Thermocouples are the most widely used temperature sensors. They are low cost, interchangeable, robust and can measure a wide range of temperatures.

Thermocouples basically consist of two dissimilar metals/alloys that when junctioned, that will generate a small EMF signal if there is a temperature difference between the hot junction, (measuring junction) and the cold junction or the (reference junction).

The EMF signal will be dependent only on the temperature difference and as such a thermocouple cannot be tested properly while both junctions are at the same temperature unless you use a thermocouple indicator.

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