Hello, I am designing a differential thermocouple (no need for reference T) and I have decided to use two AD8421 amps in order to get a 0-5V output for my DAQ system. The differential input signal is expected to be around 41u-415u using a set of K-type thermocouples.
I have imported my circuit into TINA, using the SPICE model of the amplifiers, and the calculated gain is approximately 10% higher than the expected value, as calculated from the datasheet and the diamond plot tool (41.5mV for the first amp and 4.15V for the second, for a differential input of 415uV).
Is this result reasonable since the SPICE model includes the gain error, voltage offset error and bias current error or is there a more fundamental issue? This is my first time designing an electronic circuit so please forgive the naivety of my question. I have also attached a picture of the circuit diagram in TINA, also showing the output voltages from each amp for a differential input of 415uV .