| The distributed optical fiber Raman temperature sensor (DTS) system is basedon optical fiber Raman scattering effect to measure temperature. It is a high and newtechnology developed for the measurement of temperature field in the past20years. Itcan realize the real-time, continuous measurement of temperature in a distance ofthousands of meters. And the system has reliable temperature resolution andtemperature measurement precision. Due to the inherent advantages of DTS, such as,small volume, low cost, anti electromagnetic radiation, resistance to corrosion, quickresponse and so on, it has been widely used in many occasions.In this paper, Theoretical and experimental study has been carried out to theprinciple of temperature measurement of DTS and the key technical problems in thesystem development. Wavelet denoising method for the data processing andtemperature demodulation algorithm has been emphatically introduced. This paperhas certain reference value and guiding significance for researchers. Specifically, thepaper mainly consists of the following parts.The first chapter, introduction is a brief description of the paper selected topicbasis and the research background and significance. The domestic and internationalresearch status and development trend of optical fiber sensor is introduced.The second chapter, the principle of temperature measurement of optic fiberRaman scattering. Theoretical analysis and mathematical calculation of OTDR(Optical Time Domain Reflect) technology and optical fiber Raman scattering theoryhave been done. It interprets the generating process of optical fiber Raman scatteringin the point of energy level transition and deduces Raman scattering light intensityaccording to quantum theory. It comes to a conclusion that using the ratio ofanti-Stokes and Stokes light intensity as the temperature sensitive signal. The third chapter, designing of distributed optical fiber Raman temperaturesensor. The system design process is described in detail, including light source, WDMcoupler, APD photoelectric detector and other devices of DTS. The structure diagramof DTS and some schematic circuit are shown out. The main performance indexes ofthe DTS, such as temperature resolution and spatial resolution, have been analyzedand calculated. Moreover, the corresponding measurement schemes have beenprovided.The forth chapter, wavelet denoising used in optical fiber Raman temperaturesensor. In order to improve the SNR (Ratio of Signal and Noise) of DTS, waveletdenoising algorithm is used in data processing. First the theory of wavelet transform isintroduced, and then the process of wavelet threshold denoising is discussed in detail.The results show that this method can eliminate signal noise effectively. Such, boththe resolution and precision of the measured temperature of the system can beimproved.The fifth chapter, the application and stability analysis of DTS. The measurementerror of DTS is analyzed and one temperature calibration method considering theinfluence of optical fiber loss is provided. We have analyzed the main factors thatinfluence the stability of the DTS and the problems in the application which need topay attention to. Finally, DTS is used in underground steam pipeline leakage detectingsuccessfully.The sixth chapter, the main work and conclusions of this paper are summarized.Then, several directions to continue to study are proposed.In general, we design and set up a set of distributed optical fiber Ramantemperature sensor in laboratory conditions. The system has been successfully appliedin engineering measurement and achieves good results. |
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