David,
I disagree with you here. As others have said, I have seen numerous
failures at less than the maximum required test voltage while the same
system passes at the max required voltage. It seems to me the intent was /
is / should be to verify product performance up to a maximum level, not
just at that level. The logic here would be that the "standards writing
group" would make the test cover reasonable ground up to some limit because
it is quite common that anything up to that limit could happen. The reason
for the limit is because it is uncommon for things larger / higher than the
limit to happen. Contact discharge is the only way to make reliable and
repeatable tests for ESD. No approach speed issues, etc. So testing at low
levels and working up to a maximum limit is a reasonable test method.
On the other hand, I find air discharge to be a difficult and not very
repeatable test to do which causes me to question its usefulness. Yes, I
agree that people interacting with products will more often see air
discharge rather than contact discharge. But I also find it impossible to
reliably repeat air discharge test results. The old approach speed,
distance and coordinates of contact point issue. Until someone can make an
automated air discharge tester that keeps human interactions out of the
process, I can't see it being corrected. That said, testing at lower levels
is just as necessary here.
Regards,
Scott Douglas
Senior Compliance Engineer
Narad Networks
515 Groton Road
Westford, MA 01886
office: 978 589-1869
cell: 978-239-0693
[email protected]
www.naradnetworks.com
At 08:36 AM 6/10/02 -0500, Pommerenke, David wrote:
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
