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Photoelectric Sensors
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4.
Thru-Beam Sensors
The emitters and receivers of thru-beam sensors
are housed in physically separated housings. The
emitter (E) sends signals directly to the receiver
(
R). If an object (O) interrupts the light beam,
the receiver voltage decreases and the output is
switched.
R
E
O
Features:
•
Detects nontransparent and reflective objects.
•
Wide detection ranges and high excess gain because the light
beam travels only one path, from the emitter to the receiver.
•
Low susceptibility to interference, therefore ideal for use
in difficult conditions, e.g., open-air applications or in dirty
surroundings.
•
Greater installation effort as both units must be mounted and
wired.
Typically, thru-beam sensors are used to monitor production and
packaging lines (see Fig.), fill levels in transparent containers,
and the safety of doors and hazardous areas. The latter applica-
tion area is a domain for thru-beam technology.
Receiver
Emitter
Special versions of thru-beam sensors
Photoelectric slot sensors
If there is only a short physical distance–a few mil-
limeters or centimeters–to bridge between the
emitter and the receiver, they can both be posi-
tioned opposite one another in a U-shaped hous-
ing. Compared with normal thru-beam sensors,
photoelectric slot sensors (see Fig.) benefit from
simpler electrical installation as only one device needs to be
wired. Also, the optical axes do not need to be adjusted.
E
S
S
E
Light grids
Safety applications in particular often involve mon-
itoring a large area. The easiest way to achieve
this is through the parallel arrangement of several
thru-beam sensors. All the emitters in this type of
light grid are grouped into a single housing and all
the receivers, whose switching outputs are logi-
cally linked, are grouped into another. This reduces the installa-
tion effort compared with a corresponding number of individual
thru-beam sensors. The distances between the individual beams
of the grid are application-specific.
Introduction
