Study of non-contact detection sensor based on fiber Bragg grating

According to special requirements of vibration monitoring of large rotating machinery, such as Turbine and compressor, a non-contact fiber Bragg grating (FBG) based vibration detection sensor is designed. The magnetic coupling technology and elastic diaphragm are adopted to achieve the vibration detection by changing the axial strain of optical fiber grating. This paper describes the structure and working principle of the sensor, and studies the static and dynamic characteristics of the sensor in theory, finite element analysis and experimental. The diameter and thickness of Magnetic coupling probe is respectively 12 mm and 8 mm, the effective diameter, thickness and hard-core diameter of elastic diaphragm is respectively 32 mm, 0.25 mm and 12 mm. The results show that: the relationship of distance and fiber grating wavelength is nonlinear in range 0.5mm~3.5mm of the probe and the measured object, but it has a good degree of linearity in some small-scale range. when the distance range between the probe and the measured object was 0.5 mm ~1 mm, the sensitivity was 1.63 pm/μm, nonlinearity was 7.56%; the distance range was 3 mm ~3.5 mm, sensitivity was only 0.109 pm/μm, nonlinearity was 2.08%; In the dynamic aspects, the resonance frequency is 160 Hz, and the amplitude-frequency curve of the receiving sensitivity response is relatively flat within the frequency range of 0~90 Hz.