Compensation of Thermal Transpiration Effect for Pressure Measurements by Capacitance Diaphragm Gauge

Abstract

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

Calibration of Capacitance Diaphragm Gauges with 1333 Pa full scale by Direct Comparison to Resonant Silicon Gauge and Static Expansion System

“…(2). The S(CDG-1Torr) increases with decreasing the pressure by thermal transpiration effect because CDG-1Torr has a heated sensor head at the temperature of 45 o C [10,[13][14][15].…”

“…Figure 6. Sensitivity of the CDGH-10Torr with a heated sensor head at 45oC before (a) and after (b) compensation of the thermal transpiration effect by the Takaishi-Sensui equation [15,16].…”

“…Parameters a, b, and c were equal to 12×10 5 deg 2 mmHg -2 mm -2 (6.75×10 7 K 2 Pa -2 m -2 ), 10×10 2 deg mmHg -1 mm -1 (7.50×10 3 K Pa -1 m -1 ) and 14 deg 1/2 mmHg -1/2 mm -1/2 (38.3 K 1/2 Pa -1/2 m -1/2 ), respectively. The validities of the T-S equation and these parameters are discussed in [15].…”

“…Figure 5(b) shows the compensated S(CDG-1Torr) by eq. (1)[15,16]. The S(CDG-1Torr) after the compensation by T-S equation has a constant value of 1.0081 ± 0.0014.…”

Characteristic and Maintenance of Various Total Pressure Vacuum Gauges

“…Difference of characteristics of the Pirani gauge, which was used at a CVD device for a solar panel production for six months, before and after adjusting both zero point and atmospheric pressure. Two capacitance diaphragm gauges with a full scale of 1.33×10 5 Pa, and that of 1.33×10 3 Pa were used as reference gauges.…”