A wide range constant-resistance Pirani gauge with ambient temperature compensation
J. H. English, Bruno Fletcher, Walter Steckelmacher · Journal of Scientific Instruments · 1965
The development of a Pirani gauge to cover the pressure range from 10 mtorr to 200 torr is described. A thin wire filament was used in a d.c. Wheatstone bridge with a transistor d.c. amplifier automatically varying the voltage so as to maintain the filament at constant temperature. With this arrangement, the bridge voltage is a function of pressure. It was found desirable to divide the pressure range into three sections, with automatic switching from one to the other. To measure pressures above 10 torr with any confidence it is necessary to provide ambient temperature compensation. To maintain a constant temperature difference between the gauge filament and wall, a temperature-dependent resistor was wound on the tubular gauge envelope and included in the opposite arm of the Wheatstone bridge. In addition to compensating for ambient temperature variations, this resistor also corrected for heating of the envelope, by conduction from the filament, at high pressures, thereby greatly reducing the time from switching on the filament to obtain a correct reading.