User Manual

Alarm management
Common alarms
9
160 | 353 CM110664en_07
If the notification class object contains remote alarm recipients, then it may be
appropriate to modify the default values for control of alarm queuing.
The values for [NotifThd] and [PrlmAlm] determine when a remote cable
connection (modem) is to be established, in order to inform the user of the
occurrence of alarms.
If low-priority alarms are to be forwarded immediately, the [PrlmAlm] value
must be increased (the higher the number, the lower the alarm priority). The
value for [NotifThd] must not be modified.
The value for [NotifThd] can be reduced, however, in cases where a connection
is to be established when there is a smaller number of alarms in the alarm
queue. It is important to ensure, however, that the difference between [BufSize]
and [NotifThd] does not become too great, as this is the value that controls the
deletion of alarms in the event of a queue overflow.
Note that modifying these values also affects connection costs.
It takes time to establish a connection by cable (modem). If it is likely that
further alarms will occur during this time, thereby causing the queue to
overflow, the difference between [BufSize] and [NotifThd] should be increased.
The following settings are recommended:
● Buffer size [BufSize] = 120
● Notification threshold [NotifThd] = 80
In cases of doubt, the default values should be left unchanged.
9.9 Common alarms
The BACnet object alarm states InAlarm, Unacked and Unreset are grouped in
the following blocks:
● The CommonAlarm block for Desigo PX
● The CommonEvent block for Desigo room automation
The difference between CommonAlarm and CommonEvent is, that the
CommonAlarm block supports Intrinsic Reporting. The alarm detection and
notification of the CommonEvent block is handled by a special Event Enrollment
object called CommonEventEnrollment. The CommonEventEnrollment block
also handles the common alarm reset / ack and common manual intervention
functions.
All alarms generated by alarm-generating BACnet objects on the same chart
level or subordinate charts are automatically grouped into a common alarm.
There is therefore no need for the user to create a common alarm by
establishing links or interconnections. The engineering process simply involves
placing the block at the required chart level. No other configuration steps are
necessary.
Similarly, all the alarms covered by this block can be the subject of a common
alarm reset and acknowledge.
Acknowledging the common alarm object is equivalent to acknowledging all
objects on the same and lower levels in the hierarchy.
Resetting the common alarm object is the equivalent to resetting all objects on
the same and lower levels in the hierarchy.
The same common alarm object also uses the status flag Overridden to indicate
the manual operation of one or more of the BACnet objects (with [StatFlag]
override facilities) on the same or a lower chart level. Manual intervention are
determined on the properties: Out of service [OoServ], overridden, commanding
to Prio 7 (manual switch) and Prio 8 (operator).
This diagram shows the practical application of the common alarm object
within the technical hierarchy. The common alarm object in the partial-plant
compound encompasses all the alarms of this partial plant. The higher-level
common alarm encompasses the alarms of both partial plants.
Common alarm reset /
ack
Common manual
intervention