ACOUSTICAL GAS ANALYZER

1
Lviv Politecnic National University
2
Lviv Politecnic National University

Method of measuring the relative component concentrations of two and three-component gas mixtures is proposed. The dependences of the sound velocity on the molar mass, the relative concentration, the heat capacity at constant pressure, the heat capacity at a constant volume and the absolute temperature of the gases in the mixture form the basis of the method. To improve accuracy, the change of measuring the speed on the measuring the frequency is proposed. It is shown that at constant wavelengths the frequency increases linearly with sound velocity at the gas mixture in the acoustic resonator.

The program algorithm was created with the help of Mathcad 2001 Professional. It permits the determination of three component gaseous mixture concentration at the measured frequency. First, the frequency value inherent to this mixture is compared with the values in the table. Two closest values are selected. The change in relative concentrations of gases is determined by these values. This change is split into 10 intervals. The frequency values for each interval are calculated. These frequencies are compared with the measured values. Again, there are two closest values and the cycle is repeated.

In such a way the nearest frequency increment band is narrowed in 3-orders magnitude after three iterations. Change in the concentration of particular gases could be 80% between the adjacent rows of the table. Reached value of gas concentration is one thousand times smaller than the band (0.8%) after the third iteration. The number of iterations is unlimited for this algorithm and is given in advance.

The two main factors affect the accuracy of measurements. They are the quality and the noise of the auto generator. The most common definition of Q is the ratio of the energy accumulated in the oscillation to the losses of this energy. This definition determines the design of an acoustic resonator. It should be such that the acoustic oscillations in it do not lose energy. This is necessary to ensure a high-quality resonator.

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