Design And Realization Of Optical Fiber Methane Concentration Detecting System

In recent years, the coal mine gas explosion accidents happened frequently. It brings serious harm to the state and personal property. So it's essential to detect the concentration of methane in real-time. Currently we often use catalytic combustion of methane gas detection sensor, but this sensor has short life and need to calibrate the zero point and sensitivity frequently, also it used unsafe and inconvenient. With the development of optical fiber technology, the method based on the optical spectra absorption of methane gas sensor has so many advantages such as high sensitivity, litter affected by environmental factors, easy-to-network, and so on. So this method attracts more and more attention.The system uses the principle of differential detection optical spectra absorption. The light pass the envelope filter, gas chamber, comb filter, then we sort out the reference light and signal light. Then we use two detectors for detecting the two signals. Finally we obtain the gas concentration after data acquisition and processing.This article analyzes and selects the module of light source, sensor, detector, filters and data acquisition and processing. According to the principle of differential detection complete the design and development of optical signal detection circuit. Using PIN photodiode converts the light signal into the electrical signal. At the same time using two amplifier circuit, the first amplification is DC amplifier, the second amplification is voltage amplifier. Realize the amplification of weak signal processing and achieve the requirement of circuit design.According to the experimental data and conclusions, the system can be measured with high accuracy at low concentrations. When the concentration is less than 1%, the error is less than 0.1%. When the concentration is in 1% to 4%, the error is less than 0.3%. Also it has good stability and sensitivity, reaches the requirement of the experiment. Of course, the system still has deficiencies, and needs to test and improvement further.