New approach to corrections for thermal transpiration effects in capacitance diaphragm gauges

Abstract

The sensors of capacitance diaphragm gauges (CDGs) are customarily kept at a stable elevated temperature. This greatly improves the zero stability but also introduces non-linearities at pressures below 100 Pa due to thermal transpiration. The effect of thermal transpiration has been measured for three CDG transducers and four gases - nitrogen, argon, helium and hydrogen - in a range of pressures from 10-2 Pa to 102 Pa. Normalization of the pressure scale for different gases can easily be performed using the two well-known gas parameters, viscosity and molecular mass, thus simplifying the calculation of the thermal transpiration correction when the test gas is changed. A universal expression for the thermal transpiration correction as a function of normalized pressure was determined.