Research On Data Acquisition And Processing Of Distributed Fiber Raman Temperature Sensing

As an important transport medium for gas,gas pipeline plays more and more important role in people's daily life.Due to the extension of the service life of the pipeline and maintenance inconvenience,gas pipeline leakage which present damage to people's lives and property accidents is often reported in the news.Therefore,real-time on-line detection of gas pipeline and quickly location the pipeline leakage is urgently needed to ensure the safe operation of gas pipeline.Compared with the conventional gas pipeline leakage detection methods,such as the medium detection method,the pipe wall parameter detection method,and the acoustic detection method,Raman-based distributed temperature sensing provides a new solution for pipeline leakage detection due to the advantages of long measuring distance,distributed manner,rapid response,as well as intrinsically safe,anti-electromagnetic interference,and easy laying.When the gas pipeline leakage occurs,there is a sudden temperature change around the pipe.This change in temperature will cause changes of intensity of scattering light in the fiber laid around the pipe,that is,the Raman back scattering temperature effect.Accurate measurement of the temperature can be achieved by real-time detection of light intensity changes.And through the optical time domain reflection technology,accurate positioning of gas pipeline leakage point can be obtained in order to take timely measures to carry out construction maintenance.In this paper,the basic theory of distributed Raman temperature sensing based on the back-scattering Raman temperature effect and the optical time domain reflection technique is analyzed in the space field around the leakage point.The design of the temperature sensing detection system is carried out,including the selection of the critical device pulse laser,the wavelength division multiplexer,the photoelectric detector,the acquisition card,etc.The demodulation algorithm of distributed Raman temperature signal is compared and designed.The acquisition and processing of the distributed Raman temperature sensor signal based on LabVIEW platform is realized.The enhancement of the weak signal of Raman backscatter is realized by using FPGA hardware real-time cumulative average technology,which improves the signal-to-noise ratio and real-time performance.In addition,the automatic calibration of the sensor fiber is designed,combined with LabVIEW and MALTLAB wavelet decapitation algorithm and Hermite dispersion elimination algorithm.Comparative study of the storage and query scheme of distributed fiber Raman temperature signal based on the SQL Server database and TDMS is conducted.Finally,an experimental platform based on distributed Raman temperature sensing system is established.The performance of the system is analyzed experimentally.By utilizing the general multimode fiber as the sensing transmission medium,distributed temperature sensing is realized over 10 km fiber length,with a temperature accuracy of ±1?,the spatial resolution of 1m,the positioning accuracy of±1m and the measurement time less than 5s.In addition,the gas pipeline leakage detection software based on Lab VIEW platform is designed.With the characteristics of accurate response and real-time response,the sensor prototype is successfully applied to the simulated leakage temperature of gas pipeline,which provides the theoretical basis for the application in practical project.