AbstractIn the common design of a thermal conductivity vacuum gauge according to Pirani, a thin wire is heated by an electric current and the heat loss from the wire by the heat transfer of the surrounding gas is used to derive the gas pressure. Other mechanisms of heat loss are the thermal conductivity of the wire, which transports heat to its cold ends, and the thermal radiation. In the present paper the various mechanisms of heat loss in an axially symmetric setup are investigated in detail and described by analytical formulae. Operation of the sensor by a regulated power supply allows to keep the electrical resistance of the wire and thus the mean wire temperature constant. However, changes in gas pressure affect the temperature profile along the wire and, concomitantly, the heat transfer by the wire towards its ends and the loss by thermal radiation. Experimental data of the heating power vs. pressure obtained with nitrogen and hydrogen in a typical setup are presented and compared with calculated values.