Development Of IR-absorbing Methane Detecting Instrument For Coal Mine Application

Methane has a significant absorption to IR radiation at a characteristic wavelength, and the absorption is related with concentration of methane. The IR-absorbing methane detecting instrument is designed by converting IR radiation to voltage signal, so the gas concentration is calculated. Using commercial IR-absorbing methane gas sensor-IR32BC, reasonable light source modulation circuit and signal handling circuit are designed; MSP430F149, which is a 16-bit SCM( Single Chip Microcomputer), is taken as the core of the instrument. Sampling of peak value of sine wave, digital filtering and concentration calculation etc are completed. With the SCM, six extra peripheral modules such as temperature monitoring, LCD display, data storage, serial communication, standard analog output, alarm with light and sound are also designed, and the functions are realized through programming with MSP430F149. While the detected gas concentrations are over the warning limit, which was set before, light and beep alarm signal is generated. Important data such as warning limit and latest concentrations are saved into EEPROM in case of power break. It is convenient to connect the instrument with other equipments because of the 4～20mA standard analog output, besides the distance of signal transimmision is lengthened at a certain degree. With the serial port RS-232, the instrument sends data of concentrations and origin signal to computer, all the data are stored in datasheets with database technology to meet the need of sampling and processing mass data when testing.Under laboratory conditions, the instrument is tested among the range of 5%. The result indicates that, the resolution of the instrument is 500ppm, and the accuracy is±733ppm, within certain error, the instrument has good repetition.On the basis of above work, IR-absorbing methane sensor is studied and designed, two key factors such as modulation frequency of light source and length of gas chamber are determined with experimental method. The performance of the sensor such as response time, stability, sensitivity are also tested and analyzed.