Behavior OPC Server V3 via Interface IOPCAsyncIO

Using of an OPC client¹⁾ with the older OPC standard Interface IOPCAsyncIO (OPC DA V1.0a) creates a higher communication load on the OPC client, because the OPC Server sends also the unchanged items in every scan cycle to the client.

Test setup

Reason

If OPC Items are registered via Interface IOPCAsyncIO (OPC DA V1.0a), the OPC Server sends mostly with each ready cycle a data change event, including also unchanged values. The change detection is correct when using the interface IOPCAsyncIO2 (OPC DA V2).

Workaround

• Use the interface IOPCAsyncIO2 (OPC DA V2).
• If the OPC client does not support IOPCAsyncIO2 interface, then use the OPC Server V2. The OPC Server does not show this behavior.

OPC client¹⁾:

Visualization software in VISU PMS (Fa. epro GmbH) uses an older standard OPC with the interface IID_IAdviseSink than data sink.