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[SOLVED] Input filtering for thermocouple

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denujith

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I am trying to interface Type-S thermocouple to a PIC. I am using INA126 amp for amplification. For input filtering found below circuit diagram. But I can't understand its operation.

Can anyone give me any help understand the filter operation it would be a great help. I have attached the filter circuit for your reference...
filter.JPG
 

The filter on the schematic is rather an interference suppressor as the leads from the thermocouple to opamp input may be long and not screened. As a thermocouple usually has a slow response (1...5 Hz), you can also use a feedback capacitor in the opamp circuit to make it operate as a low-pass filter.
For thermocouples, instrumentation-type amplifiers are often used which suppress CMR and interference while offering a reasonable gain. Thermocouples have a low resistance, so they are less problematic than other temperature sensors.
 
@jiripolivka Thank you a lot for your input (Y). By the way can you please explain a little bit about "CMR"? Google didn't help.
 

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