[Elecraft] Radio Shack ESD mat doesn't meet spec

[Alan Bloom]

Yes, I realize my measurement technique was not very accurate.  For one
thing, reading a meter flicker down around 10% of full scale is probably
gives no better than +/-50% or so accuracy.  But the Radio Shack
anti-static mat was reading a couple orders of magnitude greater than
the resistivity specified in the ANSI standard.  A measurement error on
the order of 50% doesn't matter.

I have just ordered another anti-static mat from Digi-Key, a 2x3-foot
desktop mat made by Desco, DK part number 16-1121-ND for $38.18.  Unlike
the Radio Shack product, this one has an actual data sheet where it
states that it meets the ANSI spec.  As a reality check I will try
measuring it using the same technique I used before.  If it also
measures too high a resistance then I will conclude that there is
something badly wrong with my measurement procedure.  But if it reads
OK, then I think we can safely assume the Radio Shack mat doesn't work
as it should.

Al N1AL


On Fri, 2010-03-26 at 14:05 -0800, Rich wrote:
> I have concerns about how that resistance was determined.  I do not think the
> methodology provides an accurate result.
> First, look at eh schematic of the 260 - there are components in series
> /parallel with the meter. Even with just the low current jack, there are
> still components in series. 
> Second, I have never, NEVER, seen an analog meter provide accurate reading
> of a peak or transient voltage. The frequency response/ transient response
> is not there. Some of the components in parallel with the meter movement are
> there to protect the meter. Additionally, there are balanced weights on the
> mechanical portion of the movement to "stabilize" the movement and thus
> decrease transient response. 
> When trying to calibrate a synchro system that was providing a sine wave of
> about 20 Hz, my Simpson (freshly calibrated) was off by more than 20 %. of
> the voltage displayed on an Oscilloscope which I was using for making the
> adjustment. 
> Third, I know of no Simpson 260 that has a lowest range of 60 micro-amps,
> everyone I know of is either 100 or 50 micro-amps. Don't knew what the new
> ones are, but am sure that none of the old big ones have that value.
> Here is a source for some info on the various Simpson meters. 
> http://simpson260.com/downloads/downloads.htm
> 
> Rich
>