| Methane (CH4) is a kind of important greenhouse gases, of all the greenhouse gases, its concentration is only lower than carbon dioxide (CO2), it is very significant to raise the atmospheric temperature. The radiation intensity of the unit mole methane is 21～23 times of carbon dioxide, its contribution to global warming is about 15% of all greenhouse gases. The farmland is one of the main sources of emissions of methane gas, methane emission rate of rapid acquisition of farmland and emission flux of information is a key technology need to be solved. At present, the static chamber and gas chromatography method was commonly used, but it has the disadvantages of cumbersome sampling procedures, high cost and no real-time monitoring. It is difficult to meet the requirements of low cost and fast detection of methane in farmland. Considering the methane gas molecules can selectively absorb certain wavelengths of infrared radiation and the absorption intensity was positively correlated with the concentration of methane, this dissertation intends to use the infrared spectrum absorption theory for the quantitative detection of methane gas in Farmland. Designed the photoelectric detection system, combined with embedded technology using STM32F103VB as micro control unit and wireless remote communication technology, designed a farmland of methane gas concentration detection system, and realized the online monitoring of emissions of methane gas from farmland.First of all, focuses on the forming principle of the molecular absorption spectrum and infrared absorption principle and differential absorption detection technology, these theories will be as the theoretical basis of the design.Secondly, based on infrared spectrum absorption theory, the technology of methane detection system was designed. Due to the small amount of methane emissions from farmland and the signal to noise ratio is low, the differential absorption detection was used to improve the detection accuracy and save costs. In the optical path, the IRL715 infrared light source and PYS3228 pyroelectric detector were selected by the theoretical analysis and the performances of various types of light source and detector were compared, and the methane sensing system was realized by designing the structure of absorption chamber. In the circuit aspects, the circuit was designed based on STM32F103VB as micro control unit. Include system power supply, light source drive and modulation and signal processing, SD card storage, clock, serial communication module and other modules. In the software, through to the programming of embedded software program for STM32 to achieve access to the detector signal, then the methane concentration was obtained by operation. The server was designed with the software of the upper computer and the database was built. The collecting data through GPRS module uploaded to the server database, at the same time it was stored in the local SD card memory. In addition, built the web side based on the database. According to the above, the mentioned methane gas on-line monitoring system was designed.Finally, the experimental analysis of methane monitoring system was made. Firstly, system calibration experiments were made, including zero point calibration and methane gas absorption experiment, according to the experimental data fitting the system characteristic curve; then the test on the system performance was also made. The experimental results showed that the system had good repeatability and stability. Through the field monitoring experiment, it was proved that the system can meet the requirement of field monitoring. |
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