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WORKING OF THERMOELECTRIC PYROMETER

The thermoelectric pyrometer may be employed at any temperature up to about 1200*C for those made of  "base metals"  and to 1500*C for "noble metals".

Base metal couples are made from nickel-chromium wire with nickel-aluminum wire for temperatures up to 1200*C ; nickel - chromium with constant wire up to 800*C. Base-metal couples oxidize more readily than noble-metal couples and they have, therefore, a much shorter life than the other. A noble-metal couple consists of one-wire of pure platinum and the other of an alloy of platinum and rhodium. This is used for temperatures up to 1500*C. The wires in the noble - metal couple do not oxidize readily.

The operation of thermoelectric pyrometers is based on the principle that when two wires of different metals are joined to form a complete electric circuit, and one junction is at a higher temperature  than the other. an electric current flows in the circuit. The magnitude of the current depends up on the metal used and the temperature difference on the junctions. 

In the practical application of this principle, an electric meter is connected to two wires which are welded together to form the hot junction. The two wires forming the junction are known as thermo-couple. The three essential parts of a thermoelectric pyrometer are the thermocouple, the galvanometer, and the wires leading from the thermocouple to the galvanometer, which is so calibrated that instead of indicating electrical units, it reads in degrees of  temperature. 


Thermoelectric furnaces


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