ATTENTION: If you configure a point in the outstation to generate DNP3 events (see DNP3 Integrity and Data Classes), we advise that you do not perform DNP3 Level 3 Scans for that point. This is because the DNP3 standard specifies that event data for a DNP3 point has to be transmitted in chronological order. As a DNP3 Level 3 Scan returns a point’s current value without any preceding DNP3 event data, the value of the point may be returned out-of-order.
You use a Level 3 Scan to scan an individual point at a specified interval. You might find this useful if you need to scan a point frequently. For example, if the point represents a counter for which you want to see live updates on your system.
You can also use a Level 3 Scan to scan points that are not polled by any other means (such as an Integrity Poll). For example, string points. However, a DNP3 device will only support Level 3 scans if the device supports DNP3 Level 3 functions. Please check that your DNP3 device supports DNP3 Level 3 functions before you enable Level 3 scanning.
Before you enable Level 3 scanning, you should also check that a Level 3 Scan is the best way to retrieve data for a point. This is because the scan adds extra load on the DNP3 communications network and on the Geo SCADA Expert server. We recommend that you consider standard DNP3 Class polls and Integrity Polls.
In order to retrieve Class 0 static (current value) data in this way, you need to:
- Enable Level 3 Scan functionality on the Point’s Form
- Configure the point to have a suitable Scan Group (Confidence Poll).
For more information on either of the above, see Configure General Point Properties.
- Use the Perform Level 3 Scan pick action to specify that the driver should poll the outstation for the point data that is assigned to a Scan Group.
Geo SCADA Expert retrieves any DNP3 Status Point data by performing a Level 3 scan.
Level 3 Scans do not apply to DNP3 Pulse Actions.
With points that are assigned a Scan Group (Confidence Interval) but are excluded from Level 3 Scans, the DNP3 driver does not schedule a poll of the outstation when the Scan Group timer expires. Instead, it updates the point’s value with the response to the next scheduled Integrity Poll.