Hi, all Just put a few words of my understanding of ESD.
ESD test is to verify the EUT immunity due to induced current (nonsense!). The current can be induced by conducted coupling (direct contact) or/and radiated coupling. My understanding of the test is that for contact discharge, conduct coupling is dominate and for air-discharge, radiated coupling is dominate. Thus for contactt discharge, if you can pass the higher level, you may not have much problem with lower levels, but although radiated coupling is not dominate for contact discharge, the effects have to be verified through testing. For air-discharge, ESD test is to verify the effects of electromagnetic field on the EUT - i.e. a kind of field immunity test. Different levels will have a different field distribution around the EUT due to the different dV/dt - Maxwell told us. Thus, the induced current is (mainly) generated by the electromagnetic field. I tested one Fire Alarm system years ago. This system has 128 ports all connected with (at least 5m) twisted wires. I noticed that the cable layout can affect result (pass or fail) significantly when doing air-discharge. However, there is no noticable difference by varying cable layout when doing contact discharge. That was my understanding comes from. Rgds, Leslie --- Hans Mellberg <[email protected]> wrote: > > > --- Benoit Nadeau <[email protected]> wrote: > > > > Bonjour de Montreal, > > > > In another life, I was working for a EMC Test lab > > and we always used the > > step by step procedure which was in the ESD > > Standard. We tested using this > > procedure for years and we did encounter some > > products who failed at low > > level ESD but had no problem at higher levels. > > > > We wondered what to conclude and had some > > hypothesis. > > > > 1) may be the current path was different at higher > > level or > > 2) Lower levels might have a slightly longer rise > > time which tends to produce > > more energy in the lower part of the frequency > > spectrum where the EUT was > > more sensible. > > > > > Partly true. The risetime changes as the voltage > increases. The > risetime "slows" (dV/dt or dI/dt value gets reduced) > down as you begin > to go over 6-8kV. I also have seen products fail at > 2-4 kV and pass at > levels 8-10 kV. This ofcourse is on air discharge > equipment where > variability of the risetime is expected. > Contact discharge equipment do not exhibit much > risetime variability > (at least not to a large degree) > > Hans T. Mellberg > EMC/ESD Consultant > member ANSI/IEEE C63.16 WG on ESD > __________________________________________________ > Do You Yahoo!? > Bid and sell for free at http://auctions.yahoo.com > > > --------- > This message is coming from the emc-pstc discussion > list. > To cancel your subscription, send mail to > [email protected] > with the single line: "unsubscribe emc-pstc" > (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list > administrators). > > > __________________________________________________ Do You Yahoo!? Bid and sell for free at http://auctions.yahoo.com --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
