Design And Implementation Of Airborne Particle Counter Based On Light Scattering Theory

Airborne particle counter (APC) is designed to measure the number and size of airborne particles in clean room for the evaluation of air cleanliness basis. As an effective air cleanliness monitoring equipment, APC has a very important position in the application of cleanliness measurement technology. To improve the performance of APC, the optimal design of it has great significance.In the analysis and comparison of several particle measurement technology commonly used, and combined with the research of APC, a new program——FPGA+double MCU control mode is put forward. The program optimized the design of the hardware of airborne particle counter. The system has the characteristics of measurement accurately, compact circuit structure, strong anti-interference ability and small volume.Based on Mie's scattering theory, the subject comprehensively used relevant algorithms to analyze the characteristics of Mie's theory by Matlab programming. This issue simulated the light scattering colorful effect of spherical particles base on MiePlot, analyzed the effect of particle diameters, index of refraction and incident wavelength on the scattered light intensity, and elaborated theoretical basis of particle measurement. The scattered light flux collected by near-forward and right angle scattered light collecting forms is calculated separately, and the result is theoretical basis of APC design. The subject simulated scattered light flux of right angle collecting forms based on Matlab. As illuminated by a linearly polarized light, the extreme of collected scattering light flux is connected with the angle between the center of detector and polarization, and simulation results provide the basis for optical sensor design.The subject completed APC's hardware design. Hardware design including:signal conditioning circuitry, FPGA counting circuit, double MCU control module, memory module, serial communications circuit, display and keyboard inputting module and power supply circuit.The subject also completed APC's software design. Software design including: multi-channel pulse counter design based on VHDL, the software design of double MCU control part. UCL computing function is increased in software design.The experiment results show that APC's self-purification time, measurement discrete degree of single particle and other related indicators meet national standards. For the 0.5 micron particles, the instrument has higher count sensitivity.In addition, the thesis also completed error analysis of Experimental results. APC's measurement Upper limit of particle concentration is analyzed and calculated according to the technical parameters of optical sensor. Finally, research of this thesis is summarized and given the direction of further study and improving.