ControlLogix Redundancy Problem

Popo Karimu · Oct 18, 2016

Good day,

I got a concern regarding the Redundancy setup. The problem is when communications get interrupted between the Primary PLC and the remote I/O rack. The outputs of a Digital Output module get triggered unintentionally shutting down critical processes in the plant. The PLC we're using is 1756-L73 with 1756-EN2T Ethernet module.

I'm wondering whether the PLC being connected to a POE network could be a problem (see attached system architecture).

Could there be a technique to make redundancy configuration fail safe? Or I probably need a comms failure signal to Secondary and remote I/O rack?! Thank you very much.

Sincerely,
AndreiK

Popo Karimu · Oct 18, 2016

The firmware that we're using is Logix Designer v24

Ken Roach · Oct 18, 2016

Thanks for the concise diagram !

Are the outputs on the remote chassis transitioning from OFF to ON, or from ON to OFF ?

Are they remaining in that state, or transitioning for a short period of time ?

Does the Secondary take over the I/O connection correctly and run the system, or does the switchover fail ?

Ethernet networks for Redundant ControlLogix need to be set up carefully. Have you talked to Rockwell about this POE switch ?

What you're describing sounds like it might be related to a bug in the 1756-EN2T firmware from a couple of years ago (Link), but that existed when a connection was dropped and re-created, not when a Redundancy switchover occurred.

Popo Karimu · Oct 18, 2016

Good day mr. Ken,

Outputs on the remote chassis transition from OFF to ON.

Transitioning occurs for a short period of time.

I tested the switchover before and was working just fine. When the comms failure to the remote chassis occurred there was no switchover. The secondary got disqualified from the Primary at the same time.

I haven't talked to Rockwell about the POE switch.

That seems to be the case! It wasn't a switchover but a communications drop.

Thank you very much!

Ken Roach said:
Thanks for the concise diagram !

Are the outputs on the remote chassis transitioning from OFF to ON, or from ON to OFF ?

Are they remaining in that state, or transitioning for a short period of time ?

Does the Secondary take over the I/O connection correctly and run the system, or does the switchover fail ?

Ethernet networks for Redundant ControlLogix need to be set up carefully. Have you talked to Rockwell about this POE switch ?

What you're describing sounds like it might be related to a bug in the 1756-EN2T firmware from a couple of years ago (Link), but that existed when a connection was dropped and re-created, not when a Redundancy switchover occurred.

kannanmkm · Oct 18, 2016

Can you share the redundant Module Model. and its stats when the RIOS goes off.

Popo Karimu · Oct 18, 2016

kannanmkm said:
Can you share the redundant Module Model. and its stats when the RIOS goes off.

hi mr. kannan,

It's 1756-RM2/A we're using.

Thanks,
Andrei K.

ControlLogix Redundancy Problem

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