Photoelectric Sensors

Photoelectric Sensors

Photoelectric sensor is made to detect objects, surface conditions, or environmental conditions between two objects.

Now it has become one of the most used sensor in product automation systems.

Working Principle of Photoelectric Sensors

A Photoelectric sensor consist of two elements, which is the emitter and the receiver. So, there is a continues light beam toward the receiver. Once the light beam is interrupted, the receiver receive less or no light. Therefore the sensor can detects that there is something in between the emitter and receiver.

Classification of Photoelectric Sensors by Sensing Principle

By considering the sensing principle of photoelectric sensors, we can divide photoelectric sensors into major categories. Sensing principal is how the light is emitted and received on the sensor.

Through-beam Sensors

Sensing object 
Reflected beam 
Transmitted beam 
The sensing object interrupts the beam. 

Retro Reflective Sensors

Reflected beam 
Sensing object 
Transmitted beam 
Sensor The sensing object interrupts the beam. 

Diffuse Reflective Sensors

Sensing object 
Reflected beam Transmitted beam 
The sensing object reflects the beam.

Other Classifications for Photoelectric Sensors

In practical usage, we meet four type of photoelectric sensors.  Those are,

  1. Sub-mnature Photoelectric Sensors
  2. Miniatue Photoelectric Sensors
  3. Compact Photo Electric Sensors
  4. Long Distance Photo Electric Sensors

Features of Photoelectric Sensors

Long Distance Range

Photoelectric Sensors have a higher sensing range compared to other sensors. Even from photoelectric sensors, Thru-beam sensors have the highest range which is 50m or more.

Non-contact detection

Since light beam is used, there is no physical touch on the product. So the sensor is more durable and doesn’t make any harm on the products.

Short Response Time

Photoelectric sensors have short response time compared to other sensoring methods like magnetic, ultrasonic, microwave, motion, position, etc. Therefore it’s much more helpful in quick indentation of products in automation processes.

Color Indentation

Color indentation is a special feature which only some special photoelectric sensors have. Even it also uses light to detect colors, the working principle is comparatively complex.

These specific type of sensors uses the reflection and absorption characteristics of  light to detect colors.

Higher Accuracy

There are advanced photoelectric sensors which the sensing accuracy is less than few micro meters.


Photoelectric sensors can be used for almost all product types. Because it can be used on any product that can block a light beam.

Downsides of Photoelectric Sensors

There few main downsides when using photoelectric sensors. Those are as follows.

  • When the lenses of the sensor get microbial contamination, it’s really difficult to clean in some conditions.
  • When the lenses covered with dirt or dust, someone have to clean them manually. Otherwise, the dirt block the light beam and give incorrect indentation.
  • When working with cold environments, the sensor get covered with water droplets. Therefore, the sensor detect incorrect indentations.

Applications of Photoelectric Sensors

Photoelectric sensors have wide range of applications such as,

  1. To detect item sizes and spot errors
  2. To detect seals on instillation bags
  3. To check the height of the object
  4. To detect whether transparent bottles are filled or not
  5. To detect automobiles in parking lots


  1. Panasonic Technical Guide – PHOTOELECTRIC SENSORS
  2. The Application and Development of Photoelectric Sensor

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