For outstations for which communications is On Demand or Periodic, see Establishment Scan.
The DNP3 driver can routinely perform various polls—an Integrity Poll, a Class 1 Poll, a Class 2 Poll, a Class 3 Poll, and/or a poll for Static String Point Data. You specify the frequency of each poll using the relevant fields on the Outstation Form.
During an Integrity Poll, the driver requests the outstation to send its Class 1, 2, and 3 event data and Class 0 static (current value) data in chronological order. (The Integrity Polling procedure differs whenever Geo SCADA Expert first establishes communications with a Direct or Shared outstation—see Establishment Scan.)
During a Class Poll, the driver requests the event data for that particular class.
During a String Points Poll, the driver retrieves static (current value) data for string points on an outstation.
An Integrity Poll is typically used to ‘synchronize’ the DNP3 master and slave databases and therefore tends to be assigned a slow poll rate. Class 1, 2, and 3 polls are typically used to retrieve individual class events at varying rates, depending on the importance of those events, with the more critical events being assigned to the classes that have the faster poll rate.
As DNP3 event data is reported by the outstation in chronological order, alarms for the point might raise and clear multiple times during a single poll, as the Geo SCADA Expert server processes each individual event.
Example:
A DNP3 outstation includes this configuration:
Integrity Polling:
Interval: 1D
Offset: Day + 1 Hour
Class 1 Polling:
Interval: 5S
Offset: M
Class 2 Polling:
Interval: 30S
Offset: M
Class 3 Polling:
Interval: 5M
Offset: H
Critical binary events are assigned Class 1.
Important analog events are assigned Class 2.
Other events are assigned Class 3.
With the above setup, Geo SCADA Expert scans the outstation at five-second intervals for Class 1 events, at 30-second intervals for Class 2 events and at five-minute intervals for Class 3 events. Additionally, at 01:00:00.000 each day, Geo SCADA Expert performs an Integrity poll on the outstation.
Some systems depend on outstations sending Unsolicited Messages to report event data to Geo SCADA Expert, rather than on regular polling of those outstations. On such systems, if too much bandwidth is being consumed, consider reducing the rate at which the DNP3 driver polls those outstations for event data.