Thermocouple as analog input?

[JMA_eng]

I would like to re-purpose an older M series NI PXI-6229 for reading J thermocouples.  Before I spend time trying this out I thought I would ask the questions.  Has anyone done this?  Does it produce good results?  The analog inputs support a +/- 0.2V range with 16 bit A2D.    The manual of the NI 6229 indicates adding a resistor to AGND when using the inputs in DIFF mode.  Directly connecting AI- to AI GND or using a 100x resistor for J thermocouple?

If I use a PXI mux, recommendations on settling time for thermocouples, before applying the A2D settling time?

Cheers,

J - 

[Benjamin.S]

Hi J,

I certainly never have tried this myself. It's possible, but you'll be losing out on some features of thermocouple hardware like CJC compensation. 

For your reference, I included a white paper regarding handling noise which may be helpful for this application.

Field Wiring and Noise Considerations for Analog Signals

https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

Best,

Ben

Technical Support Engineer

National Instruments