The IEC 61000-4-2 test standard is also pretty loose with regard to the characteristics of the ESD waveform. For example the current waveform risetime (measured in contact discharge only) is acceptable if in the range 0.6ns to 1ns (0.8ns +/- 25%). Are the effects of a pulse near 0.6ns rise time from one ESD generator going to be the same as a pulse near the 1ns rise time from another ESD generator? Both generators are within spec. Other parameters are also pretty loose.
No wonder ESD testing can sometimes drive people nuts. Jim Hulbert From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Ken Wyatt Sent: Friday, March 08, 2013 1:40 AM To: Bill Owsley Cc: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] test setup for table top ungrounded equipment 61000-4-2 IEC:2008 figure 6 page 20 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 k...@emc-seminars.com<mailto:k...@emc-seminars.com> www.emc-seminars.com<http://www.emc-seminars.com> (Sent from my iPad) On Mar 7, 2013, at 11:18 PM, Bill Owsley <wdows...@yahoo.com<mailto:wdows...@yahoo.com>> 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 <j...@jmwa.demon.co.uk<mailto:j...@jmwa.demon.co.uk>> To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> 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<mailto:d250d01e39356a4e9cc3b4b459d6655094db3...@ms-cda-01.advanced-input.com>>, dated Thu, 7 Mar 2013, "McInturff, Gary" <gary.mcintu...@esterline.com<mailto:gary.mcintu...@esterline.com>> 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<http://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. 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To post a message to the list, send your e-mail to <emc-p...@ieee.org<mailto:emc-p...@ieee.org>> 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 <emcp...@radiusnorth.net<mailto:emcp...@radiusnorth.net>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto:dhe...@gmail.com>> ________________________________ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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