Performance improvement of multi-point photoacoustic spectroscopy gas detection system by power compensation technique and fixed wavelength technique

Previous studies on the use of photoacoustic spectroscopy (PAS) techniques in the measurement of CH4 concentrations have been mainly limited to a single point measurement using only one PAS cell. A single point measurement will not satisfy the detection need, for instance in a natural gas transmission pipeline or an underground coal mine, gas explosion may occur at any point of the pipe or tunnel. Therefore, simultaneous multi-point measurements are required to obtain the gas distribution profile along the tunnel. Here we proposed and demonstrated a multi-point photoacoustic spectroscopy gas detection system based on the power compensation technique and fixed wavelength technique for CH4 detection. In the multi-point photoacoustic spectroscopy gas detection system, the gas absorption of the first PAS cell would make the measurement of the second PAS cell inaccurate. Therefore, we proposed a power compensation technique to compensate the absorbed laser power. In addition, a simple fixed wavelength technique was used in multi-point photoacoustic spectroscopy gas detection system to improve the signal to noise ratio (SNR). Finally, the experiment results showed that the two PAS cells achieved the minimum detection limit of 7.72 ppmv and 5.14 ppmv, respectively.