Westermo RedFox Series User Manual
Page 542
Westermo OS Management Guide
Version 4.17.0-0
old on the way up, and the falling threshold on the way down. However, once a
rising alarm event has occurred, a new rising alarm event cannot be generated
(for that alarm source) before the value has fallen down to the falling threshold
(and vice versa). Thus, the use of separate rising and falling thresholds creates
a hysteresis mechanism, which avoids generating multiple alarm events when a
monitored value fluctuates around the alarm threshold.
Alarm targets such as Digital-Out and the ON LED provide a summary alarm func-
tion (see
), and these targets assume that every alarm trigger
define the condition when the alarm is active (”alarm” situation) and inactive
(”normal” situation). To define this the alarm condition configuration option is
used. To warn the operator for high temperatures, the alarm condition should
be set to ”high”, see
b). If we instead wish to warn the operator for
low temperatures, the alarm condition should be set to ”low”, see
c). A
corresponding example for a Digital-In trigger is shown in
a) Digital In Sensor state
b) Digital In Trigger State (Alarm condition set to "high")
c) Digital In Trigger State (Alarm condition set to "low")
Alarm trigger "inactive"
Alarm trigger "inactive"
Low (Voltage non−present)
High (Voltage present)
Alarm trigger "active"
Alarm trigger "active"
time
time
time
Figure 24.3: Alarm condition example: The alarm trigger for digital-in can be
configured to become active when the signal is high (b) or when it is low (c).
Additional details on threshold settings and properties:
❼ The rising threshold cannot be set lower than the falling threshold.
❼ It is possible to use the same value for the rising and falling thresholds.
❼ Rising alarm events occur if the current sample value is equal or above
the rising threshold, and the previously sampled value was below the rising
threshold. A rising alarm event will also occur if the first sampled value is
equal or above this threshold, and the condition variable is configured as
rising (or any of its equivalents: high or up).
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