| The"13th Five-Year Plan"national science and technology innovation plan proposes to focus on the research of atmospheric environment pollution monitoring technology,and the development of atmospheric environment online monitoring equipment suitable for national conditions.Methane（CH4）,as the primary component of natural gas,with a content of more than 90%,is an important clean energy.As a colorless,odorless,flammable and explosive gas,CH4 leakage has brought some problems such as global warming,production safety accidents,environmental pollution and so on.Therefore,it is particularly important to monitor the atmospheric CH4concentration in real time and accurately.In addition,the CH4 sensor measured at a fixed position cannot meet the large-area atmospheric monitoring in the urban area.And traditional CH4 sensor do not have the function of publishing data through the Internet.Therefore,remote real-time data monitoring and mapping cannot be realized.In order to solve the above problems,in this thesis,a vehicle-mounted mobile mid-infrared CH4 sensor system enhanced by a real-time remote monitoring system for monitoring urban atmospheric trace CH4 concentration was designed.And key technologies and equipment are provided for real-time mapping of urban atmospheric CH4 concentration.The main research contents are summarized as follows:Firstly,the principle of infrared gas detection was studied.In order to expand the measurement range and improve the detection sensitivity,both direct absorption spectrum and wavelength modulation spectroscopy were used to detect the atmospheric CH4 concentration.In order to realize infrared absorption spectrum gas sensing with high precision and strong anti-interference ability,a mid-infrared CH4 gas molecular absorption spectrum was selected as the target spectrum.Aiming at the detection target of urban atmospheric trace CH4 gas,the spectral detection scheme of the sensor system and the vehicle-mounted mobile application scheme were designed.According to the detection scheme,the overall structure of CH4 sensor system was designed,including optical subsystem,gas pretreatment subsystem and electrical subsystem.And the working temperature and scanning current range of the laser were analyzed and determined.A compact and stable rectilinear optical sensor structure was proposed and the whole sensor system was integrated to meet the adaptability of vehicular complex environment.In addition,the modulation depth the laser was optimized.Finally,the main performance of the sensor was tested and evaluated.The experimental results of concentration calibration show that the linearity of the sensor system is very good.The detection limit is 4.10 ppbv（parts per billion in volume）with a 0.5 s averaging time and the optimal detection limit is 0.62 ppbv with a 54 s averaging time.The response time of the CH4 sensor is 1.92 s.Compared with the commercial vehicle-mounted CH4sensors,the developed vehicle-mounted mobile atmospheric CH4 sensor has a relatively advanced level in accuracy and stability.In order to realize remote,real-time and anywhere monitoring of atmospheric CH4concentration,an embedded remote monitoring system was developed.The system includes a network publishing terminal based on an embedded multi-core processor,a cloud server and an Android remote monitoring client.For the network publishing end,firstly,the hardware part was designed,including an i TOP-4412 embedded platform,a Wi Fi module,a GPS module and a touch screen module.The embedded Linux system was compiled and transplanted,and the corresponding drivers were designed according to the hardware.Finally,the software part of the network publishing terminal was designed,including the design of the flow chart,the compilation of each module program and the cross compilation of the software,so as to realize the functions of data collection,network publishing,local storage and human-computer interaction.For the cloud server,it was first configured and a Message Queuing Telemetry Transport（MQTT）broker was built to realize message transfer.A My SQL database was designed,and a background program to realize cloud storage was programed.For the Android remote monitoring client,the design included two parts:interface design and function code design.The design of the function code part adopted multi-threaded programming technology to realize the functions of CH4 concentration monitoring,Baidu Map positioning and historical data display.Finally,using the developed mid-infrared vehicle-mounted ppbv-level CH4 sensor remote monitoring system,the fixed-position and mobile atmospheric CH4 remote monitoring experiments in the campus of Jilin University were carried out,which proved that the system has long-term monitoring stability and good mobile sensing performance.Then,the vehicle-mounted mobile atmospheric CH4 remote monitoring experiment in Changchun City was carried out,which showed that the system has good practical potential and broad application prospects.The innovations of this thesis are as follows:A mid-infrared ppbv-level CH4 sensor has been developed to meet the needs of urban atmospheric trace CH4 gas detection.Based on an embedded multi-core processor,a cloud server and an Android mobile phone platform,an embedded remote monitoring system was developed by using embedded Linux technology,wireless communication technology,database technology and Android client technology,which realized the functions of CH4 concentration data and positioning data collection,storage,network publishing,remote monitoring and map mapping.The networking and intelligent of the sensor system was improved. |
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