Could the ESD discrete signal be verified indirectly from measurement in
the frequency domain with a spectrum analyzer before the advent of GHz
oscilloscopes?


Ralph McDiarmid, AScT 
Compliance Engineering Group 
Xantrex Technology Inc



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of John
Woodgate
Sent: Monday, June 08, 2009 9:47 PM
To: emc-p...@ieee.org
Subject: Re: EN61326-1: 2006

In message 
<de87437fe365cb458c265ea3d73b6f1d04aa7...@xbc-mail1.xantrex.com>, dated 
Mon, 8 Jun 2009, Ralph McDiarmid <ralph.mcdiar...@xantrex.com> writes:

>It would at least bring it into agreement with the requirements of both

>the residential and industrial 61000 generic immunity standards. (4kV 
>contact, 8kV air)

But, as Doug says, that is not a sufficient argument. Unless 4kV air can

be shown not to be adequate to prevent an unacceptable number of field 
failures due to ESD damage, it should not be raised to 8 kV.

There may be an explanation. We know that in cold northern countries, 
humidity can fall to 20% and below and a charged human body can reach a 
potential in the region of 15 kV. But this is rare, and 8 kV is 
considered sufficiently severe. Note 'considered': the only proof is 
'epidemiological' - how many field failures occur?

I suspect that most equipment to which IEC 61326 applies AND is exposed 
to ESD is used in air-conditioned spaces where humidity is kept at 
medium values and ESD voltages do not reach extreme values.

There is a further issue. Until recently, the methods of verifying the 
output of ESD test hand-pieces were subject to considerable doubt and 
much controversy. To check the output waveform, oscilloscope bandwidths 
of at least 6 GHz are required, and these were very rare. So a lot of 
historical data were collected using test equipment whose 
characteristics are subject to significant uncertainty.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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