Kodierscheibe

An encoder disc for a photoelectric shaft angle encoder includes a disc body (10) which defines first (16) and second (18) regions. The first region (16) is defined between two circles of differing radii (R1;R2) and offset centers (22;26) positioned such that the two circles are substantially tangent at one point and the smaller circle is contained within the larger circle. The second region (18) is situated adjacent to the first region (16) and the first and second regions (16;18) have differing light transmission characteristics. The first region (16) forms a measuring track which varies in width substantially sinusoidally around the disc body (10). Especially good results are obtained when the two circles are offset from the central axis of the disc body (10) by substantially equal amounts.