Two EN2TR cards in remote chassis

Is it possible to have two EN2TR cards in a remote 1756 chassis? I have a dual redundant PLC setup, the A and B chassis each with CPU, two EN2TR and RM2 cards ( so I know this is possible in Local chassis). One of these is for process network (172.18.59.x) and the other for Device level ring remote IO (10.1.5.x). The DLR RIO is 4 1756 chassis.

I want to add a second EN2TR card (eg 10.1.6.x) to the fourth DLR chassis to communicate with a number of new drivers. This would be monitoring extended parameters only as control is hard wired from the existing chassis. Is it simply a case of adding the new card to the IO tree and adding the drivers under that? Wanting to keep the drives off of the DLR.

This is a fantastic question.

The last time I looked at this in detail was a while ago, probably v18 or v19 Redundancy systems, and RSLogix 5000 would not warn you that you had placed two network bridges between the CPU and the I/O devices.

You can only have ONE network bridge between your CPU and an I/O device. It can be EtherNet/IP or ControlNet, but there can be only one. This applies to both Redundancy and ordinary controllers.

A two-hop I/O connection would even work... for a while, until there was a disconnection and the buffers would get juggled and the controller wouldn't reconnect.

Your system is unusual because you have hardwired control and you just want this connection for diagnostics messages.

You could do it by putting the modules in to the I/O tree but then inhibiting them, and using the I/O tree strictly to provide a target for MSG instructions.

If you wanted to use cyclic I/O connections to bring diagnostic and monitoring information into the controller, you would have to put a new pair of EN2T modules in the Redundancy controller chassis, to create another I/O network (DLR or non-ring).

Thanks for that Ken. It's interesting to know about the number of Ethernet bridges between controller and IO devices. This PLC is V24 running in L74 processors (I think it L73).
I'm going to have a read of the Ethernet manual for the drives, Vacon Flow100, and see if MSGs are appropriate.