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Current offset on 6221/2182A

Posted: December 12th, 2017, 10:09 am
by savitale2000
I am doing a 4-point differential conductivity measurement using a 6221 current source / 2182A voltmeter setup. The devices I am testing have a resistivity of about 1 gigaohm. They can only be operated up to about 1V. So the resulting currents are sub-nA. The problem I am having is that there appears to be a current offset, that varies randomly over time form test to test. A 0.2 nA current offset results in a 0.2 V voltage offset during the differential conductance measurement, which is far above what we need for these precision measurements.

I'm out of ideas about how to eliminate this offset current/voltage problem. Note that at the beginning of every measurement the 6221 displays “Acquiring V-Zero ...”, so I assume it is attempting some sort of voltage compensation, but unsuccessfully.