Thermocouple working and their types

 The thermocouple is an active transducer used to measure temperature. A thermocouple consists of two dissimilar metals connected together at two ends to form two junctions cold junction ( reference ) always at 0-degree Celsius and hot junction ( measuring junction  ) measures the unknown temperature.

principle : 

      1) Seebeck effect

      2) Peltier effect

      3) Thomson effect 

when two dissimilar metals are joined together and when there is a change in temperature between two junctions an emf (voltage)is generated. It is directly proportional to the change in temperature.

There are various types of thermocouples: J, k, T, N, and E are base metals most commonly used types are R, S, and B are noble metals used for high-temperature applications. Thermocouples are known for their very quick response to change in temperature.

The measuring range of the thermocouple is very much dependent on type but the overall range for all thermocouple types is -200 to 1800 c.