Polling Notes
The following notes provide information to help you decide how best to poll specific DNP3 devices and apply to both the DNP3 EIE and the DNP3 Emerson EIE.
Events
The "Events" (Event) data group is designed to be used for regular/scheduled device polling to determine if a value on the device has changed since the last poll. When the data group is polled, CygNet point updates are made to any mapped DEIDs in instantiated data groups with a matching ptId.
Example
The "AI" (Analog In) data group has a deid using ptId AI.123, which is mapped to a CygNet point. When events are polled, if there is an event for ptId AI.123, the CygNet point value will be updated accordingly.
We recommend using the default EVENT command to poll all events (class 1-3).
Event Overflow
When the Event Overflow bit (IIN.11) is set in the "Internal Indications" (IntInd) data group, it means that events are not being polled often enough. The long-term solution is to increase the polling interval for events. As a stop-gap measure, we recommend enabling the automatic INTEGRTY command type whenever the Event Overflow bit is set. It requests events for all classes 1-3 followed by class 0 (all points) in a single message. This will get everything from the device, confirming that everything is in sync (the points in CygNet match the points in the device), and then the EIE is ready to start normal polling again.
Integrity Poll
A special built-in UIS command, INTEGRITY, is available so you can build a custom integrity poll. The INTEGRITY command is used to issue an integrity poll, retrieving events for all classes 1-3 followed by class 0 (all points) in a single message. The data received from an integrity poll is split into the existing Event and AllPoints data groups for point processing and data group transaction retention. The INTEGRITY command uses a special INTEGRTY command component type. Note that getting data from the AllPoints data group can be expensive — it will get a value for every single DNP3 item (AI, AO, DI, DO, counter, string, etc…).
An integrity poll may be automatically configured to execute on a UIS restart, device reenabled, device needs time, device restart, or an event overflow condition. See the next sections.
Automatic Polling
A DNP3 field device will return internal indication data in each message header. These internal indication flags can be used to configure automatic polling in CygNet. Auto polling is configured in the device template file in the autoPoll element, and applies to all associated remote devices. When auto polling is enabled and a specified Internal Indications bit is true, the EIE automatically performs the associated configured command for the device. It provides a way to process the IIN bits from the device and optionally issue actions based on the flags returned.
An Auto poll button is available on the Device page of the Remote Device Editor to override the default settings for each remote device instance for the configured command type. See the Device Page topics for DNP3 EIE and DNP3 Emerson EIE for more information about this option.
The sample device template files provided can be configured to meet the following best practices:
- UIS device load — perform an integrity poll when the UIS is restarted or the remote device is reenabled
- IIN.1, IIN.2, IIN.3 — read events when the flags indicate class 1, 2, or 3 events are available
- IIN.4 — initiate a time sync when the flag indicates the device needs time due to a out-of-sync situation since the last poll
- IIN.7 — perform an integrity poll when the flag indicates a device restart
- IIN.11 — perform an integrity poll when the flag indicates an event overflow condition
Also see the Device Template File Properties topics for the DNP3 EIE and DNP3 Emerson EIE for more information about autoPoll.
