Is there a way to use the NI 9217(PT100 RTD Analog Input) to retrieve temperature from a thermocouple?

[Vishwaramesh]

I purchased an NI 9217 and Pt Thin Film RTDs to make a temperature measurement. But I now realize that the RTD is acting as a non-negligible heat flow path in my system and so I want to switch to a thin wire Thermocouple that touches the surface. 

But purchasing another module is a huge investment. So I am trying to find what my options are. 

Thanks for the help!

[Mr_Engineer]

Read user manual of NI 9217 for connecting RTDs at analog inputs.

Jamal

[Henrik_Volkers]

Well, the 9217 is made for 100Ohm RTDs.....

If heat transfer is a problem:

Use

-thinner wires

-smaller RTDs

But keep in mind  the 1mA excitation(/heating 😉 ) current, maybe that self heating current is too high?  (OK, the spec doesn't tell if it is applied all the time.....)

A hack (never tried) with a lot of calibration needs: (and you didn't tell us a lot about your application.... not even the temperature range)

And it can only work if the 9217 measure in DC mode..... (what I assume)

Get 1 to 3 good low tempco 100R resistors, put them together a 100RTD (CH4 😉 ) on a heat shielded metall block  to build your CJC .  (Everything with good thermal contact)

Wire the 100R Resistors in 4 wire mode, connect your TC in series to the RTD+ connection  (these connections are also placed on the CJC block)

Any TC EMF will show up as a change in the measured resistance. For a Pt100 (@ 1mA) 1K temperature change is about 380µV voltage change ....  a type K is about 10 times smaller.... uncertaincy is about 1K anyway with a TC, so expect 2K and a resolution of 0.1K ....     

How to calc the temperature is now your homework 😉 

[Henrik_Volkers]

Last remark:

You will spend a lot of time with that hack ( building the CJC block, programming, validation/calibration) ....

so getting a TC module if you need to measure with TCs is the recommended way to go....

[Henrik_Volkers]

Thank you for the Kudos 🙂

Just curious: How did you solved the problem?

Spoiler

Hey, that was a crude hack 😄

[Vishwaramesh]

I wasn't able to. I eventually had to throw money at the problem and buy a module to use thermocouples