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waterboy

Contrologix remote rack over ethernet

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If I were to configure a Controllogix rack at one end of the plant and a second rack at the far end - can I use the CPU in the first rack to control and monitor the second racks I/O if the second rack does not have a CPU, only an ENET card? Would it be as if the second racks' I/O was part of the first rack? I know it can be done if there IS a CPU in the second rack - something I have never even imagined a reason to do - but if there is no CPU ? Is this a reasonable idea to pursue? Neither side needs much horsepower (they are the beginning and the end of the same process) so a single CPU makes more sense from that perspective , but then again I don't want to swamp the network with traffic . This process is not deterministic, time accuracy closer than a couple seconds is more than adequate. I welcome your Comments or Ridicule. :)

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This is a totally ordinary thing to do with ControlLogix I/O chassis. The 1756-ENBT or 1756-EN2T modules are "bridges", which can fulfill the role either of "scanner" or "adapter" that you might be used to from the RIO days. The discrete I/O modules generally get included in a "Rack Optimized" connection, while each analog module gets its own Module connection. You can use either Multicast (so that multiple CPUs can listen in) or Unicast connections (one-to-one) for the I/O. On an unmanaged LAN, definitely use Unicast. The cyclic I/O data rate is settable for every connection; it can be as fast as 1 or 2 milliseconds, or as slow as 1 or 2 seconds. The ENET-RM001 reference manual from Rockwell might give you some good ideas about how EtherNet/IP is used for both messaging and control purposes.

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Perfect - I'm gonna set up a test set today. Thanks

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I've seen that there are inexpensive ethernet to fiber adapters that you can use to run a dedicated fiber in a situation like this and keep the I/O traffic off your plant lan. I'd strongly advise it if you can swing the cost.

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I do have fiber all over the place so I can do that. I am curious how much traffic there will be.

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Depends on the rack size and the number of connections on the rack. I always use a dedicated ENBT for remote IO and a dedicated ENBT for comm to the HMI and SCADA system. Apparently the EN2T has quite a few more connections available so any new systems will get an EN2T instead of an ENBT

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ENBT = 128 connections / 64 up and 64 down EN2T = 256 connections / 128 up and 128 down

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