Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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Glossary · Sensors and measurement

Photoelectric sensor

Also known as: Photoelectric switch, Photo eye

German: Lichtschranke

In industrial automation, a photoelectric sensor is a sensor that emits a light beam and detects objects by the change in received light, either by beam interruption (through-beam, retro-reflective) or by light reflected from the object (diffuse-reflective).

  • Sensors
  • Standards

In one sentence

A photoelectric sensor detects objects by an emitted light beam, either through beam interruption or through light reflected by the object.

Example

Photoelectric sensors along a packaging line detect product gaps and trigger the labeler at the right moment.

How it applies

  • Engineering: The three main types are through-beam, retro-reflective and diffuse-reflective. They differ in range, installation effort and sensitivity to object surfaces. Light-on or dark-on switching must match the logic in the controller.
  • Commissioning: Alignment, switching reserve and sensitivity are set on site with real objects.
  • Safety: Photoelectric sensors for process detection are not protective devices. Electro-sensitive protective equipment (ESPE) for safeguarding is designed and rated per IEC 61496 and integrated into a safety function.
  • Documentation: The German list uses Lichtschranke both for this term and for light barrier. English documentation should use the specific type where it matters and never call a process sensor a safety device.

Photoelectric sensor vs. light barrier

Photoelectric sensor is the umbrella term. A Light barrier is the beam-interruption type; diffuse sensors detect reflection instead.

By knowledge.aitechdoc.world · Published September 26, 2026 · Last reviewed

Source: IEC 60947-5-2, Low-voltage switchgear and controlgear — Part 5-2: Control circuit devices and switching elements — Proximity switches

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Knowledge and are not part of any standard.

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