[volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Laurence Motteram]

If buying new equipment is OK, then maybe look at http://www.trekinc.com/

Contacting Voltmeter 1 x 10^15 ohm up to 2 kV, or Non-Contacting models.

Best Regards,

Laurence Motteram
Calibration & Service Manager
Scientific Devices Australia
Ph: +61 (0)3 9569 1366
M: +61 (0)425 765 019
www.scientific-devices.com.au
lmotteram at scientific-devices.com.au

-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces at febo.com] On Behalf Of Dr. David Kirkby
Sent: Friday, 23 March 2018 11:33 AM
To: Discussion of precise voltage measurement
Subject: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

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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