One example that comes to mind, out of a long history of wonderment in ESD
testing, is for an air discharge, pulling the trigger causes the product to
glitch, before approaching the product target point.
Found a way around the anomaly, to find not problem with the actual air
discharge.
But then a moment later, releasing the trigger caused another glitch.
Sent ESD gun for repairs and got a 'no defect found' result.
Sent to an independent calibration lab of notable credentials, for a good to go
results.
Repeat test in our lab with the same glitchy results.
ps. on the side, I monitor the radiated emissions by using an o'scope with a
simple probe hanging open loop somewhere nearby.
The scope captured waveform indicated a wild radiated event when pressing the
trigger for an air discharge.
With resulting products glitches.
Another waveform for the actual spark, and no product glitches.
Followed by another wild radiated event upon releasing the trigger, that also
caused glitches.
Verification of the ESD waveform by using a "target" was also monitored with an
independent scope.
A thought occurred that an ESD event happens so much faster than any human
movement to move the gun towards the target fast without causing damage, that
it is silly to do so.
So I tried placing the tip a small distance from the target.
The monitoring scope indicates that the arming and air discharge seems to
happen at the same time.
The trigger release still causes the radiated event, which often triggers
another air discharge.
With the close spacing between ESD gun probe and verification target, the
immediate discharge keeps the dual discharges away.
And the waveform is nearly text book perfect, every time.
Verified !
On Tuesday, October 15, 2019, 03:50:55 PM EDT, John Woodgate
<j...@woodjohn.uk> wrote:
Well, some of the set-ups I've seen appear to accept violent mismatches, so
concern about the cables may not be misplaced. But I still think that an
in-depth study of the discharge path, from source back to source, is needed.
What is a 'reasonable waveform definition'? Do you mean a precise definition of
a realistic waveform? I think that IEC 61000-4-2 has a precise definition, but
I have no idea whether the waveform is realistic, even less whether is it a
reasonable 'average' of a range of possible waveforms. But we must note that it
is a specification to be met under verification test conditions: it does not
claim to be the waveform that actually occurs during any specific immunity
test. It could not possibly claim that.
Best wishes
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK On 2019-10-15 20:06, doug emcesd.com wrote:
Well said, Derek!
I am always amazed that EMC people worry about the measurement uncertainty of
the coax cable that connects the target to the scope yet ignore factors, like
lack of reasonable waveform definition, that have orders of magnitude more
effect on the EUT.
Doug Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email:
d...@dsmith.org Website: http://dsmith.org
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