The OPC Client connection to third party OPC Servers runs in a Windows Service called OAS Data Service. By default this Windows Service runs under the System account. Connecting to other OPC Servers on the same PC that also run under the System account is easy.
Some OPC Servers cannot run as a Windows Service, so you may need to either use the OPC Data Fix or set the OAS Data Service to run under the desktop user account so that the operating system allows the connection.
If you are receiving bad data quality from the OPC Server it is most likely due to a security logon restriction in the operating system. To correct this it is recommended to use the OPC Data Fix or set the OAS Data Service Log On to a valid user account.
View the following section on the Service Control Manager.
If the OPC Server is running as a Service you can often leave the Service Log On to the Local System account, but check the box for “allow service to interact with desktop” if DCOM security is restricting the connection.
Refer to the OPC Communications – Troubleshooting section in this help file or the following video to resolve all OPC connection issues.