When there are no data changes to report, an OPC UA server periodically sends an empty Publish response, known as a keep-alive, to confirm that the subscription is still active.
The keep-alive interval is calculated as:
Keep-alive interval = Monitoring interval × Keep-alive count
Where:
- Monitoring interval: The rate at which the server checks for value changes. (This is determined by the scan rate of the I/O tags in the subscription.)
- Keep-alive count: The number of monitoring intervals that occur before a keep-alive is sent.
By default, the VTScada OPC UA Client driver configures the keep-alive interval to be approximately one-third of the minimum subscription timeout.
If your environment requires different behavior, use this property to adjust the keep-alive count.
the driver will enforce a subscription timeout that is at least: 3 × OPCUACKeepAliveCount × Scan Rate
Section: Application
Default: OPCUAKeepAliveCount =
*No restart required (Settings.Dynamic property)
