Just to toss in another variable... We have a couple of brands of ESD testers. One will cause failures when pulling the trigger for an air discharge, and after the discharge, will cause another fail when releasing the trigger. Monoitoring with an O'scope using a field probe of a home made design demonstrates that the trigger pull and release cause a much larger ESD field event than the actual designed event to the plane. ESD is like target shooting with grenades, not exactly precise! We used to verify our ESD guns with a really well build by a craftsman faraday cage to contain the o'scope and target. And found while do the usual discharges and the operator breathing in verses breathing out effected the waveforms. We changed our procedure to setting the air discharge tip to a specific distance, then pulling the trigger since the trigger spec. was much better defined than a random gap with variable humidity. Our results always landed well within the requirements, as long as the specified distance was controlled, and the trigger was pulled after setting the distance. Otherwise is was a crap shoot! Humidity and speed of approach are highly/wildly variable. Find a way to compensate and avoid those variables and the results and waveforms settle down to very repeatable. The trigger mechanism is a well controlled device. The air discharge distance can be set by using a collet to set the spacing, calculated as you please for the test voltage. And repeatable as you send around the collet or specifiy the distance. Humidity can be better controlled by a dehumidifier blowing across the test area and humidity gauge monitoring the condition. Results tend to settle down to something you can believe... otherwise, they are all over the place. I use ESD to the horizontal and vertical coupling planes without ground as a lightning simulation. The previous EUTdemonstrates the same problem as found out in the wild, so we deemed the made up test as valid for reproducing the field problem and good for diagnosing the effects of design changes. The subsequent products designed to meet this artifical test have not had any problems in the field.
>________________________________ > From: John Woodgate <[email protected]> >To: [email protected] >Sent: Thursday, March 7, 2013 5:35 PM >Subject: Re: [PSES] test setup for table top ungrounded equipment 61000-4-2 >IEC:2008 figure 6 page 20 > >In message ><d250d01e39356a4e9cc3b4b459d6655094db3...@ms-cda-01.advanced-input.com>, dated >Thu, 7 Mar 2013, "McInturff, Gary" <[email protected]> writes: > >> My humidity was a little on the low side, about 28% and theirs was closer to >> 38% or so. > >I wasn't referring to test done at different locations; I meant that moving >the EUT from one place to another and then testing it might give results >affected by condensation, however slight. And condensation doesn't always give >better ESD test results; it alters discharge pathways and perhaps for the >worse. >-- OOO - Own Opinions Only. See www.jmwa.demon.co.uk >SHOCK HORROR! Dinosaur-like DNA found in chicken and turkey meals >John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK > >- >---------------------------------------------------------------- >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.ieee-pses.org/emc-pstc.html > >Attachments are not permitted but the IEEE PSES Online Communities site at >http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used >formats), large files, etc. > >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]> > > > - ---------------------------------------------------------------- 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.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. 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]>
