Retrieving Time-stamped Data from I/O Devices

Plant SCADA supports the retrieval of time-stamped data directly from field devices. This capability is enabled by the Driver Runtime Interface (DRI), a component that is used by some drivers, such as:

• BACNET

• DNPr

• IEC61850

• IEC870IP

• OPC

• OFSOPC

• OPCUA

• S7TCP.

  Note: Check with Technical Support if new drivers are available that support the DRI.

The DRI allows a driver to push time-stamped data from field devices into a Plant SCADA system. This means the following can be updated directly from devices:

• Time-stamped digital alarms (see Add a Time Stamped Digital Alarm)

• Time-stamped analog alarms (see Add a Time Stamped Analog Alarm)

• Double point status alarms (see Add a Double Point Status Alarm)

• Event-based trends.

When these drivers start up they scan the system for time-stamped digital alarms, time-stamped analog alarms, double point status alarms and trend events. No configuration is necessary for alarms. For event-based trends, see Configure Event Trends for a DRI Driver.

If the driver receives updated information for any detected tags, it will pass it directly on. Regular I/O server polling is no longer used.

Note: Non-timestamped alarms which are associated with a tag that uses the DRI mechanism will occasionally miss timestamped events. This will occur when multiple updates for the same tag occur within the period specified by [Alarm]ScanTime.

This mechanism can work in tandem with the tag extension feature to enable access to field-generated timestamp and quality tag values (see Tag Extensions).

Note: Prior to version 7.20, time-stamped data was manually pushed into Plant SCADA using the Cicode functions AlarmNotifyVarChange and TrnSetTable. If you are upgrading a project to a version 7.20 system with a driver that uses the new DRI push mechanism, you will no longer need to use these functions.

I/O Server Parameters

Events pushed from a DRI-supported driver can be buffered on an I/O server while an alarm or trend server is offline. The way this mechanism operates can be configured via the following parameters:

• [IOServer]MaxEventsQueued

• [IOServer]MaxEventsDrop

• [IOServer]MaxTimeInQueueMs

For more information, see IOServer Parameters.

Note: Tags associated with devices using the DRI could be set to bad quality for reasons specific to an I/O point. You need to consider the implications this may have on your Cicode. See Considering Tag Value Quality in Cicode.

See Also

Configure I/O Device Communications

Working With Device Drivers