[volt-nuts] Fluke 887 mod with LTC1050
frank.stellmach at freenet.de
Sat Apr 29 06:59:31 EDT 2017
8pA is quite good a leakage / bias current for such a differential VM,
and also for the LT1050.
What makes me wonder, why three different OpAmps should all have exactly
The variation from one OpAmp to the others should vary greatly, even if
these are from the same batch.
I don't remember your circuit, but maybe you have some sort of input
protection on the non-inverting input, and that may cause this constant
bias. Have you assembled the OpAmp completely on the PCB, or is the +
input air-wired to the polarity switch S4E ? Ordinary PCB material may
also cause leakage currents.
I would also check the switches, if they are contaminated.
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