Research On Distributed Temperature And Pressure Measurement And Signal Extraction Method Based On OFDR

With the development of optical fiber sensing technology,Optical Frequency Domain Reflectance Technology(OFDR)has been widely used in aviation measurement,geological prospecting,shape monitoring and other fields due to its advantages of high measurement accuracy and spatial resolution,realizing strain and temperature,Humidity and other physical parameters measurement.However,due to less research on its demodulation algorithm,there is still room for improvement in demodulation accuracy and speed.At the same time,the research applied to distributed temperature measurement is not yet mature,and there are few researches applied to distributed measurement.In this paper,the distributed temperature and pressure measurement and signal extraction methods based on OFDR are studied,and the OFDR demodulation process is researched and analyzed.Then,the distributed temperature and pressure measurement sensitive units and measurement systems are designed and studied,and the distributed temperature,Pressure measurement.In addition,experimental verification is carried out for the measurement ability of the oil body pressure environment,and the distributed temperature sensor is experimentally verified by the long snake laying method.The main content of the paper is as follows:1.Research the model and theory of optical frequency domain reflectometer.Combining the nature of backward Rayleigh scattering and the basic principle of optical fiber transmission,through the optical heterodyne detection model,the measurement results received by the photodetector are analyzed,and the expression of the photocurrent intensity of the photodetector is given.According to the expressions,the expressions of light frequency,light intensity and spatial position,and Rayleigh scattering are obtained.Provide a theoretical model for subsequent research.Analyze the nonlinear tuning effect of the light source in OFDR,get the main source of nonlinear results in OFDR system,and explore its solutions.2.Research on the strain signal extraction method of the optical frequency domain reflectometer.First,the signal demodulation method obtained by the photodetector in OFDR is studied,and two key extraction processes are obtained: Fourier transform applied to timefrequency domain conversion and cross-correlation calculation based on sliding window selection.Analyze the above two processes,study their calculation process in detail,and study the methods that can improve system demodulation accuracy and optimize system demodulation performance.3.The optical frequency domain reflectometer is used to realize the distributed temperature and pressure sensing system.The sensitive unit used for temperature and pressure measurement is designed,the temperature and pressure sensitive structure based on OFDR is realized,and the two physical parameters are correctly demodulated,and the linear fit reaches0.9.In order to explore the adaptability of the pressure-sensitive structure to the oil pressure environment,a further oil pressure experiment was carried out,which verified the feasibility of oil pressure measurement and reached an oil pressure measurement of 25 MPa.Test the distributed temperature measurement of the optical fiber,design a distributed measurement system,analyze the measurement results,perform two-dimensional data conversion,and finally complete the three-dimensional spatial distribution map of the distributed temperature measurement.