Study On Spatial Resolution Of Distributed Optical Fiber Temperature Sensor

Distributed optical fiber Raman temperature sensor(DTS) which composited by optical time domain reflectometer(OTDR) and optical fiber Raman scattering techniques, could be used for temperature measurement. It is a sensing system that used for the real-time online measurement of space temperature field, where optical fiber is both transmission medium and sensing medium. Comparing to the conventional temperature sensing system, DTS has many obvious advantages, such as anti-electromagnetic interference、corrosion resistance、wide temperature range、good insulation、high sensitivity and so on, it has been widely applied in oil and gas pipelines for temperature monitoring and fire alarm and large dam for water leakage surveillance. With all above, it attracts widespread attention at home and abroad and achieves rapid development.As one of the key performance indicators of DTS, spatial resolution could truly show the temperature variation along the minimum length of optical fiber and play an important role in the overall performance of system. Currently, even the spatial resolution of the system has reached about 2m, but it still could’t meet the requirements of petrochemical pipelines and high-voltage power switch. Hence, it is important to do some research on the improvement of spatial resolution of DTS, which can promote the largely scale engineering application.The research status at home and abroad、applications and development trends of DTS are introduced in detail in the thesis, as well as the theoretical basis including optical time domain reflectometry techniques and Raman scattering techniques. Three methods that used for demodulation in distributed optical fiber Raman thermometry are summarized and compared. The structure of DTS is introduced briefly, where all performance indicators are discussed. Several factors that influence the spatial resolution of DTS are analyzed and various methods that used for spatial resolution improvement are investigated in theory, subsequently, the method of dual-source auto-correction is proposed. As the primary laser and secondary laser works alternately, Anti-Stokes Raman signal、Rayleigh signal of the primary laser and Stokes Raman signal、Rayleigh signal of the secondary laser are received respectively, where two of them have the same wavelength, by means of this method, the spatial resolution of DTS could be improved effectively through elimatting the “got separated” phenomenon in singel source systems caused by the different wavelength between Anti-Stokes and Stokes Raman signal. The particular scheme and experimental results are provided and analyzed, respectively.Finally, the application cases that have been successfully implemented are introduced, in which the technical challenges are resolved, which offers an example for promoting DTS to more occasions.