Research On Optical Fiber SO₂ Detection System Based On The Theory Of Photoacoustic Effect

With the modernization of industry and the improvement of people's life, the consumption of fossil fuel, such as petroleum and coal, is being increased. Because of the equipment and combustion methods, more and more baneful gases are released into the air, which are harmful to people's health and life. Based on this fact, researching and manufacture a kind of new gas sensor with high sensitivity and real-time detection has an important theoretic and realistic significance.After comparing main advantage and disadvantage of all theories of gas concentration measurement, this thesis chooses SO2 as object to research a kind of SO2 concentration measurement apparatus on the base of theory of photoacoustic effect and the optical fiber phase modulated mechanism.Firstly, this paper introduces the molecule's structure, the molecule's spectrum and infrared spectrum structure of SO2, and then the theory of gas detection using photoacoustic effect is discussed. The design of resonant P.A. cell is one of the most important parts, including P.A. cell structure, first resonance frequency, optical reflection sets, and couple between optical fiber and P.A. cell, etc. Using CO laser as incentive source has many advantages, and optical modulating is discussed.After pin's noise and equivalent circuit are discussed, this thesis introduces technology and methods of signal management, including pre-amplifier and differential-amplifier, BPF, LIA, etc.At the end of paper, the system of photoacoustic spectrometer is proved by experiment.