Research On An Laser Doppler Velocimetry Based On DSPs

The Laser Doppler Velocimetry (LDV) is a kind of precise instrument. It is used to measure velocity of liquid. It is based on Doppler phenomenon of light. It uses particles put in liquid to scatter the laser that shines on it, then detects the change of the scattered light's frequency using photoelectric detector, finally gets the velocity of liquid according to the velocity info contained in the scattered light, because the change of frequency of the scattered light and particle's velocity is in direct ratio. The LDV has many merits, such as rapid dynamic response, good space differentiating ability, wide measure range and high precision.This article analyzes and compares existing variety of LDV technology. According to existing LDV's deficiencies such as limited signals processing ability, poor adaptability and low precision, a new design scheme of the LDV based on digital signals processing is introduced in this article.Above all, Chapter 1 shows us the purpose and significance of this subject. Chapter 2 illustrates the work principle of LDV, and gives a new kind of optical system: 1 dimension, difference, polarizing optical system. In Chapter 3, digital signal processing is introduced to analyze Doppler signal. At first, FFT is used to convert Doppler signal from time domain to frequency domain, and then the algorithm of approaching peak value is put into practice. After this, Doppler signal's frequency is obtained. According to Doppler Effect, velocity can be calculated.The design of signal sampling card of the instrument is detailedly presented in Chapter 4 and Chapter 5, including the hardware of signal sampling card based on DSP TMS320C6713 and how to programme software. This scheme can restrain noise largely, and have powerful ability of digital signal processing and compact frame.