[volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Thu Mar 22 20:58:45 EDT 2018
Electrostatic voltmeter?
Either the classical version or the modern electronic variant perhaps?
Bruce
>
> On 23 March 2018 at 13:33 "Dr. David Kirkby" <drkirkby at kirkbymicrowave.co.uk> wrote:
>
> I want to measure a high voltage, but put minimal load on the circuit.
> Looking at the Keithley electrometers, the input resistance is at least 200
> T ohms, but they tend to have a maximum of 200 V FSD.
>
> A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which
> itself is easy to measure. But one can't buy 200 T ohm resistors. I looked
> at RS in the UK, and the highest value resistor I could find is 1 T ohm,
> and they are £163 each (around $200).
>
> Maybe fabricating ones own resistor is possible, but I suspect there's a
> better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV
> range, and there's no way that can be measured with an ammeter, which would
> require an ammeter with a full scale deflection of 1 fA, which is much
> smaller than the 2 pA FSD on its most sensitive range.
>
> Any thoughts?
>
> Dr David Kirkby Ph.D C.Eng MIET
> Kirkby Microwave Ltd
> Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
> Essex, CM3 6DT, United Kingdom.
> Registered in England and Wales as company number 08914892
> http://www.kirkbymicrowave.co.uk/
> Tel 01621-680100 / +44 1621-680100
>
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