Patent ID: 6909280
Filing Date: 2005-06-21
Classification: G01B,G01D

Abstract:
1. A position detector comprising a first member, a second member, a transducer, at least one analogue to digital signal converter, and at least one digital signal processor, wherein: the first member carries a train of elements of magnetic material disposed side by side in a row having a central axis in contact with one another and constrained against movement relative to one another, wherein the train has a varying dimension in a direction perpendicular to the central axis; the first and second members are relatively movable in a direction parallel to the central axis; the second member carries the transducer; the transducer comprises transmitting and sensing means, the transmitting means arranged to produce a magnetic field through the train of elements, and the sensing means comprising at least one pick-up coil which is disposed adjacent to the train of elements, and which is arranged to detect variations in the magnetic field which are produced during relative movement between the first and second members as a result of the variation in distance between the pick-up coils and the edge of the train of elements nearest the pick-up coils, whereby the at least one pick-up coil provides an analogue signal, the amplitude of which is characteristic of the relative position of the first and second members; the at least one analogue to digital signal converter is arranged to receive an analogue signal derived from the at least one pick-up coil and to convert it to a digital signal; and the at least one digital signal processor is arranged to receive the digital signals from the at least one analogue to digital converter, and is operable, at predetermined sampling intervals, to sample the digital signals and to determine the position of the first member relative to the second member using the characteristic variation of signal amplitude with respect to the relative position of the first and second members.