There are some carbon brushes out there designed for removing static from vinyl records which should do a very gentle job of bleeding down the charge, but the best cheap solution I've used is a copper scrubbing pad (lots of contact edges) in series with a 470k resistor. A touch with a finger does pretty well if you don't mind the stimulus!
Brent DeWitt Milford, MA > -----Original Message----- > From: Scott Douglas [mailto:[email protected]] > Sent: Tuesday, April 24, 2012 9:49 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]>
