Patent ID: 7298137
Filing Date: 2007-11-20
Classification: G01D

Abstract:
1. A position sensor comprising: first and second members which are movable relative to each other along a measurement path, the first member comprising an excitation winding and the second member comprising first and second resonators spaced apart along the measurement path; an excitation signal generator operable to generate an excitation signal and to apply the excitation signal to the excitation winding to induce a first resonant signal in the first resonator and a second resonant signal in the second resonator; and an analyser operable to analyse the first and second resonant signals to determine a value representative of the relative position along the measurement path of the first and second members, the analyser operable to measure a phase of a signal formed by a weighted combination of the first and second resonant signals; wherein the analyser is operable to generate a second signal at a frequency different from that of the excitation signal, and to mix the second signal with the signal formed by a weighted combination of the first and second resonant signals to generate a third signal having a frequency component equal to the difference between the frequency of the excitation signal and that of the second signal, and to determine the said value from the phase of the third signal; wherein the excitation winding and the first resonator have a first electromagnetic coupling which varies with the relative position along the measurement path of the first and second members in accordance with a first function, and the excitation winding and the second resonator have a second electromagnetic coupling which varies with said relative position in accordance with a second function different from the first function, and wherein the first resonator is operable to introduce a first phase shift into the first resonant signal and the second resonator is operable to introduce a second phase shift, which is different from the first phase shift by one quarter of a cycle, into the second resonant signal.