Various status attributes indicate whether Geo SCADA Expert is communicating with an outstation as expected (see Status Attributes Associated with Outstations on Advanced Drivers, and see Status Attributes Associated with Channels on Advanced Drivers).
Geo SCADA Expert typically raises an alarm per affected database item should its attempts to communicate with an outstation be unsuccessful.
Geo SCADA Expert can also optionally log an entry historically for those points:
- That are on an outstation with which Geo SCADA Expert has attempted, but is unable, to establish communications
- That are on an outstation with which Geo SCADA Expert was communicating, but then loses communications
- For which the outstation’s Log Historic Value on Communication Failure feature is enabled and the Persistence Timeout has expired providing that those points fulfil the following criteria:
- Have valid configuration
- Are In Service
- Are active (rather than new points for which Geo SCADA Expert has not yet retrieved the initial value from the outstation)
- Are configured to store data historically (see Defining Historic Details for a Point).
The historic value that Geo SCADA Expert stores (‘logs’) on communication failure comprises the last known value of the point (the latest value that Geo SCADA Expert retrieved for the point before communications were lost). The entry is assigned a Quality of ‘Bad’ (see Quality). (With drivers that support additional OPC Qualities, a more specific ‘Bad’ Quality value might apply.)
You specify whether Geo SCADA Expert is to Log a Historic Value on Communication Failure using the relevant section of the outstation’s Outstation tab.
Enabled
Select this check box if the outstation’s points are to log a value historically should Geo SCADA Expert lose communications with the outstation. To log a value historically, the points has to adhere to the criteria mentioned above.
ATTENTION: We recommend that you avoid enabling this feature on outstations that have poor communications. If you do use this feature on outstations that have poor communications, ensure that you specify a suitable Persistence Timeout value. This will help to prevent Geo SCADA Expert from logging too many values due to transient communications failures.
If an outstation’s points do log a historic value on communications failure, ensure that you are aware of The Effects of Logging a Value Historically on Communication Failure.
Clear the check box if the outstation’s points are not to log a value historically specifically due to Geo SCADA Expert losing communications with the outstation. Geo SCADA Expert will still log entries in the Event Journal
Persistence Timeout
Use this field to specify the amount of time that has to elapse between:
- Geo SCADA Expert first detecting that it is no longer able to communicate successfully with the outstation
and:
- Geo SCADA Expert logging a value historically on the outstation's points as a result of that detection.
If Geo SCADA Expert has not re-established communications with the outstation by the time that this Persistence Timeout has expired, the points that match the above mentioned criteria will log a value historically.
Enter the required persistence time in the OPC Time Format. We recommend that you specify an interval that is greater than the channel's Reestablishment Interval
Specify a value of 0 if Geo SCADA Expert is to log a historic value as soon as it is no longer able to communicate successfully with the outstation. You should only specify a value of 0 for outstations with which communications are normally very reliable.
The Persistence Timeout field is ‘grayed out’ and unavailable for use if the Enabled check box is clear.
Further Information
Recommended maximum sustained rate of historic updates per point: see Operational Limitations - Server.