Connecting two 1756-L55 PLC through 1756-ENBT

[RZR]

Hi,
I want to exchange data between two L55 PLCs using ENBT
PLC1 is the main PLC and consist of 1756- CNB, L55 CPU and ENBT.
Five remote I/O racks are connected to PLC1 through ControlNet (coaxial cable).
Each I/O rack consist of 1756-CNB, DI, DO and AI modules.

PLC2 consist of 1756-L55, ENBT, DI, DO and AI modules.

I want to exchange data between PLC1 and PLC2 but PLC2 is far from PLC1.

is it possible to add a 1756-ENBT to I/O rack number 5 and then connect this new ENBT by Ethernet cable to the ENBT of PLC2 and program PLC1 to pull data from PLC2.
I already has one extra ENBT and I want to use it if this scenario is possible and avoid buying CNB and coaxial cables and also to avoid the risk of damaging underground cables in the old plant.

Thanks,

 

[Ken Roach]

Yes, this is possible with MSG instructions, but not with Produced/Consumed Tags.

You can attempt to set it up with an I/O tree configuration and Produced/Consumed Tags, and it might even work for a short while, but it will not be reliable and you should not do it.

You can read and write with MSG instructions in either PLC. It sounds like the most appropriate way is to use MSG instructions in PLC-1 that are configured to perform Read Tag services. Ideally, you can collect all the data you need to transfer into an array of DINT and/or an array of REAL tag elements, so you need just one MSG per datatype block.

The CIP Path is the essential part. CIP Paths consist of pairs of addresses that represent a Port Number and an Address, all separated by commas. Each pair can be thought of as a "hop".

Hop 1: CPU to Backplane (Port 1) then to Slot A (1756-CNB)
Hop 2: CNB to ControlNet (Port 2) then to ControlNet Node B number for "Rack 5".
Hop 3: CNB to Backplane (Port 1) then to Slot C (1756-ENBT in Rack 5)
Hop 4: ENBT to Ethernet (Port 2) then to IP Address D (1756-ENBT in Rack with PLC2)
Hop 5: ENBT to Backplane (Port 1) then to Slot E (PLC2 CPU).

That path will be entered, separated by commas, like:

1, A, 2, B, 1, C, 2, D, 1, E

The Backplane Slot and ControlNet numbers will be 1 or 2 digits, and the IP addresses will be the usual "192.168.1.1" format.

Remember that Slot numbers start at 0 on the left of a 1756 backplane. CPUs are often in Slot 0, but not always.

 

[RZR]

Thank you Ken Roach for the valuable information.
Is it possible to install the ENBT in the last slot of rack 5 as the other slots are filled with exist CNB and I/O modules and change slots will need to change I/O configuration in PLC1.

 

[Ken Roach]

Yes, the 1756-ENBT can go in any slot of the chassis.

You can even go online with PLC2 over that path, as long as you right-click and add the PLC2's 1756-ENBT IP address to the remote network once you drill down to the 1756-ENBT in "Rack 5".

Is this a Redundancy system ?

I have done messaging exactly like you describe with v15 Redundancy. The 1756-ENBT had to go in one of the ControlNet-connected I/O racks, and Rockwell CIP protocol moved smoothly through it as long as we had the CIP Path correct.

 

[RZR]

No it is not redundancy system.
I found in the store a new L61 CPU so if I add L61 to rack 5 can I then exchange produced and consumed tags with PLC 2 (L55). Is this possible?

 

[Ken Roach]

Yes, you can exchange Produced/Consumed Tags between a 1756-L55 and 1756-L61 over an EtherNet/IP network link between two 1756-ENBT modules.

There can be only one network link between two controllers that are exchanging Produced/Consumed tags. It can be a ControlNet link, or an EtherNet/IP network.

But you can't use more than one in series.

You can't go CPU -> ControlNet -> Chassis -> Ethernet -> Chassis -> CPU.

You can't go CPU -> Ethernet -> Chassis -> Ethernet -> Chassis -> CPU.

MSG instructions will transit that sort of network connection (it can be dozens of hops) but not cyclic I/O or Produced/Consumed Tags.

 

[rdrast]

Another solution, if distance is the issue, is just to run a fiber link between the two chassis. There are many out there, like this one from Tripp Lite.


If you have a clear, line of sight, path, you can also use Ethernet over Radio extenders.

 

[RZR]

rdrast
for the fiber optic we will need to dig trench and the client want to avoid it because there are many underground cables and pipes and it will cost more than using ENBT option.
The Ethernet over Radio extenders is good solution but as already have spare ENBT and L66 it will be less cost.