Distributed Optic Fiber Precaution System Based On Mixed Mach-Zehnder And OTDR Optical Path

Nowadays, our national economy is developing rapidly and sustainably, thus thecorresponding requirement for energy, especially for oil, is also imminently indemand. Since pipeline transportation is cost-effective and safe, it has become a mainmeans of transportation for oil and gas. With the fast development and the commonapplication of the pipeline transportation, the security itself attracts more attention.Because of non-human or man-made reasons, the pipeline leakage accidents occuroccasionally and result in huge property loss and environmental pollution. Recently,many colleges and research units aim at the improvement of the pipeline leakagedetection technology. Among all the detection methods, the technology based onoptical fiber develops swiftly and becomes a developing hotspot.Distributed sensing is widely applied in optical fiber sensor technology. It canwork passively and transport the signal simultaneously while sensing. The low loss oflaser and the strong anti-interference ability makes it suitable for online monitoring,especially for long distance oil and gas pipelines. With these incomparablesuperiorities, distributed fiber sensors have a good development prospect.In order to avoid the low positional precision of Mach-Zehnder interferometer,and the problem that the system can’t work after fiber cracks, a distributed opticalfiber pre-warming system which is based on a method which combines theMach-Zehnder interferometer with OTDR was proposed.The main work of this paper is as follows:1. We combined Mach-Zehnder interference with OTDR. When theMach-Zehnder interferometer cannot work as the fiber cracks, the system switched toOTDR to locate the cracked point, thus enhanced system’s reliability.2. We changed the optical path under new requirement and researched on thesystem frame.3. According to the system design, a polarization controller, a polarizationcontroller control method, an optical switch, a connection circuit for data acquisitioncard and a MCU control circuit were designed.4. A MCU program controlling liquid crystal display, AD acquisition, opticalswitch control and pulse modulation were programmed. 5. We did the field experiment and verified the performance of the system.