How does a thermocouple work?
When two wires composed of dissimilar metals are joined at both ends and one of the ends is heated, there is a continuous current which flows in the thermoelectric circuit. If this circuit is broken at the center, the net open circuit voltage (the Seebeck voltage) is a function of the junction temperature and the composition of the two metals. Which means that when the junction of the two metals is heated or cooled a voltage is produced that can be correlated back to the temperature.
Thermocouples are available in different combinations of metals or calibrations. The most common are the “Base Metal” thermocouples known as Types J, K, T, E and N. There are also high temperature calibrations – als known as Noble Metal thermocouples – Types R, S, C and GB.