IM 04L20A01-01E
1-10
Alarm Hysteresis
You can set a width (hysteresis) to the values used to activate and release alarms.
Alarm hysteresis prevents frequent activation and release of alarms when the measured
value is unstable around the alarm value. The hysteresis is fixed to 0.5% of the
measurement span (display scale width if the range is set to scale).
It is applied only on alarms set to upper/lower limit alarm on measurement channels.
The function can be turned ON/OFF. The initial value is set to [On] (use hysteresis).
The setting applies to all measurement channels.
Alarm value
Alarm release
Measured value
Alarm occurrence
Hysteresis (approx. 0.5%)
Measured value
Alarm release
Hysteresis (approx. 0.5%)
Alarm value
Alarm occurrence
Upper Limit Alarm (H)
Lower Limidt Alarm (L)
Alarm Indication
The alarm conditions are displayed as alarm icons in the status display section and
through the trend, digital, bar graph, overview and other screens. The detailed
information about the alarms is displayed in the alarm summary.
Alarm Indication Example (Overview screen)
Channel No. or tag name
Area of channels on which an
alarm is occurring is indicated
in red
Area of channels on which an
alarm is not occurring is
indicated in green
Alarm type
Hold/Non-Hold of the Alarm Indicator
There are two methods in displaying alarms. The initial value is non hold.
• Clears the alarm display when the cause of the alarm is no longer met (non-hold).
• Holds the alarm display until the alarm ACK operation is executed (hold).
The initial value is set to non-hold.
1.3 Alarm Function
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