Optimization Design Of The Photoacoustic Cell For Wavelength Modulated Photoacoustic Detection System

Safety problems of large power transformer are the key to maintain the normal life of residents and industrial electricity smoothly. Therefore, the on-line detection on the safety of large oil filled type power transformer is very necessary and important. At present, an important means of monitoring oil filled transformer running state is the on-line detection of dissolved gas in transformer oil to judge the fault types and the operating state of the power transformer, avoiding unnecessary losses of the human and financial resources and inconvenience to the people's life due to power failure.Photoacoustic spectroscopy is a technology with high sensitivity, high resolution and large dynamic range. It is capable of on-line quantitative measurement for multiple gases. The design of photoacoustic cell is an important part of photoacoustic spectroscopy. It is the carrier of the photoacoustic effect. The structure and the size of the gas cell have a direct influence on the detection sensitivity. In this paper, based on the principle of photoacoustic signal, the relationship between the amplitude and the gas concentration is established, which provides a basis for the structure design of the resonant and non-resonant photoacoustic cell.For noise characteristic of wavelength modulation and second harmonic photoacoustic signal detection technology and the beam characteristics of the excitation source, based on photoacoustic cell design theory, this paper elaborated on the relationship of the structure, size, material of resonance and non- resonance photoacoustic cell to the light acoustic signal amplitude. The relationship of resonant frequency of the resonant photoacoustic cell, the quality factor and the cell constant to the resonant cavity size was simulated by using MATLAB software, which determines the length of the longitudinal first-order resonance photoacoustic cell cavity is 120mm, radius 2mm; buffer chamber length of 60mm, with a radius of 6mm; determining a non-resonant photoacoustic cell length of 40mm, the radius of 3mm. And using Inventor software for both photoacoustic cells drew three-dimensional models and parts design drawings.Compared with the cell constant and the experimental measurement results of photoacoustic cell (cavity length 100mm, the radius of 5mm; buffer gestation is 50mm,15mm radius) which is modulated by the intensity mode, the theory predicts C2H2 detection sensitivity of the optimization design of photoacoustic cell can be improved by more than twice as high. Also the amount of sampling of the measured gas is reduced greatly. Meanwhile, the optimization design effectively improves the overall performance of the wavelength modulation acoustic optical system.