Sonic gas analyzer for hydrogen and methane

Abstract

In the late-1800s, Germans used a "methane whistle", known as a Schlagwetterpfeife, to determine the presence of hydrogen or methane in the air that was circulated in mines. This paper describes a modern version of that concept that should be suitable for safety-related applications in mines, sewers, garages that shelter hydrogen or methane-powered vehicles, etc. A compact, self-resonant standing wave tube, 2 cm in diameter and 3 cm long, is capped at both ends by two small electrodynamic speakers. The cylindrical copper resonator has two slits at the mid-plane to allow a 25 mm fan to continuously sample the air which is brought to the resonator's temperature after being drawn along the outside of the resonator body. Variation in the resonator's temperature is compensated electronically by an integrated-circuit temperature sensor that produces one microampere per Kelvin. The sensor can measure the concentration of hydrogen to an accuracy of better than ±30 ppm or methane to ±0.02% in air using phase-locked loop frequency tracking electronics and a voltage-controlled oscillator. Concentration data will be presented for several different gas mixtures and will be compared to concentrations determined by other techniques (e.g., thermal conductivity gauges).

One-Dimensional Propagation

“…9.5.4 [9]. Since the sound speed is independent of pressure and the temperature dependence can be easily compensated, being proportional to the square root of absolute temperature, 5 it is possible to build sonic gas analyzers that determine the concentration of a contaminant quickly, accurately, and inexpensively [12,13]. The helium contamination alarm, shown schematically in Fig.…”

“…The reciprocity principle dictates that if a stimulus is applied on the left side of the network, producing a response on the right side, then when the same stimulus is applied to the right side, the response on the left side must be identical to the response when the situation was reversed. 13 Reciprocity can be illustrated using the network in Fig. 10.7 with the corresponding representation as the coupled linear Eqs.…”

Determination of Binary Gas Mixtures by Measuring the Resonance Frequency in a Piezoelectric Tube

“…γ is the adiabatic index (which depends on the nature of the gas), R is the universal gas constant, T is the absolute temperature. For mixtures of different gases, the speed of sound is determined by the mean molecular mass, M mix [1].…”

Gas sensing using acoustic attenuation with improved resolution

“…Acoustics based gas sensor have been used in the past, some for specifically sensing gas concentration level in underground coal mines like methane whistle, used in German coal mines. Acoustic phenomena that are used for gas sensing are acoustic resonance [2], surface acoustic waves [9], acoustic attenuation [6], [12] and speed of sound [14]. Gases in a mixture can be identified using acoustic attenuation [3], [6], [13].…”

“…For analysis a controlled environment with stable temperature and humidity condition was designed. Acoustic resonance and SAW based sensors are even more accurate [2], [9], but there working is strongly affected by stability of the environment in the enclosing they are placed into.…”