Research And Design Of On Line Dust Monitor Based On Forward Light Scattering Principle

Dust is an important source of fine particulate matter in the atmosphere.Real-time online monitoring of dust is conducive to effective prevention and control of dust pollution.At present,there are a variety of dust monitoring methods,among which the light scattering method has the advantages of strong real-time performance,high degree of automation,low cost,etc.,therefore it has many practical applications.However,the light scattering method is subject to various factors such as particle shape,particle size distribution,chemical composition and environmental humidity,and the optical lens is susceptible to particulate matter,thereby reducing the accuracy of the light scattering dust measuring instrument,stability.Based on the above status quo,the following studies have been carried out on the measurement of dust mass concentration by light scattering method:1.Based on the MIE scattering theory,a theoretical model for measuring the dust mass concentration by group particle forward light scattering method is established.The effects of key parameters of the system,particle refractive index and external environment humidity on the scattered light intensity were systematically simulated.The increase of dimensionless parameters will lead to the near-direct distribution of light intensity;the refractive index of particles will affect the distribution of scattered light intensity,and the influence of real part of refractive index is greater than The imaginary part;the environment humidity will affect the particle size and refractive index of the particles,so the design of the instrument should be considered to reduce the interference of environmental humidity.2.The forward light scattering method based on laser square wave modulation,circulating airflow protection and STM32 single-chip microcomputer is proposed,and the prototype development is completed.A 1 Hz 50%square wave modulated laser diode is used;a PIN type photodiode and a high precision op amp are used to build a photoelectric conversion circuit.The system has an 8 hour noise of less than 2 mV;the PWM modulation and the PID algorithm are used to stably control one sample flow and two The road sweeps the airflow,the maximum error of the gas flow rate is less than 0.03 L/min within half an hour,and the purge airflow protects the lens from pollution.The signal processing and module control system based on STM32 single-chip microcomputer is designed to realize the stable operation of the system.The heating dehumidification circuit reduces the interference of relative humidity;finally,the preparation of the lower computer program and the design of the upper computer are completed,the signal output and acquisition are completed,and the time resolution is 1 s,which satisfies the real-time online measurement demand of dust.3.Completed laboratory and field test and data analysis.The laboratory results show that the statistical correlation between the instrument and the light scattering particle monitor(Met One;ES-642)can be higher than 0.95;through the field experiment and the β-ray particle monitor(Landun Optoelectronics;LGH-01B)comparison,the test comparison time is ten days,the comparison results show that the correlation coefficient of the two is 0.78,the measurement error is low,and the accurate measurement of dust can be realized.