Photoelectric sensors

Photoelectric sensors detect objects, positions and distances without contact using light. SCN supplies photoelectric sensors from Wenglor, including retro-reflex sensors such as P1EL and P2KL, through-beam sensors such as P1KE, laser sensors such as P3PC, fibre-optic amplifiers in the P1XD series and high-performance distance sensors such as CP35MHT80. They are used in industrial automation, packaging, material handling and machine building. Our engineers help you choose the right sensing principle, range, light type and output for your application.

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Photoelectric sensors – detecting objects with light in automation and packaging

A photoelectric sensor, often called a photocell or photo eye, detects objects, positions and distances without contact by emitting light and evaluating what reaches its receiver. It works on almost any material, metal or not, and over much longer distances than an inductive sensor. Typical applications are conveyors, packaging machines, material handling, robot cells and assembly lines. SCN supplies photoelectric sensors from Wenglor.

The range covers diffuse sensors that detect the object directly, retro-reflex sensors that work with a reflector – including the P2KK001 for transparent objects such as glass and PET bottles – and through-beam sensors with separate emitter and receiver, such as P1KE and ZW600. For long distances or precise positioning there are P3PC laser sensors and high-performance distance sensors with time-of-flight measurement, listed under laser sensors for distance measurement, as well as P1XD fibre-optic amplifiers for tight spaces. For metal parts at short range, see inductive sensors; all sensor types are listed under Sensors.

How to choose: start with the object (size, colour, transparency, surface) and the distance. Then pick the principle: through-beam for the longest range, retro-reflex when a reflector can be mounted opposite, diffuse when only one side is accessible. Finally choose the light type (red light, infrared or laser), output and connection.

Frequently asked questions

How does a photoelectric sensor work?

A photoelectric sensor emits red, infrared or laser light and switches its output when the amount of light reaching the receiver changes. In through-beam and retro-reflex sensors the object interrupts the beam; in a diffuse sensor the object itself reflects the light back. Because it reacts to light rather than metal, it detects almost any material, from millimetres up to tens of metres.

Through-beam, retro-reflex or diffuse – which type do I need?

Choose through-beam for the longest range and most reliable detection, retro-reflex when a reflector can be mounted opposite the sensor, and diffuse when only one side is accessible. Through-beam sensors typically reach tens of metres, retro-reflex sensors several metres and diffuse sensors up to around a metre. Diffuse sensors with background suppression ignore objects behind the target.

When do I need a laser sensor or a distance sensor?

Use a laser sensor when the object is small, the position must be precise or the beam has to pass a narrow gap, because the laser spot is small and sharp. A distance sensor measures how far away the object is, often by time of flight, and gives an analog or IO-Link value for level, stack height or positioning. See laser sensors for distance measurement.

How is a photoelectric sensor wired?

Most industrial photoelectric sensors are 3- or 4-wire devices for 10–30 V DC with a PNP or NPN switching output, connected by cable or an M8/M12 connector. Typically brown is +24 V, blue is 0 V and black is the output. A light-on or dark-on setting decides whether the output switches when the beam is clear or interrupted, and many models also offer IO-Link.

Not sure which model you need?

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Read more in our guides

Facts and advice that make the choice easier.

Photoelectric sensor types – how to choose the right oneIP ratings explained – IP65, IP67, IP68 and IP69KAll guides