Thermocouple working and properties
The working principle of thermocouple is based on three effects, discovered by Seebeck Peltier and Thomson. They are as follows:
1) Seebeck effect: See beck effect states that when two different or unlike metals are joined together at two junctions, an electromotive force (Emf) is generated at the two junctions. The amount of Emf generated is different for different combinations of the metals.
2) Peltier effect: when two dissimilar metals are joined together to form two junctions, emf is generated within the circuit due to the different temperatures of the two junctions of the circuit.
3)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.
The selection criteria for thermocouple materials:
- Temperature Range
- Melting point
- Reaction to various atmospheric conditions
- Thermoelectric output in combination
- Electrical conductance
- Interchange ability
- Chemical properties
- Abrasion and vibration resistance
- Installation requirements