Research On Optical Fiber Methane Measurement System With High Resolution

Developing the sensing system, which can detect and control inflammable, explosive, poisonous and harmful gas, has been an urgent problem to solve for domains such as coil, oil and environment monitoring at present.The paper studies optical fiber methane measurement system with high resolution, based on spectrum absorption. The system has advantages of high sensitivity, fast responding speed, large dynamic range, freedom from inflammation, explosion, and electromagnetism interfere, and real time detection from distance. The system can be used to monitor environment and monitor gas on line in formidable conditions.The paper analyzes the theory of near-infrared selective absorption of gas and gets the academic base of the methane gas measurement by absorption theory. The absorption spectrum of methane is confirmed and the spectra characteristic which is fit to low-loss optical fiber for distance transmission is also discussed.According to Beer-Lambert Law, the resolution mathematical model of gas concentration detection system based on spectrum absorption is built. From the mathematical model, the factors influencing resolution are analyzed. The methods of enhancing resolution are discussed from gas cell, coupling efficiency of light path, light source, etc.Optical fiber methane measurement system based on spectrum absorption is built, and harmonic wave detection based on DFBLD is studied. Driving circuit of LD, temperature control circuit, Preamplifier circuit, band filter and Phase-locked amplifier circuit are designed. Harmonic wave signal reflecting methane gas concentration is collected by Labview, and the signal is analyzed, which can display methane gas concentration visually. The overall experiments of gas detecting system have been carried out, which include characteristic parameter experiment, optical fiber chain loss experiment, gas absorption experiment and display comparing experiment, etc. The experiment results show that the designed spectrum absorption optical fiber gas sensing system can effectively detect the concentration parameter of the measured gas and has high resolution. The feasibility of the spectrum absorption optical fiber gas sensing detecting system has also been verified.