Controllogix Ethernet Flex I/O Reliability -recommendation

[pedroascencio 0]

Dear Sirs Currently we are evaluating a PLC architecture make up for Contrologix (ENBT) and ethernet Flex I/Os. We would like to know your recommendation, because we do not have experience with ethernet Flex I/O. We always have worked using Controlnet links. Anyone of you knows any type of problem for the ethernet link, or disadvantages respect to controlnet?. We have seen on this web page rockwell some what it is the purpose of each network. http://www.ab.com/networks/controlnet/faq.html In my point of view, despite of ethernet i/o flex seems to work without a problems, it is not for control. In my brief experience, I have used CIP protocol over ethernet (ENBT) sending messages between 2 controllers, and I have detected errors frequently. However, the link is too fast, so finally it does not affect the data transfer. We would really appreciate your comments. Kind regards Pedro Ascencio

[PLCMentor.com 60]

We regularly use ethenet I/P for our control networks as do many places from our discussions with our local rep (I have not noticed many errors accumulating as you mentioned so that may be an issue with your network). We also use the flex I/O as I think it is more straight forward for installation and troubleshooting than the point I/O. It eliminates the need for interposing terminals necessary for rack I/O due to the separate base/electronics design. Generally the plant IT guys are instantly familiar with the network and comfortable with it. High network speeds, as you mentioned, tend to make up for any issues with it being non-deterministic. It is cheaper to install and quicker to bring up than any of the other network topologies. The only gotcha I see in using ethernet I/P for control is the need for a managed switch. Without a managed switch in your design, you risk the possibility of overloading some components on your network. The AB drives are an example. They can handle a relatively low number of packets and can be overwhelmed if there are a large number of devices communicating without a managed switch. Shielded ethernet cable for your field runs are suggested. Limiting or eliminating a connection to the plant business network is also advisable.

[BobLfoot 302]

The strategy we've been using with success for a couple of years now involves a COntrol Logix Safety PLC and 4 Ethernet Modules. We spread the I/O out as follows: Ethernet Module 1 - Plant Scada and PLC Programming - 172.X.Y.Z subnet - ex = 172.192.68.1 Ethernet Module 2 - Safety I/O - 10.10.slot.X subnet ex =10.10.2.1 Ethernet Module 3 - Drives I/O - 10.10.slot.X subnet ex=10.10.3.1 Ethernet Module 4 Flex I/O - ex=10.10.4.1 ANd of course we run stratix switches and isolated copper so no two subnets every share the same hardware. Yes this is overkill as I am sure VLANs and managed switches could make it simpler, but it has been working for us.

[OkiePC 14]

WHen I first was exposed to Controllogix, Ethernet and Controlnet were about the same speed and Ethernet IP I/O was not yet fully trusted, although even at that time, around 2000, could be configured to be failsafe and as reliable as controlnet without the hassles of scheduling, coax media, and expensive adapters. Today, ethernet IP hardware is so much faster, that you are right, it is not uncommon to fins a network that is suffering from collisions and re-tries but exhibits no symptoms, due to the overwhelming speed, the right packet may get there late on the third try but in plenty of time to satisfy the required control requirements. I would view controlnet as a dying if not dead branch and definitely shift toward Ethernet IP technology. I like controlnet, If you can see the LEDs and set a node number you can troubleshoot and repair it most of the time. It is simple and wokrs or doesn't.. Ethernet IP, on the other hand, does open you up to a whole new layer of potential mystery root causes which requires you to put more thought into network design and hardware selection and configuration. Edited 9 Mar 2013 by OkiePC