Hello, I’m new here. I’m trying to build a Instrumentation amplifier that would do a 10uV -> 10mV amplification. The motivation is to measure uA currents on a small enough shunt resistor (1-10Ohm). For a proof of concept, I’ve built a circuit like the one below with a distinction that I’m powering it with two 9V batteries and am using
However, when measuring the results for different input voltages, the gain seems to vary:
I was expecting it to be constant. And here are my questions: What is a reasonable place to look for the causes of the variations? Cheap resistors? Inadequate op amp? Breadboard prototyping? 2x9V batteries as power supply? other?