Research On Comprehensive Signal Processing Technique For Optical Fiber Vibration Sensing System Based On Φ-OTDR

With the advantages of high sensitivity, large space dynamic range and high location accuracy etc., optical fiber vibration sensing technique based on cp-OTDR has widely applied in various kinds of fields, including large structure health monitoring, industry manufacture detection, perimeter security and pipeline defense. For engineering applications, researches on comprehensive signal processing technique for φ-OTDR based optical fiber vibration sensing system developed by our research group are carried out in this paper.Chapter 2 puts forward the problems of φ-OTDR based optical fiber vibration sensing system in practical applications, and proposes the comprehensive signal processing scheme. With FPGA as the kernel, ADC, DAC and USB2.0 as the function modules, the comprehensive signal processing sub-system has the functions of high-speed data acquisition, processing, communication and parameters control etc. In order to solve practical problems, the techniques of digital automatic adjustment, dynamic backscattering trace compensation, sensing data compression and framing and real-time sensing fiber fault monitoring and positioning are proposed.Chapter 3 analyzes the design of FPGA circuit and function modules of ADC, DAC, USB2.0 interface, digital control interface and power management. The PCB layout design of comprehensive signal processing sub-system is finished based on the the EMC and signal integrity analysis, and the FPGA program design for the comprehensive signal processing algorithms is completed.Chapter 4 tests and analyzes the comprehensive signal processing sub-system with the help of experimental setup. The results demonstrate that the SNR is improved greatly, the sensing blind segments is removed; the data communication rate is improved which shortens the system response time; the functions of digital automatic adjustment and the sensing fiber fault detection and location is realized, which enhances the environment adaptability and practicability of the system, meeting the requirements of engineering applications.Chapter 5 establishes an φ-OTDR based optical fiber vibration sensing demonstration system based on the comprehensive signal processing technique. The experimental results demonstrate that the demonstration system works well, and has very nice SNR and location accuracy. Integrated with the functions of voice alarm and smart video camera, the system can detect and locate the vibration events happened in every place of the sensing cable, which fits the needs of practical applications better.Chapter 6 summarizes the full paper and looks ahead the next step of the project.