NI 9213 - Must thermocouples be electrically isolated from one another?

[JB_1]

Hello,

I am attempting to measure the temperature profile of a copper plate.  I have instrumented the plate with a number of thermocouples (Omega 5TC-TT-T-T-36-36) which are attached to an NI 9213 module.  Presently I have insulated the thermocouples using a thermally conductive epoxy to ensure that there is no electrical interaction between channels.  However, I am finding that the epoxy is greatly affecting my temperature measurements, and I would like to eliminate it to improve the accuracy of my results - Is it acceptable to have the electrically conductive beads (without insulation) of the thermocouples in contact with a common electrically conductive surface?  Will this affect the accuracy of my measurements?  I have calibrated my system using a water bath, and I need to maintain a measurement accuracy in the range of +/-0.1 C°.

Any suggestions would be greatly appreciated!

Thanks!

[AnalogKid2DigitalMan]

JB_1:

I say give it a try and try to use a spearate instruemnt to compare against what your T/C's read. I have had issues with thermocouples/transmitters on equipment that had ground loop issues, I had to use isolation modules to resolve it.

I doubt that you will be able to achieve your accuracy target of +/-0.1C. The minimum error for T type T/C on the 9213 is at best ~0.7C. Accuracy for SLE T type from Omega is the greater of 0.5C or 0.4%.

-AK2DM

[Henrik_Volkers]

Like AK2DM said,  the 0.1°C is challenging ...

but not impossible if propper care, individual calibration and a reduced temperature range is taken.

It should be possible to directly connect the 'hot junction' to the copper plate with a differential measurement.

I don't know the NI9213 ( I used a HP3458)   but I did something similar successfully. (Speed wasn't a problem and averaging helped a lot)

Depending on the thickness of your copper plate errors due to thermal transfer can be a problem (choose thin TCs)

I even did surface measurments successfully with TCs on metallic surfaces with individual (but closly) bonded (electro welded) TC wires.

Today I would try it with 'this epoxy' (but sit down if you see price, space stuff).