DMM with Nanoamp Current Resolution

[macboy]

Try a Keithley 2001.
Range Resolution
200 uA 10 pA
2 mA 100 pA
20 mA 1 nA
200 mA 10 nA
2 A 100 nA

Maybe a Keithley 2000 will be ok also?

The Keithley is just a fancy op-amp with an electrometer tube input you can read the manual. It has a "fast" and "slow" mode one of which is a transimpedance amp using virtual ground this essential for measuring junction leakage where NO voltage burden is essential.

You can but several op-amps with 20fA input current and one I think at 3fA and use a big feedback resistor. You could also synthesize a big resistor with a T feedback network. The Keithely gets around 10 atto-amps or so. If you just want 10nA or 100nA full scale a chain of 1 or 10 10Meg resistors would give you a volt full scale.


If the shunt resistor approach is necessary floating everything on batteries will work, some Keithley's used mass quantities of batteries including one of those 90v B+ batteries from old radios.

You are confused, and you are confusing others too. The 2001 is a digital multimeter, not an electrometer.

 

[scott wurcer]

Which model are you referring to? The 2001 mentioned above doesn't go to electrometer territory.

Samuel

Forgot the model number, it was two piece with a custom sapphire input connector and VERY expensive. It also had an unprotected MOSFET input with what I assume some secret protection circuit since the schematic showed back to back IN914's on the input.🙂 Sorry an electrometer is overkill for this but all the ones I've used also go up to .1A full scale so you can measure any current.

 

[Samuel Groner]

Forgot the model number, it was two piece with a custom sapphire input connector and VERY expensive. It also had an unprotected MOSFET input with what I assume some secret protection circuit since the schematic showed back to back IN914's on the input.🙂 Sorry an electrometer is overkill for this but all the ones I've used also go up to .1A full scale so you can measure any current.

Perhaps the 6430? It has 10 aA resolution (and sub-fA noise).

Samuel

 

[mlise]

You did want a DMM, but if you just want to get the measurement done, get an old Boonton 95A. It's a sweet old analog meter with a big center zero (no swapping leads) dial. It goes down to +-1 pA full scale. For tweaking analog circuits, analog meters are much easier than digital too. Do you suppose the vacuum tube input counts as an electrometer?