An inductive detector operable to measure displacement along a path comprises: a first inductive arrangement; a second inductive arrangement; said second inductive arrangement being spaced from said first inductive arrangement and extending along at least part of the measurement path; at least one of said inductive arrangements comprises a winding which extends along at least part of the measurement path; and said winding comprising at least four loops in electrical series; wherein adjacent loops have opposite magnetic polarity; and the pitch distance of said winding varies at least once along the measurement path.
1. An inductive detector operable to measure displacement along a path comprising:
a first inductive arrangement;
a second inductive arrangement; said second inductive arrangement being spaced from said first inductive arrangement and extending along at least part of the measurement path;
at least one of said inductive arrangements comprising a winding which extends along at least part of the measurement path, said winding comprising at least four loops in electrical series;
wherein adjacent loops of said winding have opposite magnetic polarity;
the pitch distance of said winding varies at least once along the measurement path, wherein said pitch distance increases along the measurement path or decreases along the measurement path or varies incrementally along the measurement path; and
the other of said inductive arrangements comprises at least two targets separated by a distance which is fixed.
2. An inductive detector according to claim 1 , wherein the measurement path is circular and the pitch distance incrementally decreases along a succession of winding portions along the measurement path from a portion of maximum pitch distance to a portion of minimum pitch distance; the maximum pitch distance portion and the minimum pitch distance portion being adjacent to one another.
3. An inductive detector according to claim 1 , wherein at least one of said inductive arrangements is laminar.
4. An inductive detector according to claim 1 , wherein said winding is laminar.
5. An inductive detector according to claim 1 , comprising a first winding and a second winding; said second winding being shifted along the measurement path relative to said first winding.
6. An inductive detector according to claim 5 , wherein said second winding comprises at least four loops in electrical series wherein adjacent loops have opposite magnetic polarity and the pitch distance varies at least once along the measurement path.
7. An inductive detector according to claim 1 , wherein the loop polarity and pitch distance of at least one winding forms a unique pattern over four loops.
8. An inductive detector according to claim 1 , wherein at least one winding is at least in part planar.
9. An inductive detector according to claim 1 , further comprising a second winding and a third winding; said third winding extending along at least part of the measurement path.
10. An inductive detector according to claim 1 , wherein the measurement path is chosen from the list: linear, circular, and curvi-linear.
11. An inductive detector according to claim 1 , wherein each of said targets consist of a resonant circuit, and the distance between said resonant circuits is fixed.
12. An inductive detector according to claim 11 , wherein said resonant circuits are resonant at different frequencies.
13. An inductive detector according to claim 11 , wherein the distance between first and second inductive resonant circuits is less than the shortest pitch distance of the winding of said first inductive arrangement.
14. An inductive detector according to claim 1 , wherein:
the first and second inductive arrangements are laminar and are attached to a metallic housing;
a gap is provided between the laminar inductive arrangements; and a gap is provided between the metallic housing and the laminar arrangements;
wherein said gap between the laminar inductive arrangements is less than said gap between metallic housing and the laminar arrangements.