Alarm functions and buffered data
- Last UpdatedJul 26, 2024
- 2 minute read
The attribute, if configured for alarms, detects the alarm condition and sets an associated alarm condition attribute according to the base attribute being monitored. If the base attribute is configured with buffered data enabled, the condition attribute will also be enabled with buffered data support.
At run time, the condition attribute's buffer property will contain a VTQ buffer of true or false values representing alarm conditions corresponding to the base attribute buffer contents.
Only the most current alarm condition can be acknowledged.
For more information, see Alarms and events.
The following table describes buffer-enabled behavior for alarm functions.
|
Alarm function |
Behavior |
|---|---|
|
Detection |
With buffered data enabled for the condition attribute, the alarm condition change is detected using the buffer property of the condition attributes. Multiple alarm messages can be generated based on the buffer contents. The alarm is time-stamped with the time the alarm was recorded at the field device, not the time at which the values were received and processed within the object. A set of alarm messages corresponding to the alarm state transitions are sent to its Notification Distributor. The TimeAlarmOff attribute’s value is set to the time of the last off transition, and TimeAlarmOn to the last on transition. The InAlarm value, time and quality properties are set to the last alarm transition’s state, time and quality. |
|
Notification |
When the Notification Distributor receives a set of alarm messages, it updates the state of the record for the corresponding alarm. The set of alarm messages are forwarded to all registered alarm clients. The Notification Distributor does not send a throttling signal as a result of receiving multiple alarm messages. When the Notification Distributor receives a set of event messages from ApplicationObjects as the result of processing an attribute’s buffer, the set of event messages are forwarded to all registered event clients. |
|
Throttling |
Alarm throttling settings are ignored for alarm messages generated based on buffered data. Alarms will be generated for all alarm conditions in the buffers. If a potential throttling point is reached, the current version of Application Server provides a functionality for all alarms to be processed without system overload. |
|
Acknowledgement |
If an alarm is associated with buffered data, acknowledging an alarm only acknowledges the last alarm, and not all alarms contained in the buffer. |
|
Disabled Alarms |
If an alarm is disabled for a buffered attribute, the alarm’s Buffer property is not processed. Alarm buffers for disabled alarms are cleared. If an alarm is silenced for a buffered attribute, the alarm’s Buffer property is processed. Alarms will be generated but will not be displayed by the alarm client. |
|
Outages |
Buffered alarms and events can be lost when there is an outage because the Notification Distributor will only keep and re-send the last on-alarm message and the last off-alarm message. |