Watlow Series PD - Manual (Page 139)

Alarm Hysteresis
An alarm state is triggered when the process value
reaches the alarm high or alarm low set point. Alarm
hysteresis defines how far the process must return into
the normal operating range before the alarm can be
cleared.
Alarm hysteresis is a zone inside each alarm set
point. This zone is defined by adding the hysteresis val-
ue to the alarm low set point or subtracting the hystere-
sis value from the alarm high set point.
To view or change the Alarm Hysteresis, go to De-
vice Configuration > Alarm 1, 2, 3, 4, 5, 6, 7 or 8 >
General Alarm Settings > Alarm Hysteresis. Enter
the Alarm Hysteresis value and click the Submit button
to send the new value.
Alarm Latching
A latched alarm will remain active after the alarm
condition has passed. It can only be deactivated by the
user. An alarm that is not latched (self-clearing) will de-
activate automatically when the alarm condition has
passed.
To view or change Alarm Latching, go to Device
Configuration > Alarm 1, 2, 3, 4, 5, 6, 7 or 8 > Gen-
eral Alarm Settings > Latching. To enable latching,
select On and click the Submit button to send the new
value.
To clear a Latched Alarm once the process has re-
turned to a safe condition, go to Monitor Device >
Alarm Status > Alarm 1, 2, 3, 4, 5, 6, 7 or 8 > Latch-
ing. Click the Acknowledge link to clear the latched
alarm.
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
Tempera
ture
Alarm Hysteresis
Alarm Hysteresis
W a t l o w S e r i e s P D ■ 1 3 7 ■ C h a p t e r 1 0 F e a t u r e s