Once I got the my standard back I found all of the pertinent data and learned a few new things. Section 7.1.3 ungrounded equipment (this is edition 1.2) so the paragraph numbering could differ Basically it says the couple planes must be discharged via the 470K bleeder resistors - I had been using a braid with no resistance since I wasn't sure what the lab did and I couldn't replicate their data For any points of the EUT that can have a direct discharge they also require a similar cable to earth reference plane. Unfortunately the standard then goes back to discussing the HCP and the VCP in the next paragraph and again discusses the bleeder cable. It's unfortunate because the paragraph that follows then mentions that the bleeder resistor can influence the test results of some equipment stating that in case of dispute a test with the cable disconnecting during ESD pulse takes precedence. I read that to mean the cable to the directed discharge points of the EUT, two paragraphs previously, and not the HCP and VCP planes referenced in the immediately preceding paragraph. My thought is that throughout the tests these coupling plane resistors are always in place - again except the floor standing units which sit over the ground reference rather than a HCP - and the removed cable having test preference is to any metallic parts of the EUT. One still discharges between ESD events - apply ESD to metallic part, discharge with bleeder cable, ESD event .....etc.
One last item - the Rationale for all of this discharge between ESD events makes note that "it is possible that the EUT or part(s) of the EUT can be stressed up to twice the intended test voltage. Therefore, double-insulated equipment could be charged at an unrealistically high charge, by accumulating sever ESD discharges on the capacitance of the class II insulation..." Ho How does the charge exceed the applied gun discharge. If I am at 4kV for example, the ungrounded equipment rises to 4kV until it's removed or disappointed, but how would another charge of the same level increase it. If I switch from a positive to a negative polarity I see the doubling of the level, but not during repeated discharges of the same polarity and same level. I can see that if I don't' drain the charge from the ungrounded system it will remain at 4 kV and then next discharge attempt may not occur since the gun and the surface of the EUT are at the same potential - but I don't see the doubling. Any clues for me? Thanks all that have responded I think Doug Smith mentioned a cheap ESD brush in one of his tid-bits but I couldn't find the reference. In my case the cable will work fine but all of a sudden I have a need to have this brush in my arsenal Gary -----Original Message----- From: Scott Douglas [mailto:[email protected]] Sent: Tuesday, April 24, 2012 6:49 PM To: [email protected] Subject: Re: [PSES] Safety cost and ESD Brian, In a prior life we had several products that were sensitive to charge build-up. When they asked me about the problem I showed them where the ESD standard allows discharging between hits. We used the same sort of process - 470k resistor in series with the ground braid attached to the HCP. I once saw a brush with a ground strap (with the resistors in it) used for this sort of thing. Never have been able to source one though. Scott On 4/24/2012 8:04 PM, Brian Oconnell wrote: > For automotive stuff (ISO10605), I have to be careful about bleeding charge > after each iteration because test level = 25kV. I use a 470k Resistor > attached in series with a short braid that is screwed into the ref plane, > and touch the UUT. The strap is used for discharge only and is not attached > during testing. I have seen the commercial CISPR25 labs do similar. > > I have not seen the discharge create additional problems - perhaps I have > just been lucky. Opinions whether this is a 'respectable' test technique? > > Brian > > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of Conway, > Patrick > Sent: Tuesday, April 24, 2012 3:53 PM > To: McInturff, Gary; [email protected] > Subject: RE: [PSES] Safety cost and ESD > > This is a classic test problem. I've seen this several times. For this > setup, there is no place for the charge to dissipate between zaps. So, how > to discharge between zaps? The easy answer is to briefly connect a strap > from apparatus to ground. But that casues lots of problems, including false > "failures". > > The reason? The discharge created when using a zero Ohm strap is > uncontrolled. If you remove the "bleed" resistor, then the discharge is not > bleeding slowly, it becomes another form of an ESD discharge. The problem > is that the waveform will not be representative of the human-body-model. > > Designers of ESD equipment go to a lof trouble designing those ESD guns. > They must conform to an exact waveshape. But the zero-Ohm ground strap has > none of the circuit elements to shape the curve. So there is a likelyhood > of a faster rise time, more ringing, etc. All things that no longer > represent the HBM. If ths waveshape causes upset in the appratus it > cannot be considered a failure since the waveform is not HBM. > > Check with your customer on how they are testing. If the appratus survives > the zap from the gun, but is upset when they discharge with the strap, then > you have the asnwer. The easy solution for "Test" is to place the bleed > resistor back into the discharge strap and see if the appratus survives. > > The zero Ohm ground strap is not a real-world HBM scenario, and certainly > not in conformance with EN61000-4-2 or any of the HBM standards. On the > other hand, if your product is not subject to HBM, or your product needs > testing to a user-scenario that includes a strap discharge, then that is a > perfectly good test. > > // > Patrick > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > Different question about ESD. > > I have a component we tested on the normal 55024 directed ESD table for a > table top mounted device. Worked fine, problem is that the customer places > this on a large metallic roll around pedestal on rubber wheels. When they > send it to a lab and test it this way there is a problem. I don't have the > pedestal so I'm trying to simulate with my table and removing the 1 mohm > bleeder resistor. Between discharges to the table, I ground a braided strap > attached to the table top to my reference plane below. I get very similar > results then. What should the braid really look like - should it just be a > short, should it have some bleed resistance in it. I chose none since the > discharge is going to be people touching the pedestal or other furniture > that is grounded. > > What does the standard say about the VCP and HCP? > > Gary McInturff > Reliability/Compliance Engineer > > > // > Patrick > > From: McInturff, Gary [mailto:[email protected]] > Sent: Monday, April 23, 2012 12:37 PM > To: [email protected] > Subject: [PSES] Safety cost and ESD > > Given the implementation differences between US/Canada(?) and EU on the > medical 60601-1 standards. EU the June, US June 2013. How are folks handling > new products being introduced now or in the very near future? Just got a > quote back and the US certifier wants to charge me twice once for the 2nd > edition and then to transition to the 3rd edition. I anyone else running > aground on this. Seems like this should be happening on both sides of the > pond - since a CB report to 3rd edition would run into the second edition > enforcement in the US (and maybe Canada - I don't know their implementation > date). > > To be fair - I get good service once I get past the sticker shock and don't > have any complaints from that standpoint. In fact I enjoy the engineering > staff I work with. > > Different question about ESD. > > I have a component we tested on the normal 55024 directed ESD table for a > table top mounted device. Worked fine, problem is that the customer places > this on a large metallic roll around pedestal on rubber wheels. When they > send it to a lab and test it this way there is a problem. I don't have the > pedestal so I'm trying to simulate with my table and removing the 1 mohm > bleeder resistor. Between discharges to the table, I ground a braided strap > attached to the table top to my reference plane below. I get very similar > results then. What should the braid really look like - should it just be a > short, should it have some bleed resistance in it. I chose none since the > discharge is going to be people touching the pedestal or other furniture > that is grounded. > > What does the standard say about the VCP and HCP? > > Gary McInturff > Reliability/Compliance Engineer > > - > ---------------------------------------------------------------- > 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]>
