Research On Vibration Signal Acquisition And Analysis Based On Optical Fiber ?-OTDR

The case of bottlenecks in the sensing mode,sensing sensitivity and real-time performance of traditional sensing technology,fiber-optic sensing technology as a new sensing technology,using optical fiber as the sensing medium,with high sensitivity,large transmission bandwidth,strong real-time advantages,It has outstanding performance in the fields of construction engineering,petrochemicals,and biomedicine.The optical fiber?-OTDR vibration detection system utilizes the optical fiber sensing technology to solve the problems of detecting dead zones and complex networking in the traditional vibration detection,and it has the characteristics of long sensing distance,wide coverage and high sensitivity,so it widely used in peripheral security monitoring,oil and gas pipeline safety monitoring and many other fields.However,the ?-OTDR vibration detection system has a complex instrument composition.In order to ensure system spatial resolution,signal-to-noise ratio and other indicator,its data acquisition system needs to maintain high-speed acquisition.Which leads to the problems of large data volume and data transmission,resulting in a large size,high cost and update difficulty.Therefore,this paper designs a data acquisition scheme by analyzing the Rayleigh backscattering signal in the?-OTDR vibration detection system,optimizes the data processing algorithm and produces a prototype.While ensuring the performance of the ?-OTDR vibration detection system,the equipment volume is greatly reduced and the cost is reduced.The specific research contents are as follows:(1)Study the principle of Rayleigh backscattering signal in optical fiber.On this basis,the theoretical analysis of ?-OTDR vibration detection system and the principle of coherent detection are studied.Study the main parameters of the system and its effects.Finally,the data acquisition scheme of the ?-OTDR vibration detection system based on FPGA is determined.(2)According to the data acquisition scheme designed in this paper,the data acquisition system is classified according to the functional circuit,and the chip selection and circuit design are carried out.In order to achieve high-speed,stable and reliable data transmission,a special SI design is performed on the key signal lines.Functional verification and performance testing were performed on the PCB.(3)Software design on the built hardware platform.Divide the software into modules according to the top-down approach.At the same time,the system algorithm is optimizedin the process of software design: the problem of data positive processing in IQ demodulation algorithm and the selection of N value in differential accumulation algorithm.Thereby reducing the amount of data in the system,increasing the signal-to-noise ratio of the system,and the prototype verification and function optimization of the system were completed.(4)Simulated vibration experiments and vehicle vibration experiments were carried out in the laboratory and the highway tunnel respectively.In the simulated vibration experiment,the signal-to-noise ratio of the system is 14.8dB on the 2.8km sensing fiber;the spatial resolution is 30m;the refresh rate is 1Hz,and the dynamic response is good.The vibration signal was also detected in the vehicle vibration experiment.It proves that the data acquisition system designed in this paper has good performance and the design scheme is effective,Which achieves the signal acquisition and processing of ?-OTDR vibration detection system.