Temperature-stable quartz oscillator and its applications in pressure gauges, gas sensing, and gas concentration measurements

Abstract

In this paper, a temperature-stable quartz oscillator (TSQO) is introduced that eliminates the influence of temperature on the output, which is the electrical impedance (Z)-converted voltage. Z depends on the pressure, viscosity, and density of the measured gas. Temperature stability was confirmed for temperatures varying from 30 to 300 °C at atmospheric pressure. As temperature was increased from 31 to 200 °C, fluctuations were decreased to below 0.30% of the average TSQO output. The TSQO exhibited an improved temperature stability compared with the output fluctuation of a conventional quartz oscillator, which is usually approximately 2.0% of the output voltage over the temperature range of 15–85 °C. The measured fluctuation in the TSQO output over the temperature range of 31–100 °C is 0.22%, which is acceptable for outdoor hydrogen sensing. This is because the fluctuations are smaller than the 0.33% change induced by hydrogen (H2) contamination at a concentration of 0.33 vol. %. The concentration of contaminated hydrogen is sufficiently less than the minimum detection level, which is one-fourth of the fluctuation introduced by low-level explosions of H2 in air (4%). The TSQO output could be implemented in various measurement applications. The dependence of the TSQO output on the total pressure in the range of 0.5–100 kPa indicates that it can function as a pressure gauge. The difference between the TSQO output measured for pure nitrogen (N2) and 0.5 and 1.0 vol. % H2 in N2 at atmospheric pressure indicates that the TSQO can operate as a hydrogen sensor. Moreover, depending on the TSQO output on hydrogen concentration at atmospheric pressure confirmed that the TSQO can be used to measure hydrogen concentration. The hydrogen sensing and concentration measurement applications stated above were possible up to 300 °C. Therefore, it can be concluded that the TSQO is practically useful for carrying out various measurements under the conditions of temperature fluctuations and exhibits an optimum performance in the temperature range of 31−300 °C.