Design Of Laser Doppler Velocimeter Based On DSP

In order to reduce the rate of waster, Laser Doppler Velocimeter (LDV) is needed tomeasure the velocity of steel in steelworks. LDV is a kind of real-time instrument, based onLaser Doppler effect. The signal of Doppler is involved in the light scattered from the movingsurface. LDV has liners and non-contact characteristics, so it can measure the velocity of amoving surface immediately and precisely. It is superior than the coding device used in manysteelworks presently.The Two-beam Differential Doppler Effect has been studied in this paper, based onwhich we designed a LDV system. This system is composed of two parts: the optical systemand the signal processing system. Semiconductor laser is used to erect laser in the shape of "1".The frame of two-beam lights scattered backward is designed to direct the beams. And anAPD is employed to collect the optical signal and convert it to electric signal. The signalcollected by APD is filtered by 200-step band-pass FIR filter firstly, and then be changedfrom time-domain to frequency-domain using Fast Fourier Transform, after that Dopplersignal can be picked up from noise.Two steps should be done to carry out the digital signal processing system, the hardwareand the software. The DM642 produced by Texas Instrument is employed as the core chip todo digital signal process. It is superior in doing signal processing, and it can do FIR and FFTin real-time, in the same time, the interfaces can make data input and output conveniently.Prefiler and magnify circuit have been designed, and 12bit ADC is used to implement ananalog and digital signals convert. The software is programmed through Code ComposerStudio (CCS).Finally, the analyses results proved that this system could meet the demand of practicalapplication. This paper studied the characteristics of the system and how to improve it.