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2)
Alarm with conditioned reset
Are alarms that, when is running the manual reset ,activate the alarm in OFF condition only if the alarm
condition is no longer present.
For the conditioned alarms we have two types:
I.
Alarms that require manual reset only after alarm condition has been eliminated
(Otherwise remain in alarm).
This is the type of reset on this controller.
II.
Alarms that, if they are resetted when the alarm condition is still present, store the reset and run
automatically when the alarm condition disappears.
It should however be noted that, even for resetting, has been developed a multitude of variations and types
to meet the varied needs of the plant. As mentioned above describes only the most common condition and
those normally present on the controllers.
14.3.6
Alarm mask
As we have said in many cases the alarm produces a physical action on the system.
Obviously, however, the alarm is usually set to report defects when the system is "fully operational".
The conditions of the plant startup or after a set point change does not satisfy the condition "fully operational"
and can cause unwanted alarmi.
To avoid unwanted alarms were studied different solutions according to the type of system where the alarm
is applied.
In the controller has been implemented a solution due to the measure.
If at the start up is detected an alarm condition, this condition is ignored until the measure reaches the area
where the alarm is OFF, then the alarm resumed normal function.
If the alarm is programmed as band alarm or deviation, the standby function masks the alarm condition in
start un and set point variation, until the value of process variable reaches the alarm threshold with
hysteresis .
If is a process alarm the alarm conditions mask only during start up.
Se l'allarme è di processo, maschera le condizioni di allarme solamente in accensione.
