Cut Sheet

Volume 8—Sensing Solutions CA08100010E—November 2012 www.eaton.com V8-T12-37
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12.1
Sensor Learning Course
Learning Module 23: Limit Switches, Proximity Sensors and Photoelectric Sensors
Output Timing Modes
When a sensor is operated
without a logic module, the
output is generated for the
length of time the object is
detected.
Some sensors are available
with a logic module to allow
setting timing functions.
Let’s look at each logic
function, as shown in the
following illustrations.
Logic Functions
ON Delay Logic
This allows the output signal
to turn on only after the
target has been detected for
a predetermined period of
time. The output turns off as
soon as the target passes out
of range.
ON delay is useful in bin fill or
jam detection because the
sensor will not false trigger
on the normal flow of objects
going past.
OFF Delay Logic
For applications where there
is a problem with signal loss
in the system, this function
turns the output on when the
object is detected, and then
holds the ON signal for a set
period of time after the object
is no longer detected.
ON/OFF Delay Logic
This logic function combines
the ON delay logic and OFF
delay logic—the output is
only generated after the
target has been detected for
a set period of time, and will
remain on after the target is
no longer detected for a set
period of time.
The mode smooths the
output of the sensor for
applications such as jam
detection, fill level detection
and edge guide.
One-Shot Logic
This type of logic generates
an output of a set length no
matter how long an object is
detected. A one-shot can be
programmed to trigger on the
leading or trailing edge of a
target. A one-shot ON signal
must time out before it can
detect another input.
This logic is useful in
applications that require an
output of specified length.
Retriggerable
One-Shot Logic
This mode generates an
output of predetermined
length whenever an object is
detected. The sequence
restarts each time an object
is detected, and will remain
triggered as long as a stream
of objects are detected
before the one-shot times
out. A retriggerable one-shot
is useful in detecting
underspeed conditions on
conveyor lines.
Delayed One-Shot Logic
Combines on delay and one-
shot logic. The one-shot
feature is delayed for a
predetermined period of time
after an object is detected. A
delayed one-shot is useful
where the photoelectric
control cannot be mounted
exactly where the action is
taking place. This includes
applications like paint booths,
high temperature ovens or
drying bins.
Underspeed
Detection Logic
Operates identically to a
retriggerable one-shot. It
detects speeds that fall
below a certain
predetermined level.
In addition, the underspeed
detector has a built-in latch
feature that shuts the system
down completely when the
speed slows to a preset level.
This prevents the one-shot
from retriggering once it
times out, eliminating erratic
switching while the motor is
winding down.
Underspeed/Overspeed
Detection Logic
Detects both overspeed and
underspeed conditions. The
detector is set to count a
certain number of objects in a
specified amount of time. If
the system operates either at
a higher or lower rate, an
output is generated.
Input
Signal
Output
Signal
ON
Delay
ON
Delay
Input
Signal
Output
Signal
OFF
Delay
OFF
Delay
OFF
Delay
Input
Signal
Output
Signal
ON
Delay
OFF
Delay
Input
Signal
Output
Signal
One-Shot
Pulse
One-Shot
Pulse
Input
Signal
One-Shot
Pulse
One-Shot
Pulse
Output
Signal
One-Shot
Pulse
Input
Signal
Output
Signal
Delay
One-
Shot
Pulse
Delay
Input
Signal
Underspeed
Output
Signal
OverspeedUnderspeed
Input
Signal
Output
Signal