Research On Key Technologies Of Oxygen Analyzer Based On TDLAS

In the industrial production field of petrochemistry,biochemical pharmacy,iron and steel smelting,and some others,the oxygen concentration determines not only combustion efficiency but also the composition and content of the exhaust gas.To monitor the oxygen concentration in real time is helpful to optimize the combustion process and improve production quality.Meanwhile,it’s very meaningful for environmental protection and production safety.On the basis of analyzing common methods of detecting oxygen concentration and combining with the existing technology all over the world,the whole project of oxygen concentration measurement system has been designed in this thesis,which is based on TDLAS(Tunable Diode Laser Absorption Spectroscopy).And some of the main technologies were discussed and analyzed.Firstly,based on analyzing the characteristics of the oxygen absorption lines and the theory of Lambert-Beer’s law,the technical principle of TDLAS applied to oxygen concentration determination is derived and analyzed.Thus.the overall design scheme of oxygen analyzer system is formulated and simulated using Matlab.Based on this,this thesis mainly designed circuits for the laser source and detector.In the section of laser source,the temperature control circuit based on LTC1923 was designed to control temperature of tunable semiconductor laser,with the purpose of locking the wavelength in the center of the oxygen absorption lines.And then,the driving circuit for laser diode and modulation signal generating circuit were designed.The later generates a high-frequency sine wave and a low-frequency sawtooth wave,which superimpose upon the driving circuit to tune the injection current of the laser for wavelength modulation.In the signal processing unit of detector,current-to-voltage conversion cu-cuit and filter amplifier circuit were designed to preprocess the signal received by photodiode.Then,two lock-in amplifier circuits based on CD-552R3 and two reference signals generating circuit with 90° phase difference were designed to demodulate second harmonic signal containing the information of oxygen concentration.At the same time,the influences of the phase difference between the testing signal and the reference signal on the harmonic signal were eliminated.Finally,these circuits were verified by building a systematic testing platform.Based on the detailed theoretical analysis and program design,the feasibility of this system was demonstrated through simulation analysis.The test results showed that the scheme and circuits designed are able to complete the detection of oxygen concentration.This may be employed in the further study of oxygen concentration measurement.