Optimization Of Distributed Optical Fiber Temperature Measurement System Based On Raman Scattering

Distributed Raman fiber sensing technology can achieve long-distance and large-scale accurate temperature monitoring,which is widely used in subway tunnels,oil and gas pipelines,smart power grids and other large-scale infrastructure,with great social demand and application prospect.However,in the practical use of distributed optical fiber Raman temperature measurement system,there are also the following problems: The Raman scattering signal in the system is extremely weak,there is a low SNR of the system;Because the wavelength of Raman stokes light is different from that of anti-Stokes light,and the relative refractive index of the light with different wavelength is different in the optical fiber,the transmission speed will be different,and ultimately affect the temperature measurement accuracy and spatial resolution of the system.APD temperature drift phenomenon also exists in the system,which increases the temperature measurement error of the system.If the temperature of the cable is inconsistent,the system cannot be calibrated as a whole and cannot measure the temperature.In view of the above problems,the optimization research of distributed Raman temperature measurement system is carried out in this paper.The specific work is as follows:(1)Aiming at the problems of low SIGNal-to-noise ratio(SNR)and dispersion effect of distributed Raman system,the accumulative average algorithm and denoising algorithm are firstly adopted to improve the SNR of the system;A polynomial interpolation method is proposed to eliminate the dispersion effect of light.The experimental data prove that the temperature curve of the demodulation system fluctuates from above 3℃ to less than 1℃through the optimization of the algorithm,which improves the measurement accuracy and data stability of the system.Moreover,the original bandwidth of the system has not been changed and the spatial resolution of the system has not been affected.(2)A method of introducing reference fiber is proposed to eliminate the APD temperature drift phenomenon in the system.The experimental results show that the temperature errors of the system are within 1℃ with the increase of the working temperature of APD and amplifier circuit.It is proved that this method improves the long-term stability of the system by collecting the temperature data of four test points for a long time.The system is tested at 45℃,60℃ and 80℃ respectively,and the temperature measurement accuracy of the system is about 1℃.The experimental results prove the effectiveness of this method.(3)A temperature demodulation algorithm suitable for laid optical cables is proposed.This algorithm can demodulate sensing optical cables at different temperatures and expand the application scenarios of the system.Through experimental verification,3600 demodulation temperature values were recorded in 4 test points,and the standard deviation was calculated,and the standard deviation was less than 1℃.Experimental results show that this temperature demodulation algorithm can be effectively applied to the application of optical cable laid.(4)Complete the hardware construction of this topic,and design a human-computer interaction software interface in the lab VIEW environment.Finally,the distributed Raman temperature measurement system designed in this topic was arranged in the communication room of Yanshan Campus of Guangxi Normal University for the current application test,and the system worked steadily for 6 months.