Note: this is a re-send since the list server is acting odd along with my computer since connecting tonight. **scan for everything - mine says its clear but ... **
I can understand the Blackwood Labs position, but certainly not the attitude, having worked at a test lab myself. Where I've worked, we tested to the standard, and recommended additional testing to higher levels, pointing out the standards remark about the level being the minimum requirement to market the product and certainly not the covering the "extreme" events that may occur; much like Mr.Smith recommends. Now working for a manufacturer, we have a product assurance lab that does test to well above the requirements of the standards. We have also had to deal with the winter returns Mr. Smith mentions and have developed ESD tests the replicate the symptoms. They are not the usual "standards" test, but they do demonstrate the problem so it can be debugged and fixed. No complaints or returns so far this winter. Another standard that is a bit mis-leading has to do with the power dips and dropouts (ok, I can't remember every one of the numbers). We have found, in the wild, as in returns, that the few parameters called out in the standard do not come anywhere close to finding the problems that can occur. However, the tests we have developed do take somewhat longer to complete, but the products now will handle "any" power variation. Again, no returns yet for this solved problem. Thanks to Blackwood Labs for my continued employment. ps. We have tested up to 200 V/m sweep trying to get a fail. That's the advantage of an in-house lab - you get to blowup the EUT and have a couple of beers with the engineers over the spectacular fireball that spewed out of the vents. I love the smell of burning part's first thing in the morning. Mr. Nobody, otherwise known as, - Bill ________________________________ From: Doug Smith <d...@emcesd.com> To: "John Davies, Blackwood Labs" <j...@blackwoodemc.co.uk> Cc: "John Davies, Blackwood Labs" <jdav...@blackwood-labs.co.uk>; Ken Wyatt <k...@emc-seminars.com>; EMC-PSTC@LISTSERV.IEEE.ORG Sent: Wed, January 6, 2010 10:02:45 PM Subject: Re: [PSES] ESD Test Failure of Stainless USB Mouse 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 > > snipping Ken Wyatts part out as a possible part of the reply problem. > > (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> > > -- ___ _ 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: d...@dsmith.org \ _ / ] \ _ / 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 <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>
