Oxygen Concentration Detecting By Using Laser Diode Wavelength-Modulation Technology

Oxygen is an important gas in daily life and industry. Looking for a practical, accurate method and equipment for the detection of oxygen concentration in the industry surroundings, especially in the exhaust gas of boiler, has significant practical sense for improving the production efficiency and combustion utilization ratio, and reducing the environment pollution.The state of oxygen concentration detection was comprehensively surveyed in this thesis. Merits and demerits of each method and equipment were commented. Then, the idea that detecting oxygen concentration by using laser diode wavelength modulation and harmonic signal treatment was proposed.The characteristics of oxygen absorption spectrum were emphasized based on the theory of gas absorption spectrum. This work was helpful to set up and actualize detection scheme.The followings were deeply and comprehensively discussed in this thesis: laser diode characteristics, controlling of the wavelength modulation of laser diode, detecting of the oxygen absorption, treatment of the harmonic signal and selection of the parameters, improvement of the signal to noise ratio and the test precision, etc. An experimental system has been set up based on the detection theory. The Virtual Instrument technology was introduced in the system, which is convenient for detection controlling and data processing.The experiments for actual oxygen concentration detecting had been carried out repeatedly and the some satisfied results had been acquired. The experimental system runs well. The output data from the experimental system had a good repeatability and a good linear relation with the oxygen concentration. This work provided the theoretic and experimental basis for further research and practice in our future work. This is also the first time attempt to realizing oxygen concentration determination by using spectrum absorption method domestically.