Rockwell Automation 9301 Series RSView32 Users Guide - Manual (Page 131)

Configuring alarms
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6–5
Alarm faults
A variable threshold must not become higher than the threshold
above it or lower than the threshold below it. If this happens, an alarm
fault is generated for the monitored tag. To correct an alarm fault, you
must reconfigure the variable threshold so it does not overlap either of
its neighbors. This can become complex when the neighboring
thresholds are themselves variable, because these boundaries are
determined dynamically at runtime.
When an alarm fault is generated, the following actions occur:
the tag’s alarm status stays where it was before the alarm fault
an alarm fault is reported to all configured alarm reporting devices,
such as the alarm log file and printer
the alarm fault status bit for the tag is set in the value table, which
notifies other applications that an alarm fault has been generated
the Alarm Type column in the alarm summary states that the tag is
in “Alarm Fault”
When the faulty thresholds are returned to their normal operating
range, the alarm fault condition is cleared. The out–of–alarm–fault
status is generated and logged, and alarms for that tag resume normal
operation.
Deadband
With certain kinds of measured values, such as line pressure, tag values
can fluctuate rapidly above and below a critical threshold. Where such
conditions exist, you can create a deadband as a buffer to prevent the
fluctuations from triggering and retriggering unnecessary alarms. If
the threshold is increasing—monitoring rising values—the deadband
range lies below the threshold. If the threshold is decreasing—
monitoring falling values—the deadband lies above the threshold.
1.