Photoelectric Sensor | Diffuse & Distance Suppliers

Photoelectric sensors use light to detect objects or determine if an object is missing. One of the main uses for photoelectric sensors is on production lines. They can count products or components as they pass on a conveyor belt. They can also tell if an object is the wrong shape and shouldn’t be there or if an object is the wrong way around.

Elsewhere photoelectric sensors are used to detect people at automatic doors and stop the doors from closing as they walk through.

In fact, you’ll find photoelectric sensors pretty much anywhere automatic and repeated object detection makes processes easier – the automotive industry, food manufacturing, bottling plants, and material handling; they even have wide-ranging applications in transportation.

Each photoelectric sensor has an emitter which sends out a beam of light. A receiver positioned directly opposite on, for example, a conveyor belt receives this light beam. This type of photoelectric sensor is called a through-beam sensor as there are two parts forming a beam of light. When an object moves through the beam, it breaks the connection between the emitter and receiver and the sensor output will turn off. This registers on a PLC as a count or whatever the system has been set up to record.

• Through-beam photoelectric sensors have two parts – an emitter and a receiver – that need to be facing each other and aligned to send an unbroken beam. They have the longest detection range of all photoelectric sensors but struggle to detect thin, clear objects.
• Retroreflective photoelectric sensors have both an emitter and receiver together in the same component. The emitter directs light at a reflector which shoots it straight back to the receiver. They have a shorter detection range than through-beam sensors.
• Diffused photoelectric sensors also have both an emitter and receiver in the same unit, but no reflector. The light is only bounced back to the receiver when an object passes in front of the beam. Diffused sensors have the shortest detection range.

They do, there are four options:

• Two-wire sensors turn output devices on and off via a simple switch and have a high current capability.
• Three-wire sensors use transistor outputs with lower current for PLC inputs.
• PNP output sensors send positive voltage signals when the sensor output goes on.
• NPN output sensors send ground signals when the sensor output goes on.

• Where will the sensors be used? Bottling plant? Automotive manufacture? Food manufacture?
• What type of sensor suits your needs best? Through-beam, retroreflective or diffused?
• Do sensors need the maximum range?
• What beam size is best?
• What’s the best sensor output? Two-wire, three-wire, PNP or NPN?

The cheapest photoelectric sensors only cost about $50, but good mid-range units are around $240 while high range through-beam sensors are $570 or thereabouts.

There are really only a couple of things that go wrong with a photoelectric sensor. One, it starts sensing things that aren’t there. Two, it doesn’t sense things that are there.

If either of those happens:

• Clean the sensor with a soft, dry cloth and use a mild cleanser if there is visible dirt. realign everything in case the beam has got out of sync between the emitter and receiver or the emitter and reflector.
• Check the voltage, amps and current to make sure everything is at the right levels.