Design Of Distributed Optical Fiber Vibration Instrument Based On FPGA

The vibration signal detection usually adopts the point separated sensor as the signal acquisition device,which has a beneficial effect on mechanical equipment fault detection,but it is not suitable for long distance distributed vibration measurement.As a novel detection method of distributed vibration signal,the phase sensitive reflection time domain reflectometry(?-OTDR)has overcome the shortcomings and has been widely used in the field of vibration.In practical engineering,the fast and transient vibration signal has a high demand for data acquisition rate and data transmission speed.FPGA is widely used in high speed signal acquisition because of its advantages of fast running,high flexibility and high speed processing.It is necessary to apply the FPGA technology in distributed optical fiber vibration sensing system to realize the real-time processing and demodulation of the vibration signal.In order to realize the real-time positioning and demodulation of the vibration events,this paper designs and implements a distributed optical fiber vibrometer based on FPGA.The entire measurement system is composed of three parts: distributed optical vibration measurement platform,high speed data acquisition system and PC software interface.The distributed optical measurement platform as the first part of the system implementation will convert external vibration signal for changing the optical signal,and then through the photoelectric conversion into electrical signals.As the middle layer of the system,the high speed data acquisition system converts the analog signal output from the photoelectric converter into the digital signal and processes the data,and then transfers the data to the host computer.Host computer software interface will receive the data from the design of the algorithm program,the results output,providing the entire system control and data display function.The main research contents are as follows:First of all,combine modulation of optical phase by vibration signal and the light intensity caused by optical phase to realize the demodulation of the vibration signal,and then expounds the basic principle of vibration detection.According to the requirements of the device selection and design of distributed fiber vibration measurement system of vibration detection scheme based on the principle,establishes the optical platform with ?-OTDR distributed vibration detection.The backscattering signal of the optical platform is captured by the oscilloscope and the Matlab is used to analyze the backscattering curve.Then,a high-speed data acquisition system based on AD9226 chip and Altera chip FPGA is designed.First,the overall data acquisition scheme is determined after the signal characteristics of the system are studied.Then,two kinds of data acquisition schemes are proposed,which are a single point data acquisition scheme based on serial port transmission and a continuous data acquisition scheme based on USB2.0 transmission.The basic principle of USB2.0,CY7C68013 A and Slave FIFO are described in detail on the one hand,and on the other hand,the timing of data reading and writing.The high-speed data acquisition system is associated with the optical platform to verify the distributed real-time acquisition.Through the research of the MFC program development framework and the visualization requirements of the system.The overall program of monitoring interface of PC is designed,and the main function modules and the code of software implementation are explained in detail,including parameter setting,data processing and signal display unit.At last,the real-time data display and storage functions are realized.Finally,a complete distributed vibration measurement system is established.The important parameters and performance indexes of the system are analyzed by experiments.The experimental results show that the distributed vibration measurement system can realize the positioning error of 20 m and the spatial resolution of 30 m on the sensing range of 11.5km.The linearity of the frequency response is good,the response time of the system of the distributed optical fiber vibration instrument based on FPGA is fast,and all the indexes of the system meet the requirements of the project.At the same time,the system can response to the sine wave,square wave and regular impact signal,the experimental results are bright and effective.