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: An electromagnetic suspension system for a vehicle has an electromagnet with an upright portion having a lift magnetizing winding and outwardly-extending arms at the top and bottom of this upright portion. Pole pieces on the four arms co-operate with reaction rails having corresponding surfaces. The vehicle can operate with a left-hand or a right-hand reaction rail or with both rails, thereby enabling gaps to be provided in rails at track junctions. Lateral guidance windings are provided on the lower arms of the magnet and the lower pole faces slope to the horizontal, in the lateral direction of the track so that, at a track junction, by emergizing appropriate windings, the vehicle is guided to a selected track. The lower arms are longer than the upper arms to give, as a result of the leakage flux, lateral damping.