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Research On Fiber Bragg Grating Cantilever Vibration Sensor

Posted on:2008-10-21Degree:MasterType:Thesis
Country:ChinaCandidate:C H LuFull Text:PDF
GTID:2178360212479719Subject:Measuring and Testing Technology and Instruments
Abstract/Summary:PDF Full Text Request
Vibration parameters such as frequency and acceleration etc. are often used to analyze mechanical faults in mechanical vibration fault diagnosis system, so it is especially important to measure vibration parameters accurately. However, the present-day vibration measurement system mainly consists of electromagnetic sensors, whose sensitivity is low with poor ability to resist electromagnetic interference so that the system is far from many practical applications. Accordingly, research & development of vibration sensors of new types can be the key to improving the existing vibration measurement system. The emergence of Fiber Bragg Grating (FBG) sensing technology can provide a good technical means to develop the current vibration sensor technology. FBG sensor with high sensitivity, wide dynamic range, immunity to electromagnetic interference, low cost, and small size, etc. will hold great applicable potentiality in the sensing field.In this paper, a design of FBG cantilever vibration sensor applied to mechanical vibration fault detection is presented. The sensor is based on fiber Bragg grating strain sensing principle so that it is characterized by high sensitivity, good insulation, small size, light weight, premium immunity to electromagnetic interference and easy remote monitoring. In actual measurement, it is necessary to install the sensor on the objects to be measured so that it is safe and convenient in use so as to realize absolute measurement.This sensor consists of a bimetallic cantilever; one end of which is fixed on the foundation support, and the other end is a mass block M, a FBG sticked on the beam is in the vicinity of fixed end. In measuring the mechanical vibration, the sensor seat should be fixed on vibration sources so that they can vibrate together, whereby causing the mass block M to vibration. And under the inertia action, the cantilever will produce strain to cause FBG to contract and stretch,whereby causing the variations in Bragg reflection wavelength. If the vibration is the simple-harmonic vibration, Bragg reflection wavelength will change periodically. Accordingly, the vibration measurement can be achieved via the detection of Bragg wavelength variations. It is proved that change of the Bragg reflection wavelength of FBG showed a linear relationship with amplitude of acceleration, through theoretical analysis, whereby obtaining that acceleration measurement range can be: 0-203g, wavelength sensitivity, 0.01nm/g; frequency measurement range, 20Hz-160Hz and the inherent frequency of 199.5Hz. ANSYS software is used to analysis the mode; a specific vibration sensor demodulation circuit converting optical signals into voltage signals is also presented. Finally, vibration acceleration amplitude and frequency is showed through oscilloscope; to solve problem of temperature-strain cross-sensitivity of the sensor, a real-time measurement of temperature was tested .On the basis of which the demodulation of simultaneous vibration/temperature double parameters is designed, whereby laying a good foundation for the following-up work.
Keywords/Search Tags:fiber Bragg grating, Bragg reflection wavelength, mechanical vibration fault diagnosis, bimetallic cantilever, modal analysis
PDF Full Text Request
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