An Acoustic Gas Analyzer
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An Acoustic Gas Analyzer V. N. Alferova,* and D. A. Vasilieva a
Logunov Institute of High Energy Physics, Kurchatov Institute National Research Center, Moscow, 142281 Russia * e-mail: [email protected] Received March 18, 2020; revised April 3, 2020; accepted April 6, 2020
Abstract—Methods for measuring the composition of a binary gas mixture using the dependence of the speed of sound in a gas on its molecular weight, in particular, using an acoustic resonator, are considered. The described atmospheric hydrogen sensor target station for the cyclotron of the S-70 accelerator, which allows the production of medical isotopes, as well as a sensor for the content of neon in helium during its liquefaction, was developed based on this principle at the Kurchatov Institute IHEP SIC. Optimization of the resonator characteristics allowed a resolution of 10–5. DOI: 10.1134/S0020441220050085
INTRODUCTION High-precision measurements of the composition of two-component gas mixtures, including in a continuous mode, can be required during the operation of accelerators and physical installations. The appearance of a new gas in the atmosphere can lead to the initiation of an undesirable process. In our case, the source of the signal about the beginning of such a process is a sensor of the content of hydrogen in the atmosphere of the target station developed at the Kurchatov Institute Research Center IHEP for the S-70 cyclotron, which allows the production of medical isotopes [1]. Hydrogen may appear during depressurization of the target. Therefore, the sensor must provide continuous measurements and have high sensitivity in order to record the early stage of development of a dangerous situation. In addition to controlling the appearance of hydrogen, it is necessary to measure the composition of gaseous helium before liquefying it. Several measurement principles are used. The most common measurements using industrial devices are optical and electrochemical. Their attractiveness is due to the possibility of both real-time measurements and multicomponent analysis. Their disadvantage is low accuracy. High precision instruments (no worse than 10–4) belong to the class of laboratory instruments. The spectrometry and mass spectrometry principles are used. Spectrometric measurements are associated, as a rule, with sampling using span gases. These appliances are complex and expensive. At the same time, measurement of the speed of sound in a gas, depending on its molecular weight, can be performed with high accuracy using acoustic ana-
lyzers, whose principle is based on the use of this dependence. The speed of sound v is calculated by the following formula
v =
γRT , M
where γ = C p /Cv is the adiabatic index; Cp is the heat capacity of gas at constant pressure; Cv = C p − R is the heat capacity of the gas at a constant volume; M is the molecular weight of the gas; R is the universal gas constant; T, K, is the gas temperature. If we know the molecular weight of the main and impurity gases, then the speed of sound
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