Thermocouples and Platinum Resistance
Thermometers

A thermocouple is fundamentally a pair of electrical conductors of dissimilar metals so as to produce a thermal emf when the junctions are held at different temperatures.

The emf generated is not merely at the hot juction of two conductors i.e. the sensing point but all along the length of the conductors from sensing point to the cold junction i.e. where the conductors are terminated on the temperature measuring/controlling instrument.

Thus for proper functioning of the thermocouple, the complete thermocouple wiring, from the sensing point i.e. the hot junction to the instrument terminals i.e. cold junction has to be done with the same conductor material of which the thermocouple is made of.

As it is not practical to have one thermocouple having such long lead length, thus, the normal practice is to use separate cable of same or equivalent thermoelectric characteristics.

The type of cable is called compensating cable.

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