Redundant ControlLogix PLC and a Third Party

E

Thread Starter

E. van Putten

For a new installation we are planning to use Allen-Bradley PLCs.

Our system will consist of a redundant ControlLogix5571 pair connected to a fiber optic ethernet ring (remote I/O racks).

The question I have is: how to link our redundant PLC pair to a third party PLC (also using Allen-Bradley).

For "political" reasons, it is not allowed to have the third party in our fiber optic ring.

It was decided there will be a single (non-redundant) ethernet connection running from our system to the customer's PLC.

Now if it was a single (non-redundant) setup, one would probably just add a communications processor (network card) to the CPU-rack and that would be it.

However, what to do in case of a redundant CPU pair?
Is there a way both CPUs can share the single ethernet link to the third party?
 
Add 2 ENBT modules, one in each of racks. For example, let's call one module 'A' and the other 'B'.

Install 2 switches (managed, or configurable to enable rapid spanning tree protocol (RSTP) or fast recovery of (FRNT)).

For mesh:
Connect 'A' to switch 1 and switch 2. Connect 'B' to switch 1 and 2. Connect switch 1 to switch 2 with another cat5 cord. Your non-redundant connection can be connected to either switch. This configuration creates a separate mesh just for your connection. Enable RSTP in both switches.

For ring:
Connect 'A' to switch 1 and switch 2. Connect 'B' to switch 1 and 2. Use two cat5 cords to connect switches 1 and 2 together. Enable FRNT (or the equivalent protocol if you are not using Westermo switches).
 
You could also use a single ENBT in a remote rack if you have it. In this setup, you have 2 redundant chassis (4, 7, 10 slot), and 1 (or more) non-redundant I/O. The ENBT could be installed in one of the remote racks.
 
That's quite neat! I didn't expect that was possible!

> You could also use a single ENBT in a remote rack if you
> have it. In this setup, you have 2 redundant chassis (4, 7,
> 10 slot), and 1 (or more) non-redundant I/O. The ENBT could
> be installed in one of the remote racks.
 
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