What is a thermocouple (TC) and how does it work?
- A thermocouple (TC) is a temperature sensor. It reads the temperature in the kiln and gives the information to the control or pyrometer.
- A TC is made from 2 different metals. Type K TCs are alumel (-) and chromel (+). Alumel is magnetic, chromel is not. Also, when examined closely, alumel is a bit more copper-colored and chromel is a bit more silvery. Type S TCs are Platinum and Platinum with 10% Rodium.
- Once the two metals are welded together, a small millivoltage is actually generated from the welded joint. This millivoltage changes degree by degree as the kiln gets hotter/ colder.
- The millivoltage can be sensed by the control or by a pyrometer, and each different amount of millivoltage is assigned to a different temperature. The control can translate the millivoltage signal into a recognizable temperature.
- Because the signal is in millivolts any point of resistance in the circuit will change the millivolt value and the corresponding displayed temp reading. Old TC wires, a poor connection, or overheated/ pinched TC wires are the most common ways to have an inaccurate TC reading.
- Because there is more than one TC in the kiln it becomes difficult for the controller to even out the different temps when one of them is not reading accurately. E- 1 and the elements that seem fine are the result when this happens.
December 21, 2024
