Beam of invisible pulsed modulated infra - red light is produced by emitter. This beam is sensed by receiver at another end (in through beam version) or reflected by object and received by receiver placed near emitter (in diffuse version). When this beam is interrupted by object, the receiver signal gets changed and signal is produced.

Beam of invisible pulsed modulated infra - red light is produced by emitter. This beam is sensed by receiver at another end (in through beam version) or reflected by object and received by receiver placed near emitter (in diffuse version). When this beam is interrupted by object, the receiver signal gets changed and signal is produced.