Precise evaluation of thermal transpiration effect for calibration of capacitance diaphragm gauge

The pressure ratio due to thermal transpiration was measured by using two high-accuracy capacitance diaphragm gauges (CDGs) with sapphire diaphragms using a method independent of the temperature dependence of the CDGs. Two-step compensation for the thermal transpiration effect was performed because two pipes connected in series with different inner diameters (4.4 and 10.16 mm) were used to link the CDG to the vacuum chamber. The measurements agreed with calculations by the Takaishi–Sensui equation [Trans. Farad. Soc. 59, 2503 (1963)] using the constants A*, B*, and C* proposed by Setina [Metrologia 36, 623–626 (1999)] within 0.22% in the range of 23–100 °C and from 1.4 to 15 Pa. It was also experimentally confirmed that this compensation method for thermal transpiration is suitable for routine calibration of CDGs.