[volt-nuts] Fluke 887 mod with LTC1050

[Frank Stellmach]

Randy,

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 
-8pA.

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.

Frank