The thermal transpiration eŠect shown in intermediate ‰ow and molecular ‰ow regions in‰uences the sensitivity of a capacitance diaphragm gauge (CDG) with a temperature controlled sensor head. This apparent change in the sensitivity of CDG owing to the thermal transpiration eŠect has to be compensated for precise pressure measurements in the range of lower than 150 Pa. In this study, the method and the uncertainty of the compensation are reported.Seven types of equations for the thermal transpiration eŠect were compared with the calibration results of high accuracy CDGs by the static expansion system. Takaishi The calibration results of CDGs also show that increasing the temperature of the vacuum chamber from 22.5°C to 26.0°C caused decreasing the sensitivity of CDGs by the thermal transpiration eŠect. The magnitude of the decrease in the sensitivity was from 0.09 for 10 Pa to 0.5 for 0.1 Pa.Such apparent changes in the sensitivity owing to the thermal transpiration eŠect could be compensated within 0.2 by TakaishiSensui equation using parameters quoted from the catalog and the literature values. In addition, this deviation could be reduced to less than 0.1 byˆtting Takaishi-Sensui equation using the parameter c or the sensor temperature T 2 .
. は じ め に
<p>Two capacitance diaphragm gauges (CDGs) with 1333 Pa full scale, with a heated sensor head and an unheated one, respectively, were calibrated by three different methods; direct comparison to a resonant silicon gauge calibrated by a pressure balance, direct comparison to a CDG with 133 Pa full scale calibrated by a static expansion method, and the static expansion method. The calibration results of the three calibration methods show good agreement within their claimed uncertainties. Calibrated higher pressure points of CDGs by the pressure balance and lower pressure ones by the static expansion system are linearly interpolated within the calibrated uncertainty. Here, compensation of the thermal transpiration effect is important when a CDG is used with a heated sensor head.</p>
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