Optical fiber grating sensing method applied to small-size fire source monitoring

Patent metadata

Field	Value
Publication number	US-11313737-B2
Application number	US-202117387995-A
Country	US
Kind code	B2
Filing date	Jul 28, 2021
Priority date	May 9, 2020
Publication date	Apr 26, 2022
Grant date	Apr 26, 2022

Abstract

An optical fiber grating sensing method applied to small-scale fire source monitoring are provided, distinguishing two concepts of a spatial resolution and a perception resolution, under the premise of ensuring the spatial resolution of a traditional fiber Bragg grating sensing system, only increase the number of fiber Bragg gratings covered by a single pulsed optical signal without changing a pulse width of a pulsed optical signal, so as to improve the perception resolution of the system without increasing the requirements for a hardware circuit, and truly shorten an interval between adjacent fiber Bragg gratings. Improving the perception resolution of the system, which not only ensures the spatial resolution of the system, but also realizes the monitoring of small-scale fire sources; by adopting a simple feature extraction algorithm to obtain fire temperature information in different areas, the temperature detection speed of the system is fast.

First claim

What is claimed is:

1. An optical fiber grating sensing method applied to small-scale fire source monitoring, comprising following steps:
S 1 , engraving n fiber Bragg gratings with equal intervals on a single optical fiber continuously to form an identical ultra-weak fiber Bragg grating sensor network of large-capacity, an interval between adjacent fiber Bragg gratings is ΔL, recording the effective detection length of the identical ultra-weak fiber Bragg grating sensor network as L fiber , and then L fiber =n*ΔL;
S 2 , dividing the identical ultra-weak fiber Bragg grating sensor network into 2N regions of equal length, and m fiber Bragg gratings are distributed in each area, denoting a length of each area as D, and then D=m*ΔL=L fiber /2N, and a spatial resolution of the identical ultra-weak fiber Bragg grating sensor network is D, and the spatial resolution D is constant;
S 3 , inputting a pulsed optical signal into the identical ultra-weak fiber Bragg grating sensor network, a pulse width of a single pulsed optical signal covers all fiber Bragg grating an area, recording the pulse width of the pulsed optical signal as t, and recording a period as T; then t=2n eff D/c, T>2n eff L fiber /c, including n eff is a refractive index of a fiber core, and c is a propagation speed of light in vacuum;
S 4 , inputting pulsed optical signal to the identical ultra-weak fiber Bragg grating sensor network, reflection spectrum signals of m fiber Bragg gratings in each area are superimposed to form an overall regional spectrum signal;
S 5 , summarizing and classifying the overall regional spectrum, establishing different data processing mechanisms according to the overall regional spectrum, and obtaining detailed temperature information, so as to monitor a small-scale fire source;
wherein, the overall regional spectrum in S 5 including four features, which are respectively denoted as feature 1, feature 2, feature 3, and feature 4;
feature 1: when all fiber Bragg gratings in the area are under a same condition, a center wavelength of all fiber Bragg gratings in the area changes with the temperature, a spectrum of all fiber Bragg gratings are superimposed into the overall regional spectrum, and the overall regional spectral shape is similar to that of a single fiber Bragg grating while a peak intensity is m times the peak intensity of the single fiber Bragg grating, further, the overall regional spectrum shows an overall movement;
feature 2: when an area of only the single fiber Bragg grating in the area changes, the single fiber Bragg grating is recorded as FBG #n, a spectrum of FBG #n gradually separates from the overall regional spectrum and moves toward a long wavelength direction, and, further, a main peak intensity of the overall regional spectrum drops to (m−1)/m of an overall regional spectrum peak intensity under feature 1;
feature 3, when multiple fiber Bragg gratings in the area are affected by a same temperature and change, the overall regional spectrum shows that the main peak intensity drops to (m−x)/m of an overall regional spectral intensity under feature 1, and x is a number of affected fiber Bragg grating, an intensity of a side peak increases to x/m, and the intensity of the side peak moves with temperature;
