In this topic, you study the definition, theory & diagram of Seebeck Effect. And the construction and use of thermocouple. What is thermo-electricity?
In 1824 scientist Seebeck of Britain observed that when the junction of two dissimilar metals is heated up an electric current flows in the circuit. Thus current can be easily measured by means of a galvanometer or millivoltmeter. This e.m.f. is known as thermo-electric e.m.f., the combination is known as the thermocouple and the phenomenon of producing the e.m.f. is known as the Seebeck effect.
Consider two dissimilar metals copper and iron joined at A and B as shown in Fig. 23.36. The junction is heated up. The e.m.f. is produced. The magnitude depends upon the temperatures between the cold and hot junctions. At hot junction the current flows from copper A Iron to iron while at cold junction current flows from iron to copper.
Combinations Of thermocouple. The B materials used in practice depends upon the Fig. 23.36. Thermocouple. temperature range to be measured. The platinum with rhodium is suitable for 14000C chromel to alumel is suitable for 1 1000C. Iron to constantan is suitable for 9000C and copper to constantan is suitable for 3000C.
Uses. The thermocouples are used for measuring temperature. Such devices are employed with the instrument, the thermocoupling will supply the energy and the instrument will work as the load. The pyrometer are the examples, the pyrometer is cheap, easy and can be used to measure the temperature up to 14000C and even higher.