Trace C2H2 Detection based on Cantilever Enhanced Photoacoustic Spectroscopy

Abstract

Acetylene $\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)$ is an important characteristic gas produced by transformer internal faults. Detection of its concentration at trace level is the basis of dissolved gas analysis in oil. In this paper, we studied the quantitative detection of C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> based on cantilever enhanced photoacoustic spectroscopy (CEPAS). Based on the infrared absorption effect of gas molecules, we selected the absorption line with a wave number of $6539.457 \mathrm{~cm}^{-1}$ as the detection point, and also simulated the effect of gas temperature and pressure on its absorption coefficient. In addition, for the CEPAS gas detection system built, we studied the frequency domain distribution characteristics of photoacoustic (PA) signals, and carried out quantitative detection experiments for trace C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . The results show that the absorption coefficient decreases by about 17 % from $10^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$ at a pressure of 1.0 atm, while the absorption coefficient increases by only about 1.4 % from 0.6 atm to 1.0 atm at a temperature of $25^{\circ} \mathrm{C}$. The signal-to-noise ratio is highest when the modulation frequency is $20 \mathrm{~Hz}$. In addition, the pure PA signal showed a good linear relationship with C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> concentration in the $\mathbf{N}_{2}$ background, with a good fit of more than 0.99, and reached the lower limit of gas-phase theoretical detection of 0.122 ppm for C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> .