What are Photoelectric Sensors?

Phil Shepley

Photoelectric sensors, also known as photoeyes, are electronic devices that are used to sense the presence or absence of an object, or to measure the distance to the object, sometimes simultaneously, and do so for a wide variety of applications. They utilize light that is usually in the infrared spectrum to do so, which is sent through a light transmitter and is sometimes sensed by a photoelectric receiver, but the latter component is not always necessary. There are many different uses for different types of photoelectric sensors, for example they are used commonly in automated manufacturing, transportation, aerospace technologies, the health care industry and more.

Many combat aircraft, including the Russian Su-25, are fitted with infrared arrays for the detection and tracking of enemy targets.
Many combat aircraft, including the Russian Su-25, are fitted with infrared arrays for the detection and tracking of enemy targets.

A common type of photoeye is the self-contained photoelectric sensor, which does not use a receiver, and can have a counting display, can be integrated into a specific machine to help control its functions, or can also be built with an array of specialized features. An example of its use would be on an assembly line where it could be set up to sense the presence of objects moving down the belt to count them, determine defects, establish the rate at which items are being produced, and more. Another common place for self-contained photoelectric sensors is above automatic doors to detect the presence of people walking in and to open the door for them.

In high-speed manufacturing, photoelectric eyes are also used as safety devices that can shut a machine off automatically if production stops, or if they detect the presence of foreign objects or people around components that are dangerous or could cause serious malfunctions. Often, machine designs incorporate photoeyes that will not even allow the equipment to operate at all if anything is blocking light from the sensor.

Security photoelectric sensors can trigger alarms if a person, animal, or object crosses their infrared beam. The photoeyes can utilize the photoelectric receiver, which is placed opposite the transmitter to create an infrared beam of light that will set off the alarm the moment the transmitter senses that the light is not being reflected back. There are smoke alarms that are built with photoelectric sensors, which operate on the same principle. When smoke enters the alarm, it scatters the infrared beam and sets it off. Photoeyes can also be designed to operate in an opposite manner, so that they will be set off only when the light is allowed to travel from the transmitter to the receiver and back.

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Discussion Comments


@SkyWhisperer - Yeah, but I don’t think that would cover every scenario. I believe the object would need to be near the garage door bottom to trip the sensor. If you had something which did not protrude out of the bottom (like a broom through the back window, maybe) then I don’t think it would trip.

Personally, I wish they had a sensor that would detect when your car is backing up if the garage door is down. In my old house, I had the garage door half way down and then I backed up – bang, I made a big dent in the garage door.

Nothing tripped; the door didn’t rise to get out of my way. I just had forgotten that it was half way down. There’s no technology to fix dumb I guess.


I believe that we have a photoelectric sensor in our home – or in our garage, to be more specific.

I think that the garage door opener has such a sensor at the floor of the garage. The sensors uses a beam to make sure that nothing is blocking the garage door when it closes.

I think this would work in most scenarios that you can imagine. For example, if car wasn’t completely enclosed in the garage and its bumper was sticking out, then it would trip the sensor.

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