Patent ID: 8482302

Claim:
A device for determining a clearance between a member and a surface over and relative to which the member moves, the device comprising: a first reference element; a second reference element facing the first reference element, and being movable to alter a distance to the first reference element; a fastening system for fastening the device to the member so that, during relative motion, the first reference element is held in a fixed position relative to the member and the second reference element slides over the surface, wherein the member is a rotatable member and the surface is a curved surface around and relative to which the rotatable member rotates; an urging arrangement which urges the second reference element into contact with the surface so that, as the second reference element slides over the surface and the clearance between the member and the surface varies, the second reference element moves relative to the first reference element; a sensor which measures the distance between the first and second reference elements; and an angular measurement system positioned on the rotatable member, which measures an angle of rotation of the rotatable member.