Hi Bob, I would like to correct the noise voltage for the trial circuit without INA129 as below. I am sorry for giving not accurate value which could give another hint. But above has still some voltage error noise at the ADC code output, and I understand that your statement was exactly right that "the 50/60 Hz is not common to both inputs and is passed through to the device resulting in noise in the output code. It is actually a difference signal with the AC signal riding on the AINP input and the AINN input filtered by the reference cap." 1uF cap may not only work for reference tank/noise filter but affects AINN which may differ from AINP common noise. We see no issue for actual thermocouple measurement but only manufacturing test which can NOT change R6161 in some reason. The test also can NOT change configuration of PGA (can not bypass with ADS124S06 ). Therefore; As one of solutions, the customer added RC filter between INA and ADC and observed improvement. And another potential solution to use differential output INA. If there is recommend INA instead of INA129 , please kindly let me know. About verification described in your last paragraph it goes away the error by removing the R6161 and shorting INA inputs. Thank you very much for your support. Masa
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