| Since the 20th century, vibration examination technique has gotten a huge development. It has experienced three stages: mechanical, electricial, and optical measurement technology. Currently, the electricial vibration seneor is widely used because of its mature technique and high senstivity, but it need insulating process and it is affected by electromagnetism interference easily, so that the purpose of producting safely is difficult to achieve. In a word, on account of these disadvantages of electricial vibration seneors, their application in high-voltage, large magnetic field such as power plant, has a lot of limitation. At the same time, the fiber-optic sensing technology which has many advantages such as high senstivity, small size, light weight, essential safety, anti-electromagnetism interference and corrosion resistance etc, represent the development direction of novel sensors. Therefore, in this paper optical fiber sensing technology and vibration detection technology is connected together, and vibration demodulation system based on optical fiber sensing technology is developed.In this paper, the following several topics are mainly studied:1) Fiber Bragg grating sensor working principle was analysized in detail based on coupled-mode theory, and fiber Bragg grating temperature and strain model was founded. At the same time, a new FBG vibration sensor was designed and vibration testing system was set up to verify the performance of fiber grating sensor. The experimental results as follows: the inherent frequency of the fiber grating vibration sensor is 250Hz; at low-frequency from 10Hz to 120Hz, the vibration sensor has a better response; the sensor can detect the smallest vibration intensity up to 2 micrometer. All the parameters satisfy the requirements of the Fan Vibration Detecting System.2) From analysis of optical coupling phenomenon based on local coupled-mode theory of slowly variable non-formal waveguide, Mathematical relationship of oupling outputs, coupling length and variation of refractivethe index was enduced. After analysis of the effect of vabriation to oupling outputs was achieved, coupling low frequency fiber-optic vibration sensor and high frequency fiber-optic vibration sensor were designed separately using single-mode optical fiber coupler. In Compare experiment of low-frequency coupling fiber-optic vibration sensor and FBG vibration sensor, low-frequency coupling fiber-optic vibration sensor respones more quick than FBG vibration sensor to striking signal, while the FBG sensor has bigger damping and decay faster, but they agree with ench other to periodic signal of 30Hz-50Hz. In Compare experiment of high-frequency coupling fiber-optic vibration sensor andpiezoelectricity vibration sensor, amplitude of the fiber-optic couplers is bigger than that of andpiezoelectricity vibration sensor, while they agree with ench other to vabriation signal of 2 KHz to 6 KHz.3) An integrated fiber-optic vibration demodulation system was designed, and hardware design and software design were introduced in detaile. Actual circuit schematic diagrams for the hardware circuit design, from the chioce of the photodiode, front-end current-voltage conversion circuit, amplifier, to the peripheral devices of LPC2148 were given out and the and the attention of the design process was pointed out. In the process of designing software, it was introduced that the port process of theμC/OS-II real-time embedded operating system on LPC2148, the interruption design of the vibration system demodulation system inμC/OS-II system, as well as the procedures for the design of the functions of the various tasks and their interrelationships. Finally, the implementation of USB Communications between PC and demodulation system was explained.4) According to the theoretical analysis and experimental results of the study, the fiber Bragg grating sensor was trialed in Fan vibration detection project at 500,000 KW generating units in a Generating Company, and it has achieved the desired results. |
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