Device Properties — Monitored Items
Subscriptions contain monitored items, also called tags. The Monitored Items group is used to configure how fast tags are updated as well as how tag updates are handled by the OPC UA server.
Sample Interval: Specify the fastest rate at which the monitored items are updated. A value of -1 defaults the interval to the subscription's Publishing Interval. A value of zero indicates that the OPC UA Server should use the fastest practical rate. The valid range is -1 to 50000. The default is 500 milliseconds, which is half of the default Publishing Interval.
Caution: If data is changing faster than the Publishing Interval, the Sample Interval must be set to half the Publishing Interval. This ensures data updates at the Publishing Interval. For example, if the Publishing Interval is 10000 ms and data is changing every 100 ms, the Sample Interval must be at least 5000 ms. This ensures data updates every 10000 ms. Queue Size: Specify the number of data updates that the OPC UA Server queues for the subscription. A value of 1 disables queuing. Values greater than 1 enable queuing. The valid range is 1 to 100. The default is 1.
Discard Oldest: Specify the discard policy of the queue. When enabled, the oldest notification in the queue is discarded and is not sent to the driver. When disabled, the newest notification is discarded and not sent to the driver. The default is enabled.
Note: Notifications are only discarded if the queue fills up before the Publishing Interval expires. Deadband Type: Specify the type of deadband filter to be applied to data changes. There are three options: None, Percent, and Absolute. None disabled deadband. Percent sends data updates only if the change is larger than a percentage of the maximum range for the tag. Absolute sends data updates if the change is greater than a specified value. The valid range is 0 to 9,999,999,999. The default is None.
Deadband Value: Specify the value of the deadband. If the Deadband Type is set to Percent, this value is a percentage (such as, 10=10%). If the Deadband Type is set to Absolute, this value is the exact value. The valid range is 0 to 9,999,999,999. The default is 0.