Applies To:
  • CitectSCADA 5.xx, 6.XX, 7.00
  • CitectHMI 5.xx, 6.XX, 7.00

How do I setup basic IO redundancy?

Basic Steps to I/O Redundancy:

1) Create a Primary and Standby I/O Server in the Project Editor.

2) Create the I/O Devices for BOTH I/O Servers. Eg. If you have 2 PLC's you will have 2 for EACH I/O server. Set the Startup Mode to Primary for the Primary I/O Server devices and Startup Mode to Standby for the Standby I/O Server devices. Make sure that the redundant I/O devices have the same unit number (the name can be different - eg. PRIMARYPLC and STANDBYPLC)

3) Run the computer setup wizard and select which I/O server you want to be. This is also where you decide what role you want to take in regards to Alarms, Trends and Reports. Clients know where to get the I/O information from by looking at the project (Eg. PLC1 is primary on IOServer1 so I'll look there first - if I can't get it I'll go and ask the Standby) Remember that redundancy is client based and works by the clients being able to get data from 2 (or more) places if servers are offline.

4) Run the servers and clients. Shutting down either server will mean that the clients should now connect to the other server to get the data.

When you make a change on one server make a backup and restore it onto the standby. You will have to shutdown and restart each PC (but this can be done separately so that there is no downtime). You also need to restore onto any clients.

You need to run the computer setup wizard to define the ROLE of the PC you are running it on. If you change projects you need to run it again to tell the PC that you now want to run project XYZ and be I/O server ABC for example.

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