| AVS 62nd International Symposium & Exhibition | |
| Vacuum Technology | Wednesday Sessions |
| Session VT-WeA |
| Session: | Vacuum Quality and Partial Pressure Analysis |
| Presenter: | Atsushi Suzuki, AIST, Japan |
| Correspondent: | Click to Email |
A quartz friction pressure gauge (Q-gauge) is advantageous because it can measure pressures in the range of 0.01 kPa to 100 kPa and because the size of a quartz oscillator is less than 1x1 cm2. The underlying principle of Q-gauge use in pressure measurement is that the electric impedance (Z) of the quartz oscillator depends on the viscosity and gas density of the measured gas. When the total absolute pressure is known, then properties related to viscosity and molecular weight can be obtained from Z.
This is important because it enables changes in viscosity and molecular weight of the measured gas to be detected in addition to changes in pressure. Thus, many types of methods are made possible, such as hydrogen gas sensing, hydrogen concentration measurement, partial pressure measurements of binary gas mixtures such as ozone-oxygen and silane-hydrogen, and measurements of gas decomposition efficiency and composition changes induced by plasma.
However, the disadvantage of these measurements using a quartz oscillator is that the output Z from the quartz oscillator is affected by temperature. This temperature dependence must be corrected in particular for uses of hydrogen sensing outdoors and in other applications in which temperature changes.
In this presentation, a novel temperature-stable quartz oscillator (TSQO) will be introduced. The output from the TSQO used in this study was the electric-impedance converted voltage, which represents Z. First of all, it was shown that this output depended on the total pressure from 0.01 kPa to 100 kPa, indicating that this TSQO works well as a Q-gauge device. Fluctuation of the reading output at constant temperature was 0.06% of the total output.
Temperature stability was confirmed at atmospheric pressure and for temperatures varying from 15 °C to 50 °C. With this temperature change, the change of the TSQO output was less than 0.2% of the reading output. Because the output fluctuation of a conventional quartz oscillator across the temperature range above is normally about 2.0% of the reading output, it was shown that temperature stability was attained by the TSQO. The measured degree of output fluctuation for this TSQO is acceptable for hydrogen sensing because it is smaller than the 0.2% change induced by contamination of hydrogen concentration and less than one-fourth of the fluctuation introduced by low-level explosions of hydrogen in air (4%), which is the necessary minimum detection level. Therefore, it can be concluded that this TSQO is practically useful for various measurements that involve hydrogen sensing anywhere that temperature fluctuates.
This work was supported by ISPS KAKENHI Grant Number 24560070.