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Study On Distributed Optical Fiber Vibration Sensing Technology Based On SOP Changes Delay Estimation

Posted on:2013-03-24Degree:MasterType:Thesis
Country:ChinaCandidate:C GaoFull Text:PDF
GTID:2248330362461806Subject:Information and Communication Engineering
Abstract/Summary:PDF Full Text Request
Pipeline transportation system as a safe, economical transportation method has been widely used in petroleum, natural gas and other industrial sectors, but in recent years, the pipeline petroleum stolen cases have occasionally occurred, resulting in huge economic loss, which makes oil and gas pipelines automatic monitoring technology become increasingly important nowadays. In this paper, to meet the early warning requirement of oil and gas pipelines, we proposed a distributed optical fiber sensing system based on SOP (state of polarization) changes delay estimation for optical fiber as the sensing signal which has high polarization sensitivity, high positioning accuracy, real-time distributed fiber optic sensing system.Of the proposed delay estimation based on changes in the polarization state of a distributed optical fiber sensing system, two optical signals are fed into the sensing fiber bi-directionally, disturbance vibration will cause both the forward and reverse optical signal polarization state of light changes in the respective end from the partial use of polarization changes detected and converted into light intensity information. The principle of sensor system for sensing the polarization of consist of detailed analysis and research, we propose the corresponding sensing system solutions, introduce the system’s components, light source’s driving circuit, the receiving system consisted of the photodiode and the preamplifier, and we performed photodiode receiver circuit’s linear range test.Distributed sensing system based on this principle and system structure, we proposed the corresponding detection and location of distributed sensing method, the use of two-way signal delay difference between the intrusive events along the pipeline to determine location information. A theoretical analysis is conducted for reasons of the formation of the two-way signal delay difference, and illustrates the use of cross-correlation algorithm to calculate the distributed sensing positioning theory’s time delay difference. Cross-power spectrum using FFT-based correlation method and the Hilbert transform of the delay estimation method, effectively reducing the amount which directly related to the calculation method and contributed a substantial increase in the real-time positioning.Experimental results show the correctness of the positioning principle, the two received signals using FFT cross-correlation algorithm, to locate points on the polarization disturbance, and obtained good results, wich can locate the vibration signal from the sensing distance up to 45 km, absolute positioning error around 100-metre level. The experimental result maximum absolute error is within 300 meters, positioning accuracy of up to 0.8%. This system has simple structure high positioning accuracy, and it uses the mature stable commercial devices which would have excellent application prospects in long-distance pipeline leak detection and vandalism.
Keywords/Search Tags:optical communication, distributed optical fiber sensing, polarization detection, FFT cross-correlation algorithm
PDF Full Text Request
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