Research On PGC Digital Demodulation System Of Distributed Optical Fiber Sensor Based On MCU

Interferometric distributed optic-fiber can be applied on the submarine pipeline structure health monitoring.It is able to detect and locate the leaking point when the submarine pipeline leakage accident happened.As the submarine environment is harsh,the pipeline leakage accidents happen frequently,the distributed optic-fiber leakage detection technology attracts attention from all over the world in this field.The method of signal demodulation of interferometric distributed optic-fiber sensor has directly impact on the detection performance of the system.Compared with the traditional analog demodulation device,the phase highfrequency carrier demodulation(PGC)has more simple structure,so it is widely used.But the demodulation accuracy of traditional analog device is low.In this dissertation,a digital demodulation circuit based on GD32F103ZET6 processing chip was designed,and PGC digital demodulation system of interferometric distributed opticfiber sensor is also discussed.(1)The principle of interferometric distributed optic-fiber based on Sagnac and Mach-Zehnder hybrid interferometor are analyzed and the principle of phase modulation of the system is analyzed and compared.The phase carrier demodulation technology of interferometric light signal is studied by theoretical analysis and mathematical deducing,and its feasibility is also verified.At the same time,at the base of the research of the filtering algorithm,the tradtional Kalman filter algorithm is improved to be used in digital demodulation system.(2)Principle analysis for the key technology of PGC digital demodulation was studied.Getting The disadvantages of analog demodulation and advantage of digital demodulation are compared in details.Meanwhile,making principle analysis for the Zero interpolation technology which is one of key technology of PGC digital demodulation.The zero interpolation sampling simulation analysis was carried out in Matlab software platform.The carrier frequency is 300 kHz.According to Nyquist sampling theorem,the sampling frequency is 1MHz.Sampling point N is 1024,and then double the zero interpolation,that is,10240,observing the changes of time domain spectrum before and after doubling the zero interpolation.The comparison was presented in simulation.Finally,the feasibility of zero interpolation technology is confirmed.(3)Improving the leakage detection device based on interference optic-fiber sensor,the digital circuit of PGC demodulation was developed in detection system,and researching the digital algorithm of PGC demodulation as well.Besides the host computer software of detection system is also designed,which can gather real-time transmission of test data and real-time display of detection data with waveform.(4)The interferometric distributed optic-fiber sensor leak detection device were tested in experiments.Experimental results show that making reduplicative experiment comparison and analysis on the small-scale experimental platform in the lab.the distance between the leakage point and the Faraday rotation mirror is 8045 m,and the correspondent leakage distance in experimental theory the distance is 8188.7m,so the absolute error is 143.7,the relative error is 1.75%.