The Oil Gas Monitoring System Design Based On Photoacoustic Spectroscopy

Photoacoustic spectroscopy technology is an ideal multi-component gas detection method because of its high sensitivity, good selectivity, and fast response characteristics. However, the resonance condition is challenging for mass production, difficult to be adapted to the industrial field. On the other hand, the non-resonant operation suffers from a weak signal with low frequency, while the amplitude of the demand detection range is relatively large, which seriously hinder the application of photoacoustic spectroscopy detection technology. This work focused on the non-resonant operation to carry out the following tasks.A transformer oil gas monitoring system based on non-resonant photoacoustic detection technique is developed. The electric modulated infrared light passes through six high transmittance narrowband filter in order to filter the assigned wavelength light corresponding to the target gas. Afterwards the light passes through a non-resonant photoacoustic cell to generate photoacoustic effect. The signal is measured by high pressure field sensitivity microphone. Then the signal processing circuit calculates the gas concentration data.A non-resonant state photoacoustic cell is designed and implemented. The COMSOL Multiphysics multi-physics finite element analysis software was used to verify the work status for the resonant frequency modulation sensitivity and to illustrate the difficulties in industry application. It also verified the effect of the buffer chamber structure which can alleviate some coherent noise. The photoacoustic cell structure design was demonstrated considering the retention of the buffer chamber and the microphone size. The photoacoustic cell structure design and assembly programs are also provided.The work designs and implements the corresponding system requirements weak signal measurement circuit which includes receiving amplifiers and processing control part. The signal required is very weak; it also gets a long measurement scope with low frequency. Based on this situation, the lock-in amplifier circuit, 24-bit high precision Sigma-delta-ADC, low-noise zero-drift op amp and differential transmission between the electric boards are used in this system.The gas measuring system has completed carbon dioxide, carbon monoxide, calibration experiment methane, ethane, ethylene and acetylene all six gases detection. The gas detection sensitivity can be as low as 10 ppm, the system has a good linearity calibration with stable operation.