Redundant Switchover Failure and Two Lower Nodes

[justjack]

I have a redundant ControlLogix system that fails during switchover. I have seen the answers to similar questions stating that redundancy requires two lower nodes in my network, and believe this is likely to be my problem. I have multiple nodes on the network, but all have higher addresses.

1) Is the solution as simple as reassigning addresses to the controllers or some other ControlNet device?
2) If so, what steps do I take to do this without interfering with anything else in the system?

Thanks

 

[Ken Roach]

Welcome to the Forum.

You're likely correct: the way that the ControlNet modules "swap nodes" requires them to be momentarily disconnected from the network, so they cannot fulfill the "moderator" role that the lowest-numbered device usually plays. This results in a ControlNet network restart, and thus dropped Connections, if there are not at least two other live nodes on the network at lower node numbers.

Details are in Chapter 2 of both the Standard and Enhanced ControlLogix Reundancy User Manuals, 1756-UM523 and 1756-UM535, both on the RA Literature Website.

In my most recent ControlLogix Redundancy system, we made the I/O racks nodes 1,2,3,4,5 and the controller chassis nodes 10 and 11.

You can't make these changes to an operating system; you will need to shut the whole thing down, re-configure the 1756-CNB(R)/CN2(R) modules (rotary switches), reconfigure the target addresses in RSLogix 5000, reload the program and reschedule the network.

 

[justjack]

Thanks for your help! Your posts have helped me many times when searching for PLC answers!