RMC PLC Networking with ethernet

Hi all,

Currently we use 4 or 5 RMC’s communicating via Ethernet to a Control Logix PLC.

Currently we use a Sixnet ET-GT-9ES-1 switch, however we have had some difficulty when the switch starts up and the RMC fails to recieve some information(Parameter tables) from the PLC. We believe that it is a problem with the switch. We have tried a newer version of their firmware they released to address the problem which has reduced but it remains to be an issue. The problem seems to occur more often when more than 3 or 4 RMC’s are on the network.

My question is has anyone had reliable sucsess with another manufactures switch? Perhaps N-Tron?

A second question would be what advantages if any could we expect to see if we went to a managed switch?

Our network.
In the Control Logix rack we have one Ethernet card that communicates with the HMI and mill network. We have a second Ethernet card that communicates thru the Sixnet Switch, to up to 5 RMC’s each with a mix of Quadrature and MDT/SSI cards.



Thank you for your assistance Peter in advance

I am sure that Peter Nachtwey will answer this question with a lot more knowledge or authority than I can (he owns the company that makes the RMCs) but i suggest looking at a switch that has IGMP level 2 snooping ability. Read up on Ethernet/IP multicast. AB has whitepapers on their website. Regards Alan Case

The Ethernet ports on the RMC100s are 10 Mbs half duplex. The switch must be able to detect this. Most switches can.
4 RMCs on a network should be no problem. However, you should heed Alan's warning about the needing a managed switch if you have more devices than just the RMCs on the network.

Use the RMCWin->Windows->Ethernet Statics dialog box to monitor colisions and other errors. There are also two other Ethernet dialog boxes that are handy for debugging Ethernet problems.

Download the TCPDemo.exe from our website. It can also provide performance information.

Managed Switches

I guess my question boils down to this.
On a network comprised soley of say 5 RMC's and 1 Control Logix Ethernet Card, would a managed switch improve performance enough to justify the added cost/complexity. I believe I understand that RMC's use multicast. And Multicast would send packets to all the 4 other RMC's aswell as the Ethernet Card in the PLC. Would this added traffic cause a problem. Peter, would you expect it to cause any issues? Would a managed switch stop the multicast traffic from reaching the other RMC's? are RMC's capable of handling this unsolicited traffic?
I guess Im asking would you suspect it is a problem with the network design (ie. not using a managed switch) or a problem with the particular make of switch.

I didn't have a whole lot of luck finding the tcpdemo file on Delta's website, but fortunately Peter had directly linked it a while back, and the link still works... Here.

You shouldn't have problems with just 5 RMCs.

jetwax said:

I guess my question boils down to this.
On a network comprised soley of say 5 RMC's and 1 Control Logix Ethernet Card, would a managed switch improve performance enough to justify the added cost/complexity. I believe I understand that RMC's use multicast. And Multicast would send packets to all the 4 other RMC's aswell as the Ethernet Card in the PLC. Would this added traffic cause a problem. Peter, would you expect it to cause any issues?

Click to expand...

No, we have had 11 RMCs on a switch. It works, but there are many collisions. What about tht Ethernet dianostics I asked about above?

jetwax said:

Would a managed switch stop the multicast traffic from reaching the other RMC's? are RMC's capable of handling this unsolicited traffic?

Click to expand...

The RMCs get all the packets and must filter through them till they get packets meant for that particular RMC. There is a limited number of buffers in the Ethernet chip. We know it is possible for a flood of packets to overload the on chip Ethernet buffers but if this happens the packets that are sent in message mode are retried. You should lose a message in message mode.

jetwax said:

I guess Im asking would you suspect it is a problem with the network design (ie. not using a managed switch) or a problem with the particular make of switch.

Click to expand...

I wouldn't know about that brand of switch. Obviously we can't try them all. Switches are cheap enough that you should get a good one and not waste too much time. The RMC's Ethernet is Ethernet/IP certified by the ODVA labs. What about the Ethernet diagnostics? The RMC's Ethernet diangnostics are pretty good. What is the RPI set to?

Thanks for post the direct link for me Tom. I am in the field now and couldn't do that from here. Our website got re-arranged a couple of weeks ago.