Patent ID: 8020453

Claim:
An inductive position detector comprising: an electrical intermediate a inductive device defining a measurement path; and an inductive antenna comprising at least two receive windings which have a fixed relative spacing along the measurement path; said electrical intermediate inductive device being a distinct device from said antenna wherein: relative movement of the electrical intermediate inductive device and the inductive antenna changes the position of the inductive antenna on the measurement path; the electrical intermediate inductive device comprises a substantially laminar passive resonant circuit formed by at least an outward conductive winding, a return conductive winding and a capacitor arranged in series with the conductive windings; the outward winding and the return winding of said electrical intermediate inductive device cross to form at least two inductive loops of opposite current flow, in use, and the transverse distance of the outward winding to the measurement path varies with distance along the measurement path according to a predefined relationship such that the mutual inductance of the receive windings of said antenna and the passive resonant circuit of said electrical intermediate inductive device is a function of the position of the antenna on the measurement path; and the antenna is configured to induce an alternating current in the passive resonant circuit of said electrical intermediate inductive device, in use, such that the induced alternating current in the passive resonant circuit induces an alternating signal in the receive windings of said antenna by virtue of the mutual inductance of the receive windings of said antenna and the passive resonant circuit of said electrical intermediate inductive device, which signal is indicative of the position of the antenna on the measurement path; wherein said passive resonant circuit of said electrical intermediate inductive device comprises at least one pick-up winding in series with said outward and return conductive windings; said pick-up winding having substantially constant width along the measurement path.