Applies To:
  • CitectSCADA 1.xx, 2.xx, 3.xx, 4.xx, 5.xx

I have two I/O Servers effectively Primary and Standby for two PLCs. Each has an I/O Device with a Startup Mode of Primary and Standby respectively. When a page requesting data is displayed on the standby I/O server a hardware alarm "PLC Server Stand-by I/O Device activated" is generated. This problem can be caused by having a separate project for each I/O server where the project on one I/O server does not reference the other I/O server. At startup Citect checks the list of I/O servers and establishes a session with each I/O server on the list. If the I/O server is not on the list then no session is established and the redundancy will not work. 

Ideally you would use one project with two I/O servers defined in it. If you already have two separate projects developed then simply add the communication details for both I/O servers to each project.