I wrote an article on testing ESD simulators and mentioned the variability, especially for air discharge. There will also be variability between manufacturers and between test setups. I guess that's why contact discharge was developed. The article may be downloaded from here:
http://www.tmworld.com/design/design-and-prototyping/4380116/Check-ESD-simulators-first The article refers to a presentation by Greg Senko and I with more detail on the variability (approach and angle of approach). The link in the article isn't correct, but a search should get you the presentation. Ken Kenneth Wyatt Wyatt Technical Services LLC Woodland Park, CO [email protected] www.emc-seminars.com (Sent from my iPad) On Mar 7, 2013, at 11:18 PM, Bill Owsley <[email protected]> wrote: > 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]> - ---------------------------------------------------------------- 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]>
