How does photoelectric work

W.eat for F.Abrikautomation

Source: MICRO-EPSILON Eltrotec GmbH

definition

Photoelectric optical sensors, also known as optosensors, serve as switching sensors for contactless detection of the presence of objects, for measuring geometric sizes and positions with low requirements and for color controls. Optical sensors are understood here as sensors that typically use LEDs as a light source, but not laser light. Compared to laser sensors, photoelectric sensors offer shorter ranges, lower accuracy and are more sensitive to interfering light. Optoelectronic components such as photo resistors, diodes or transistors, which detect the emitted light directly or via a reflection, serve as receivers. Important types are light barriers, light buttons, light grids or color sensors.
A functional sensor unit comprises the light source, the photoelectric receiver and an integrated or external evaluation unit with an interface as an active element.

Working principle

One-way light barriers, retro-reflective light barriers, light grids and light guide light barriers all use the principle that an object interrupts the point-like emitted light beam and the interruption triggers a switching process.
In contrast, reflex light scanners detect the objects directly at a fixed, adjustable distance and are similar to reflex light barriers made up of a light source and receiving unit in one housing.
An example of analog light barriers are measuring light barriers, in which the light from the transmitter diode is fanned out via optics to form a parallel light band and directed to a receiver on the opposite side. If an object partially interrupts the light band, the position and size of the object is determined via the shadowing on the receiver and a proportional analog signal is output.
Color sensors detect the light reflected from the object, usually guided by three-area photodiodes, whereby the color values ​​of the three spectral colors red, green and blue can be recorded and evaluated.

Area of ​​application

Photoelectric optical sensors offer a simple and inexpensive solution for the contactless detection of objects made of almost any material at smaller distances. Photoelectric barriers and fiber optic switches are used as universally applicable sensors for contactless presence detection and for counting objects in conveyor and queue areas. Measuring light barriers also allow simple size and position determinations in a smaller monitoring area, light grids serve as switching or measuring sensors for two-dimensional detection in a larger area monitoring area.
Color sensors are used as components for the construction of inspection and sorting stations for simple applications. B. for object recognition, for checks for presence, completeness and correct expression of colored surfaces and markings.
Users are in-house equipment manufacturing as well as special machine and plant engineering for a large number of industries as well as packaging, storage and conveying technology.

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