what is a photoelectric sensor

By Matt Reinstetle

As the manufacturing world becomes more integrated with automated technology, it’s important to understand how this technology can help you. Industrial automation can make the lives of those working on the production floor easier and help increase a company’s productivity. One type of those devices helping workers is known as photoelectric sensors.

Photoelectric sensors come in many different forms and can be used in a variety of industries to accomplish a diverse list of tasks. In order to know which sensor is best, below is a breakdown of what is a photoelectric sensor?

What is a Photoelectric Sensor?

A photoelectric sensor is a device that detects a difference in the light level received from the light source. The sensor is made up of a light source, an amplifier, signal converter, and an output.

Three Types of Photoelectric Sensors

There are three major types of photoelectric sensors: thru-beam, retroreflective, and diffused. Each sensor has its own strengths and can be used in a variety of ways.


In thru-beam sensing, also known as opposed mode, two separate devices are used to make or break a beam. One sensor houses the light emitter while the other houses the receiver. A thru-beam sensor detects objects when an object interrupts the light beam between the two sensors.

Thru-beam sensors can be used to:

  • Detect very small objects.
  • Detect the fill levels inside containers.
  • Detect spliced or overlapped materials.
  • Detect the precise location of a specific object.
  • Detect the contents of a container.
  • Detect opaque objects.

The advantages of using a thru-beam sensor are that it’s the most accurate type of sensor and has the longest sensing range of the three. Thru-beam sensors are also the best choice when using them in a dirty environment. It’s important to keep in mind that there will be at least two separate parts which need to be installed in order to make this device work correctly.


In retroreflective sensing, both the light source and the receiving device are found in the same housing. The sensor works in tandem with a reflector. The light emitted from the sensor is aimed at the reflector, which is then sent back to the light receiving element. The sensor detects the presence of an object when the light path is interrupted.

In addition to retroreflective sensing, there is polarized retroreflective sensing. Polarized retroreflective sensing features a polarized optical block which reduces the response to “hot spot” glare from a shiny surface of the detected object. 

Retroreflective sensors can be used to:

  • Detect large objects.
  • Detect objects moving at high speeds.
  • Detect reflective tape at high speeds.
  • Sense a transparent (clear) glass or plastic product.

Retroreflective is a more affordable and only slightly less accurate option than thru-beam sensors. When working with clear or transparent products, retroreflective sensors are the best option. Another advantage is that retroreflective sensors only need to be wired on one side while thru-beam sensors require wiring on both sides of the device.


In optical proximity sensing, also known as diffuse, the light source and the receiver are housed in the same device. Diffused sensors detect objects when the light beam, emitted towards the target, is reflected back to the sensor by the target. What makes diffused sensors a great automation option is that they are more compact than typical units, as all components are in a single housing.

Diffused sensors can be used to:

  • Detect multiple objects on a common conveyor system.
  • Detect translucent objects.
  • Detect the fill level inside containers.
  • Detect the presence of parts, boxes, and web materials.
  • Detect specific identifying features to determine an object’s orientation.
  • Detect unwanted conditions for product inspection tasks.

Diffused sensors are the easiest to install because everything is included in a single device and is a cost-effective sensing solution. The drawbacks to diffused sensors are they are less accurate when used in position detecting than thru-beam and retroreflective sensors and they are not as effective on translucent objects. In addition, these sensors can be the most affected by color, texture, the angle of incidents, target characteristics, and dirty environments.

How Can I Purchase a Photoelectric Sensor?

Here at TRI-TRONICS, we specialize in making photoelectric sensors, rotary encoders, and elevator door protection. We have a wide variety of sensors best suited for a diverse set of tasks in the field of industrial automation.

We understand that our customers have a job to do and have no time for issues. That is why every product TRI-TRONICS builds is made to be easy to use and durable enough to stand the test of time. We also offer product customization and private labeling upon request.

For product inquiries, please give us a call at (800) 237-0946 or email us at info@ttco.com.