DLR network topology recomendations

[RickyRud]

Hi everyone,

I have never done DLR networks before and would love to get some feedback on some of the design methodologies that the hardware engineers in my office are playing with.

We have two isolated subsystems with 37 devices each. These sub-systems have their own PLC (1756-L72) on a 10 Rack chassis. The devices communicate to the PLC via an 1756-EN2TR card in their respective DLR networks (All devices are DLR capable). We need to find a way for these 2 PLCs on seperate subsystems to communicate with each other (for produced/consumed tag purposes).

Is it possible to add a 2nd EN2TR card on their respective PLC racks and connect them in a second ring network? In other words, is it possible to have two parallel ring networks?

Thanks!!

 

[ASF]

Yes, that's absolutely possible. Although I'd question the need for a ring network with only two devices on it - I'd just run a single cable.

 

[JeremyM]

Yes, that's absolutely possible. Although I'd question the need for a ring network with only two devices on it - I'd just run a single cable.

Here's my "but what if...":

Adding future devices into the ring would be straightforward - open the ring, insert device, close the ring, continue, no downtime.

 

[AustralIan]

I imagine you want to do:

L72  EN2TR  EN2TR
      | |    | |
L72  EN2TR  EN2TR

I have no way of testing this, but I imagine you would need to set up an I/O tree with BOTH views of the remote processor, eg. PLANT2PLC_NETWORK1 PLANT2PLC_NETWORK2.

You would then need to have two tags per consumed tag, and write logic to compare them as well as take into account the comms lost flag.

 

[ASF]

Here's my "but what if...":

Adding future devices into the ring would be straightforward - open the ring, insert device, close the ring, continue, no downtime.

True. Although it still seems a bit overkill - I would probably just add the third device without making it into a loop, and then close the loop when downtime permitted. I guess it depends on the industry, and how often you get an opportunity to do things like this!

 

[Paullys50]

Or just break out the ring networks with a 1783-NATR and map the PLC IP address from one network to the other.

Use 1 1783-ETAP (No NAT, so cheaper) on the first system and 1783-NATR (NAT) on the second system, then connect a wire. Configure the 1783-NATR to translate an IP address to the other network. Probably cheaper than buying EN2T/R cards.

 

[RickyRud]

Thanks for your responses gents! really appreciate it!

As Jeremy mentioned above, we may have to potentially add more devices to the ring in the future and / or connect to existing systems. Hence the second ring network. Another constraint we have is that the customer does not want any managed switches in the network (I think they are scared of someone hacking into their system haha) and want redundancy. So I am not sure if we can use 1783-NATR module without a switch.

I also read somewhere that it is possible to connect a remote IO in a ring network that has multiple PLCs in it. The only caveat is that just ONE plc has control of it. The other one can only be configured as 'listen only'. Is that true? Also what happens if the controlling PLC goes offline? Do the other PLCs loose communication with that IO module as well?

 

[robertmee]

FYI there is a limitation to the number of some devices in a Ring. I just did a plant wide installation with multiple ring networks, and ran into a problem because the client installed DLR Stratix switches on every MCC column in the plant. It took a couple of days with AB Tech support to sort that one out. Had to move some of the switches off the ring to a standard star configuration. I don't remember off hand the number, but it seemed like it was less than 10 switches. Devices like AENTR's and 20CommR Drives seemed to be ok.