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Optical System Design of a Portable Laser Doppler Velocimeter

Author: GongRenMin
Tutor: XieHongBo
School: Tianjin University
Course: Optical Engineering
Keywords: Laser Technology Photodetector Laser Doppler effect Digital Signal Processing
CLC: TN247
Type: Master's thesis
Year: 2010
Downloads: 209
Quote: 0
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Abstract


Laser Doppler velocimetry technique is the Doppler frequency of scattered light by detecting the fluid motion particles , and based on a linear relationship between the fluid velocity and Doppler frequency , to obtain the fluid velocity information . The spatial resolution can reach micrometers , the characterization flow rate of the Doppler signal light carrier , measuring fast dynamic response . As a non-contact measurement techniques , it can be used at high temperatures , toxic , corrosive fluid such as speed measurement without interference , and the fluid . In order to measure the flow rate of the industrial production fixed sources of pollution soot , this research project a portable laser Doppler velocimetry system based on a dual - beam mode , the system is composed mainly by the optical system and the signal acquisition and processing system . The role of the optical system is the fluid velocity information is modulated onto the optical signal , and to achieve the photoelectric conversion . The collimator using a semiconductor laser as a light source , The depolarizer dichroic prism isosceles right-angle prism , and a focusing lens to achieve a beam of the laser beam focus, the interference fringe is formed . Soot particles to be measured passes through the interference fringes , the scattered light emitted by the receiving lens , the pinhole diaphragm focused onto the avalanche photodiode (APD) , the to achieve Doppler optical signal detection . Signal acquisition and processing system consists of signal conditioning circuits , analog-to-digital ( A / D ) conversion circuit , a central processing unit , a data storage unit , and a variety of interface circuit . APD output of the first signal via the signal conditioning circuits for amplification, filtering , and then into a digital signal by the A / D conversion circuit changes . TI's C6000 DSP as the central processing unit , the signal from the A / D converter circuit fast Fourier transform, the Doppler frequency . Calculated according to the linear relationship of the Doppler frequency and the fluid velocity , the velocity of the fluid . Finally, build the experimental device, a preliminary experimental study , the experiment proved the feasibility of the speed optical system .

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Laser technology, the maser > Optical detection techniques
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