Research On Signal Processing System Of Laser Doppler Flow Velocity Measurement

The laser Doppler velocity measurement system involves multiple disciplines such as optics,electronics,and computer.Among the universities across the country,some colleges and universities offer laser Doppler velocimetry related experimental courses.However,domestic related mature products are relatively few,while foreign products are expensive,resulting in extremely high costs for teaching related experimental courses.At the same time,the signal processing system affects the accuracy of the laser Doppler velocity measurement system to a certain extent.Therefore,it is of great significance to carry out research on the signal processing system of low-cost laser Doppler flow measurement instruments for experimental teaching.This thesis is aimed at the needs of the laser Doppler velocity measurement system for experimental teaching,based on the analysis and investigation of the laser Doppler velocity measurement system,especially the current research status of the signal processing system,execute the research of laser Doppler flow velocity measurement signal processing system,completed the design and debugging of the circuit board,built a laser Doppler flow velocity test platform,finished system measurement and analysis.The main research work is as follows:(1)Comparative analysis of three commonly used laser Doppler velocity measurement systems to measure optical path modes and typical Doppler signal processing techniques,designed the overall scheme of the system.(2)Designed a hardware circuit processing scheme,completed the design and debugging of the front current-voltage conversion circuit,amplifying and filtering circuit and other circuits,the collection of scattered light signals is realized.(3)Designed a signal processing scheme of FFT + phase difference correction algorithm,using FFT to get the Doppler frequency shift value,and using the phase difference correction algorithm to correct,completed the software design of the host computer,realized real-time digital processing of Doppler signals and display of flow velocity measurement results.(4)Carried out the simulation calculation of particle followability in the fluid,explored the velocity relationship between silicon carbide tracer particles and water flow,the effects of silicon carbide tracer particles of different diameters and different total amounts of silicon carbide tracer particles added to the water on the scattered light signal were explored.(5)Built a laser Doppler flow velocity test platform,completed the test and analysis of the system,in the flow velocity measurement range of 0.56 ～ 1.20m/s,relative measurement error is better than 4%,the linearity is 0.99464,satisfying the requirements of teaching experiments.