Hi all.
I have been working on an instrumentational amplifier circuit to amplify a 0-10mv differential voltage (Loadcell) up to 0-2.5V to be read by and Arduino ADC
Currently I have tried using an INA129 and an INA128. Both of these amplifiers are giving me about a 80mV offset voltage at the output even when the inputs are tied together. I decided to build a circuit on a bread board to test the amplifiers incase my PCB design was wrong. Even using a gain of 1 and and connecting the the inputs together I still get the 80mV offset. The offset its self is not a problem except it you mathematically subtract it from the output the linearity is out by about 25% (not good for accurately measuring force). Below is the circuit any comments would be much appreciated.
P.S. I have a few amplifiers and it seams to be the same with all of them