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Study on Key Technology of Distributed Optic-Fiber Sensing System Based on Sagnac Interfering Principle for Long-Distance Pipelines Sabotage Acts

Author: LinLei
Tutor: ChenWeiMin
School: Chongqing University
Course: Precision instruments and machinery
Keywords: Damage Warning Sagnac Distributed Optical Fiber Vibration Fiber coupler
CLC: TP29-A2
Type: Master's thesis
Year: 2009
Downloads: 163
Quote: 5
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Abstract


The long-distance oil and gas pipelines has the characteristics of high temperature, high pressure, flammable and explosive, will lead to major accidents in the event of a leak and caused huge economic losses. In recent years, some Touyou Stolen barbaric construction vandalism is a serious threat to the security of the pipeline. The existing pipeline safety monitoring methods can only passively detected the leak after the spill occurred, can not avoid the loss. Therefore, to achieve early warning of the threat of vandalism of pipeline safety, would be of great social and economic benefits. Sagnac interferometric distributed fiber sensing warning system because of its high sensitivity, the detection point is infinitely more, installation, easy maintenance and so become the focus of the study, but to make the fiber optic sensing system can locate the actual pipeline safety threat warning must start from the destruction of signal characteristics, the establishment of the early warning system and demodulation method, specific research several key technologies: ① In order to understand the characteristics of vandalism from mining, drilling, and other acts of sabotage caused the vibration signal generation and propagation mechanism, this paper were constructed vandalism caused focal vibration model, ground motion wave model, and role in longitudinal wave (P-wave), pipeline vandalism fiber sensing model. From the time domain and frequency domain testing and analysis of a typical vandalism characteristics consistent with theoretical model to prove that the sabotage of the multi-frequency components in the fiber optic sensor induced phase shift of the same frequency components, and made the identification of the type of vandalism. ② In order to improve the sensitivity of the Sagnac interferometer system, from the transverse coupling of the optical waveguide theory to derive the 2 × 2 coupler and the characteristics of the 3 × 3 coupler obtained using a 3 × 3 coupler instead of 2 × 2 coupler improve the sensitivity of the system. ③ design demodulation method does not depend on the frequency characteristics of sabotage, improved interference early warning system based on the 3 × 3 coupler Sagnac principle, add fiber delay loop, using pulsed light source, by comparing multiple response amplitude able to detect the occurrence of the vibration caused by the location of the primary ring due to external damage event, accurate positioning mathematical model, a positioning method is not dependent on the frequency characteristics of the external forces. The ④ build experimental system, the total length of 10Km sensing fiber using a phase modulator simulated acts of sabotage, the positioning accuracy of less than 100m. This result proves several key early warning system of distributed optical fiber sensing technology, design one can achieve the long-distance oil and gas pipeline safety warning distributed optical fiber sensing system, the structure is reasonable, accurate positioning, with a very The great practical value.

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