Research On Distributed Optical Fiber Sensor High Speed Signal Detection System Based On FPGA

The monitoring of debris flow geosound and the security prewarning of high-voltage transmission network put forward higher and higher requirements for high-speed continuous processing capability of distributed optical fiber sensor.In order to slove the problem of slow demodulation speed and loss of effective data in the traditional signal processing method of upper computer,combining FPGA and distributed optical fiber sensing technology,a distributed optical fiber sensing high-speed signal detection system based on FPGA is constructed.The optical signal is converted to digital signal by high-speed A/D module and demodulated in the FPGA.Finally,the demodulated data is transmitted to the host computer by the PCIe high-speed serial protocol for display,thus realizing the high-speed demodulation of the optical fiber sensing signal.The main contents of this paper are as follows:(1)Aiming at the problem of weak signal intensity of Rayleigh scattering and low signal-to-noise ratio of demodulated signal,an enhanced ?-OTDR system based on weak fiber grating array is studied.The possible noise effects of different laser linewidth,multiple reflection crosstalk and spectral shadow effect on high-speed signal processing of FPGA are analyzed.The necessity of moving average algorithm to reduce system noise is analyzed theoretically,and an improved arc tangent demodulation algorithm is proposed.The algorithm is simulated under the ideal,asymmetry phase and unequal DC condition.The correctness of the algorithm is verified,and possible error analysis is carried out.(2)The design flow of the FPGA and the implementation method of the logic module are studied,and the signal and pipeline processing methods across the clock domain are analyzed.The high-speed signal detection logic module with the main controller of the FPGA is realized by Verilog language.The performance parameters of AD9250 A/D chip of ADI company are analyzed.Two kinds of Xilinx's FPGA chips are analyzed and compared,and XC7A200TFBG676-2 is chosen as the main control chip.Moving average and Arc tangent demodulation algorithm are implemented in FPGA(3)A distributed optical fiber sensor high-speed signal detection system based on FPGA is built.According to the application scenario,the characteristics of the ultrasonic signal generated by partial discharge are studied.Experiments show that the frequency response range of the system is from 100 Hz to 18 KHz.It realizes the function of continuous acquisition.With 1000 gratings demodulated at one trigger period,the throughput of 20 KHz can be achieved.In the case of actual partial discharge,the accurate measurement of partial discharge signal is realized.The frequency range of the measured signal is from 10 KHz to 15 KHz.Experiments show that the system with wide frequency response range and high sensitivity,can achieve continuous signal acquisition and high-speed processing.