Patent ID: 6884991

Claim:
Apparatus for measuring an angular position of a member that is rotatable about an axis and for counting the number of rotations of the member about the axis, said apparatus comprising: a first data ring centered on the axis and rotatable about the axis with the member, said first data ring including binary bit indicators for indicating an absolute angular position of the member; means for reading said binary bit indicators of said first data ring and providing a first signal indicative of said absolute angular position of the member, said first signal having a first resolution capable of detecting a first predetermined amount of change in the angular position of the member; a second data ring centered on the axis and rotatable about the axis with the member, said second data ring including binary bit indicators for indicating incremental changes in the angular position of the member; means for reading said binary bit indicators of said second data ring and providing a second signal indicative of said incremental changes in angular position of the member, said second signal having a second resolution capable of detecting a second predetermined amount of change in the angular position of the member, said second predetermined amount being less than said first predetermined amount; and means for receiving said first and second signals and using said first and second signals to calculate a calculated absolute angular position of the member, said calculated absolute angular position of the member having a resolution equal to said second resolution.