, it gives absolutely no result against the >> standard. My >> customer is paying for a result against a standard - that is all I >> need to >> give him! If I return his sample in a damaged state because I over >> tested >> then what? >> >> If the product fails at 4.1kV (the example given below by Ken) then >> that's a >> pass - simply that - it meets the requirement for 4kV. >> >> (4.1kV is actually a bad example level for ESD because the tolerance >> on the >> output of an ESD gun is 5% meaning that a pass at 4.1kV could be >> considered >> to be marginal. 0.2kV is 5% of 4kV, so if the failure threshold was at >> 4.25kV then it would be definitely a pass. 4.1kV is debatable.) >> >> I would never, never, never, ever apply 20kV or more to a product >> when the >> requirement of the standard, the requirement for compliance, the >> requirement >> of the customer, is just 4kV! Why would I? >> >> I wonder where does this ideal "test to failure" approach stop? Who >> runs a >> 3V/m radiated immunity sweep followed by a 10V/m sweep, then a 20V/m >> sweep >> when testing to EN 55024? Nobody does! >> >> Best Regards, >> John Davies >> Managing Director >> Blackwood Labs >> >> >> -----Original Message----- >> From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Ken >> Wyatt >> Sent: 06 January 2010 18:36 >> To: d...@dsmith.org >> Cc: EMC-PSTC@LISTSERV.IEEE.ORG >> Subject: Re: [PSES] ESD Test Failure of Stainless USB Mouse >> >> I wholeheartedly agree with Doug on this point. In fact, just to >> extend his concept further, I like to always test to failure, even >> beyond the regulatory limit. That way, you can determine the margin. >> If a product passes at 4kV, but fails at 4.1kV, I'd really like to >> know that! :-) >> >> Ken >> ---------------------------------------------- >> Wyatt Technical Services, LLC >> 56 Aspen Dr. >> Woodland Park, CO 80863 >> >> Email: k...@emc-seminars.com >> Web: www.emc-seminars.com >> http://www.linkedin.com/in/kennethwyatt >> >> (719) 310-5418 >> >> >> >> On Jan 6, 2010, at 11:15 AM, Doug Smith wrote: >> >>> Just a thought on ESD testing. The actual failure level should >>> always be determined, not just that the test was not passed. For >>> instance, suppose you are trying for 4 kV contact mode but fail and >>> the failure happens at 1.5 kV. You try something, but unit still >>> fails. However, the failure level increased to 3 kV. This is very >>> important. Either more of the same technique should be tried or you >>> have peeled one layer of the ESD onion and now another mechanism >>> controls the response. I recently had a product that had three >>> distinct mechanisms and all had to be fixed simultaneously for the >>> product to work. A solution would never happen if one tried >>> experiments one at a time and just looking at the pass-fail state on >>> a product like this. >> - >> ---------------------------------------------------------------- >> This message is from the IEEE Product Safety Engineering Society >> emc-pstc >> discussion list. To post a message to the list, send your e-mail to >> <emc-p...@ieee.org> >> >> All emc-pstc postings are archived and searchable on the web at: >> http://www.ieeecommunities.org/emc-pstc >> Graphics (in well-used formats), large files, etc. can be posted to that >> URL. >> >> Website: http://www.ieee-pses.org/ >> 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<emcp...@socal.rr.com> >> Mike Cantwell<mcantw...@ieee.org> >> >> For policy questions, send mail to: >> Jim Bacher:<j.bac...@ieee.org> >> David Heald:<dhe...@gmail.com> >> > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ 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 <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
