Improvement On Calculation And Detection Method Of Particle Scattered Light Distribution

Laser particle sizer which based on Mie scattering is widely used in particle sizemeasurement. Accurate particle scattered light data (“scattered light distribution”) isone of the basic conditions for the design and manufacture of high-precision laserparticle sizer. This contains two aspects, one is the priorly accurate calculating of lightenergy distribution (“light energy distribution matrix”) of particle (from submicron tothousands of microns) on the particular instrument and the other is the accuratemeasuring of light energy distribution. At present, difficulties and problems remain inthese two aspects. The main reasons are as follows: first, the rigorous electromagneticwave theory (Mie scattering theory) based scattered light intensity formula is amultiple infinite series, while the energy function is the integrator of light intensity ondetection surface, leading to complicate calculation; second, the measurement of lightenergy distribution is influenced by various factors like the electronic noise,background light and the total reflection of the optical system. This paper, studies onhow to improve the accuracy and stability of the measurement of laser particle sizer,are carried out according to the existing problems in laser particle sizer.Main work and innovation are as follows:1. By the study on Mie theory, a new rectangular detector integral method tocalculate the light energy is presented which have enough accuracy and greatly reducethe computing time in normal incidence light path and oblique incident light path.2. Factors which affect the accuracy of the light energy distribution matrix areassessed.3. The accuracy and stability of the measurement of the OMEC existing laserparticle sizer is improved by the use of new energy distribution matrix. In addition,the abnormal moving of the main peak of light energy distribution is observed, theimpact of the abnormal moving on particle size measurement is then analysed and thesolution to reduce the impact is proposed.4. Through theoretical simulation and experiment, the adverse influence of thecurrent direct subtract way to eliminate background on particle size measurement isanalysed and confirmed, then the improved data processing methods is proposedwhich can effectively solve the scattering signal loss problem of large particle caused by the subtraction method.5. The oblique incident light path is established and the advantage of thisoptical path for the measurement of sub-micron particles is proved.