Fiber Optic Raman Distributed High Temperature Measurement System

The safe production of high-temperature related industries such as heat pipeline,oil well mining,and aluminum rod deep well casting cannot be separated from accurate and timely temperature monitoring.The leakage of high-temperature water from heat pipelines affects the quality of life of a large number of urban residents and even threatens personal safety,while the leakage of high-temperature aluminum liquid in the process of aluminum rod deep-well casting can explode if not detected in time,and many aluminum liquid leakage accidents in previous years have caused a large number of casualties and property damage.Compared with the traditional temperature sensor,fiber optic Raman distributed temperature measurement system with its long temperature measurement distance,anti-electromagnetic interference,fast response time,easy to lay and other characteristics have been widely concerned,while the spatial resolution of fiber optic Raman distributed temperature measurement system is limited by the laser pulse width,there is the problem of large temperature measurement error when the fiber length is too short,so we designed a fiber optic Raman distributed high temperature measurement system for the problem,and completed the following work.And the following work was accomplished:(1)The advantages and disadvantages of three temperature demodulation methods commonly used in fiber optic Raman distributed temperature measurement systems are analyzed,and a two-way demodulation method based on anti-Stokes and Stokes light is selected,and the demodulation method is improved by using a dynamic temperature compensation method with poor attenuation coefficient for the disadvantages of this method at large temperature widths.(2)The overall structure of the fiber optic Raman distributed high temperature measurement system was designed according to the demodulation method,and the selection of each module was completed.Based on the needs of different temperature measurement ranges,three different coating sensing fibers were selected.The main indexes of the system were analyzed with the parameters of each device.(3)To address the problem of insufficient temperature responsiveness of the system due to the placement of fiber in the high temperature region shorter than the laser pulse width,a method of Raman signal segmentation and reconstruction was proposed by analyzing the characteristics of the backscattered Raman signal at a small high temperature region.The temperature error of 0.72 m acrylate coated fiber placed at92.1°C was reduced from 33.9°C to 5.8°C,and the temperature error of 1m polyimide coated fiber at 300°C was reduced from 104.6°C to 4.5°C under the laser pulse width of 20 ns.(4)The high temperature test platform was built according to the test requirements,and the temperature resistance range of acrylate,polyimide and copper coatings were tested,as well as the performance of temperature measurement accuracy,attenuation and stability at different temperatures.In the test results,the acrylate coated fiber can achieve ±1℃ temperature accuracy and 1.5m spatial resolution index within10℃～90℃;the polyimide coated fiber can be within 300℃ achieve ±2℃ temperature accuracy and 1.1m spatial resolution after applying signal analysis and reconstruction algorithm;copper coated optical fiber achieves ±2℃ temperature accuracy within30℃～130℃,and ±10℃ temperature accuracy within 130℃～370℃ because of objective factors such as difficulty of metal material coating process and change of material properties due to oxidation.(5)The results of the field test of fiber optic Raman distributed high temperature measurement system in thermal pipeline leakage and aluminum rod deep well casting were analyzed,and the results showed that the system can accurately monitor the temperature changes along the fiber,and has a vast application prospect in the field of high temperature leakage monitoring.