Watlow PM PLUS™ 6 • 97 • Chapter 8: Features
Hysteresis
An alarm state is triggered when the process value reaches the high or low set point. Hysteresis defines
how far the process must return into the normal operating range before the alarm can be cleared.
Hysteresis is a zone inside each alarm set point defined by adding the hysteresis value to the low set point
or subtracting the hysteresis value from the high set point.
To view or change hysteresis Operations — Setup — Alarm — Alarm [1,2,3,4] — Hysteresis — and enter the
value to be added to the low set point, or subtracted from the high set point.
Normal Operating Range
Low Side Alarm Range
High Side Alarm Range
High Set Point
Low Set Point
Time
Alarm Set Points and Hysteresis
Hysteresis
Hysteresis
Latching
A latched alarm will remain active after the alarm condition has passed. An active message, such as an
alarm message, will cause the normal Home Screen display to toggle with the active message. Press the
Home key to silence the active message.
An alarm that is not latched (self-clearing) will deactivate automatically when the alarm condition has
passed.
Turn latching on or off with Latching
1. Go to
Setup Page, Alarm - Alarm [1234]
2. Select Non-Latching or Latching.
3. Press the Home icon to exit configuration.
Normal Operating Range
High
Set Point
Time
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
Hysteresis