[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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