Cut Sheet

V8-T12-14 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
Special Purpose—
Gravity Return
Unlike other rotary limit
switches, this switch has no
spring return mechanism.
The weight of the operating
lever must provide the
force to return it to its free
position. This switch is
usually mounted with the
operating head facing down.
It is often used in applications
where very low operating
forces from the target are
required.
Special Purpose—
Neutral Position
With this limit switch, the
direction of operation can
be detected.
One set of contacts is
actuated when the lever is
moved in one direction, and a
second set of contacts is
actuated when the lever is
moved in the other direction.
In the Workplace
In some manufacturing plants, rooms need to be closed off
quickly because of contamination or fire. To help facilitate this
process, high-speed doors have been developed. These doors
may move as quickly as six feet per second.
Limit Switches Help Operate This High-Speed Door
At such speeds, the door would destroy itself quickly, if not for
the use of limit switches. The limits switches are used to slow
the door just before it is fully opened or fully closed.
Object
moves
lever
Weight of lever (gravity)
returns it to free position
CCW
CW
Special Purpose—
Tw o S t e p
This switch operates to
perform two functions with
one switch. One set of
contacts is activated after the
lever is rotated 10°, and
another set is activated at a
20° rotation (in the same
direction).
This switch can monitor an
object’s height, orientation,
position, completeness of
assembly, and so on.
Review 2
Answer the following questions without referring to the material
just presented. Begin the next section when you are confident
that you understand what you’ve already read.
1. The three main components of a limit switch are:
________________________
________________________
________________________
Match the terminology to the proper description:
8. The ability of a switch to repeat its characteristics from
one operation to the next is called the switch’s repeat
accuracy. TRUE FALSE
Answers to Review 2 are on Page V8-T12-41.
CW
CCW
10°
20°
20°
10°
2. Initial position ______ A. Distance the actuator can
travel safely beyond the
operating point
3. Pre-travel distance ______ B. Maximum allowable
distance the actuator can
travel
4. Operating point ______ C. Actuator and contacts are
in the normal, or
untriggered position
5. Overtravel ______ D. Actuator’s position at
which the contacts
change state
6. Release point ______ E. Actuator position where
the contacts are reset to
their normal “untriggered”
state
7. Total travel ______ F. Actuator travel from
contact with the target
until the operating point