| In the fields of power,environmental protection,etc.,high-precision detection of trace gases is essential to the safety of production equipment and staff.Gas detection technology based on photoacoustic spectroscopy technology has received extensive attention in the field of gas detection due to its high precision,high selectivity,no carrier gas,and online detection.In this paper,the simulation and experimental research of photoacoustic spectroscopy gas sensing system is carried out to meet the needs of transformer fault gas detection and analysis.The main research work is:(1)Based on the theory of infrared absorption spectroscopy,the factors affecting the broadening of the gas absorption spectrum are analyzed,and the line-by-line integration model is used to calculate and analyze the gas absorption coefficient of the target gas in the infrared wavelength range.Starting from the generation mechanism of the photoacoustic effect,the cylindrical photoacoustic cell used to generate the photoacoustic signal is deduced in the resonant and non-resonant working modes of the photogenerated acoustic pressure distribution and amplitude.The sound tank structure design and parameter optimization provide a theoretical basis.Theoretically analyze the principle of resonant photoacoustic spectroscopy using wavelength modulation-second harmonic(WM-2f)and derive the expression of the second harmonic amplitude,which provides guidance for gas concentration detection and subsequent improvement.(2)The optical simulation software is used to build the optical path model,and the nonresonant photoacoustic spectroscopy system is simulated and experimentally studied.The influence of reflector structure parameters and different photoacoustic cells on the performance of the system’s signal-to-noise ratio is studied,and a beam-matched non-resonant photoacoustic spectroscopy system is proposed.The reflector and photoacoustic cell with different parameter models were prepared in experiments and tested on the actual non-resonant gas detection system.It was verified that the beam-matched photoacoustic spectroscopy system can improve the system signal-to-noise ratio and Detection sensitivity.(3)Based on the principle of resonant photoacoustic spectroscopy,a resonant acetylene gas sensing system using a near-infrared DFB laser and a one-dimensional longitudinal cylindrical photoacoustic cell was built and tested.The WM-2f technology is used to modulate the laser and the fiber amplifier(EDFA)is used to amplify the laser power.The aperture and length design of the photoacoustic cell is improved to make the system have a higher cell constant.The system is optimized by optimizing the modulation depth and resonant frequency scanning,and the detection limit of 109 ppb is obtained.The introduction of a mirror in the exit window to enhance the amplitude of the photoacoustic signal finally achieved the lowest detection limit of 47 ppb. |
