[volt-nuts] Fluke 887 mod with LTC1050

Frank Stellmach 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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