Study Of Non-Contact Magnetic Coupling Displacement Sensor On Fiber Bragg Grating

Numerous industrial practices require measuring the displacement of objects, especially to satisfy the special requirements of vibration monitoring of large rotating machinery, such as Turbine and compressor. Adopting non-contact measurement is an important developing direction in displacement sensing technology currently. This also puts forward the objective demand to the displacement measurement by the production time. Therefore, based on such development needs a non-contact fiber Bragg grating (FBG) based vibration detection sensor is designed, which the magnetic coupling technology and elastic diaphragm are adopted to achieve the vibration detection by changing the axial strain of optical fiber grating. This designed sensor comprehends advantages of optical fiber sensor, which is explosion-proof and easy distance telemetry, as well, it also combines oil resistance and availability in the high dust environment if utilizes magnetic field measurement method. It is expected to solve the problem of long-distance and non-contact monitoring to the physical deformation displacement in the inflammable, explosive and high dust high oil pollution environment.This thesis refers to several subjects such as mechanism, material, and information. Main jobs completed are as follows:1. Analyze the domestic technology on non-contact sensor, compare their working principles, merits and experimental data. Expound the working principle of FBG and theory of the fiber Bragg grating coupling model; analyze the sensing properties of FBG in strain, temperature and pressure.2. Devise a non-contact magnetic coupling displacement sensor based on optical fiber Bragg grating with temperature compensation.3. Analyze the magnetic coupling probe. Based on the modeling theory of FEM (Finite Element Method), and the electromagnetic foundational theory. The finite element model is built by simplifying appropriately the original model, selecting the element type, meshing and defining the boundary conditions. Then, the model is solved, and the result from analysis is compared with that from the works home and abroad, which strengthens the validity of the model. 4. Proceed static, dynamic and temperature test on this designed sensor, and analyze the correlative data, the relationship of distance and fiber grating wavelength is nonlinear in range0.5mm-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 was0.5mm～1mm, the sensitivity was1.627pm/μm; the distance range was3mm～3.5mm, sensitivity was only0.104pm/μm5. Analyze the reasons of the tested data from the two aspects of theory and experiment comprehensively, and make recommendations and opinions on the improvement of the sensor.The innovations of the thesis mainly include following aspects:1. The modeling method of the magnetic analysis of the sensor is formed, which can provide some references to others.2. The effects of the parameters to the properties of the sensor are studied by FEM, and the results from analysis are compared with that from works home and abroad. Which indicates FEM may simulate the properties of the sensor well.