feature 4, when multiple fiber Bragg gratings in the area change under a influence of different temperatures, the overall regional spectrum shows that the main peak intensity drops to (m−x)/m of the overall regional spectrum intensity under feature 1, x is the number of affected fiber Bragg gratings, and a shape of side peaks changes with the temperature of each fiber Bragg grating, a width of the spectrum of the overall region represents the size of a temperature gradient of the fiber Bragg grating in the area, and an intensity distribution of the side peaks is related to the number of fiber Bragg gratings on different temperature gradients;
the data processing mechanism in S 5 comprising following steps:
S 101 , a system initialization: maintaining all fiber Bragg gratings in the identical ultra-weak fiber Bragg grating sensor network at a same reference temperature C, then obtaining a maximum value of the overall regional spectrum of each area and a corresponding wavelength as reference value of the system, the maximum value of the overall regional spectrum is denoted as M i , and the corresponding wavelength of M i is denoted as λ i , where i represents a ith area, obtaining a sidelobe intensity on both sides of the regional spectrum, recording a left sidelobe intensity as S Left , and a right sidelobe intensity as S Right , recording a wavelength λ Left_i corresponding to an intensity of a leftmost sg times S Left of the overall regional spectrum and a wavelength λ Right_i corresponding to the intensity of a rightmost sg times S Right of the overall regional spectrum as a calibration value of the system the value of sg is based on the system's calibration value;
S 102 , obtaining the maximum value MAX of the overall regional spectrum of area i and a wavelength λ corresponding to MAX when the system is running in real time, and comparing MAX with M i ; region
if MAX and M i are equal, the overall regional spectrum of area i belonging to feature 1, and a highest temperature value of area i is recorded as T i , Ti=C+k*(λ−λ i ), and k is a temperature/wavelength coefficient of fiber Bragg grating;
if MAX and M i are not equal, proceeding to S 103 ;
S 103 , determining whether the maximum MAX of the overall regional spectrum of the area i satisfies MAX≥(m−1)/m*M i ;
if MAX≥(m−1)/m*M i , executing S 104 ; if equator MAX≥(m−1)/m*M i is not satisfied, then traversing a spectrum data of the whole area, finding two peak points MAX L and MAX R , and executing S 105 ;
S 104 , comparing the wavelength λ corresponding to MAX with λ t ;
if λ and λ i are equal, then the overall regional spectrum of area i belonging to feature 2, and the highest temperature value of area i: T i =C+k*(λ Right −λ Right_i ), λ Right is the wavelength at sg times S Right intensity on a far right side of the overall regional spectrum;
if λ and λ i are not equal, the overall regional spectrum of area i belonging to feature 4, and the highest temperature in area i is T i =C+k*(λ Right −λ Right_i ), the temperature value of other fiber Bragg grating is C+k*(λ−λ i );
S 105 , determining whether a sum of intensities of the two peak points MAX L and MAX R is equal to M i ;
if MAX L and MAX R is equal to M i , the overall regional spectrum of area i belongs to feature 3, and fiber Bragg gratings in area i are divided into two groups, fiber Bragg gratings in each group are affected by the same temperature and the number of fiber Bragg gratings in each group is m*MAX L /(MAX L +MAX R ) and m*MAX R /(MAX L +MAX R ), obtaining the wavelength λ L and λ R corresponding to the two peak points MAX L and MAX R , and the temperature information of the two groups of fiber Bragg gratings in area i are respectively: T L =C+k*(λ L −λ i ), T R =C+k*(λ R −λ i );
if MAX L and MAX R is not equal to M i , the overall regional spectrum of area i belonging to feature 4, the highest temperature of area i is C+k*(λ Right −λ Right_i ), and a lowest temperature is C+k*(λ Left −λ Left_i ), λ Left is the wavelength at sg times S Right intensity at the leftmost side of the spectrum.

2. The optical fiber grating sensing method applied to small-scale fire source monitoring according to claim 1 , wherein a value range of ΔL in the S 1 is from 8 cm to 20 cm.

Assignees

• Li Zhengying
• Wang Lixin
• Wang Honghai
• Guo Huiyong
• Jiang Desheng
• Wang Jiaqi
• Univ Wuhan Tech

Inventors

• Li Zhengying
• Wang Lixin
• Wang Honghai
• Guo Huiyong
• Jiang Desheng
• Wang Jiaqi

Classifications

• G08B29/185

  Signal analysis techniques for reducing or preventing false alarms or for enhancing the reliability of the system · CPC title

• G08B17/06

  Electric actuation of the alarm, e.g. using a thermally-operated switch · CPC title

• G01K2003/145

  Hotspot localization · CPC title

• G01K11/3206 Primary

  at discrete locations in the fibre, e.g. using Bragg scattering · CPC title

• G08B17/00

  Fire alarms; Alarms responsive to explosion · CPC title