Self-monitoring optical encoder for wavelength division multiplexing optical sensors

A self-monitoring optical sensor for determining the position of an object, comprising:

• a light source;
• a fiber optic cable positioned to receive light from the light source;
• a wavelength division multiplexer, coupled to the fiber optic cable, for dividing light received on the fiber optic cable into a plurality of spectral bands;
• a code plate coupled to the object whose position is to be sensed, wherein the code plate is positioned to receive the plurality of spectral bands created by the wavelength division multiplexer, the code plate defining a number of discrete positions that are marked by a plurality of tracks having reflective and absorptive segments that form a code indicative of each discrete position, the code plate further including a monitoring track that encodes an expected number of absorptive segments at each discrete position of the code plate;
• and
• a detector circuit that receives light reflected off the code plate and analyzes the effected light to determine the position of the object, wherein the detector circuit further detects a number of absorptive segments in the code plate at a discrete position and the number of expected absorptive elements that is encoded in the monitoring track for the discrete position in order to determine if there is a fault in the code plate.