[SOLVED] Input filtering for thermocouple

[denujith]

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...

 

[jiripolivka]

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.

 

[denujith]

@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.

 

[godfreyl]

CMR = Common Mode Rejection.
You'll have more luck if you search for CMRR (common mode rejection ratio).
Common-mode rejection ratio - Wikipedia

 

[denujith]

Thank you