(i) The heater element
(ii) Thermo-element
(iii) A permanent magnet moving coil instrument Heater Element As the most important application of thermocouple instruments is the measurement of current and voltage at high frequencies, therefore, the heater element of such entrustment should be free from skin effects. In order to minimize the skin effects we must use very fine wire of non-magnetic material having a current. But for measurement of higher values of current (above 3A) a short length of thin walled tubing is used. Thermo-element The action of the thermo-electric instruments is as follows:
(i) Electrical energy is converted to the thermal energy in the heater element. Most of the heat energy is dissipated away and a portion of it is transferred to the hot junction.
(ii) The heat energy transferred to the junction is converted back to electrical energy by seebeck effect.
(iii) The output of the thermocouple is connected to the PMMC instrument.
However the overall efficiency of the system is very low.
The combination of heater element and thermocouple acting as an energy converter is known as a thero-element. A thermo-eIement, together with a PMMC instrument constitutes a thermo-couple ammeter, milliammeter, or a voltmeter.
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