Development Of Gas Optical Fiber Sensing Instrument For Coal Mine Application

The gas is one of the sources which are the major natural disaster in the coal mine. Fire damp explosion not only influences the normal production of the mineral, but also threatens to the safety of the coal mine workers seriously .It is very important to measure the distribution of methane concentration in real-time.This article is based on the principle of gas spectral absorption, develop the optical fiber gas sensor, take some industrialization experiment, to make sure that the system can be applied in the industrial field. In this article we focus on the research of the detection of CH₄ , and develop the optical fiber gas sensor which has realized the function that it can continuously detects the concentration of methane in the environment of excavating working face, wind laneway and so on. Besides, it can display the instant concentration, output the frequency signal which is proportional to the measured methane concentration, alarm at the threshold of limitation and so on. Our circuit design is safety in essence and we take verification to it, make sure that it can be used in many dangerous coal mines. In the coal mine safety monitoring system, the optical fiber sensor can be used with other coal mine safety monitoring systems, which are compatible.The main work in this article include the aspect as follows:1) Some research were done on the working principle of tunable diode laser absorption spectroscopy (TDLAS), use the wavelength modulation and harmonic detection technology to improve detection sensitivity, and based on the gas absorption peak that is selected, the DFB LD which wavelength is 1665nm is selected as the light source.2) According to the theoretical analysis, the light path and circuit were designed. The feeble signal is obtained by Four-Channel, Four-Quadrant Analog Multiplier MLT04, and the phase locked amplify circuit eliminate the effects of the phase difference between the test signal and the reference signal which causes by the delay of the optical fiber transmission and the circuit itself, and get the second harmonic amplitude information from the hardware directly. 3) In view of poor working environment for coal mine, the structure of the sensor's shell and the gas chamber were designed specially, and take waterproof and dust control measures for some important parts; in accordance with the requirements of national standard GB3836.4-2000, the circuit is safety in essence, and also the infrared remote control circuit, numerical code tube display circuit, sound and light alarm circuit are designed.4) Some experiments were done to the instrument, such as mechanical reliability, temperature stability and detection performance and so on. So make it sure that it can be suitable for coal mine use.5) Some experiments had been done in a coal mine, including the adaptive experiment of our system to the mine environment, the compatibility experiment of our system to the existing coal mine safety monitoring system and the long-term stability experiment of our system.