Performance Improvement For Distributed Fiber Temperature Sensor System And Research On Fire Source Localization

Optical fiber distributed temperature sensor(DTS)is a kind of real-time and continuous monitoring space temperature field sensing technology along the fiber direction,which can be wildly applied in safety and health monitoring of large infrastructure projects,such as warehousing and oil&gas pipelines.The temperature measurement is gained based on the temperature effect of the Raman scattered light.Combined with optical time domain reflectometer(OTDR)technology getting the localization to the position of the optical fiber at various points,the temperatures at various points along the optical fiber can be achieved.As an important part of safety and health monitoring technology,fire early warning technology provides a powerful guarantee for the early detection of fire,and can effectively avoid the disastrous consequences of the fire.The main work of this thesis is focused on the performance optimization method of the DTS system and the fire source localization method based on the DTS system.The main contents are as follows:Firstly,the principles of Raman scattering and OTDR technology in DTS system are described,and three temperature demodulation methods of DTS system are analyzed and compared.Secondly,the experimental setup of the DTS system has been developed based on the theory of DTS system and the performance index is discussed.A linear fitting calibration method is proposed to improve the spatial resolution of the system.The experimental results show that the spatial resolution of the systern is improved from 5m to 1m,which effectively reduces the errors from the measured temperature to actual temperature.In addition,a loop configuration of DTS system is employed to eliminate the effects of different attenuation coefficient between stokes Raman scattering and anti-stokes Raman scattering light.The influence of the part of Rayleigh noise in the Raman scattering light caused by the lack of WDM isolation is analyzed.The temperature demodulation method is proposed by means of pre-calibration to deduct the Rayleigh noise,which effectively improves the accuracy of temperature measurement system.Finally,fire source localization methods with double parallel fibers structure and perpendicular fibers structure are proposed based on the analysis of the temperature field in closed room and the advantages of easily installing optical fiber and real-time remote temperature monitoring.A method of moving average is adopted to minimize the error range of fire location coordinates.Regional counting method is proposed torealize visualization of fire source position.Combined with the cubic spline interpolation coordinates,the required time of fire location is much reduced.The method of double fiber orthogonal structure fire source location is relatively simple and easy to operate.Two calibrating methods are put forward to modify the deviation of fire location caused by the uneven ceiling of the open cabinet,including temperature curve moving average method and peak half width method.The results show that the fire position can be located fast and accurately.