Cut Sheet

V8-T12-24 Volume 8—Sensing Solutions CA08100010E—November 2012 www.eaton.com
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12.1
Sensor Learning Course
Learning Module 23: Limit Switches, Proximity Sensors and Photoelectric Sensors
Photoelectric Sensors
The photoelectric sensor is a
device with tremendous
versatility and relatively low
cost. Photoelectric sensors
can detect objects more
quickly and at further
distances than many
competitive technologies. For
these reasons, photoelectric
sensors are quickly becoming
one of the most popular
forms of automatic sensing
used in manufacturing.
Photoelectric Sensors
Applications
Photoelectric sensors can
provide solutions to a number
of sensing situations. Some
of the common uses for
photoelectric sensors
include:
Material Handling. A sensor
can ensure that products
move along a conveyor line in
an orderly manner. The
sensor will stop the operation
if a jam occurs. And items
can be counted as they move
down the line.
Packaging. Sensors can
verify that containers are
filled properly, labeled
properly and have tamper-
proof seals in place.
Machine Operation.
Sensors can watch to verify
that a machine is operating
properly, materials are
present and tooling is not
broken.
Paper Industry. Sensors can
detect web flaws, web
splice, clear web and paper
presence, while maintaining
high web speeds.
Design Flexibility
Photoelectric sensors offer
design flexibility to handle
many types of situations.
There are a variety of ways
the transmitter and receiver
can be arranged to meet the
needs of the application.
Modes of Operation
We will briefly introduce you to these modes, and fully explain
them later.
Photoelectric Sensor Operation Modes
In the Workplace
At the tollbooth, the gate raises only when you have tossed
in your coins. But how does the gate know when to drop
back into place?
A Photoelectric Sensor Prevents Commuters from Following
You Through the Toll Booth for Free
The gate is controlled by a photoelectric sensor that detects
your car as it passes through the beam.
Mode Description
Thru-beam A source unit in one location sends a
light beam to a detector unit in another
location. An object is detected when it
passes between the source unit and
the detector unit, interrupting the light
beam.
Reflex (retro-reflective) The source and detector are housed in
one package and placed on the same
side of the target object’s path. When
the object passes by, the source signal
is reflected back to the detector by a
retroreflector.
Diffuse reflective The source and detector are housed in
one package and placed on the same
side of the target object’s path. When
the object passes by, the source signal
is reflected back to the detector off the
target object itself.
Background rejection
(Perfect Prox
®
)
This is a special type of diffuse
reflective sensor that includes two
detectors. This arrangement allows the
sensor to detect targets reliably within
a defined range, and to ignore objects
just outside of this range. Unlike a
standard diffuse reflective sensor, color
or reflectivity has minimal effect on the
sensing range of a Perfect Prox sensor.
Detector
Source
Target
Target
Reex
Sensor
Retroreector
Diffuse
Reective
Sensor
Target
Fixed Focus
Perfect Prox
Sensor
Target
Background
Thru-Beam
Reflex
Diffuse Reflective
Background Rejection