Theory And Experiment Research On Fiber Optic Distributed Temperature Sensor System

The technology of fiber optic distributed sensing was brought forward in the end of 1970's. Since then a series of distributed sensing systems based on different mechanism were studied and used in many fields gradually. Nowadays, this has been one of the most promising technology in fiber optic sensor. The fiber optic distributed temperature sensor system can sense the change of temperature along the optical fiber by the form of continuous function of distance.The fiber used in fiber optic distributed sensor is not only transport media but also sensing media. It has the characteristics of resistance to electromagnetic interfere, against fire, small size and little effect to temperature field. The back scattering Raman signal with the information of temperature is quite weak and even completely submerged in noise. The measurement accuracy of the whole system has relationship with the denoising level to anti-Stokes and Stokes back scattering. Weak signal measurement is must be used in this system. This dissertation takes deep research and analysis on the fiber optic distributed temperature sensor. The main contributions are as follows:(1) The spontaneous Raman scattering in optical fiber is quantitatively analyzed and the relationship between spontaneous Raman scattering and the temperature of fiber in the sensing field is studied. Furthermore, the relationship between anti-Stokes light and temperature in practical use is established. The condition that ensure the spontaneous Raman scattering is confirmed based on the analysis of transforming from spontaneous Raman scattering to stimulated Raman scattering which has important instructional significance to the designation of fiber optic distributed temperature sensor.(2) The central wavelength is discussed based on the combination of signal-to-noise ratio, temperature sensitivity of system and operating stability. The formulation of optimum avalanche gains is figured out based on several factors as light power, heat noise and dull current, which provides foundation of analyzing the operation state of APD.(3) The response speed of system is improved by combining average and Wavelet transforming in signal processing. (4) A high accuracy constant temperature control system was designed which put vital components and calibration fiber in the same thermostat. It can improve the stability and reliability of the system.(5) An excellent driving circuit of laser was designed, which can control the shape and width of impulse light effectively and ensure the characteristic of distributed fiber optic temperature sensor system.(6) Each PCB part of system is analyzed and researched based on the characteristics of distributed fiber optic temperature signal. (7) The space and temperature resolution of the fiber optic distributed temperature sensor are improved by using neural network to process signals;The structure of network is designed and a new study method of nerve network provided;this method can quicken the convergent speed in nerve network study;...