Abstract: An apparatus for monitoring the inductance of a coil (L1) which is not part of a resonant circuit including a second coil (L2) connected in series with the first mentioned coil and a resonant circuit which is formed by connection of a capacitor (C5) to the second coil, or optionally (C2) to a third coil (L3) which is in a mutually inductive relationship with the second coil so that the second and third coils act as the primary and secondary coils of a transformer (M), a device (1) for injecting into the circuit containing the first mentioned and second coils an a.c. signal of substantially constant peak voltage amplitude having a frequency within the resonance peak of the resonant circuit, and an amplitude detector (5) for measuring the amplitude of the voltage across a component of the resonant circuit. The apparatus may be employed as so-called integral control in closed loop control of the suspension of an object by the first mentioned coil.

Abstract: An apparatus for the electromagnetic control of the suspension of an object including an electromagnet including an inductive coil, a source of electric power for the electromagnet which source includes a controllable electric supply device capable of delivering a controlled electric supply to the coil of the electromagnet, a control signal producer for producing an error control signal in response to an incremental change in a parameter related to the position of the object relative to the electromagnet and a negative feedback control loop for feeding an error control signal generated by the control signal producer to the electrical supply device to adjust the electrical supply to the coil so as to stabilise the suspension of the object relative to the electromagnet, wherein the control signal producer includes a detector for detecting the component V.sub.

Abstract: A method of controlling the electromagnets of a magnetic bearing comprises the steps of (1) deriving from a first sensor a first signal representative of the absolute position of a shaft supported in the bearing, (2) limiting the first signal to a first control range which defines a range of shaft displacement, from any desired position smaller than the full range of possible displacements within which the restoring force is related to the displacement sensed, (3) deriving a second signal substantially independent of the first signal and also representative of the absolute position, (4) processing the second signal to derive therefrom a third signal representing the rate of change of the absolute position over the full range of possible shaft displacements, (5) combining the first and third signals to produce a control signal, and (6) applying the control signal to control the electromagnets so as to restore the shaft to the desired position in the bearing.

Abstract: Axial magnetic bearings are described suitable for use where high loads and high rotational speeds are found together. The bearings comprises an assembly where, for thrusts along the shaft in one direction, the shaft has, in relation thereto, two axially spaced, and radially extending, thrust accepting faces, a generally channel-shaped, annular electromagnet surrounding the shaft, with a radially extending face of each pole of the electromagnet adjacent to an individually associated thrust face.