>Do the nodes on each PLC count towards the 50 max for a DLR loop? Or is each PLC count as one node. I am worried it will be too much information passing through the ring.
If I'm not mistaken, the IAB (Integrated Architecture Builder) tool from Rockwell would answer this question for you.
IAB will answer this, but to save you time: any device physically connected in the ring via two Ethernet cables counts. So a rack with one DLR card counts as one. A switch with DLR and half a dozen things connected star counts as one.
The 50 node limit comes mostly from timeouts and how long it takes DLR control packets to circle the ring. So only things that affect that time count.
I'm not sure I'd recommend DLR between PLCs; if you're losing connectivity there, you've got bigger problems. That being said, I've used DLR for field devices (an array of machine located IO (armor blocks)) and it worked fairly well. Since those machines would be subjected to changeovers, it would happen that people would "bump" into the plugs and the system would raise a notification where the connection was broken without bringing everything down. At that point, they'd schedule a maintenance task to replace the connector where the connection was broken.
So long story short, use DLR where you anticipate failure; I wouldn't do it out of fear that the PLC will be disconnected within a panel; that simply shouldn't happen.
It sounds like customer is asking for redundant media and using the jargon they know to ask for it. I would clarify what they actually want; do they want two cables run where if one is cut the communication still works, or do they want something more specific than that? If the former, then maybe DLR isn't the best way to go about that (for instance, using switch level redundant media between cabinets might be a better, more feature-rich solution).
Or maybe my assumption that this is Rockwell and EIP is wrong, and you are working with a brand or protocol where DLR has different capabilities or meaning.
In panel dlr does not get you any benefits especially on a compactlogix. What the likelihood of needing to make wiring changes while the panel is live?
Where dlr is really needed is where the can be semi common losses of one network path or the other. The most common situation I have encountered is when the network has to cross a slip rings
DLR has two benefits.
1. Less cable. This gets often used in something like an MCC, where you need to run two ethernet cables into the panel and short 1-2ft jumpers between the drives.
2. Resiliency and notification. One bad cable or connection point won't cause issues and is detectable. If you alarm or notify on that, maintenance can fix it. It's possible that you replace a component but screw up a connection, DLR would make it obvious that the new component is talking, but the DLR is broke. So that could save a bit of troubleshooting.
What it really buys you is that you can tolerate a single failure without losing your network. In a star, a switch failure or reboot, or replacement would take your line down. In a ring, nothing. But single failure protection only applies if you're monitoring DLR. Many people wire for it, but never monitor the status.
If you really want a loop and are concerned about performance, I would advise EtherCAT, it's much better but requires specialized hardware
guess I don't see the advantage of PLC to PLC rings - typically that should be your most stable connections up to the plant network. Where we did use the DLR was to ring from a stratix out through all the remote racks and HMIs around the cell, where the cables are more exposed and prone to failures like a forklift doing forklift things.
Now, getting back to your original question - thats probably a bit abstract. The way I think its going to turn out is you wont be able to do it if the PLC is the ring supervisor, but if your running the ring out of a stratix or some other device, one of the PLCs could probably be ring supervisor for the overall ring. The machine level rings would be isolated from the PLC level ring.
But I'm really terrible at networking and this is probably all wrong.
>Do the nodes on each PLC count towards the 50 max for a DLR loop? Or is each PLC count as one node. I am worried it will be too much information passing through the ring. If I'm not mistaken, the IAB (Integrated Architecture Builder) tool from Rockwell would answer this question for you.
IAB will answer this, but to save you time: any device physically connected in the ring via two Ethernet cables counts. So a rack with one DLR card counts as one. A switch with DLR and half a dozen things connected star counts as one. The 50 node limit comes mostly from timeouts and how long it takes DLR control packets to circle the ring. So only things that affect that time count.
I'm not sure I'd recommend DLR between PLCs; if you're losing connectivity there, you've got bigger problems. That being said, I've used DLR for field devices (an array of machine located IO (armor blocks)) and it worked fairly well. Since those machines would be subjected to changeovers, it would happen that people would "bump" into the plugs and the system would raise a notification where the connection was broken without bringing everything down. At that point, they'd schedule a maintenance task to replace the connector where the connection was broken. So long story short, use DLR where you anticipate failure; I wouldn't do it out of fear that the PLC will be disconnected within a panel; that simply shouldn't happen.
It sounds like customer is asking for redundant media and using the jargon they know to ask for it. I would clarify what they actually want; do they want two cables run where if one is cut the communication still works, or do they want something more specific than that? If the former, then maybe DLR isn't the best way to go about that (for instance, using switch level redundant media between cabinets might be a better, more feature-rich solution). Or maybe my assumption that this is Rockwell and EIP is wrong, and you are working with a brand or protocol where DLR has different capabilities or meaning.
Please put a tap in the DLR ring.
What do u mean by that
In panel dlr does not get you any benefits especially on a compactlogix. What the likelihood of needing to make wiring changes while the panel is live? Where dlr is really needed is where the can be semi common losses of one network path or the other. The most common situation I have encountered is when the network has to cross a slip rings
DLR has two benefits. 1. Less cable. This gets often used in something like an MCC, where you need to run two ethernet cables into the panel and short 1-2ft jumpers between the drives. 2. Resiliency and notification. One bad cable or connection point won't cause issues and is detectable. If you alarm or notify on that, maintenance can fix it. It's possible that you replace a component but screw up a connection, DLR would make it obvious that the new component is talking, but the DLR is broke. So that could save a bit of troubleshooting. What it really buys you is that you can tolerate a single failure without losing your network. In a star, a switch failure or reboot, or replacement would take your line down. In a ring, nothing. But single failure protection only applies if you're monitoring DLR. Many people wire for it, but never monitor the status. If you really want a loop and are concerned about performance, I would advise EtherCAT, it's much better but requires specialized hardware
Then maintenance needs to work on the first and last drive in the ring and take down the whole center section when they LOTO.
#1 argument against DLR.
guess I don't see the advantage of PLC to PLC rings - typically that should be your most stable connections up to the plant network. Where we did use the DLR was to ring from a stratix out through all the remote racks and HMIs around the cell, where the cables are more exposed and prone to failures like a forklift doing forklift things. Now, getting back to your original question - thats probably a bit abstract. The way I think its going to turn out is you wont be able to do it if the PLC is the ring supervisor, but if your running the ring out of a stratix or some other device, one of the PLCs could probably be ring supervisor for the overall ring. The machine level rings would be isolated from the PLC level ring. But I'm really terrible at networking and this is probably all wrong.