Add the thermocouple signal directly to the rear electrode AD. It is clearly a positive voltage mv signal. The measured AD is indeed negative. FFF6 fluctuates upwards. There is also a problem with the pre-amplification. Touch the hot end of the thermocouple with a voltmeter. The measured output signal keeps rising, but it really drops after being amplified by the meter. I don’t know what to do? 18b20 for the cold end.
Misa Posté sur October 7, 2020
If there is a signal source, you can use the signal source to simulate the sensor input on the input terminal. If the sensor is actually connected, you may want to see how your shield is connected.
Alphonse Posté sur October 7, 2020
You can debug the two levels separately, adjust AD first,
Is your AD acquisition voltage OK? You can input a voltage to see the output, right?
There should be no problem up front, an instrumentation amplifier.
Serra Posté sur October 7, 2020
Don’t trust the data after AD too much,
Directly use a high-precision voltmeter or oscilloscope to measure the voltage and waveform across C17 and the thermocouple,
Also pay attention to the input common mode voltage of AD620, because it is single-ended power supply. The REF pin of AD620 cannot change the common-mode voltage range of the AD620 input terminal, but can only change the common-mode voltage of the output signal.
