Cut Sheet

V8-T12-12 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
Mounting Location
Limit switches should
never be mounted in
locations that could allow
false operations by normal
movements of operator or
machine components. They
should be mounted rigidly, be
maintenance accessible and
have the cover plate facing
that access point.
If liquid intrusion is a
possibility, the switch should
be mounted face down to
allow gravity to prevent
seepage through the seals on
the operating head. All
conduit connections should
be tightly sealed.
In applications where
machining chips or other
debris accumulates, the limit
switch should be mounted in
a location, or at such an
angle, that minimizes buildup
on the operating head.
Limit Switch Types
There are three basic classifications of limit switches available.
●
Standard industrial
●
Hazardous location
●
Precision
Let’s spend some time looking at each.
Standard Industrial Switch
Often the first choice for
industrial applications, this
switch functions in a variety
of rugged industrial
environments. This type
of switch can be subjected
to oil, grease, dirt, high-
pressure wash-down,
shock, vibration, and so on.
Typically, these devices
meet NEMA
®
enclosure
ratings of 1, 3, 3S, 4, 6, 12
and 13. An explanation of
these ratings can be found
in “Enclosure Ratings”
on Page V8-T12-39.
Standard Industrial Switch
1
Actuator/Operating Head
2
Switch Body
3
Receptacle/Terminals
1
23
In the Workplace
At this leading frozen food processor, an automatic pallet
stacking system is used. This system uses a wobble stick limit
switch to detect when the pallets have been loaded to their
desired level.
Into the Freezer
The switch then signals the conveyor to send the load through
an automatic vertical rise door into the freezer for quick freezing.
Most limit switches on the
market today are a plug-in
type design, which means
that the operating head,
switch body and receptacle
are separate components. If
the switch becomes
damaged or fails, it can be
replaced in the field in less
than a minute, without
rewiring the switch. Simply
remove the switch body, and
the wiring remains intact in
the receptacle. The majority
of new industrial applications
use the plug-in type due to its
flexibility and ruggedness.
Non plug-in types are a
popular design for DIN rail
mounted limit switches.
These switches are built to
meet dimensional and
operational standards set in
Europe. They have typically
the same electrical contact
and enclosure ratings as
the regular heavy-duty
switches, but often their
electrical and mechanical
life is not as long. They are
an economical alternative for
applications where the switch
is not subjected to physical
abuse.