The Mine-used Methane Detecting And Alarm Device Based On NDIR

China is a coal mining and consumption power. Coal resources has irreplaceableimportant position in the short term, as one of the most important energy in industrialproduction, In recent years, the coal mine accidents occur frequently, and caused greatcasualties and property losses, in which gas explosion accounts for a large part of thereasons of the accidents. The main composition of the gas is methane, which is acolorless, odorless material. A certain concentration of methane can make people lack ofoxygen and suffocation. When the environment concentration reaches about5%in air, itwould explode. Therefore in the coal mine gas concentration accurately be detected andalarmed in time is very necessary.Electrochemical device is the most commonly used methane concentration sensorin coal mine based on principle of exothermic catalytic combustion now. The sensorssensitivity is low, its accuracy is poor, its measuring range is small, and it gets easilyaged and poisoned. It requires constantly calibration and it has short service life. Inrecent years, the methane sensor based on NDIR have development to a certain degree,it overcomes the limitations of the catalytic elements to some extent. But due to thecomplex signal processing of the infrared absorption gas sensor, and the high prices ofstable devices, it has not gained popularity in the use of coal mine methaneconcentration detection.The research will lead to a low-cost methane concentration detector used in coalmine. This equipment is based on the theory of NDIR. It has main functions of real-timeconcentration detection, sound and light alarming, two-wire output signal, and theuser-defined remote control setting.I designed and developed the cut off in concert withthat at the same time. According to the requirements of cost control, I chooseSTC12C5A60S2microcontroller as the core processors. The display parts according tothe requirements of the coal mine safety production use three digital tubes. The outputsignal of PWM is the square wave signal. I adopt the integration of the infraredreceiving head and remote control in control segment, which is convenient for users toset the alarm limit.I select infrared illuminant IR715as the light from a Germany company calledPerkinElmer, it has high reliability, and its stable working life can reach40000hours.The light source is the most commonly used in the infrared gas detection. I selectPYS3228-TC Pyroelectric sensors as the detector. Pyroelectric Detector infrared sensorunder the action of modulated light source, can output sine signal after amplified.PYS3228can work under normal temperature conditions, which do not needrefrigeration. It has low price, good stability, and high cost performance. In this paper, I expound the design of signal processing circuit of the detector indetail. I put forward the design thought of original amplifier, rectifier, and filter incomparison of similar products. I make the targeted design combined with theenvironment of coal mine and complete the hardware design and the software program.Then I focus on introducing the intrinsic safety and explosion-proof related knowledge.Finally I complete the system experiments and error analysis.