Signal Processing Solution Of Laser Doppler Velocimeter Based On FPGA

Laser Doppler velocimeter is a kind of non-contact measurement device based on optical Doppler phenomena and has advantages of high accuracy,wide measurement range,short response time and excellent stability of scaling factor.Therefore,it is widely applied in industrial speed measurement and speed measurement for military vehicles.However,the laser Doppler signals are very weak;they change rapidly a nd cover a wide frequency range.Consequently,for the signal process ing system of a laser Doppler velocimeter,it is important and urgent to reduce the noise level,increase the measurement range,ensure the accuracy,and improve the capability of real-time analysis.In this paper,a signal processing system of laser Doppler velocimeter based on FPGA was proposed to replace the traditional dual core signal processing system based on FPGA and DSP chips,so that data interaction between the dual cores was eliminated,the data updating and delay time were reduced and the real-time analysis capability was improved.Moreover,a finite impulse response filter was used to suppress low-frequency noise.The frequency spectrum was retrieved by the fast Fourier transform with a Hanning window.The frequency spectrum was subsequently converted into the power spectrum and the spectrum peak was sought out and adjusted by the energy centrobaric correction method.Then the velocity of the moving object was calculated based on the adjusted frequency.The result was uploaded to the personal computer through a USB port,and the Lab VIEW program was used to store and display the data.In order to expand the measurement range,an adaptive algorithm of sampling frequency was proposed,in which the sampling frequency was adjusted automatically based on current Doppler frequency.The hardware circuit proposed in this paper took careful consideration on practical problems like electro magnetic compatibility,signal stability and miniaturization of the circuit.The stability and reliability of the algorithm was proved using the independently developed circuit,which is useful for the promotion of the application of laser Doppler velocimeter.The experiment results showed that the accuracy was better than 4.1‰,the data delay was less than 1.2ms,the data updating period was less than 0.4ms.