Thermocouple is a electrical device that converts the heat energy into electrical form of energy. Thermocouple follows the thermoelectric effect and produces a usable temperature dependent voltage. Although usable emf is induced in thermocouple, the induced emf is very small.
Thermo-couple basically works on basis of three principles:
1) Seebeck Effect:
The Seebeck effect states that when two
different or unlike metals are joined together at two junctions and the two junctions are provided by two different temperatures, an
electromotive force (emf) is generated between the two junctions. The amount of emf
generated is different for different combinations of the metals and is directly proportional to the change in temperature between two junctions.
2) Peltier Effect:
Peltier effect is the converse of Seebeck effect. Peltier effect states that when two different or unlike metals are joined together at two junctions and emf is provided between them, temperature difference is created in the two junctions. In this case, the temperature of one of the junction increases and other decreases. The temperature difference is directly proportional to the emf provided and also depends upon the metals used.
3) Thompson Effect:
As per the Thomson effect, when two unlike metals are joined together
forming two junctions, the potential exists within the circuit due to
temperature gradient along the entire length of the conductors within the
circuit.
Working Principle of Thermocouple
Thermocouple basically works on the principle of thermoelectric effect. When two different metals are joined together at two junctions and these two junctions are kept at different temperatures (lets call the hot junction which has greater temperature and cold junction which has lower temperature) the kinetic energy of the molecules of both the metals at the hot junction increases and the kinetic energy of molecules of both metals at cold junction of thermocouple decreases. Further, the heat tries to transfer from hot junction to cold junction through both the metals to balance both the junctions at same temperature. At this initial situation, the electrons from hot junction passes to cold junction carrying the heat energy through both metals and accumulates at cold junction. With the accumulation of electrons in cold junction, the negative charge in cold junction increases and deficiency of electrons in hot junction i.e. positive charge in hot junction increases. This difference in charge in the two junctions creates the electromotive force that makes the electron to move in a particular direction to produce current. However, as the two different metals are used, they have different specific heat capacity and different conductivity. Hence, the rate of transfer of heat is not equal in these metals. As a result, one of the metal starts the flow of electron from cold junction to cold junction and current starts to flow in the thermocouple loop.
Working Principle of Thermocouple
Thermocouple basically works on the principle of thermoelectric effect. When two different metals are joined together at two junctions and these two junctions are kept at different temperatures (lets call the hot junction which has greater temperature and cold junction which has lower temperature) the kinetic energy of the molecules of both the metals at the hot junction increases and the kinetic energy of molecules of both metals at cold junction of thermocouple decreases. Further, the heat tries to transfer from hot junction to cold junction through both the metals to balance both the junctions at same temperature. At this initial situation, the electrons from hot junction passes to cold junction carrying the heat energy through both metals and accumulates at cold junction. With the accumulation of electrons in cold junction, the negative charge in cold junction increases and deficiency of electrons in hot junction i.e. positive charge in hot junction increases. This difference in charge in the two junctions creates the electromotive force that makes the electron to move in a particular direction to produce current. However, as the two different metals are used, they have different specific heat capacity and different conductivity. Hence, the rate of transfer of heat is not equal in these metals. As a result, one of the metal starts the flow of electron from cold junction to cold junction and current starts to flow in the thermocouple loop.
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| Thermocouple |
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