Temperature Alarm Method And Temperature Precision Improvement For Distributed Fiber Raman Temperature Sensor System

With the ever-increasing demand in human production and life,temperature measurement technology has been continuously researched studied and developed from electrical temperature sensors to optical fiber temperature sensors.The distributed optical fiber temperature sensor system(DTS)uses optical fiber as its transmission medium and sensing element,and fully utilizes the advantages of high sensitivity,electricalinsulation,large signal transmission bandwidth,anti-electromagnet-is interference,flexibility,and lightness of the optical fiber.It achieves the accurate measurement of distributed and continuous temperature field along the sensing fiber distribution.It shows its unique advantages in the field of temperature measurement,and pushes the temperature measurement technology to a new level.DTS mainly relies on the backscattered light that carries the temperature information generated when the pulsed light is transmitted in the optical fiber to demodulate the temperature,and then locates according to the optical time domain reflectometry technology(OTDR)to obtain the temperature-position information along the optical fiber distribution.In many different kinds of DTS,the distributed Raman temperature sensor system used back-side Raman scattering light to demodulate the temperature information,that has a very obvious temperature-sensitive effect in the silica optical fiber,and it is not susceptible to nonlinear effects.It is widely used in electric power,transportation,frefighting,petrochemical,aerospace and other important fields.This paper focuses on the distributed Raman temperature measurement system,improves the temperature alarm method of the system,and proposes a method to improve the temperature accuracy.The paper mainly includes the following aspects:1.Introducing the Raman scattering principle and the optical time domain reflectometry technique(OTDR)applied in DTS.By comparing the three demodulation methods of the distributed Ranman temperature sensor system,identified with the reference light path of Stokes of double light path system structure.2.Explaining the principle for model selection of the main components in the system,selecting the appropriate components to build the system,introducing the main performance indicators of the system(temperature measurement accuracy,temperature resolution,spatial resolution,spatial positioning accuracy,and measurement time,etc.)in detail,and briefly analyzing some influencing factors of these performance indicators.3.Simulating the fire alarm experiment,improving the existing alarm method applied to DTS,and determine the alarm method of three temperature alarm methods run simultaneously include the constant temperature alarm method,differential temperature alarm method and temperature prediction method.The introduction of the light intensity judgment method in the differential temperature alarm effectively reduce the probability of false alarm compared with the existing method relying only on the temperature change rate alarm;In optical fiber temperature prediction method using the change of coefficient of dispersion of the current and past temperature to judge and predict temperature changes in the future,effectively reducing the system's response time of constant temperature alarm from 25s to less than 15s.4.Analyzing the source of Rayleigh noise and its effect in single-path and dual-paths demodulation on the system temperature precision,measure the Rayleigh noise in the system,and propose a method to eliminate Rayleigh noise by introducing a circulator,this method effectively make the system temperature precision increases from ±20? to ± 1?.