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100G -1000G Resistors

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magic:

--- Quote from: wraper on May 13, 2023, 10:18:26 pm ---This is not Bulgarian but Soviet and has datasheet.
https://www.quartz1.com/price/PIC/480Q0717900.pdf
http://www.155la3.ru/datafiles/kvm_kim_klm_tu_1977.pdf
You can google translate it and ask if something is not clear, I speak Russian. КВМ are vacuum composite resistors. +1000/-2000ppm/oC TC, -60/+85oC, 100V max. Rated to drift not more than 30% during 10k hours of operation and not more than 25% during 12 years of storage.

--- End quote ---
This is correct, including the voltage rating, and I seem to recall that people tested them and found them to fail instantly at less than 1kV.

I have a few of those resistors and their tolerance after all those years is quite sloppy, particularly the 100GΩ ones. Most were 90~95GΩ and the worst ~70G, all measured by applying 100V in series with a 10MΩ DMM and doing the obvious math.

magic:

--- Quote from: jwet on May 13, 2023, 09:19:54 pm ---I can stack a couple but the capacitance quickly gets out of hand.

--- End quote ---
I don't understand this remark. Connecting capacitors in series decreases end-to-end capacitance, and resistors have low capacitance to begin with.

In fact, I think a physically long string of 1GΩ resistors would have much less capacitance than one small 100GΩ resistor.

jwet:
Tim Fox- I could be wrong about who made Victoreen R's- I was told this somewhere along the line.  Victoreen had a lot little specialty shops in that big place near Shaker Heights.  There was a little shop for making those view through electrometer based dosimeter pens, quite an operation- saw it around 1986.

jwet:
Magic- My capacitance concern is node capacitance to "ground", not across the R's- even on a teflon standoff, its difficult not to pickup a pF of stray.  1000G x 1 pF makes for s 1 sec RC product, even at lower resistances like 10G,  its easy to get into motor boating- low frequency oscillation in anything with feedback.  Guarding can help but it all gets kind of ugly at these voltage and currents.

jwet:
pcm81- I think something like you're talking about is what my customer wants to do but he wants to do the test in the field.  He doesn't want to issue his field tech a fancy Keithley electrometer and the cheaper megger like gadgets available won't go down low enough in leakage.  End equipment is Ion mobility spectrometers- the detectors used at airports for explosives.

I'm going to rethink my approach.  When you get yourself designed into a box like this, its best to back out and try something else.  I originally wanted to do it with an integrator but they didn't like the slow reading speeds it would give them (1/sec).

Thanks all.

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