Research On Resolution Of Raman Backscattering Distributed Optical Fiber Temperature Fire Alarm System

Distributed optical fiber temperature fire alarm system, for its particular advantage, was gradually applied to kinds of temperature measurement occasions, such as fire detection in subway and cable tunnel, temperature monitor in dam concrete and oil well. However, different situations had different requirements on time resolution, spatial resolution, temperature resolution and temperature measurement distance. In the past researches, researchers usually chosen one index as their focus and studied the index’s influence factors and measurements for improvements. But those studies had not dug into the influences among those resolutions. This article mainly worked on the subjects as below:Firstly, the text reviewed the positioning principle, basing on Optical Time-Domain Reflectometry, and Raman scattering temperature measurement principle. Second, it explained the system’s components and working process briefly. Next, it specified the choosing of main devices in the system hardware, research and production of the related circuit. Finally, this article introduced the methods of signal processing and point calibration one by one.To improve system’s stability, set about improving Stability of the devices and SNR of system. Specific measures: a) Using the method of constant temperature and voltage in APD, explaining the reason of not taking the method of reverse bias voltage- temperature compensation; b) Taking the method of constant temperature in laser; c) Combining the wavelet denoise technique and technique of digital accumulation and averaging to improve SNR of system. Finally, it will prove the stability and reliability of system through experiments.Doing theoretical research on system’s resolution indexes, including the definition of resolution, influence factors and improving measures. This article especially calculated the computational formula of temperature resolution in details. What’s more, basing on the computational formula, the research found out a relation formula between resolutions and temperature measurement distance, pointing out that those four indexes influence each other, and there is no way to improve one index without sacrificing other indexes.The study did lots of experiments on system’s time, space, temperature resolution and temperature measurement distance by making measuring methods of resolutions. According to the experimental results, researcher drawn three-dimensional column diagram about the relationships of distance, spatial resolution and temperature resolution in different times, verified the results of theoretical analysis, provided a reference for practical application of system model selection. At last, the researcher illustrated how to choose the right system which has different resolutions according to the application situations.