A thermocouple is a sensor for measuring temperature. It consists of two dissimilar metals joined together at one end, which produce a small voltage(in mv) at a given temperature. This voltage is measured and interpreted by thermocouple thermometer.
A thermocouple circuit is formed when two dissimilar metals are joined at both ends and there is a difference in temperature between the two ends. This difference in temperature creates a small current and is called the Seebeck effect after Thomas Seebeck who discovered this phenomenon in 1821.
If two dissimilar metals are joined to form a closed circuit, there will be two junctions where they meet each other. If one of these junctions is heated, then a current flows in the circuit which can be detected by a galvanometer. The amount of current depends on the difference in temperature between the two junctions and the type of the two metals. This was observed by Seebeck and hence known as Seebeck effect.
When there is a difference in temperature between the two ends of this circuit, a small voltage is formed within the circuit. This voltage or EMF (electromotive force) is usually measured in the 1/1000th of a volt (mill volt). Most people’s body produces more voltage than that. The higher the difference in temperature, higher the voltage is. If the right pairs of materials are used, these thermocouple circuits can be used to measure temperature.
COLD JUNCTION (ROOM TEMPERATURE)
The junction that is put into the process in which temperature is being measured is called the HOT JUNCTION. The other junction which is at the last point of thermocouple material and which is almost always at some kind of measuring instrument is called the COLD JUNCTION.