Photoelectric Sensors

A photoelectric sensor detects objects with a beam of light — usually modulated red or infrared LED light — instead of physical contact. An emitter sends the beam and a receiver watches it: the sensor switches its output when the target either interrupts the beam (through-beam, retro-reflective, slot types) or reflects light back to the receiver (diffuse-reflection and background-suppression types). Because detection is optical, it works on nearly any material — cardboard, glass, plastic, metal, liquid — at ranges from millimetres to tens of metres, far beyond what inductive proximity switches can reach.

Choose by reliability need and mounting freedom. Through-beam (separate emitter and receiver) gives the longest range and the highest excess gain — best for dusty environments and opaque targets, but needs wiring on both sides. Retro-reflective needs wiring on one side only, with a corner-cube reflector opposite; use a polarized version for shiny targets. Diffuse-reflection is the simplest to install (one housing, no reflector) but its range depends on target colour and surface, so keep a healthy margin. Background suppression (BGS) is the diffuse upgrade for when a wall, roller or machine frame sits close behind the target.

Whenever something reflective sits just behind the target. An ordinary diffuse sensor decides by intensity — a bright background can return more light than a dark target and cause false triggering. A BGS sensor decides by geometry: using triangulation onto a position-sensitive receiver, it responds only to objects inside its set cutoff distance and ignores anything beyond, even a white wall a few centimetres back. That also makes BGS far more colour-independent — a black target and a white target trip at nearly the same distance.

A slot or fork sensor is a through-beam pair built into one U-shaped housing, factory-aligned, so you get through-beam reliability with single-device installation and wiring. The trade-off is that the target must pass through the fixed slot width. Slot sensors excel at label detection, edge counting, small-part drop detection in feeder chutes and shaft/disc position sensing, where the object path is known and narrow.

No. General-purpose photoelectric sensors have no IEC 61496 rating, no self-checking dual channels and no OSSD outputs, so they must not be used alone for personnel protection. For point-of-operation or perimeter guarding, use a certified safety light curtain (Type 4, e.g. the DAIDISIKE DQC series) or a safety laser scanner, and keep photoelectric sensors for object detection, counting and positioning tasks.