Vic, I agree, your product is probably seeing field failures because of the dry conditions. These dry conditions make the probability of an ESD event higher. This is due to the fact that, as personnel walk across carpets or rub their clothing on chairs, there is no humidity in the air to help bleed and equalize charge. So, they have a higher probability of charging up and a higher probability of discharging to your equipment. (You probably already know this.)
Of course, your problems may not be due to people discharging to your equipment. It could be due to some other source of ESD. It could be a discharge from a nearby object. However, the same argument holds. The dry atmosphere increases the probability. (Hence the static cling present in clothes that come out of a dryer.) So, in both cases, you are probably seeing more failures in a dry atmosphere because the probability of an ESD event is higher. Higher failure rates in dry atmospheres are due to this probability increase. The higher failure rate is probably not due to a dry atmosphere ESD event being different from a humid atmosphere ESD event. For testing, you are already generating the ESD event with a simulator. The ESD generator takes probability out of the equation. You can generate a discharge whenever you want. So, in my humble opinion you don't need to simulate the dry conditions. I would simply follow IEC 1000-4-2, which recommends test conditions with a humidity level between 30% and 60%. With this combination of ESD generator and humidity, you should get a discharge whenever you want; and it should couple to the victim in proper fashion. I agree that you will see different performance at different levels. I have seen failures at 4KV air discharge that are not repeatable with 8KV air discharge. So it is worth the time to test at lower levels until you get up to the compliance level that you are shooting for. Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | > -----Original Message----- > From: Gibling, Vic [SMTP:vic.gibl...@marconi.com] > Sent: Wednesday, June 12, 2002 3:26 AM > To: emc-p...@majordomo.ieee.org > Subject: An ESD question > > > > Dear Group > > I tried to find David Pommerenke article's in the Journal of ESD on the Web > but alas no downloadable version was found, so may I ask the group a > question? > > We have an ESD field failure which is occurring in dry hot countries ( no > surprise )which can be recreated with an ESD of -800V. In an attempt to get > a high incidence of discharges we used a dehumidifier to create a dry > environment. The result was a reduction in discharges. > > Thinking the problem through -now- as a dry atmosphere will encourage the > production of high level ESD and a humid environment inhibits the charge to > a lesser level, presumably because it 'leaks' away. Then is it wrong for us > to attempt to 'dry' the local atmosphere in the hope of gaining consistent > ESD from an ESD gun, that is to say the more humid the environment the more > efficiently the discharge will transfer to the victim? > > Incidentally, to add to the thread regarding intermediate level testing for > ESD and EFT. This exercise has revealed different failure mechanisms at > different ESD levels. > > Your views would be appreciated. > > Vic Gibling > Compliance Engineer > Marconi Applied Technologies > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > majord...@ieee.org > with the single line:> > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: emc-p...@hypercom.com > Dave Heald: davehe...@attbi.com > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > All emc-pstc postings are archived and searchable on the web at: > http://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
