The Principles of Operation of Thermocouple gauges measure pressure in terms of the amount of heat that gas will conduct away from a hot wire. The sensing element is a combination heater and thermocouple. Cross-shaped, it is formed by joining two short resistance wires of different compositions, a method of construction which gives excellent shock resistance and yet provides the minimum mass required for fast response. With a fixed heater power, the temperature of the junction, which depends on the conductivity of the gas, is indicated by the voltage output of the thermocouple. As the pressure drops, the thermocouple gets hotter and its output increases. Readout is accomplished on a millivolt meter calibrated to indicate pressure. $95.00. (1020833)
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