Applies To:
  • CitectSCADA
  • CitectHMI
Summary:
How do you configure redundancy when using CitectSCADA with the RSLinx OPC Server where you have redundant paths (topics) to your PLC (i.e. multiple network interface cards in either or both the PLC and PC).

You cannot setup different OpcAccessPaths in the citect.ini file as with CitectSCADA redundancy each I/O Device must have the same name which makes this impossible.

 

Solution:
Create an "alias topic" in RSLinx and CitectSCADA will treat it as a single access path. RSLinx will then handle the redundancy internally. You can choose if it switches paths (topics) on an error or manually etc.

Alias topics in RSLinx have a problem whereby they do not pass on the quality information of the topics which they contain. I.e. if one topic fails RSLinx will switch to the other topic. However if all topics fail the Alias topic will still report good quality. This make this solution unsuitable for Citect & OPC applications that utilise ‘status tags’.

For recent versions of the OPC driver there is no longer the requirement that the names of redundant units be the same (only the number) so it is now possible to setup different OpcAccessPaths in the Citect.ini file.

 
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