Design And Research On The Portable Ir-Absorbing Methane Detecting Instrument

In the process of building new countryside in China in recent years, energy has become a prominent issue. Biogas energy, as a clean non-polluting bio-energy, becomes the first choice of energy construction in rural areas. In recent years, China has made some progress on the construction of biogas projects and supported biogas service system. In the system of biogas technology service, the detection of the methane concentration is an important part of the judgment and excludability to the digester failure,so methane detection method and the development detection instrument is very necessary.This project aims to study the methane detector features to applicate to rural digesters, with its functions including methane gas concentration and the concentration of the ambient temperature detection and audible, and visual alarm equipment, and relevant gas analysis equipment and signal processing devices.The main work is as follows:(1) Analyzing the application of the methane detector in the biogas system, clearifying the object of research, and determining the way to infrared methane detection which takes infrared absorption as its principle. Clarifying the specific functions and parameters of the infrared methane detector according to the specific requirements of rural marsh gas detection.(2)Introducing the basic principles of infrared methane detector briefly. Selecting IR715infrared lamp and PYD212infrared pyroelectric infrared detector as a detector sensor excitation light source and signal receiver. Designing sealed chamber for portable instruments based on the basic principle of infrared detection of methane.(3)Selecting the microprocessor of MSP430F149as the instrument. The light modulation circuit is designed to modulate infrared light. and the signal conditioning circuit, process amplifying and filtering of the detector output signal. Designing a miniature pump equipment to the device according to the characteristics of the sealed chamber.A keyboard circuit and the temperature detection circuit were included in hardware circuit and the LCD circuit.(4)The functional modules of the instrument software are designed, and the program is built for the IAR Embedded Workbench IDE, written in C language. Many devices are designed in the program, including a light modulation procedure design, sampling procedures, the relay delay procedure, temperature testing procedures and keyboard functional programming.(5)The curve of infrared sensor output value and the gas concentration is figured out through the calibration experiments, and fitted the specific equation. The resulting equation is written to the MCU, as a formula to measure methane gas. Then the error analysis and parametric analysis are conducted.The infrared absorption of methane detector is produced by the experiment, and can accurately detect the concentration of methane gas,namely, a resolution of1000ppm, full scale accuracy of±8.11%FS, response time of3seconds.