Cut Sheet

V8-T12-4 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
Welcome
Welcome to Module 23, which is about sensors. As the name implies,
sensors are devices that sense the presence or absence of objects.
Sensors perform a number of functions in automated manufacturing and
material handling systems. For example, sensors can determine if an object
is present, if tooling is broken, or if product is running down a conveyor line.
This module will take you through the basic operation and application of
three major sensor categories: Limit Switches, Proximity Sensors and
Photoelectric Sensors.
Like the other modules in this series, this one presents small, manageable
sections of new material followed by a series of questions about that
material. Study the material carefully then answer the questions without
referring back to what you’ve just read. You are the best judge of how well
you grasp the material. Review the material as often as you think necessary.
The most important thing is establishing a solid foundation to build on as you
move from topic to topic and module to module.
A Note on Font Styles
Key points are in bold.
Sensor Basics
A manual switch enables an
operator to interact with a
machine. If, for example, an
operator sees a problem on a
manufacturing line, he could
move a switch to stop the
line. Or, think of a light switch
in your home. If you (the
operator) want the light
turned on, you have to move
the switch.
A sensor can be thought of
as an automatic switch. In a
factory, a sensor can be used
to detect a problem on the
line and stop the line
automatically. Or, in your
home, a sensor could be
used as a security device
to detect an open window
or door.
Sensors have contributed
significantly to recent
advances in manufacturing
technology. Using a sensor
makes a process or system
more automated and
removes the need for human
operators to monitor and
control the situation.
The three main categories of
sensors are limit switches,
proximity sensors and
photoelectric sensors. Let’s
take a moment to look at
each type of sensor.
Limit Switch
Limit Switch with Standard
Roller Lever
A limit switch is an
electromechanical device.
A part of the limit switch,
called an Actuator, is placed
in the path of an oncoming
object, such as a box on a
conveyor. When the object
contacts the actuator, the
contacts in the limit switch
are opened (or closed,
depending on the limit
switch’s design) to stop
(or start) the flow of current
in the electrical circuit.
Proximity Sensor
Proximity Sensor Types
This type of sensor uses an
electromagnetic field to
detect when an object is
near. There is no physical
contact between the object
and the sensor. Inductive
proximity sensors detect only
metal objects. Capacitive
proximity sensors can sense
both metallic and non-metallic
objects.
Think of a manufacturing
process where the alignment
of a part is critical. A
proximity sensor can be used
to make sure the part is
aligned within a certain
tolerance. If the part is not
properly aligned, the
proximity sensor will be
triggered.
This type of sensor is
generally used to sense at
distances less than one inch.
Typical Sensors