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 > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
