Article
Article
Pirani gage
Article By:
Comeau, Richard Foxboro Company, Foxboro, Massachusetts.
Last reviewed:January 2020
DOI:https://doi.org/10.1036/1097-8542.519500
A type of instrument used to measure vacuum by utilizing a resistance change due to a temperature change in a filament. This fine-wire filament, one of the four electrical resistances forming a Wheatstone bridge circuit, is exposed to the vacuum to be measured. Electric current heats the wire; the surrounding gas (in the vacuum) conducts heat away from the wire. At a stable vacuum, the wire quickly reaches equilibrium temperature. If the pressure rises, the gas carries away more heat, and the temperature of the wire decreases (see illustration). Since the resistance of the filament is a function of temperature, the electrical balance of the Wheatstone bridge is changed. The output meter is usually a microammeter calibrated in torrs or millitorrs (1 torr = 102 pascals).
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