Photoelectric sensors represent perhaps the largest variety of problem solving choices in the industrial sensor market. Today's photoelectric sensor technology has advanced to the point where it is common to find a unit that will detect a target less than 1 mm in diameter while other units have a sensing range up to 60 m. There are many configurations of photoelectric sensors available, including laser-based and fiber optic. Probably the easiest way to describe the operating principal is the emitter transmits a beam of light either visible or infrared, which is directed to and detected by the receiver. Although many housings and designs are available, photoelectric sensors operate on the same principal.