ACOUSTIC MEASUREMENT OF GAS COMPOSITION

Nicolae-Marius Bârlea

Tehnical University of Cluj-Napoca,Physics Department, 
Str. C. Daicoviciu 15, ROMANIA,
E-mail: mbirlea@phys.utcluj.ro 

The gas composition measurement is an important aim both in the industrial processes and in the domestic area. The sound velocity is an attractive property to use for the gas composition measurement because of the low power consumption and to the fact it is direct related to the molar mass of the gas [1]: 

		v = [∙P/]1/2 = [∙R∙T/M]1/2 							(1)

where:	 - gas adiabatic constant; R - universal gas constant; M - molar mass of the gas;  - gas density; T - gas temperature; P - gas pressure. 

In this paper we propose the piezoelectric Helmholtz resonator for this kind of application, because the resonance frequency of the device is direct related to the sound velocity [5, 6]:

		f = [v/(2∙)]·[S/(∙V)]1/2 							(2)

The conclusion of this experiment is that Helmholtz resonator is a sensitive device for the gas composition measurement in the percent range of the binary mixtures of gas with different molar masses, like H2, CH4, CO2, propane or butane in air. It remains to solve the influence of the temperature gas detector.

The experimental arrangement.
REFERENCES
1.	M. W. Zemansky, R. H. Dittman, Heat and Thermodynamics (McGraw-Hill International book 1982) p. 120. 
2.	I. Felea (coord.), Circuite cu tranzistoare in industrie, vol 1, p 433
3.	H. S. Shillingford, Brit. Commun. and  Electronics, 1 (Jan. 1961), p. 26.
4.	I. Făcăoaru, Măsurări şi control cu ultrasunete, Editura Tehnica 1965, p. 531 
5.	D.Stanomir, Electroacoustic Systems (Ed. Tech. 1984, in roumanian), p. 189.
6.	N. M. Barlea, Fizica senzorilor, Editura Albastra 2000, p. 155