A photoelectric sensor emits a light beam (visible or infrared) from its light-emitting element.A reflective-type photoelectric sensor is used to detect the light beam reflected from the target.A thrubeam type sensor is used to measure the change in light quantity caused by the target crossing the optical axis.

Both the light emitting and light receiving elements are contained in a single housing. The sensor receives the light reflected from the target.

Both the light emitting and light receiving elements are contained in same housing. The light from the emitting element hits the reflector and returns to the light receiving element. When a target is present, the light is interrupted.

The transmitter and receiver are separated. When the target is between the transmitter and receiver, the light is interrupted.