User Manual

E
vents and COV reporting
Sources and causes of system events
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8 Events and COV reporting
Events
System events are messages which inform a client (e.g., Desigo CC) of specific events in an automation
station, such as:
● Change in operating state of the automation station (STOP, RUN)
● Overflow of the operating hours counter built into certain I/O objects
Conceptually, system events are similar to alarms, however, they differ from alarms in some ways:
● System events have no memory, that is, they do not have a finite state machine.
● System events do not affect the status of a plant, that is, they can occur in any alarm state without
influencing it.
● System events are displayed, but do not need to be acknowledged or reset.
System events are forwarded to clients using the same mechanism as alarms.
COV reporting
If a value of a specific process variable changes, the change is transmitted to other system components by
means of Change Of Value (COV) reporting. Polling is used only in exceptional cases. COV reporting can be
used to transfer value changes to several automation stations. A COV notification is issued only when the
value of the process variable changes in comparison with the preset or default incremental value. There is
no need to poll the process variables at regular intervals.
There are two roles:
● COV-Server: The automation station which reads the process variable and whose change of value is to
be reported.
● COV-Client: The recipient of the COV notifications. This may be another automation station or a
BACnet client.
8.1 Sources and causes of system events
The source of a system event is a function block (as with alarms). System events can originate from the
same block types as alarms:
● Analog Input/Output/Value
● Binary Input/Output/Value
● Multistate Input/Output/Value
● BACnet Device Info Object (not in Desigo room automation)
Every block type capable of generating a system event has a clearly defined set of system event triggers.
Event-generating block types Description
Operating hours counter The input, output and value objects of the Binary and Multistate types have an inbuilt operating
hours counter. A system event is generated when the operating hours limit is exceeded or when
the maintenance interval has expired.
BACnet Device Info Object The BACnet Device Info Object detects the causes of system events which apply to the
automation station as a whole. The following causes are detected:
- Change of operating state (start and stop the program)
- Restart after a power-up
- Primary server has found a new backup server on the network
- Backup server has found the primary server
8.2 Routing system events
System events are forwarded to clients using the same mechanism as alarms. They are forwarded to all
temporary and configured alarm recipients in accordance with the settings in the associated Notification
Class objects.
Comparison with the alarm strategy
System events cannot be acknowledged or reset. A Confirmed Event Notification message is sent to all
alarm recipients. The Notify_Type data field in the message defines that the event is a system event and