OPC DA Server Instances ?
Many OPC DA servers are implemented to support a single device and can run only as one instance per machine. A second server instance would fail or work improperly, e.g. because a communication port is not available. However, DCOM in the default configuration starts a separate server instance for each connecting client user account. A remote client typically accesses the server in another user account than a local client application. To prevent DCOM from starting multiple server instances the OPC server DCOM configuration needs to be changed to a ‘Specific User’ account instead of the ‘Launching User’. This configuration definition is in the DCOMCNFG Identity tab. The option ‘Interactive User’ is not recommended. A DANsrv based OCP DA server can be implemented to run as multiple instances to support multiple devices. In this case each server instance must have its executables in a different directory and must be configured with a unique CLSID and ProgID. For clients these instances of
