INNO fibre optic temperature sensors ,temperature monitoring systems.
Fiber Bragg Grating Temperature Sensing Fire Detection System
Fiber Bragg Grating (FBG) utilizes the photosensitivity of fiber core materials and forms periodic refractive index changes along the axial direction in a specific way in the fiber core, forming an optical device with FBG structure. FBG has the characteristic of narrowband reflection. When the incident broadband light source passes through FBG, only narrowband light signals with wavelengths that meet the phase matching conditions can be reflected, while other wavelengths of light signals transmit into the fiber and continue to propagate forward. Related studies have shown that within a wide temperature range and without the influence of other external factors, there is a good linear relationship between the wavelength shift of FBG reflection center caused by temperature changes and temperature changes. By measuring the wavelength change of the FBG reflection center, the temperature change of the surrounding environment of the FBG can be obtained.
Structure of Fiber Bragg Grating Temperature Sensing Fire Detection System
Composition of Fiber Bragg Grating Temperature Sensing Fire Detection System
The fiber optic grating temperature sensing fire detection system is mainly used for online real-time monitoring of the temperature in the monitoring area, displaying temperature changes in the area, and providing alarms in case of abnormal temperature rise. The fiber optic grating temperature sensing fire detection system mainly consists of an alarm device, a wavelength demodulation device, a fiber optic grating temperature sensing probe, a transmission optical cable, and a computer.
The fiber optic grating temperature sensing probes arranged at various monitoring points are connected through transmission optical cables, and together with broadband light sources and wavelength demodulation devices, form a temperature sensing fire detector; In order to distinguish the detection positions, each fiber Bragg grating temperature sensing probe corresponds to different reflection wavelengths in the initial state. The fiber Bragg grating wavelength demodulation device monitors the reflection wavelength and its changes of each probe in real time to obtain the corresponding temperature changes at the monitoring points; The reflected light sensing signal is transmitted to the computer system for processing through optical fibers and wavelength demodulation devices. The wavelength demodulation device is the demodulation part of the fiber Bragg grating temperature sensing fire detection system, which is composed of a photodetector, an optical splitter, a wavelength adjustment setting unit, a broadband light source, a constant temperature demodulator, and corresponding electronic circuits. The wavelength demodulation device communicates with the data terminal host through USB or RS232, and data processing is achieved through software in the data terminal host to achieve real-time monitoring and alarm of on-site temperature sensing signals.
Characteristics of Fiber Bragg Grating Temperature Sensing Fire Detection System
The fiber optic grating temperature fire detection system is used to detect fires through fiber optic grating temperature sensors distributed at various monitoring points. The monitoring area is limited by the location of the fiber optic grating temperature sensors. However, due to the high temperature sensitivity of fiber optic gratings and the existing wavelength demodulation technology that can fully demodulate their reflected wavelength signals, the fiber optic grating temperature fire detection system still has extremely high sensitivity. The temperature measurement accuracy can reach ± 2 ℃, and the wavelength signal is more stable than the light intensity signal, which is not affected by the attenuation or insertion loss of the light source. Compared with distributed fiber optic temperature fire detection systems, it has higher accuracy and better anti-interference ability. At the same time, the price of ordinary broadband light sources is much lower than that of high-quality laser light sources, It also makes it more cost-effective compared to distributed fiber optic temperature sensing fire detection systems.
The Application of Fiber Optic Temperature Sensing Fire Detection System
Installation method of fiber optic grating temperature sensing fire detection system
In the interval tunnel, the main sources of heat that promote the increase of environmental temperature are thermal radiation and thermal convection. Convective heat is propagated through the accumulation of hot air at the top of the tunnel, while radiative heat is propagated in a straight line. When a fire occurs inside the carriage, heat is radiated out through the window glass in the early stages of the fire. Only when the fire is intense, heat convection becomes the main mode of heat transmission. Due to the fact that fire detection in subway tunnels is mainly aimed at the early stages of fires, in order to achieve early display and alarm of fires inside the carriages, the characteristics of heat radiation mainly transmitted through the windows during the early stages of fires inside the carriages are addressed,
The distributed fiber optic temperature sensing fire detection system and fiber optic grating temperature sensing fire detection system should be installed on the inner wall of the tunnel at heights such as train windows with distributed temperature sensing fiber optic and fiber optic grating temperature sensing probes. In addition, to achieve early display and alarm of fires caused by cable short circuits or open circuits, distributed fiber optic temperature sensing fire detection systems and fiber optic grating temperature sensing fire detection systems should be installed on both sides of the tunnel with distributed temperature sensing optical fibers and fiber optic grating temperature sensing probes installed on strong and weak cable trays.
Networking method
The host of the distributed fiber optic temperature sensing fire detection system and fiber optic grating temperature sensing fire detection system can be connected to the upper level comprehensive monitoring system switch through Ethernet in the form of RJ485 interface, uploading all temperature monitoring information in the system. The upper level comprehensive monitoring system completes functions such as control, monitoring, and management, and monitors temperature, fire situation, and equipment operation in real time.
Distributed fiber optic temperature sensing fire detection system and fiber optic grating temperature sensing
The fire detection system can be connected to the host of the fire automatic alarm system through relay contacts (or communication interfaces), and output alarm signals when a fire occurs, achieving fire alarm linkage. The distributed fiber optic temperature sensing fire detection system and fiber optic grating temperature sensing fire detection system can be connected to the environment and equipment monitoring system equipment through relay contacts. They can serve as interval temperature sensors for the BAS system, achieving real-time monitoring and linkage control of environmental temperature, energy conservation and emission reduction, and can work together with the BAS system to control the blocking mode when tunnel trains are blocked. Based on the above analysis, it can be seen that distributed fiber optic temperature sensing fire detection systems and fiber optic grating temperature sensing fire detection systems each have their own advantages and disadvantages, and can be applied targeted to different situations. For tunnels with longer subway sections, a distributed fiber optic temperature sensing fire detection system can be used if the total system price allows for continuous monitoring of temperature changes; For stations with inconvenient operation and maintenance, such as platform boards or cable interlayers, as well as important equipment rooms, the use of fiber optic grating temperature sensing fire detection systems can greatly improve the accuracy of temperature monitoring. Practical applications have proven that distributed fiber optic temperature sensing fire detection systems and fiber optic grating temperature sensing fire detection systems, with their respective good characteristics, have become powerful supplements to traditional temperature sensing fire automatic alarm systems. It is expected that their applications in the field of rail transit will become increasingly widespread.