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AD8421 gain error

Question asked by NickP on Apr 24, 2016
Latest reply on Apr 27, 2016 by NickP

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 .