I wish to check the calibration of a thermocouple instrument by injecting a voltage taken from the thermocouple reference tables. I have compensating cable from the instrument to a T/C socket where I will be injecting my voltage. I know the cold junction temperature (and therefore equivalent emf), but I think I will have another 'cold' junction where my copper leads from the voltage source connect to the thermocouple socket.

I tried calculating the emf based on the instrument's cold junction temperature but it was wrong by a few degrees, but if I used room temperature in the calculation the calibration was correct.

How do I calculate the emf I need, do I need to take into account the second junction I make when I connect my voltage source?

Hope this makes sense

Thanks

 

Take a look at this....... http://www.omega.com/techref/thermoref.html

 

If I remember correctly, a "millivolt precision potentiometer" is used as the voltage source for creating reference tables for thermocouples and associated electronics.

Leeds and Northrop was the big name in these devices - on board precision voltage source (wet cell sealed battery). For example...

http://www.ebay.com/itm/LEEDS-AND-N...171?pt=LH_DefaultDomain_0&hash=item25812b821b

 

http://www.nist.gov/calibrations/upload/sp250-35.pdf
http://www.euramet.org/fileadmin/do..._cg-8__v_2.1_Calibration_of_Thermocouples.pdf
http://www.astm.org/Standards/E220.htm