Study On The Measurement System For Aerosol Mass Concentration By The Particle Group Light Scattering Based On The FPGA

Aerosol mass concentration is one of the important parameters to evaluate the atmospheric environment. The real-time monitor of it is imminent, while the light scattering method of particle group has the advantages of fast, high precision and wide concentration range,as well as it can be measured online. In this paper,a set of aerosol mass concentration measurement system based on particle group's light scattering is studied and designed. In a word,the main work of this paper includes:A fractal model of inversing the aerosol mass concentration by using the amplitude distribution of condensate voltage signal is established, based on supposing the particle group is equivalent to an agglomerate particle when it passes through the laser. The model makes full use of the voltage signal amplitude of agglomerate particles and the signal number information, as well as the particle morphology factors, which can effectively improve the inversion accuracy.Based on the fractal model, a multi-channel circuit for collecting and processing signals is designed. The high-speed ADC is controlled by the FPGA for signal acquisition in the circuit, and STM32 is responsible for the relevant data processing and peripheral device control. In the signal acquisition circuit, the inversion speed of the system is effectively improved by dividing the non-uniform channels.Considering the wide range of light scattering method on measuring the aerosol concentration,a subsection method is presented to calibrate the parameters in the fractal model. The results show that the mass concentration obtained by the fractal model is in good agreement with that of the experiment, when the relative humidity is within 60% and the mass concentration is between 0.5 and 13.0 mg / m3.The average relative errors are 5.6% and 6.0%, respectively. However, the relative errors of the mass concentration inversed by voltage integral are 11.0% and 18.5%,respectively. The involved results show that the aerosol mass concentration is more accurate by using the scattered light signal amplitude distribution of the aggregates of particles.Under the condition of high humidity, the effect of relative humidity on the spherical particle's scattering coefficient is firstly calculated by using the Mie scattering theory. Then, based on PSO algorithm processing the relation between the relative humidity and aerosol mass concentration calibration parameters in fractal model is obtained by using the standard instrument at the same time with the experimental device of this paper. Based on which, the calibration parameters can be corrected in real time, and the experimental results show that the PSO algorithm can improve the accuracy of light scattering method inversion model for real-time measurement.In a word, the involved research of this paper is in line with the current needs of real-time monitoring of atmospheric environment, which has great significance to the prevention of air pollution and the protection of human health.