Study On The Field Calibration Technology Of Vehicle Exhaust Remote Sensing System

Vehicle exhaust remote sensing monitoring systems are widely used to screen highemission vehicles.Due to the inherent characteristics of the system and the impact of outdoor environment,the measurement data of the exhaust remote sensing monitoring system will have different degrees of measurement errors,The remote sensing monitoring system for vehicle exhaust should be regularly calibrated.At present,the calibration of the national standard for the vehicle exhaust remote sensing monitoring system of mainly relies on the separate calibration of its main modules such as gas measurement and velocity acceleration in the laboratory to infer the measurement error of the calibrated objects.Without considering the impact of on-site measured environment and vehicle driving conditions on exhaust measurement results,it cannot truly reflect the measurement error of the exhaust remote sensing monitoring system.In this study,a feasible on-site calibration method is proposed based on the existing calibration methods and the actual operation of the motor vehicle exhaust remote sensing monitoring system.In order to overcome the impact of on-site environmental factors and gas turbulence diffusion on the test results,a closed gas chamber was used as the stable test object in the on-site calibration experiment.During the experiment,standard mixed gases were introduced into the closed gas chamber to simulate the exhaust gas of different component concentrations.The gas chamber is fixed at the tail of the mobile calibration device,and transparent calcium fluoride glass is installed on both sides,making it convenient for the calibrated object,namely the telemetry system,to conduct on-site testing.At the same time,a high-precision gas analyzer is used as an on-site calibration device to carry out calibration experimental research.The main research contents are as follows:(1)The quantum cascade lasers with narrow linewidth are used as the light source.Based on the spectral measurement technology,a high-precision gas analyzer with higher sensitivity and faster response speed is designed as the on-site calibration device.The measurement accuracy and measurement uncertainty of the gas analyzer were systematically tested and analyzed.The results show that the relative error of the gas analyzer for the concentration measurement results of each component in the closed gas chamber is less than 2%,and the measurement uncertainty is less than 1.7%(k=2).The relative error and measurement uncertainty of the gas analyzer meet the accuracy requirements for calibration instruments in national standard(relative error less than 3%,measurement uncertainty less than 2%),which can effectively carry out the calibration of the concentration measurement module of the exhaust gas remote sensing monitoring system.(2)A mobile on-site calibration system has been developed using electric vehicle as a carrier.The hardware part is mainly composed of gas analyzer,closed gas chamber,gas path control module,velocity accelerometer and industrial computer.The upper computer developed a data acquisition and calibration system application software using C #.The upper computer uses a local area network to enable the industrial control computer to control the electromagnetic valve to introduce mixed gases of different component concentrations into the gas chamber(simulating exhaust gas).After the gas in the gas chamber stabilizes,the gas analyzer tests the gas concentration in the gas chamber.The industrial control computer obtains on-site data such as gas concentration,velocity,and acceleration of the mobile calibration device,and transmits relevant information in real-time to the upper computer.(3)Conduct on-site calibration experiments.The STGR660 model vehicle exhaust remote sensing monitoring system produced by a manufacturer was selected for calibration.Experimental tests were conducted on a mobile on-site calibration platform at different speeds(0km/h,10km/h,20km/h,30km/h,40km/h,50km/h)to obtain gas concentration measurement information of the calibration object under different moving speeds.The velocity and acceleration module of the calibration object was tested separately.Finally,error analysis and uncertainty evaluation were conducted on the measurement results of the calibration object.