Design Of Harmful Gas Detection And Monitoring System For Urban Sewage Pipeline

The construction of the city water pipe corridor is accompanied by the development of the city,the increase of the safety accident of the water pipe corridor,so that design of monitoring system for the city water pipe corridor becomes the research hotspot.According to the project's requirement of monitoring the sewer,this thesis puts forward the design scheme of the sewer monitoring system based on LPWAN(Low-Power Wide-Area Network),which is capable of intelligent monitoring task of the sewer.The monitoring system of the water pipe corridor covers several modules.In this thesis,three main modules are designed: sensor monitoring module,front-end equipment communication module and repeater.The sensor module is designed based on MSP430,the main function of the sensor monitoring module is to monitor the flammable,toxic,harmful gases and water level information in the sewer,as well as the state of manhole covers;The main function of the front-end communication module is to send the data collected by the sensor to the repeater and to receive the work instruction sent by the repeater to control the sensor monitoring mode.The repeater has two functions: During the process of receiving information,the repeater is responsible for receiving the sensor measurement data carried by the high frequency signal and transmitting the data information to the network through the LTE module;During the transmission of the command,repeater receives the command from the monitoring center by the LTE module and sends the command to the front-end monitoring system via the high frequency signal.Short-wave antenna of the front-end device is designed,the antenna is a small loop antenna with a 20 cm diameter.The antenna is simulated by FEKO,simulation results show that the impedance bandwidth is 26.9-27.25 MHz with return loss more than 10 d B.And the adaptive impedance matching circuit of small loop antenna is designed by ADS.The FEKO simulation is used to study the performance of the antenna in installation environment,and installation scheme of the front-end equipment is obtained.The miniature dipole antenna for the repeater is designed,FEKO is used to simulate the antenna,and the feeder balun is designed for the antenna.The local oscillator frequency source is designed based on ADF4351 chip,output frequency of the local oscillator is 142.32 MHz,frequency stability is high,and phase noise is low.Three filters are designed with ADS.The three filters are based on the Butterworth filter and passband ripple is small.Completed the construction of the transceiver RF front-end system,transmitting gain is 15.26 d B,receiving gain is 13.35 d B.