Design Of Shallow Gas Detector Based On ARM

In the field of geological exploration and underground engineering, shallow gas brings a great trouble to the construction process. The leakage and eruption of shallow gas during the construction process will cause heavy casualties and damages to survey equipment, which may also result in a change of the physical properties of sediments and eventually lead to the unsymmetry or direct damage of exploration equipment or buildings. The main component of shallow gas is one of the sources of the global greenhouse effect, and its leak and eruption will cause environmental damages. Therefore, study on high-accuracy and nondestructive measurement method for shallow gas has become an urgent need of geological survey, underground construction and environmental protection in China.The research content of this paper is part of the "study of gas-bearing sediment model and acoustic measurement method in Gulf of Hangzhou". A shallow gas detector based on the technology of ARM and embedded Linux has been designed, which is used for research on the relationship between change of gas concentration and acoustic properties. Shallow gas detector can also be used to quickly detect the main gas concentrations in shallow gas region.According to an investigation report of underground harmful gas, The characteristics of shallow gas was researched, The demand of the shallow gas detector was put forward, The gas sensor based on Non-Dispersive infrared(NDIR) was used to detect methane and carbon dioxide, The microprocessor S3C2440 A and embedded Linux were used as the system platform. The schematic circuit and PCB have been finished, and the debugging work of hardware has been fulfilled. The dual channel ADC Linux driver has been designed to implement A/D conversion. Anti-pulse average filter algorithm has been designed for data processing, and the gas concentration data store function has been realized through the embedded SQLite database. Qt Creator was used to design an instrument interface which can show real-time concentration, historical data and the data curve respectively. Finally, the shallow gas detector access network through Wi-Fi, embedded Web server running on the system was used to interact with a Web browser. The Web page has been designed to achieve remote observation gas concentration data.Finally, the flow ratio mixing method has been adopted to prepare different standard concentration gases. Calibration of the instrument and repeated experiment has been performed on the shallow gas measurement experimental platform. The calibration curve of CH4 and CO2 obtained through the calibration experiment. The relative standard deviation of CH4 and CO2 is 1.16% and 0.78% obtained by repeated experiment. The measuring range of CH4 and CO2 was 0-5%VOL and 0-100%VOL respectively. When the fiducial probabilityis is 95%, measurement uncertainty of CH4 and CO2 was 2.52% and 2.16% respectively.