Research On Optoelectronics Detecting System Of Methane Concentration

Gas explosion has become one of the topmost causes of Chinese coal mines' disasters, the important factors are various, such as using unqualified, not adequate,low sensitivity, overdue devices or equipments. As far as the gas explosion itself is concerned, the three necessary conditions should be met:1). the concentration of the methane inside the coal is between 5% and 16%; 2). the high temperature source(>650℃) exists in the gas explosion sensitive period; 3). the oxygenous concentration is more than 12%. About the third condition, it is always satisfied because this is a prerequisite requirement for people to work and stay in the coal mine. Therefore, how to avoid the gas gathering to reach the critical concentration and stop ignition source is the most important methods to prevent the explosion. The fire resources is rather difficult to eradicate due to the machines, electric appliances using in the mine, thus the key important method to prevent the explosion falls on how to detect the gas concentration timely and precisely.For this, in this dissertation, two systems were designed: the distributed methane detecting system and the portable methane detecting system. The distributed methane detecting system is designed based on light interfence theory and Beer-Lambert law and using CCD to collect the intensity variations of the interfence fringes to obtain back the concentration of the Methane. On the other hand, the portable detecting system for the operators can be used to detect the gas concentration on the real place and real time and send out the alarming signal, both the vocal and the light, immediately. The two designed systems are featured as the followings:1) The methane concentration is obtained by detecting the intensities of the interference fringes, not calculating the movement of the interference fringes. This detecting method avoids withereding the detectors in a new envoriment, also reduces the errors brought about people's reading the movements of the interference fringes.2) The two interferometers were designed in these detecting systems, one is acted as the measurement interferometer which is composed of two lights, one light is through the standard gas cell ,the other light is through the methane; and the other interferometer is used as reference interferometer, and the two lights both are exposed in the methane. The reference interferometer can be used to compensate the measurement tolerances caused due to the optical resources and the outer environments' fluctuations, thus the detecting precision can be further improved.3) The simple structure of the gas cell and without using the blast pump , the whole system can operate stably.4) The distributed gas concentration detecting system is developed based on CCD image technology and the LabVIEW platform, and there are functions of the real-time data collecting, analyzing, displaying and also the long-distance data communication, save and playback. And it also provides that data used to analyze the gas concentration variation status systematically and scientifically.5) Chip CPLD (EPM7064 for detail) is adopt in the portable detecting system to generate the precise time sequence signal for CCD, thus the system avoids to use large quantities of electric components. At the same time, the ARM7TDMI-S(LPC2220) featured fast processing speed, rich connectors was used to process the video signal output from CCD. And also the system is with functions of displaying the methane concentration on the LCD, giving sound and light alarms and downloading the data from the networks etc..6) The detecting systems are characterized as high stability, good explosion preventing capability, long life time etc., and meet the requirements of the issued by the nation.