Polling

In addition to the available OPC UA subscriptions, the adapter can collect time-series data from selected dynamic variables by polling the data source(s).

The option to poll an item can be done using the scheduleId parameter in data selection. Configuring this parameter allows you to specify the items you want the adapter to request data from and also define the frequency at which the adapter calls these values. The adapter collects data from OPC UA devices at the polling rates that you specify.

The scheduleId parameter must be defined before you can use the polling feature. If no schedules are defined, the adapter creates a ScheduleId1 parameter by default with a collection period of five (5) seconds.

If a valid scheduleId is specified for a data selection Item, the item is polled. If an invalid scheduleId is specified, no data will be collected for that item. If a ScheduleId is not specified, the item will be subscribed. See Configure schedules for additional information.

The rate for retrieving data is set using the period parameter when configuring a schedules.

Note: The OPC UA adapter supports Alarms and Conditions events generated in real-time but polling for event items is not supported.