Research On In-situ Measurement Technology Of Particle Size In Seawater By Laser Scattering Method

The particle size measurement of suspended particles in seawater plays an important role in marine science.In the 1970s,the theory that the intensity distribution of light scattering of particles can be used for particle size measurement was first proposed,and the laser particle sizer began to develop rapidly on this basis.After several decades of development,LIS ST-100 produced in the United States has been widely used in marine particle size measurement.Domestic laser particle sizers are mainly used for powder measurement,but there is no laser particle sizer specially used for seawater particle size measurement.In this paper,the importance of particle size measurement in oceanography is analyzed in detail,the development status of laser particle size analyzer at home and abroad is described,and a special device for particle size measurement in marine environment is proposedIn this paper,based on the scattering principle,the derivation process and calculation process are introduced in detail.According to the principle,the design process of the optical path is carried out,the selection of each part of the optical path is completed,and the optical path system is successfully built.The particle size range of the system is 4?m-450?m.The light path system completes the acquisition of scattered light of particles,and the circuit system is designed for the collection of scattered light.As a bridge between the optical structure and the circuit,the detector transforms the optical signal into photocurrent Through the signal processing,input to STM32F303 for internal acquisition,and complete 32 channels of voltage acquisition.In addition,the power module,storage module and so on are also designed.Finally,the data acquisition and transmission process are completed through the writing of embedded program.The light path and circuit are designed to measure the scattering light of particlesThe scattering principle of the system includes Mie scattering and Fraunhofer diffraction.The application range of the particle size measurement system based on the two principles is limited.In order to obtain good measurement accuracy,the stability of the system is guaranteed through modeling and experimental analysis of the two scattering principles.The Mie scattering curve is also related to the refractive index,while the Fraunhofer diffraction is only related to the particle size,not to the refractive index Experiments show that Mie scattering and Fraunhofer diffraction have good approximation with the increase of particle size,and the coincidence degree between Mie scattering intensity curve and diffraction is better with larger refractive index.The results show that 90%of the light energy is distributed in the first three rings when the particle size is 200?m,and the light energy is distributed in each ring when the particle size is 10?m.