What is the role of thermocouple?

Thermocouple is a heat sensing device.

It is made up of 2 dissimilar metals twisted/joined at one end called a junction and that is made Hot and the other end or tell end is cold (may be at 0 degree C). then a voltage is developed accross the two dissimilar metal, this principle is called SEEBECK EFFECT.

The voltage developed is directly propersional to the difference in temperature.