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:[email protected]] > Sent: 06 January 2010 19:33 > To: 'Ken Wyatt'; '[email protected]' > Cc: '[email protected]' > 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: [email protected] [mailto:[email protected]] On Behalf Of Ken Wyatt > Sent: 06 January 2010 18:36 > To: [email protected] > Cc: [email protected] > 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: [email protected] > 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 > <[email protected]> > > 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<[email protected]> > Mike Cantwell<[email protected]> > > For policy questions, send mail to: > Jim Bacher:<[email protected]> > David Heald:<[email protected]> > > -- ___ _ Doug Smith \ / ) P.O. Box 1457 ========= Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-----( ) | o | Email: [email protected] \ _ / ] \ _ / Website: http://www.dsmith.org - 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 <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
