Freelance, OPC server
I have never used redundant OPC server connected with single/redundant freelance controller AC800F, Also Freelance OPC server F do not have any feature or configuration regarding OPC redundancy.
But yes you can interface with thirdparty PLC irrespective of OPC redundancy, attached here with example of configuration of S7-315 PLC interfaced over OPC.
Elmar is right - when referring to OPC- Gateway node ( in CBF Project tree) in CBF for sharing the Freelance Controller data to third party opc clients like 800xA etc. Two OPC Gateways nodes can be configured in duplicate for this purpose and the OPC clients (800xA) will decide the switch over.
If the question is about configuring third party PLC - OPC Servers into freelance System using OPC-S Node ( Freelance Digivis as OPC-Client)-This is not supported for redundancy, as it is not possible to specify two IP addresses for an OPC-S ( OPC Server) node in CBF for third party PLC.
A Quick way around is to have two OPC-Server instances of 3rd party PLCs running in two different PCs ( with OPC Tunnel installed). When there is a failure of the configured OPC Server, the IP Address of OPC-S node in CBF need to be changed manually to the standby OPC Server PC address and the Digivis Stations can be downloaded again to resume normal operation.
Hope this information helps you.