Absolute position encoder scale having plates alternating with varying recesses

A position sensing device usable to measure a position of a first member with respect to a second member along a measuring axis, the position sensing device comprising:

• a scale including a portion comprising a scale pattern extending along the measuring axis direction;
• and
• a read head for being moved relative to the scale pattern along the measuring axis direction, the read head comprising an excitation portion that excites the eddy currents in the scale pattern, and a signal portion that outputs position signals that vary depending on the eddy currents;
• wherein:
• the scale pattern comprises:
• a plurality of first scale element zones arranged periodically along the measuring axis direction, wherein the first scale element zones include a first type of scale element;
• and
• a plurality of second scale element zones arranged periodically along the measuring axis direction and interleaved with the plurality of first periodic scale element zones such that the first and second scale element zones repeat periodically along the measuring axis direction according to a scale wavelength P, wherein the second scale element zones include a second type of scale element having a characteristic that is varied in an absolute signal range along the scale pattern to provide a different respective eddy current response in different respective second scale element zones in the absolute signal range;
• and
• the signal portion is responsive to the respective eddy currents to output absolute position signals having a signal characteristic that varies along the absolute signal range to uniquely indicate respective positions along the absolute signal range.