Within the sphere of industrial automation, the word ‘sensor’ typically refers to presence sensing devices such as limit switch, photo eye (photoelectric) and laser sensors.

Photo EyesIndustrial sensors come in all shapes, sizes, and technologies and are considered the eyes and ears of factory floors. Each technology has unique strengths and weaknesses, making the requirements of the application itself the determining factor of which technology should be chosen. The most common are inductive, capacitive, photoelectric, magnetic and ultrasonic.

Photo eyes, or photoelectric sensors, emit a beam of light that is used to detect the presence or absence of items and equipment; or changes in surface conditions. Operation combines a light source and an emitter, and a receiver that detects changes in light intensity reflected by the target object. When the light is interrupted or reflected by an object, the change in light patterns is measured by a receiver, and the object or surface is recognized. As a result, they are very common in industrial manufacturing fields, such as material handling, packaging, food and beverage, medical, and many others.

A through-beam photoelectric sensor uses a configuration where the emitter and receiver are in different housings. Through-beam photo eyes provide the longest operating distances since the emitter shines light directly to the receiver.


There are three major types of photo eyes available:

Through-beam sensing, also known as opposed mode, uses two separate devices to break a beam. One sensor houses the light emitter while the other houses the receiver. A through-beam sensor detects objects when an object interrupts the light beam between the two sensors. They 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

Retroreflective sensing uses both the light source and the receiving source, located in the same housing. The sensor works together with the reflector. As the light is emitted from the sensor, it is aimed at the reflector, and it is then sent back to the light receiving element, detecting the presence of an object when the light path is interrupted. They are best used in these types of situations to:

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

Diffused sensing, or optical proximity sensing, the light source and receiver are also 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

Photoelectric sensors are also available with a variety of characteristics, such as:

Background suppression sensors are extremely effective when the target and background have similar reflectivity (for example, light returned to the sensor from the target is roughly equal to the light reflecting from the background) or when dark targets are to be sensed against a lighter, more reflective background.

Color and contrast sensors can be true RGB color recognition sensors that are designed for industrial use and sensors that detect registration marks with a wide range of background colors, including hard to read pastels.

Optical fork photoelectric sensors are a cost-effective, and easy-to-apply method when small part detection is necessary. They eliminate the alignment and adjustment issues associated with other transmitted-beam sensing solutions.

Universe Optics takes pride in developing a precision lens designed specifically for the type of photo eye equipment you are manufacturing. Let us put our skills and expertise to work for you.