Watlow EZ-ZONE PM - Manual (Page 81)

Watlow EZ-ZONE ® PM Limit Controller • 78 • Chapter 8 Features
Alarm Hysteresis
An alarm state is triggered when the process value reach-
es the alarm high or alarm low set point. Alarm hyster-
esis defines how far the process must return into the nor-
mal 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 value to the
alarm low set point or subtracting the hysteresis value
from the alarm high set point.
View or change alarm hysteresis with Hysteresis
[`A;hy] (Setup Page, Alarm Menu).
Alarm Latching
A latched alarm will remain active after the alarm condition has passed. To clear a latched alarm, press the
Reset
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 Latching [`A;LA] (Setup Page, Alarm Menu).
Alarm Silencing
Alarm silencing allows the operator to disable the alarm output while the controller is in an alarm state. The
process value or temperature 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 Silencing [`A;Si] (Setup Page, Alarm Menu).
Alarm Blocking
Alarm blocking allows a system to warm up after it has been started up. With alarm blocking on, an alarm is
not triggered when the process temperature is initially lower than the alarm low set point. The process tem-
perature has to enter the normal operating range beyond the hysteresis zone to activate the alarm function.
Turn alarm blocking on or off with Blocking [`A;bL] (Setup Page, Alarm Menu).
Normal Operating Range
Alarm High
Set Point
Time
Temperature
Alarm Low
Set Point
Alarm Response with Hysteresis
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 Set Points and Hysteresis
Alarm Hysteresis
Alarm Hysteresis