What is the difference between OPC-UA Stale Threshold and scan class stale timeout for a direct scanclass with opc tag ?
The OPC-UA stale threshold is used to define a contract between the server and the drivers. It’s a multiplier, used with the OPC-UA subscription item’s sampling interval, that yields a maximum amount of time a driver can be “late” updating the value of a subscription item before it is marked stale.
The scan class stale timeout is only relevant when the scan class is external. From the user manual: “How long to wait before the tags in the scan class are determined to be “stale” (not running). This is calculated off of the last expected execution time of the scan class, and is particularly important for scan classes executed by other drivers through the external SQLTags provider. This property is not used by internal providers.”