General > General Technical Chat

100G -1000G Resistors

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jonpaul:
get a Sensitive Research  Electrostatic Voltmeter 

Avail as surplus, $40..250, in ranges 5kV ...100 kV, zero current.


Jon

jwet:
Need quantity 150 and long term support for field service people.  I mentioned this above as an electrostatic voltmeter- a standard solution for 1/2 the problem but also pretty fragile for a tech servcing airport equipment.

bdunham7:

--- Quote from: jwet on May 16, 2023, 12:26:51 pm ---not require a transit case.

--- End quote ---

Now they're getting silly.


--- Quote ---I don't know if you've ever seen a nulling voltmeter- Fluke made them before sexy DMM's- they were kind of cal lab oddities. 

--- End quote ---

Yes, that is what I was thinking of, except that if they are always reading the same voltage you could simplify the design a bit.  It's not hard to design a device to put out a fixed or adjustable 2-2.5kV by using a lower-impedance feedback design, then null your measured voltage to it.  Insulation testers come to mind as a source.   I still have no idea how you could produce a tested and certified product like this in that low of a volume for well under $4k.  It's good they're paying you upfront.

jonpaul:
There are small cased ESVM with 10..20 kV ranges for field use. They are rugged and are on ebay perhaps $40..100 ea


Jon

jwet:
bunham7- I agree with everything you and others have said.  I even think that the customer knows its semi impossible.  They just can't buy something this expensive without a pretty good paper trail.  I think I'm a pawn probably but its ok- its interesting and has low risk- the only deliverable is a report.

The voltage nulling technique is looking pretty good and I think I get the electrometer for free- I'm supposed to show them all reasonable solutions with analysis of pros and cons.  One nice second order thing about the voltage nulling is that it reduces the effects of voltage coefficient as there is no voltage across the big input R.  I have found some very high value R's but the VCR's are such as to create huge errors (30%+!) if not cancelled with this nulling.  The best are 250 ppm/V- time 2kv gives you 50%!  This is not a brute force problem.

jonpaul- thank you, I have one in a faux wood box but I'll look on line at the ruggedized ones.  They do use things like my model now but they ship them to the techs and the techs ship them back to a cal lab on return for surveillance and checks.  Thanks

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