This is the simple circuit of an Instrumentation Amplifier (IA) with R=20k as in AD524.
The output voltage is:
Vout = (V1-V2)(1+ 40k/Rg)
, where Rg is the resistor in the middle between the two inverting inputs in the first stage of the IA. It is responsible for adjusting the gain to the desired value.
Note: Rg should be big enough to maintain the output voltage below the saturation value of the op-amp to ensure correct output reading.
