What are Photoelectric Proximity Sensors? Its Working, Advantages,Disadvantages & Applications

A proximity sensor is a non-contact sensor that detects the presence of an object (also known as the “target”) when it enters the sensor’s field of view. The sensor may detect a target via sound, light, infrared radiation (IR), or electromagnetic fields, depending on the type of proximity sensor.

About Photoelectric Proximity Sensors - Allied Electronics & Automation

Since photoelectric technology has advanced so quickly, they are employed in a variety of applications and sectors, but they’re most commonly seen in manufacturing and packaging. The operating principle of a photoelectric proximity sensor is discussed in this blog.

What Is a Photoelectric Proximity Sensor?

Photoelectric Sensors detect objects, changes in surface conditions, and other items through a variety of optical properties.

A Photoelectric Sensor consists primarily of an Emitter for emitting light and a Receiver for receiving light. When emitted light is interrupted or reflected by the sensing object, it changes the amount of light that arrives at the Receiver. The Receiver detects this change and converts it to an electrical output. The light source for the majority of Photoelectric Sensors is infrared or visible light (generally red, or green/blue for identifying colors).

Photoelectric Sensors are classified as shown in the figure below. 

  • Through-beam Sensors

It identifies a presence when an object disrupts this stream of light. This type of configuration requires the use of two components: an emitter and a separate detector, making it a little more difficult to install and connect. However, it has the advantage of being the most accurate and having the longest sensing range of all the sensing modalities.

For greater precision and detection, new laser diode emitter variants can transmit a well-collimated beam 60 meters. Some through-beam laser sensors can detect an item the size of a fly at these distances, which becomes 0.01 mm at close range. Effective sensing in the presence of heavy airborne pollutants is a feature specific to through beam photoelectric sensors.

  • Retro-reflective Sensors

Detection occurs in this method when the light path is broken or disturbed. The light emitting and receiving elements are housed in the same housing. The light from the emitting element passes through the reflector and is reflected back to the light receiving element. The light is interrupted when a target is present. One advantage of employing a retro-reflective sensor over a through-beam sensor is the convenience of only having to wire one side; the opposite side merely has to place a reflector.

  • Diffuse-reflective Sensors

Emitters and receivers are housed together, similar to retro-reflective sensors. Both the light emitting and light receiving devices are contained in a single housing in this Diffuse technique. The light reflected from the target is detected by the sensor.

Diffuse photoelectric sensors are similar in some respects to reflective sensors. This is because like reflective sensors they emit a light beam in the direction of the object to be detected. Instead of a reflector reflecting light back to a detector, the object to be sensed acts as the reflector, bouncing some of the light back to be detected and report the presence of an object.

The diffuse sensors are most commonly found in public restroom sinks, where they operate automatic faucets. Hands placed beneath the spray head act as a reflector, causing a water valve to open (in this case). Because diffuse sensors are color-dependent, some versions are useful for discriminating dark and light objects in applications that need contrast-based sorting or quality control.


  • Long Sensing Distance

Through-beam Sensor, for example, can detect things from a distance of more than 10 metres. With magnetic, ultrasonic, or other sensing modalities, this is impossible.

  • Virtually No Sensing Object Restrictions

Since these Sensors work on the idea that an object interrupts or reflects light, they are not limited to detecting metal things like Proximity Sensors. As a result, they can detect almost any object, including glass, plastic, wood, and liquids.

  •  Fast Response Time

Because light travels at such a high speed, the response time is extremely quick, and the Sensor performs no mechanical activities because all circuits are made up of electronic components.

  • High Resolution

The incredibly high resolution achieved with these Sensors derives from advanced design technologies that yielded a very small spot beam and a unique optical system for receiving light. These developments enable detecting very small objects, as well as precise position detection.

  • Non-contact Sensing

There is little chance of damaging sensing objects or Sensors because objects can be detected without physical contact.

This ensures years of Sensor service.

  • Color Identification

The rate at which an object reflects or absorbs light depends on both the wavelength of the emitted light and the color of the object. This property can be used to detect colors.

  • Easy Adjustment

Positioning the beam on an object is simple with models that emit visible light because the beam is visible

Advantages of Photoelectric sensor

Following are the advantages of Photoelectric sensor:

  • It senses all kinds of materials.
  • It has a longer life.
  • It has a long sensing range and is very reliable.
  • It has a very fast response time.
  • It is less costly.
  • Diffuse photoelectric sensor detects small objects including color mark and label detection.
  • Retro-reflective type can detect transparent objects.
  • Thru beam type can detect long range and it is tolerant of dirty environment.

Disadvantages of Photoelectric sensor

Following are the disadvantages of Photoelectric sensor:

  • Over coarse of time lens get contaminated.
  • It’s sensing range is affected due to color and reflectivity of the target.
  • Thru beam type requires transmitter (Tx) and receiver (Rx) at two separate locations. Retroreflective type requires reflector in addition to Tx/Rx. This makes system installation complex.

Applications of Photoelectric Proximity Sensor

Photoelectric proximity sensors are used in a variety of applications.

  • Checking objects on production lines or conveyors:

Photoelectric sensors can measure the size of a product to detect any faults or simply to detect its absence. As well as detecting issues such as mismatched bottle closures. They’re common in the food and pharmaceutical industries, as well as packaging facilities.

  • Counting of small objects

Small things may fall from a vibrating conveyor belt into a packaging system or bag in various manufacturing situations, and a photoelectric sensor may count them.

  • Detection of colours

Through scanning independently in red, green and blue light, with applications in multiple processes in the printing and packaging sectors.

  • Monitoring bigger areas for objects with light grids:

Instead of using several sensors, a light grid covers a two-dimensional area with parallel beams of light.

  • Measuring distance:

A triangulation procedure compares reflected laser beams with several sensors and can be used to accurately measure position and distance. For example, in automated transportation applications or to check the location of production systems.

  • Logistics and materials handling

In automated warehouses with robotic pickers or trucks rely on position and object sensing to operate efficiently and safely.

  • Automatic doors

In buildings or public transport, photoelectric sensors detect when someone is standing by a door.

Hope this blog helps you to understand basics of Photoelectric proximity sensors, its working, applications, and advantages and disadvantages.We ,MATHA ELECTRONICS  will come back with more informative blogs.

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