Page 288 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

There are three main effects related to thermoelectricity
1 The see beck effect
The See beck effect is a phenomenon in which a temperature difference between two dissimilar electrical
conductors or Semiconductors produces a voltage difference between the two substances.
2 The thomson effect
Thomson effect, the evolution or absorption of heat when electric current passes through a circuit composed of a
single material that has a temperature difference along its length.
3 The peltier effect
Peltier effect, the cooling of one junction and the heating of the other when electric current is maintained in
a circuit of material consisting of two dissimilar conductors; the effect is even stronger in circuits containing
dissimilar semiconductors.

The above figure shows the copper-constantan thermocouple. a battery is inserted in the circuit. It is found that
the heat is absorbed at one junction (junction gets cooled) and liberated at the other junction (it gets heated).
Thermocouples Common thermocouple types
Metal Type

T Copper and constantan
J Iron and constantan
E Nickel (10% chromium and constantan
K Nickel and Nickel (5% aluminum/silicon

Advantages
• Extremely strong and robust
• Shock and vibration resistant
• Offers wide temperature range
• Easy to manufacture

• No power supply required for excitation
• No self-heating involved
• Available in small sizes also
• High degree of versatility and flexibility

Disadvantages
• Thermocouples generate a quite low level output signal. Besides, the resulting output tends to be non-linear
due to which a sensitive and stable device is needed for temperature measurement.

• Installation of a thermocouple also necessitates tremendous care so that the possible noise sources could be
diminished.
• Moreover, the hardware employed for measurement should also offer excellent noise rejection capability.

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CITS : Power - Electrician & Wireman - Lesson 50-53 CITS : Power - Electrician & Wireman - Lesson 50-53