Cut Sheet

Volume 8—Sensing Solutions CA08100010E—November 2012 www.eaton.com V8-T12-9
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12.1
Sensor Learning Course
Learning Module 23: Limit Switches, Proximity Sensors and Photoelectric Sensors
Actuators and Operating Heads
Choosing the proper actuator
(also called an operating
head) for a limit switch
depends on a number of
application-specific factors.
To select an actuator, you
need to know shape,
speed, direction and total
travel specifications.
Operating heads fall into two
broad types: Maintained
Contact and Momentary
Contact. Momentary
contacts return to their
normal state as soon as
the actuator passes its
release point. This type of
operating head is also called
“spring-return.”
With a maintained contact
operating head, the contacts
remain in the “triggered”
position even after the
actuator has been released.
They are reset only by
further mechanical action
of the operating head. For
example, on rotary operating
heads, the contacts are
reset by rotation in the
opposite direction.
Actuators can take the form
of rotary levers or plungers.
We will look at specific
actuator types on the next
few pages.
Rotary Lever Actuators
A typical lever actuator
functions something like this:
a cam or plate hits the end
of the lever arm, which
rotates a shaft and
operates the contacts in the
switch.
The rotation may be
momentary (spring-returned)
or maintained. A lever arm
can be a rod or a roller of a
fixed or adjustable size. It
may be made from any
number of materials.
A rotary lever actuator is
usually the best choice for
the majority of applications. It
can be used in any application
where the cam moves
perpendicular to the lever’s
rotational shaft. This type of
actuator also offers the
benefit of a long life.
Let’s take a look at the
different rotary lever actuator
types available.
Rotary Lever Actuators and Limit Switches
Lever Type Application
Standard roller Used for most rotary lever applications. Available in various lengths. Roller
typically made of Nylatron
®
for smooth operation and long wear.
Ball bearing roller Used where abrasive dust would cause undue wear of standard nylatron rollers.
Also used with high-speed cams.
Adjustable length Used where the length of arm required is not known when devices are ordered or
where the target size or location may change from day to day. An operator can
adjust the arm length before beginning production.
Forked Used with maintained contact style switches. When rollers are on opposite
sides, one cam will trip the switch and the second will reset the switch. When
rollers are on the same side, one cam trips and resets the switch. Applied where
the target approaches from two sides, such as a grinder that works back and
forth.
Offset Used to obtain different cam track dimensions.
Standard Roller
Ball Bearing Roller
Adjustable Length
Forked
Offset