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" <[email protected]> on 06/10/2002 06:36:46 AM
Please respond to "Pommerenke, David" <[email protected]>
To: "Neil Helsby" <[email protected]>, [email protected]
cc: [email protected] (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:[email protected]]
Sent: Monday, June 10, 2002 4:56 AM
To: [email protected]
Cc: [email protected]
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
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