Photoelectric proximity sensors utilize changes in transmitted light observed by an optical receiver to sense the passage or movement of a target object, sending an output to a control system. Retroreflective photoelectric proximity sensors consist of a transmitter and receiver in one housing installed across from a reflector. The reflector observes the change caused by a target object passing between the two components. Reflectors for photoelectric proximity sensors pair with a retroreflective proximity sensor, rebounding the light beam to the transmitter. Diffuse photoelectric proximity sensors depend on the target object to reflect the transmitter’s beam to the receiver. Through-beam photoelectric proximity sensors consist of a transmitter and receiver installed across from each other on a conveyor or other moving target. The receiver observes the change caused by a target object passing between the two components. Fiber optic sensors consist of an amplifier that emits light and reads the reflection off the target object. A fiber optic cable carries both the light and the amplifier’s observation to the PLC.