Light Barriers0 pages

Light barriers
Functional principles

Reflection Light Barriers

Light Barriers and Active Infrared Detectors
are optoelectronic sensors which detect persons an objects using light without any physical contact being established. The way in
which they function is simple but effective.
Light Barriers respond to each interruption of
the beam between the light transmitter and
receiver. Active Infrared Detectors, on the
other hand, detect an object as soon as the
light reflected by the surface of the object is
received. Once an object has been detected,
the sensor generates a definded electrical
output signal. Evaluation electronics and
relay or transistor outputs are thus just as
much a part of the sensor as the light transmitter and receiver. The applications of the
two basic detection principles are very diverse. In order to do justice to this diversity,
various different functional sensor types
were developed from these two basic principles.

The light transmitter and receiver are in one
housing. A retro-reflector must be installed
in the beam path of the transmitter in such a
way that it is physically separate from these.

For example, the principle of the one-waybeam Light Barrier was developed further to
produce the Reflection Light Barrier. If required, this can also be equipped with polarisation filters. In order to prevent the Active
Infrared Detector from being affected by environmental interference, the reflection principle was combined with the triangulation
method. The devices are thus capable of
masking undesired optical reflections in the
background.

One-way-beam Light Barriers
The light transmitter and receiver are in separate housings with their respective optical
systems pointing toward each other.
Functional principles and diagram
The beam of light only passes along the path
from the transmitter to the receiver once
which means extensive ranges and high operating reserve. Objects which interrupt the
beam trigger a switching operation.

Functional principles and diagram
Each object in the scanning area trips the
switching function. The scanning range depends, to a large extent, on the reflectance of
the object to be detected.

Functional principles and diagram
The light from the transmitter is reflected towards the receiver. Objects which interrupt
the beam trigger a switching operation.

Advantage
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Advantages
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Only one device can be connected and
installed

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Custom-built reflectors available

Reflection Light Barriers with
polarisation filters
Polarisation filters are installed upstream of
the transmitter and receiver optical systems.
These filters define two polarisation planes
which have been rotated 90°.
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No reflector is necessary as the object
itself is the reflector

Active Infrared Detectors with
background suppression
The transmitter and receiver are in one housing. Their separate otpical systems are
aligned so that they are at an angle to each
other. The intersection point of the two optical axes is the upper boundary of the scanning area.
Functional principles and diagram
The receiver determines whether the beam it
receives is reflected by an object within the
scanning area or outside it (background).

Functional principles and diagram

The receiver only picks up the transmitter
light from the triple reflector as this polarises the light in the desired manner. Objects
with glossy surfaces, which likewise act as
reflectors but do not change the polarisation,
are thus detected reliably.

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Advantages
■ Almost constant scanning range for reflective objects with diffuse reflectances
which vary greatly
■ Reliable detection of dark objects against
light backgrounds
■ Insensitive towards undesired reflection
from objects in the background
■ Very high operating reserve

Special variants
Advantage
■

The beam is cleanly interrupted in the
case of glossy and reflective objects

Advantages
■

Operates reliably even under unfavourable environmental conditions

■

Switching point can be reproduced
easily

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Reflective, non-transparent objects are
detected without any difficulty

Active Infrared Detectors
The transmitter and receiver are in one housing. In contrast to the Reflection Light Barrier, the beam is reflected by the object itself.

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Safety Light Barriers
Data transmission Light Barriers
Increased-safety type Light Barriers
Laser Light Barriers
Printed label readers

Typical applications
Variety of every-day applications. A number
of interesting and type-specific applications
can be found in our detailed product
brochures.