Position detection using a spaced apart array of magnetic field generators and plural sensing loop circuits offset from one another in the measurement direction

DETAILED DESCRIPTION According to one aspect, the present invention provides a sensor head for use in an apparatus for indicating the position of a movable member relative to a fixed member, the sensor head comprising: at least two sensor windings, mounted on the sensor head, each comprising at least one period of series connected alternate sense loops of conductor, wherein each sensor winding is spatially separated in the measurement direction and wherein the arrangement of the multi-turn sensor windings is such that their respective mid-points substantially coincide.
Such a configuration of sensor head is advantageous in that it is less sensitive to longitudinal tilt of the sensor head relative to the other member.
Each sensor winding can be defined by conductors on a plurality of layers of a printed circuit board.
This has the advantage of reduced manufacturing cost.
Preferably, the sensor windings are defined by two complementary repetitive patterns of conductors mounted on two sides of the printed circuit board, and wherein each side of the printed circuit board carries a portion of each repetitive pattern.
With this arrangement, the sensitivity of the position encoder to roll of the sensor head relative to the fixed track is reduced.
An embodiment of the present invention provides an apparatus for indicating the position of a movable member relative to a fixed member, comprising: a plurality of magnetic field responsive elements equally spaced along the fixed member; and a sensor head as described above, mounted for movement with the movable member, and arranged such that when the magnetic field responsive elements are energised, signals are induced in the sensor windings which are dependent upon the position of the movable member relative to the fixed member.
Preferably, the magnetic field responsive elements are resonant circuits, as this allows a pulse-echo mode of operation.