9213 Input Calibration

[Tony_Dean]

I am trying to calibrate a thermocouple input on a 9213 module by injecting an emf from a precision voltage source (see attached sketch). The problem I have is determining what voltage to inject. I have the correct thermocouple table but I am not sure whether I need to take into account the temperature of the 'cold' junction at the module terminals (29 degrees) or the temperature of the junction created where my voltage source connects to the compensating cable (20 degrees). Or maybe its a combination of the two!

If it makes any difference, the 9213 is configured for voltage measurement (not temperature) and the cold junction compensation is done by reading the module's cold junction temperature and adding in the equivalent thermocouple emf.

Can anyone please advise.

Thanks

[Kev_R]

Hi Tony_Dean, 

I am an Applications Engineer for NIUk. I will be assisting you on this issue. 

Here is a link to the calibration procedure for the 9213 module. 

http://www.ni.com/pdf/manuals/372676a.pdf

Hopefully this will be what you after. 

I look forward to hearing from you. 

Kind Regards

[Tony_Dean · Accepted solution]

Thanks for the reply but unfortunately, the document in the link does not address my problem.

My problem arises because of the thermocouple compensating cable between the terminals of the 9213 and the thermocouple socket into which I inject my calibration voltages. However, I think I have figure out a solution myself and I have included it below in case anyone else has similar issues.

If I first apply zero microvolts into the thermocouple socket and take a measurement on the 9213, the measurement is the emf generated in the compensating cable due to the difference between the 9213's cold junction and the temperature at the thermocouple socket. If I subtract this emf from the injected voltages during calibration, it eliminates the error and gives me a true result.