Research On The Volatile Organic Compounds Detection Technology And Experiment

Volatile organic compounds(VOCs)gas not only has great influence on the ecological environment,but also has great harm to human health.Therefore,VOCs gas detection has become an important part of air pollution monitoring.At present,most VOCs detection devices that already exist in the market are developed based on imported detectors.Some detection devices have problems of poor repeatability,poor stability and low detection accuracy.Therefore,it has important social and economic benefits to carry out research on VOCs detector and develop VOCs detection system suitable for actual detection requirements.Based on the analysis of VOCs detection methods and detector development at home and abroad,the photoionization detector is selected as detector of VOCs detection system.In terms of theoretical research,the principle and technology of photoionization detection are analyzed and studied.Based on the research on the principle of photoionization detection,the key parameters affecting photocurrent are analyzed and obtained.In terms of technical research,multi-physical field simulation software is used to simulate and optimize the gas path structure,electrode plate spacing and inter-electrode plate voltage in the ionization chamber of the photoionization detector.Based on this,the photoionization detector is developed.According to the characteristics of weak induced current and easy interference of the photoionization detector,a signal amplification circuit for nanoampere current output is developed by adopting transimpedance amplifier and multi-channel analog selector,combined with guard ring,guard layer and shielding technology.At the same time,a high-frequency driving circuit suitable for photoionization detector is developed to realize the excitation of vacuum UV lamp.In terms of experiments,a VOCs detection control system is developed based on STM32F103C8T6 microcontroller.In order to meet the measurement requirements of online detection,the C/S architecture is used to develop the upper computer software system,completes the construction of database server and the development of client and server software,and realizes remote detection and control.Based on the calibration of the system,the performance of the system is verified by experiments.The experimental results show that under the same conditions,the relative standard deviation,absolute error and average deviation of repeated measurement results for single gas are 3.10%,-0.045ppm and 0.025ppm,respectively.The relative standard deviation of the measured results is 4.108%for long-term baseline measurement.In the linear experiment,the correlation coefficient of the fitting curve is 0.992,and the determination coefficient is 0.984.The detection limit of toluene in the system reaches 50ppb,which can meet the measurement accuracy requirements,and the system can be used for actual detection.