| Nano-particle size measurement is of great significance for the application and development of nano-technology.Dynamic light scattering method,as an important method for measuring the particle size and distribution of nanoparticles,is widely used in the field of nanometer measurement.In order to achieve accurate measurement of nano-particle size in the range of 1-1000 nm,a multi-angle dynamic light scattering measurement system based on FPGA(Field Programmable Logic Gate Array)is developed in this paper.The system can stably obtain particles with multiple scattering angles information,the main work is as follows:(1)Based on the principle of particle size measurement based on photon-related technology,a dynamic light scattering particle size measurement system is developed.A laser light source emitted by a helium-neon laser is vertically injected into a constant temperature liquid with cell containing sample particles.A photomultiplier tube is placed every 15~owithin the range of the scattering angle 0-180~oto complete the reception and conversion of the fluctuating scattered light intensity signal,to achieve multi-angle dynamic light scattering particle size measurement.(2)Aiming at the problems of missing numbers and multiple counts in high-frequency signal acquisition,a dual-counter switching method based on FPGA technology is proposed.Two counters that do not interfere with each other are used to complete continuous and seamless counting of pulse signals,ensuring parallel processing of acquisition and processing,making sure that no data is lost during the process;a large number of pulse count values are buffered through the DDR3memory,and the data is transmitted to the upper computer for high-speed and stable storage via the USB communication interface.(3)Based on the insufficient performance of linear and exponential correlators,a proportionally adjustable digital photon correlator based on high-speed signal acquisition is developed.The value of the autocorrelation function can be directly calculated by FPGA,and the upper computer can adjust the correlator channel ratio.The dynamic range is up to 10~5,which greatly improves the measurement efficiency of the system.(4)The particle size inversion calculation is realized in the host computer.A large number of polystyrene aqueous solution particle measurement experiments are performed by the system.The effect of different experimental parameters on the autocorrelation curve characteristics is studied,and the particle size measurement results of commercial boards are used in comparative analysis.The results show that the self-developed multi-angle dynamic light scattering measurement system can accurately obtain the particle size value,the measurement repeatability is better than commercial board and the difference is within 0.5%,which verifies the high stability and accuracy of the measurement system. |
