GB1418261A - Radial displacement detection device for a magnetic bearing - Google Patents

Abstract

1418261 Measuring displacements electrically SOC EUROPEENNE DE PROPULSION 17 Jan 1974 [18 Jan 1973] 02270/74 Heading G1N The radial displacements of a rotor 2 (Fig. 1) mounted on a fixed shaft 4 on magnetic bearings 3 and driven by a motor 5, are measured at each end 2a, 2b of the rotor by a detector 1 comprising a fixed disc 1a (Fig. 2) carrying a symmetrical arrangement of U-shaped cores 1d-1k, each wound with a coil whose inductance is determined by the size of the air gap between the ends of the U-shaped core and a surrounding magnetic ring 2d attached to the rotor 2. The cores 1d-1g are symmetrically located at 30 degrees to an XX' axis on the disc 1a, and the other cores 1h-1k are similarly located with respect to a perpendicular YY' axis on the disc. The coils 1d-1g are wound in series with a wire 11, and the coils 1h-1k are wound in series with a wire lm, to give the polarities shown when energized with one half-cycle of an A.C. supply. Centre taps 1n, lo, respectively are provided for each group of windings. When the rotor 2 is displaced radially, e.g. to the right along axis XX', the inductances of coils le, 1d increase and the inductances of coils lf, 1g correspondingly decrease, producing a corresponding signal on centre tap 1n. Similarly radial displacement along axis YY, produces a corresponding signal on centre tap lo. If the rotor 2 is not perfectly circular, the changes in the air gap between the rotating ring 2d and the static disc 1a form a series of harmonics of the fundamental displacement signal. Considering coils 1d-1g measuring XX' displacements, all the even harmonics produce equal inductance changes in the coils on either side of the centre tap In and therefore produce no resultant output signal on that lead. Also the pairs of coils 1d, 1e and 1f, 1g on each side of the centre tap 1 n are displaced by 60 degrees and connected in series, whereby the effects of the third harmonic are eliminated. By further duplication of coils and selected spacing it is possible to eliminate the effect of further odd harmonics.