Handling Memory Limits For Opc Ua Alarms And Conditions - Siemens SIMATIC ET 200AL System Manual

Special features of Alarms and Conditions comments for the OPC UA server of the CPU
You have the possibility to add comments to alarm objects of the
"SimaticAlarmConditionType" type with the AddComment method. A comment is also set
when the Acknowledge method is called. The "AddComment" method can be called several
times.
• A comment was save in the "Comment" event field. The "Comment.SourceTimestamp"
indicates the last time at which a comment was set.
• The "Time" time stamp marks the last modification time of the alarm object.
When the "AddComment" method is called, "Time" and "Comment.SourceTimestamp" are
identical.
When the "Acknowledge" method is called, the two time stamps may differ, since the
acknowledgment is asynchronous.
The support of comments for OPC UA Alarms and Conditions is mandatory. The SIMATIC
alarm system does not know corresponding comments for alarms. Therefore, some special
features have to be considered:
• There is only one comment:
There is only one comment for an alarm object, so that an existing comment is always
overwritten when several method calls are made in succession.
• Lifetime and time stamp:
Comments are only stored at the current alarm object. If the alarm object no longer exists,
e.g. after a server restart, the comment no longer exists either. The corresponding
"Comment" and "Comment.SourceTimestamp" event fields are then reset (zero).
The "Time" event field is then set as if the method call "AddComment" did not exist.
Example: If you comment on an unacknowledged Alarms object, the "Time" event field
receives the time of this comment change. After a server restart, the "Time" event field
does not show the time when the comment was set, but the time when the
corresponding Event arrived.
9.3.6.7

Handling memory limits for OPC UA Alarms and Conditions

The OPC UA server of the S7-1500 CPU has product-specific limited memory capacity for the
"Alarms and Conditions" function (see CPU specifications).
Two memory pools for different categories of alarms are available:
• Pool only for ProgramAlarms (corresponds to program-related alarm originators
(producers) such as program alarms via Program_Alarm, ProDiag, Graph)
• Pool only for SystemDiagnostics (corresponds to system diagnostic alarms)
Under unfavorable conditions (e.g. alarm burst) the CPU cannot make all pending alarms
(ProgramAlarms or SystemDiagnostics) from the SIMATIC alarm area available to the OPC UA
Alarms and Conditions system. However, alarms are not lost in this case.
You have the possibility to react to this overload event in the user program. According to your
application you can use the "ConditionRefresh" method to make alarms that "did not make it
into the OPC UA Alarms and Conditions system" available to the OPC UA Alarms and
Conditions system again.
Communication
Function Manual, 05/2021, A5E03735815-AJ
OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
301