Photoelectric sensors as "artificial eyes" are no longer an option in automation technology. They are utilised in situations when accurate and non-contact detection of object positions is essential. It makes no difference what the material of the thing to be detected is. Photoelectric sensors offer a substantially larger sensing zone than inductive sensors. A long range distinguishes through-beam sensors. The system is divided into two parts: a transmitter and a receiver. The transmitter and receiver for retro-reflective sensors are combined into a single enclosure. The transmitted light is reflected back to the receiver via a reflector. Diffuse reflection sensors are used to detect objects directly. The transmitter and receiver are housed in the same unit.