It depends a bit how you are doing the write.

I assume that you are using variable components and PsOPCConnector to link the variables to the OPC Items in the server. In this case, the connector is reacting to requests in the variables to change the value by making a write request to the OPC server. Again several options:

1. PsOPCConnector.AsyncWrite = False

The write is made immediately and if it succeeds, the variable value is changed respectively. In case of an error, you should get an exception.

2. PsOPCConnector.AsyncWrite = True

The write is made immediately using IOPCAsyncIO2.Write (or IOPCAsyncIO.Write for DA1.0 servers), but the value is not changed in the variable. If the write succeeds, the value will be changed when the next data change message confirms that it was changed in the server.

Writing errors are really not handled in this case, but you can handle them in your own code by using the event of the internal OPCGroup object: PsOPCConnector.OPCGroup.OnWriteCompleted, which is triggered whenever the client gets a response to the write request from the server.

So the easier way would be to use synchronous writes, even if you are monitoring the data changes asynchronously, by setting AsyncWrite := False, even if you have Async := True. Async writes are possible, but not necessary for efficient functionality, unless you have very slow writes to the server or if you are writing often to the server (in which case it may be also good to pack the writes together by setting PsOPCConnector.TriggerVarChange := tmDelayed, which makes it really asynchronous)

AsyncRefreshInterval is actually just a safe guard. Unfortunately, OPC DA does not enable a mechanism to guarantee that the client gets all data changes from the server, for example during short-term network breaks, if the messages are lost. In this case it is theoretically possible that the item values in the client are no more in sync with the server. By using AsyncRefreshInterval, the PsOPCConnector will send a specific Refresh request to the server that makes the server to send all current values to the client ensuring that all values are always up to date. But, if you don’t have problems in your network, this is indeed unnecessary. Or you can make it happen very rarely, e.g. every 10 minutes.

Good that you found a way to do it. This is not always that simple as the exact behaviour depends very much on the server.