Not to mention the vastly different current risetimes. Low voltage discharges actually have higher di/dt values than high voltage ones (and therefore higher interference potential).
Doug don_borow...@selinc.com wrote: > > Let me add a bit on the air discharge side. > > You will want to do the lower voltage discharge tests because the path the > discharge takes may change with voltage. I have seen several instances where > connectors (sub-min D types, if I remember correctly) were mounted on metal > panels. At higher voltages, the path between the ESD gun and the grounded > shell > of the connector would break down first. At lower voltages, the connector pins > could be approached without breakdown to the shell, and the discharge would > occur to the connector pins. > > Don Borowski > Schweitzer Engineering Labs > Pullman, WA > > "Pommerenke, David" <davi...@ece.umr.edu> on 06/10/2002 06:36:46 AM > > Please respond to "Pommerenke, David" <davi...@ece.umr.edu> > > To: "Neil Helsby" <nei...@solid-state-logic.com>, > emc-p...@majordomo.ieee.org > cc: kro...@yahoo.com (bcc: Don Borowski/SEL) > Subject: RE: IEC 61000-4-2 ESD & 61000-4-5 Surge lower levels > > Dear Group, > > For most EUTs there is no need to do lower level testing in contact mode ESD. > The time is better spend (meaning a better test results uncertainty is > achieved) > if the number of discharges is increased at the highest test level (hundreds > is > a good number). Although it is possible that a system fails at e.g., 2 kV > contact mode (e.g., incomplete reset) and passes at 4 kV contact mode (full > self-recovering quick reset) the likelyhood of that happening is not that > large > to require it in a standard. > > For air discharge lower level testing is needed, as the risetime is often much > lower at lower voltages. Of course, if no discharge occurs, no further testing > at even lower levels makes sense. > > I do know that what I am saying violates the present IEC 61000-4-2 standard. > ut > it reflects the coming version of IEC 61000-4-2. The standard does not intend > to > protect agains every possible ESD failure. > > I would like to receive your input, as I am one of the US-representatives in > IEC > TC77b WG-9 (ESD). > > David Pommerenke > > -----Original Message----- > From: Neil Helsby [mailto:nei...@solid-state-logic.com] > Sent: Monday, June 10, 2002 4:56 AM > To: emc-p...@majordomo.ieee.org > Cc: kro...@yahoo.com > Subject: Re: IEC 61000-4-2 ESD & 61000-4-5 Surge lower levels > > I think there are two points here. > > 1) If you believe that in the environment in which it will be > used, your product may be subject to levels in excess of that defined > in the standard, you must test to that higher level. > > 2) Yes, failures can occur at mid range levels. We have just > recently experienced this problem with ESD. Below about 3.5 kV and > above about 4.5 kV the product worked fine. But at 4 kV we > experienced a failure mode. If we had only tested at 8 kV we would > have missed the problem. > > I also had a problem some years ago with mains voltage dips > to 0V. Having a test set that enabled the period to be varied in ms > increments, I discovered a problem affecting a voltage regulator. > When the mains dip was between about 16 ms and 35 ms, the regulator > went into a bistable mode switching on then off at each pulse. > Outside these periods, it worked satisfactorily, eventually losing > output when the period was extended. > > The problem with investigating these types of failure is determining > the size of step between measurements. Too short a step and you will > be testing forever, too long and you could miss a narrow band of > problem. > > Regards, > > Neil Helsby > > ********************************************************************** > This email and any files transmitted with it are confidential and > intended solely for the use of the individual or entity to whom they > are addressed. 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