Thermal conductivity gauges

Abstract

Because it is a function of the gas pressure, the rate of heat transfer through a gas can, after a suitable calibration, be used to give an indication of the pressure. This principle was first put to use in the field of high vacuum by Pirani in 1906¹, when it became important to measure with some accuracy the pressure inside electric lamp bulbs. Pirani showed that the heat transfer could best be measured by observing the rate of loss of heat from a thin wire suspended freely in the vacuum chamber. The heat loss from the wire is the sum of the following four components: (i) conduction; (ii) convection; (iii) radiation and (iv) conduction along the wire to the end supports. The first and, in some special gauges, the second of these components are useful in pressure measurement, as both are dependent upon gas pressure.