We are currently using controlnet to network our drives to Controllogix PLC systems. I had a vendor wanting to use Ethernet/IP for a network of VFDs on a Controllogix project. It would be a dedicated network. I wanted to get the opinions on this issue. Thanks for your input in advance.

Without knowing the number of devices and brands, or if you plan to expand the system, I would say no. Allen Bradley Ethernet is marginally deterministic and the more units you place on the network the more difficult it becomes. Mixing this with other devices such as Operator interfaces and such devices, especially if they are not AB devices it becomes worse. A Managed switch can assist with predictability, again is device, and transaction dependent. Depending on the control logix you are using and the Ethernet card there are additional limitations.

Your best bet is device net or control net.

That is my 2 cents

If it's fans and pumps and the like, hands down, go Ethernet/IP. Watch out if you are using 20-COMM-E's or 22-COMM-E's. They are very sensitive to packets per second limitations (very limited processors). If you overshoot, you lose control over the drive. I just put in an application this way and it works great.

If you are doing motion control, "it depends". Ethernet can certainly be used. The problem with Ethernet lies in it's flexibility. You have lots of flexibility and control over your network architecture, much more so than Controlnet. The underlying architecture is also capable of much higher speeds. The flexibility is also the problem...you HAVE to do some planning and design up front if you are going to have a successful system. If the goal is to use a motion controller where you are sending commands over Ethernet, again, within reason, no problem.

However, if the drive/motion control path IS Ethernet, this is where it gets critical. Buy a copy of RSNetworx for Ethernet/IP just like with Controlnet because the big key here is planning. Make sure to install managed industrial grade switches (Cisco/AB is NOT an industrial grade switch, it arbitrarily locks up ports and requires administrative access if there is any electrical interference). Make sure to maintain an IGMP querier possibly with backup queriers. Use QoS, maximum packet rate controls, etc., to put gaurantees on your network availability. This is true even with a dedicated network. Use a switch capable of PTP (IEEE 1588). Do it all correctly and it will be faster and cheaper than Controlnet or Devicenet. Do it wrong, disaster.

Rod - we have two AB Ethernet Drive with ControlLogix Systems complte with their custom stratix switch going in our plant in January. THe training and demo units look real promising, but as Paul said and I'll paraphrase "The Devil is in The Details". We're going with IP by Port on the switch and DCHP/BOOTP on all devices. This makes drive replacement plug and play. Keep in touch and I'll let you know how it goes.

We haven't had any problems but VFDs are not the same as servos so speed and being deterministic is not an issue.