OPC UA manually request the subscribe data after boot or disconnect

PLCnext Technology & PLCnext Controls
1

Hello,

In a project we are working on, 3 PLCnext controllers are working as OPC UA clients and 1 as OPC UA server. When data changes on a client, we want to write that data to the server. The other clients are subscribed to that data on the server and will receive the new value.
This all works pretty well except when a client loses power or when the connection from a client is not present at the moment the server receives an update. We want to read the data we are subscribed to when we want to update it manually.
For example, could we trigger a read to the OPC UA server for the variables we are subscribed to, not based on a cycle time, but based on an event?
Or could we use the OPC UA ResendData method? For this we would need a subscriptionID.

Any ideas on this topic would be greatly appreciated.

2

Hello,
The OPC_UA_Client subscribes to the data from the OPC_UA_Server permanently (based on the cyclic time). This is the reason for the “subscription”. Maybe you can realize this feature by creating and comparing the timestamps variable on the OPC_UA_Client and the OPC_UA_Server as a kind of “keep alive” and, if the difference between the timestamps exceeds the defined limit, switch to a manual value (by implementing the state machine)?
BR Eduard