Research On Particle Size Measurement Method Of Suspended Particulate Matter In Water By Static Light Scattering Method Based On CMOS Detector

The suspended particulate matter in the water body will cause serious damage to the water environment,leading to the death of fish,shortening the service life of the reservoir,increasing the cost of water environment treatment,and polluting the air.Therefore,it is very important to realize the particle size measurement of suspended particulate matter in water bodies,which can provide data reference and technical guidance for water quality monitoring,water body protection and water environment governance.The static light scattering method has gradually become the most widely used technology for particle size measurement of suspended particles due to its advantages of high degree of automation,fast measurement speed and wide range.The traditional static light scattering method for particle size measurement of suspended particles uses photodetector arrays to collect scattered light signals.Such detectors have problems such as the need to adjust the center spot,complex mechanical structure,custom photodetectors,high cost,and complex process.In contrast,CMOS detectors have the advantages of not needing to adjust the center spot,low development cost,and high reliability.Therefore,the particle size measurement technology of suspended particles based on static light scattering method based on CMOS detector has gradually become a new research trend.However,the suspended particle size measurement system based on CMOS detector needs to be further improved in terms of measurement accuracy and measurement upper limit.Aiming at this problem,based on Mie’s scattering theory,this paper deeply studies the method for improving the measurement accuracy and measurement upper limit of suspended particle size based on CMOS detectors.The main work and research results are as follows.(1)From the perspective of demand and practical application,the background and research significance of this thesis are expounded.The research status of particle size measurement of suspended particulate matter in water based on CMOS detector is introduced,the existing problems are analyzed,and the research direction and target are determined.(2)An experimental system for particle size measurement of suspended particles in water by static light scattering method based on CMOS detector was constructed,and the collection of scattered light signal images of suspended particles in water was realized.In this paper,standard samples with particle sizes of 9.86μm,120μm,500μm and 1000μm were used for experiments.The results show that the scattered light images of the collected standard samples are clearly visible;as the particle size increases,the scattering angle of suspended particles decreases,It is consistent with Mie’s scattering theory.Experiments show that the experimental system for particle size measurement of suspended particles in water by static light scattering method based on CMOS detectors designed in this paper can complete the collection of scattered light signals of particles to be measured.(3)The Mie scattering theory model is studied,the light energy coefficient matrix and light energy distribution vector are deduced,and the particle size inversion of the scattered light signal images of the collected water suspended particles is carried out by using the Chahine inversion algorithm.The experiments were carried out with standard samples with particle sizes of 9.86μm,120μm,500μm and 1000μm respectively.The results show that the maximum relative error of the measurement results of the 9.86μm standard sample is 17.2%,and the error is relatively small;the maximum error of the experimental results of the 120μm standard sample is 56.9%,the error is relatively large;the D10 and D50 errors of the experimental results of the 500μm standard sample are relatively large,52.7% and 31.9% respectively;the relative errors of D10,D50 and D90 in the experimental results of the 1000μm standard sample are 63.6%、58.4%.and 45.6%respectively,both exceeding the reasonable range.Experiments have shown that the traditional particle size measurement method based on CMOS detectors has high accuracy when measuring suspended particles with a particle size of several microns to tens of microns;however,when measuring suspended particles with a particle size of several hundreds of microns,the accuracy However,for suspended particles with a particle size close to millimeters,there will be serious errors in the measurement results of traditional methods.(4)Aiming at the problem that the traditional background subtraction method has a large error in the particle size measurement system based on CMOS detector,a method based on baseline subtraction is proposed to correct the background interference and improve the measurement accuracy.The standard samples with particle sizes of 9.86μm and 120μm were used to compare the measurement results of the direct subtraction method and the baseline method.The results showed that,compared with the direct subtraction method,the relative errors of D10,D50 and D90 of the 9.86μm standard sample measured by the baseline method decreased from 17.2%,10.0% and 0.1% to 11.6%,3.4% and 0.1% respectively;the 120μm standard sample The relative errors of D10,D50 and D90 decreased from 56.9%,17.2% and 8.1% to0.4%,0.8% and 2.8%,respectively.The experimental results show that the baseline method can improve the accuracy of particle size measurement of suspended particles in water by static light scattering method based on CMOS detector.(5)In view of the problem that the traditional measurement method cannot obtain the correct light energy distribution curve of suspended particles in the experimental system based on CMOS detectors,resulting in a lower upper limit of the particle size measurement of suspended particles,a method of fitting the light energy distribution curve combined with partition measurement is proposed.method,the upper limit of the measurement of the experimental system was increased to 1000μm.Using 500μm standard sample and 1000μm standard sample to conduct experiments,the results show that the maximum relative error of 500μm standard sample is 13.9%,and the maximum relative error of 1000μm standard sample is 25.5%,both within a reasonable range.The experimental results show that the method of fitting light energy distribution can greatly improve the upper limit of particle size measurement of suspended particles in water by static light scattering method based on CMOS detector.In this paper,the background noise is removed based on the baseline method,and the accuracy of the system measurement is improved;the method of fitting the light energy distribution is used to improve the measurement upper limit of the system.The research provides a method,which is of great significance to the particle size measurement and monitoring of suspended particulate matter in water.