The principle on which the modern thermocouple operates is derived from Seeback’s discovery that if a circuit is formed using two dissimilar metal Conductors with one junction at a higher temperature than other, then a current will flow in the circuit. The resultant emf. is proportional to the temperature difference between the junctions .
For many industries heating processes particularly those carried out at high temperature a Thermocouple is the most accurate convenient and simple method for temperature measurement.