Design And Signal Processing Of Distributed Optical Fiber Temperature Sensing System

Research on distributed optical fiber sensing technology could be traced back to the late 1970s. With more than thirty years development and research, this technology has been widely applied in various fields. As an important branch of distributed optical fiber sensing technology, distributed optical fiber temperature sensing technology has been focused studied by research institutions and enterprises all round the world.Different from the single-point temperature sensors, distributed fiber optical temperature sensors could collect multi-point temperature information and accurately locate in real time by using optical time domain reflectometry technology on a single fiber. The fiber is not only the signal transmission medium, but also the sensor of temperature information as well. Distributed fiber optical temperature sensor is incomparable especially in the explosive, strong electromagnetic interference, corrosion resistance and complex geographical environment. Thus, it surely has broad market prospects.This paper describes the basic principle of distributed Raman fiber optic temperature measurement technology theory - optical time domain reflectometry, and Raman scattering temperature effect principle, and introduced several other common fiber optical temperature sensing technology.According to the theory above, this paper designs the distributed optical fiber temperature measurement system which includes optical signal transmission unit, photoelectric detection unit, the signal acquisition unit, etc. and describes the working principle and performance of these components. This paper also analyzes some vital indicators of the system performance, for instance, the best working wavelength of LD, avalanche multiplication coefficient of APD, the accuracy of capture cards and so on. This paper presents several methods to improve system performance and some options to resolve system stability has been proposed.For the analog temperature signal, several demodulation methods have been derived. Dual-channel demodulation by the anti-Stokes with Stokes has been selected in this dissertation. In order to eliminate differences in channel sensitivity to temperature measurement system, a calibration area has been established and discussed comprehensively. As to the weak signal in Raman scattering, the average time-domain superposition algorithm and wavelet multi-resolution analysis has been used to reduce the noise and extract the useful signal in order to improve the signal-noise ratio significantly.