I do have one story from the trenches, involving a laptop, ESD and "non-standard testing".
...back in the day, at a previous company... we had a customer complaint about a mysterious lockup. There is a side-story about sales, management, pressure, schedule, cost and all that noise. But sparing that, the lockup could only be duplicated by floating the laptop and discharging to the MODEM connector several times. No bleed-off between zaps. Eventually a secondary discharge was heard inside the laptop. Apparently the MODEM circuit has some floating circuits due to TELCO hi-pot requirements. The circuit did fine under TELCO testing, which I recall went to 3kV. But if the stored charge in the MODEM circuit got to about 7 kV, then there was a secondary arc to another circuit and havoc ensued. It was an interesting lesson for me about the (negative)virtues of isolated circuits inside an apparatus. As far as I know, this type of test was never adopted by any standards body, but it became a regular part of my internal engineering testing. // Patrick -----Original Message----- From: Brian Oconnell [mailto:oconne...@tamuracorp.com] Sent: Tuesday, April 24, 2012 6:05 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Safety cost and ESD 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: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Conway, Patrick Sent: Tuesday, April 24, 2012 3:53 PM To: McInturff, Gary; EMC-PSTC@LISTSERV.IEEE.ORG 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:gary.mcintu...@esterline.com] Sent: Monday, April 23, 2012 12:37 PM To: EMC-PSTC@LISTSERV.IEEE.ORG 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. 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