Watlow Series SD Limit - Manual (Page 45)

Alarm Set Points
The alarm high set point defines the process value or
temperature that will trigger a high side alarm. It must
be higher than the alarm low set point and lower than
the high limit of the sensor range.
The alarm low set point defines the temperature
that will trigger a low side alarm. It must be lower than
the alarm high set point and higher than the low limit
of the sensor range.
View or change alarm set points with the Operations
Page parameters.
Limit or Alarm Hysteresis
A limit or alarm state is triggered when the process val-
ue reaches the limit or alarm high set point value or limit
or alarm low set point. Hysteresis defines how far the
process must return into the normal operating range be-
fore the limit or alarm output can be cleared.
Hysteresis is a zone inside each limit or alarm set
point. This zone is defined by adding the hysteresis value
to the low set point or subtracting the hysteresis value
from the high set point.
View or change limit or alarm hysteresis for output 1,
2, or 3 Hysteresis, [hyS1], [hyS2] or [hys3] (Setup
Page).
Alarm Latching
A latched alarm will remain active after the alarm con-
dition has passed. To clear a latched alarm, press the
RESET Key. It can only be deactivated by the user. An
alarm that is not latched (self-clearing) will deactivate
automatically when the alarm condition has passed.
Turn alarm latching on or off with Alarm 1, 2, or 3
Latching [LAt1], [LAt2] or [LAt3] (Setup Page).
Alarm Silencing
Alarm silencing has two uses:
1. It is often used to allow a system to warm up after
it has been started up. With alarm silencing on, an
alarm is not triggered when the process tempera-
ture is initially lower than the alarm low set point.
The process temperature has to enter the normal
operating range beyond the hysteresis zone to acti-
vate the alarm function.
2. Alarm silencing also allows the operator to disable
the alarm output while the controller is in an alarm
state by pressing the RESET Key. The process tem-
perature has to enter the normal operating range
beyond the hysteresis zone to activate the alarm
output function again.
Turn alarm silencing on or off with Alarm 2 or 3 Si-
lencing [Sil2] or [Sil3] (Setup Page).
Retransmit
The retransmit feature allows a process output to
provide an analog signal that represents the set point or
actual process value. The signal may serve as a remote
set point for another controller or as an input for a chart
recorder to document system performance over time.
Any process output can be configured as a retransmit
output.
Communications
Normal Operating Range
Alarm
enabled
here
Alarm
triggered
here
Startup,
Alarm
disabled
Time
Temperature
Alarm High
Set Point
Alarm Low
Set Point
Process
Temperature
Hysteresis
Hysteresis
Normal Operating Range
Alarm High
Set Point
Time
Temperature
Alarm Low
Set Point
The alarm state continues until the
temperature drops to the Alarm High
Set Point minus the hysteresis. A
latching alarm could be turned off by
the operator at this point. A non-
latching alarm would turn off
automatically.
The alarm state begins when the temperature
reaches the Alarm High Set Point
Process
Temperature
Alarm Hysteresis
Normal Operating Range
Low Side Alarm Range
High Side Alarm Range Alarm High Set Point
Alarm Low Set Point
Time
Temperature
Alarm Hysteresis
Alarm Hysteresis
Wa t l o w S e r i e s S D L i m i t ■ 4 3 ■ C h a p t e r 9 F e a t u r e s