Method To Improve The Accuracy And Real-time Performance Of Distributed Optical Fiber Temperature Measurement Syste

Raman-based distributed optical fiber temperature sensor can achieve a wide range of high-precision temperature monitoring,and is widely used in many fields such as power engineering,petrochemical industry and pipeline monitoring.However,in the existing RDTS system,there is a problem that the system temperature measurement accuracy decreases due to the difference between the attenuation coefficient of Stokes light and AntiStokes light and abrupt loss of optical fibers.At the same time,the traditional signal processing method is more than 10,000 times heavy cumulative average technology,which improves the signal-to-noise ratio at the expense of system response speed.Therefore,improving the system temperature measurement accuracy and response speed is the focus of RDTS system optimization research.In order to solve the above problems,a double-end injection ring demodulation method is used to avoid the temperature measurement accuracy degradation caused by the difference between the attenuation coefficient of Stokes light and Anti-Stokes light,and to improve the measurement accuracy and stability of the system.On this basis,the noise of the system is reduced by the combination of 1000 times light cumulative average and wavelet threshold denoising,which improves the signal-to-noise ratio of the system and the response speed of the system.The main research work in this thesis is as follows:(1)The principle of optical time domain reflection and the temperature sensitivity of Raman scattering signals in optical fibers and the temperature demodulation method of RDTS system are analyzed.It is verified experimentally that the double-end injection ring demodulation method can solve the problem that the difference between the attenuation coefficient of Stokes light and Anti-Stokes light limits the accuracy of temperature measurement in traditional single-end RDTS system and eliminate the local physical disturbance of optical fiber.The experimental results show that the temperature measurement accuracy of the whole curve is improved from 3.9℃(>8km)to 1.7℃(>8km).(2)The effect of high temperature on the temperature measurement accuracy of RDTS system is analyzed.Stokes light intensity values and Anti-Stokes light intensity values corresponding to 120℃～800℃ are measured by experiments.Correction parameters of RDTS at high temperature are fitted to achieve accurate temperature measurement.The results show that the maximum relative deviation is less than 1% at high temperature.(3)The noise characteristics of RDTS system are analyzed,and the denoising effect and processing speed of the cumulative average algorithm and the wavelet threshold denoising algorithm are verified experimentally.A denoising method combining light cumulative averaging with wavelet threshold is proposed,which improves the signal-tonoise ratio of RDTS system and significantly reduces the response time.Compared with traditional heavy cumulative averaging algorithm,the processing time of this algorithm is reduced from 2.6s to 0.2s,while the signal-to-noise ratio can still reach about 36 d B.(4)The FPGA firmware for the light cumulative averaging and wavelet threshold denoising algorithm is designed,and a fast RDTS temperature measurement system based on the FPGA is implemented.Finally,the performance of the proposed RDTS system is tested.The test results show that the temperature measurement range of the system can reach 800℃,the temperature measurement accuracy is about 1℃,and the response time is less than 1s.