Research On Fire Alarm Technology Based On Fiber Bragg Grating

With the continuous development of the social economy and improvement of national security awareness,traffic security problems need to be solved urgently.As an important part of transportation,tunnel security is,therefore,receiving more and more attention.Due to the tunnels' characteristic of heavy smoke,semi-closed,dim light,etc.,tunnel fire will cause severe consequences.Therefore,real-time detection of the temperature inside the tunnel,the establishment of an accurate alarm threshold setting scheme,and timely and effective alarm have certain research significance.Due to the special tunnel environment,smoke-sensitive and photosensitive sensors have limitations.By contrast,the temperature-sensitive FBG sense with its high resistance to electromagnetic interference,long-term stability,high measurement sensitivity,and long-distance transmission is more suitable to measure tunnel fire temperatures.Firstly,the paper introduces and analyzes specifically the research status of the tunnel fire temperature field simulation method and tunnel fire detection technology commonly used at home and abroad.By comparing the existing fire detection technology,a scheme of tunnel fire alarm systems based on fiber grating is proposed.The FDS(Fire Dynamics Simulator)software was used to simulate the tunnel fire roof temperature.The relationship between the tunnel fire temperature and the wind speed was studied from the aspects of vehicle size,ambient temperature,and fire source power to deduct the calculation formula of the wind speed and ? T(fire temperature and The relationship between the difference in ambient temperature).A fire alarm strategy combining a fixed threshold and the dynamic threshold is proposed,which is the conventional fire determination method.According to it,the temperature of the tunnel ceiling greater than 50? will alarm,and if it is lower than 50?,the relationship between temperature rise and wind speed is obtained based on the tunnel size.The curve,which in turn determines the dynamic alarm threshold.The combination of a fixed threshold and dynamic threshold can solve the problem of false negative reporting by fire routine fixed threshold method.Secondly,the overall scheme of the hardware part is introduced,and the appropriate device is selected.The related principles or characteristics of main components such as ASE source,FBGA demodulator,and optical circulator are described in detail.The software part ofthe overall scheme is introduced.The data is sent to the host computer through the USB port.The host computer program is written in MFC,and the data is stored in the database.The database uses SQL SERVER 2008 with a large storage capacity.The user display interface,designed by using Visual Studio2015 webpage,performs the function of temperature display,alarm,and historical data chart display through reading data from the database.Finally,the hardware and software parts of the system are connected to complete the entire system.The calibration experiment was carried out to obtain a linear relationship between the center wavelength and the temperature giving the measurement accuracy of the system.The scale tunnel model was built for laboratory simulation experiments.The principle of scale and the given basis of fire source power were analyzed in detail.The theoretical and experimental comparisons of the simulation experiments were carried out,and the feasibility of the tunnel fire alarm system was proved.