1. THERMOCOUPLES THEORY
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In 1834 Jean C.A. Peltier reported that when a current fows
across the junction of two metals, it gives rise to absorption or
liberation of heat (depending upon the direction of the current).
If the current happens to fow in the same direction as the cur-
rent produced by the ‘Seebeck Effect’ at the hot junction (T2),
heat is absorbed whereas at the cold junction (T1) heat is libe-
rated.
For example:
• Heat is absorbed (T+_ t) when:
a current fows across a copper-constantan hot junction from
the constantan (B) to the copper (A), minus to plus.
• Conversely, heat is liberated (T- _ t) when:
a current fows across the same junction from copper (A) to
constantan (B), plus to minus (fg. 2).
T.J. Seebeck discovered the phenomenon of thermo electricity in
1821. He found the so called ‘Seebeck Effect’: if a formed circuit
consists of two dissimilar metallic conductors A & B and one of
the junctions of A & B is at a temperature T1 while the other
junction is at a higher temperature T2; then a current will fow in
the circuit and will continue to fow as long as the two junctions
have different temperatures.
The E.M.F. (electromotive force) that produces this current is
called the ‘Seebeck Thermal EMF’: if A is (+) compared to (B),
then the current fows from A to B at T1 (fg. 1).
Fig. 1 Seebeck Effect
B (–)
T 1 < T 2
Current
Flow
A (+)
T 1
T 2
SEEBECK EFFECT
PELTIER EFFECT
Fig. 2 Peltier Effect
B (–)
T 1 < T 2
Seeback
Current Flow
A (+)
T 1 t
T 2 t