Study on magnetic coupling FBG displacement sensor

For displacement measuring, non-contacting measurement is not only an important development direction, but also an objective demand of productive practice. A non-contacting magnetic coupling displacement sensor based on fiber Bragg grating, FBG, sensing technology is researched in the paper, which combines advantages of FBG sensor with ones of magnetic measuring methods such as flame protection, remote monitoring, oil corrupt, work in dust-laden atmosphere. So it is hopeful that remote and non-contacting measurement for displacement is carried out in flammable, combustible, dust-laden and high oil corrupt atmosphere. Its sensing principle is, two pieces of flat cylinder-shaped permanent magnet are linked by soft magnetic material to form an U-type probe, thus a closed magnetic circuit is formed from this U-type probe and the measured moving object, by which the transferring relation between the gap and magnetic field force can be established, and then by means of a planar circular sheet the magnetic coupling force can be converted into the sensing FBG axial strain, thus the central wavelength of the FBG sensor will shift and the displacement of measured moving object can be obtained by detecting the shift. Some experiments are done to research its static and dynamic performance. The results indicate that this non-contact displacement cell is a nonlinear sensor, but after being processed piecewise, its output can be considered approximately linear within a little displacement. It has good dynamic frequency response characteristics and the maximum response frequency is about 50Hz, and moreover, the problem about temperature compensation in dynamic measuring process can be settled well by using a disposal way that the difference between wave top and wave trough is defined as a sensing signal. So it is feasible for the sensor to monitor axial or radial vibration of such high-speed rotary machines.