Thermocouple Simulation to Transmitter

[s1eddaa]

Hey guys, I am an apprentice and had a situation come up where I needed to verify the transmitter electronics for 2 different thermocouple types (J and K) for a TSHH application. Is there any reason why I couldn't use my J type thermocouple miniplug when sourcing to a transmitter set for K type while using my fluke 725 if it is set to source K type? Could I not even use just regular copper leads when sourcing these transmitters?

My current understanding is that when the 2 metals of a thermocouple touch, they generate a small mV signal proportional to temperature that is then read by the transmitter. When sourcing with a process calibrator, the 2 metals that make up the thermocouple never touch and the mv signal is purely sourced by the process calibrator instead of the interaction between the 2 metals by my current understanding. Any help is appreciated, thanks!

[rolfk]

Each connection between two metals IS a thermocouple. The generated potential is specific to the metal-metal connection and depends both on the material of both contacts and the temperature each contact is at. Since you have to connect your process calibrator somehow to your measurement device, you have at least two connection points that are forming a thermocouple in some way. The according connectors for each thermocouple type are mostly there to avoid introducing extra unnecessary contact points of two different metals between the actual wire and the connector contacts that form each their own thermocouple element.

And since calibration is about trying to get the most accurate measurement possible to then calibrate the reading of your device to that expected value, it would seem useful to try to reduce as many measurement errors as possible, even if they are in theory small and in the case of those connectors often tend to compensate each other because of opposite polarity on the two contacts.

[Minions]

Here is a good guideline from TI covering the different thermocouples.