Applies To:
  • CitectSCADA 5.xx
Summary:
I have a project with a primary and a standby I/O Server, each with one real PLC and one memory PLC for temporary storage. The project is very slow to start and communications is not working reliably. I have not setup the standby I/O Server yet.

My current setup is -

I/O Devices form:
IOServA
Name: IOdev1 IODev2
Number: 1 20
Port: Port1_Board1 MEMORY
Startup Mode: Primary
IOServB
Name: IOdev1 IODev2
Number: 1 20
Port: Port1_Board1 MEMORY
Startup Mode: Standby

Is there anything that should be changed?

 

Solution:
To configure I/O Device redundancy, you need to assign the same Name and Number to two or more I/O Devices in a project and then set one of these to Primary and all others to Standby (or StandbyWrite as required).

Memory PLC devices are strictly local to each Citect PC and do not share data and do not support a redundant setup. If you have memory PLCs on different I/O Servers that have the same Number, then they will automatically be considered as redundant and this will cause unexpected communications problems in your project.

To correct the above example, the memory PLC device "IODev2" should be set to a different number on IOServB -

eg. IODev2 21 MEMORY

Note: If you want to share data between Citect PCs or require redundancy, then use DiskPLCs instead of memory PLCs. See Q2228 for information on configuring redundant DiskPLCs.

 
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