Research On Performance Optimization Method Of Distributed Raman Optical Fiber Temperature Measurement System

The distributed Raman fiber optic temperature measurement system can achieve real-time measurement of spatial temperature,and is widely used in large-scale temperature safety monitoring fields such as transportation infrastructure,coal mine and oil field mining,and power grid cable operation status evaluation.However,in practical applications,the distributed Raman temperature measurement system has the following problems: the inconsistent transmission speed of the two signal beams of Raman scattering can cause misalignment,leading to errors in demodulation temperature;When there are multiple connection points in the sensing fiber,the connection loss causes a deviation in the temperature behind the connection point;The original signal strength of the system is weak,and the temperature resolution is low.In response to the above issues,this article conducts research on the temperature measurement principle,structural design,and performance optimization methods of the system.The specific work completed is as follows:(1)Analyze the Raman scattering temperature measurement theory,design and build a distributed Raman temperature measurement system based on dual ratio demodulation.The system has a temperature accuracy of ±1℃,a fiber optic measurement length of6 km,and a spatial resolution of 1m,achieving complete machine integration.(2)In response to the problem of asynchronous Raman scattering signals in the system,based on the principle of linear increase in position error with fiber length,a dispersion calibration method with multiple segment translations was used to correct.The scattering position error of Raman and anti Stokes light in the results did not exceed one sampling point,eliminating temperature errors caused by dispersion misalignment.For the case that the accurate boundary point of the temperature region cannot be obtained,the translation interval length is calculated by using the two positions of the reference fiber connection and the tail reflection peak.(3)A multi segment calibration method based on Raman ratio is proposed to achieve connection point compensation in response to the problem of significant errors in temperature measurement results in the presence of multiple connectors in sensing optical fibers.In the 6.47 km sensing fiber optic test composed of four optical fibers,the temperature error was reduced from 7.21 ℃ to 0.75 ℃ compared to the entire attenuation compensation through connection loss compensation.(4)A demodulation scheme based on variable pulse width differential signal is proposed to address the problem of low signal-to-noise ratio in the system.The scheme uses 60/70 ns pulse light measurement results as a difference,and combines the analysis of the superposition characteristics of scattered light within the pulse width to calculate the accurate temperature of the heating area using the differential signal.The experimental results show that this method improves the temperature resolution from 2.19℃to 1.15℃ while ensuring a spatial resolution of 1m in the system.