Study On Key Technologies Of Online Laser Particle Size Measurement System

Particle size and its distribution are employed as the critical parameters to estimate and characterize the qualities and performances of the products.As the level of automation in industrial production increases,the demand for online monitoring of particle size distribution is becoming more and more urgent,and the requirements for the accuracy and stability of measurement results are constantly increasing.Due to the fast measurement speed and no contamination to the measured samples,the online particle size measurement technology based on the light scattering method has great advantages in real-time monitoring.Online laser particle size measurement also need to solve the problems of continuous sampling,more reasonable optical parameters configuration,optimized data inversion algorithm,etc.This paper studied the key technologies of wet online laser particle size measurement system.1.The light scattering mechanisms of online laser particle size measurement were studied: the numerical solution methods of two light scattering models,Mie scattering and Fraunhofer diffraction,were analyzed.By comparing the intensity patterns calculated by Mie scattering theory and Fraunhfoer diffraction theory,the application conditions of Fraunhofer diffraction were discussed deeply from two aspects of particle size and scattering angle respectively,which provides a theoretical basis for the study of the inversion algorithm.2.The sampling and dispersion devices were designed: the sampling tube was used to perform sampling on the original product of particles to be tested in the production pipeline;the ultrasonic device and the agitator were to realize the sufficient and rapid dispersion of the sample particles in the medium;the three peristaltic pumps realize the delivery of the original sample solution,the diluted sample solution and the distilled water,respectively.The original solution was judged whether it needs to be diluted by measuring its scattered intensity and if necessary,the dilution ratio was determined.3.The optical system parameters were optimized: the reasonable selection of pinhole size in the expanded and collimated beam system was analyzed.The relationship between the focal length of Fourier lens and the measurement range was studied.To avoid the effect of vignetting on the online laser particle size measurement,the maximum distance form the sample cell to the Fourier lens was derived.The linear array CCD was combined with the rectangular gradient neutral attenuator to receive the scattered light of the measured particles,which expands the dynamic range of CCD.4.The Chin-Shifrin integral transform algorithm based on the Fraunhofer diffraction theory for recovering particle size distribution was studied: for the selection of angular parameters of the algorithm,the effects of the angular truncation error and light intensity approximation error on the inversion results of the algorithm were analyzed respectively.The optimized selection criteria of the angular parameters were determined.The performance of the optimized selection criteria were verified by three aspects,which are comparing with other different angular selection criteria.,recovering the different particle size distributions by using the angular parameters calculated the optimized selection criteria,and determining the practicality of the optimized selection criteria by combining the linear array CCD characteristics.According to the balance relationship between the angular truncation error and the theoretical error of the light intensity on the inversion accuracy,the selection range of the optimal scattering light was determined.In this paper,the wet sampling and dispersing device was designed,the optical system parameters were optimized,and the Chin-Shifrin integral transform inversion algorithm was improved.The design of the online laser particle size measurement system was completed,which can meet the requirements of online measurement.