Explain the principle of a thermocouple. Give two examples of some common thermocouples.

Thermocouples: They are used for the measurement of temperature. While two wires of various type metals are joined together an emf exits across the junction that dependent on the kinds of metals or alloys used and also directly proportional to temperature of junction. Depending upon the range of temperature to be measured, esxact materials are to be selected for a thermocouple. When one junction termed as the cold junction is held at an identified constant temperature, the emf produced becomes measure of the temperature of other junction. The emf generated by a thermocouple is very small but this can be measured along with reasonable accuracy through a sensitive moving coil millivoltmeter that can be calibrated in terms of temperature. Several of the materials used for thermocouples are iron/constantan and copper/constantan.