| Fire disaster endangers mankind's life and wealth, and endangers social safety, so mankind has been always looking for the method to eliminate or reduce fire disaster. The system of detecting temperature is one of the means of predicting fire disaster, it traces surrounding temperature in real time and sends out alarms while surrounding temperature rise abnormally or attain over threshold of temperature.Traditional method of detecting temperature is linear type power cable sensitive to temperature, but it is a sensor with electric power, and can not fit to some special fields such as petroleum, chemical, military and so on in which the sensors is required prevent of blast in essence; the method of detecting temperature based on the technology of Raman scatting, in which the weak signal processing technique is required and the instrument is complicated, does not response to temperature signal quickly and can not fit to predict fire disaster very well.Fiber Bragg grating sensor has excellent character to temperature, Fiber Bragg grating is used as sensor to detect temperature and the identical Fiber Bragg grating technology is introduced to fulfill fire alarm system in this dissertation, which is applied widely in the field of petrifaction. The project of this dissertation is sourced from the develop project of new product in science and research ministry "fire alarm system based on detecting temperature"(project No. [2004]ED760001), and the research project in science and technology HuBei province "fiber grating temperature sensor and fire alarming system based on sensing temperature"(project No. 2003AA101B02).In this thesis, the basic theory of fiber grating sensing has been presented from coupled mode theory to fiber grating Bragg equation; the technology of wave demodulation is the key of fiber sensing technology, the method and principle of some demodulators have been presented, and the demodulator designed and studied in the central of fiber sensing technology WuHan university of technology has been recommended specially.Based on analysis and experiment, the character sensitive to temperature of FBG sensors encapsulated are revealed. Furthering the analysis and experiment, the quadratic approximating to real signal-temperature curve has been educed, which ensures the precision of measurement in detecting temperature..In this thesis, the work mechanism of identical FBG technology is discussed in detail, and the fire alarm system based on detecting temperature in large scale is fulfilled, and the problem that the quantity of FBG sensor is restricted by the bandwidth of SLED and demodulator is solved. Being aimed at the identical FBG technology, the demodulating complex method that the edge wavelength of spectrum and central wavelength of spectrum are demodulated at same time is proposed firstly, by this method, the special requirement of identical FBG sensors demodulation is not only satisfied with but the problem that the detection precision is infected by SLED weaken is solved also. In this thesis, the method of combining identical FBG technology and wavelength division multiplex technology is adopted too, and the fire zone can be located in the fire alarm system. Further developing fire alarm system, the project of fire alarming system with function of locating zone accurately based on encode fiber grating technology has been discussed.In the end of this thesis, the layout about the information processor of fire alarming system is presented. It presents mostly the signal collecting and communication of data exchanging in interior and exterior. At last, two specific applications corresponding to two methods those are identical FBG technology and identical FBG technology & wavelength division multiplex technology are presented separately. And prospect for study in fiber sensing in future is present. |
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