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poovs

10/100/1000Mbps PLC Ethernet Comm Module(s)

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We are seeing more and more security consultants and engineers write specifications around 1000Mbps (1Gbps) local networks for the control system lans. Up to date the only thing we have been able to do is provide 1Gbps at the network level and the node level at the HMI clients (PCs equipped with 1Gbps NICs). It seems that these 'engineers' are writing specs around a technology that (to my knowledge) does not exist at the PLC level yet. The reason for this post is to gather information from any/all of you who are aware of a 1Gbps ethernet communication module for any of the major PLC manufacturers (AB, GE, Omron). thanks ahead of time for any info, -poovs

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Nothing on the Mitsubishi side. Just checked my catalogs. Of course, they sometimes have stuff in development or released in Japan that isn't available state-side, but I haven't heard of anything.

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Never seen a gigabit Ethernet card for any PLC. Mitsubishi is 10/100, so is Omron, and last I knew about Modicon and Siemens (years ago) they were still 10/100. Sometimes engineers write these things because they have no idea what they are talking about, just want the latest and greatest thing they saw in a magazine (see the lines of people waiting for Iphones), and sometimes it's because one particular vendor does and they are trying to lock them in...

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This has been my consensus as well. I just want to be sure before we go back to the engineers and consultants and inform them that they are specifying equipment/technology that does not exist at this time. thanks for the info: PLEASE, keep it coming I'd like to hear from more...

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Gigabit ethernet may or may not ever make sense in this application. However, running Cat 6 cable instead of Cat 5 or 5e totally makes sense. Why not? It's almost the same price. Your major expense is running the cables/conduit/etc. I don't know that it will ever be a necessary requirement with current PLCs or even HMI PCs. High performance workstation hard drives peak at about 30megs/sec - 100Mbit isn't likely to slow you down much there. Even streaming video is fine. Fast pipes between switches, segments, and high performance servers makes sense. You also want to make sure that your switch can truly handle enough point to point 100Mbit connections. A nice thing about running Cat 6 is that you can just change out your switch or add Gig-E later. Would you need 48 gig-E ports now? I seriously doubt it. Would it be nice to have the capability with all your cables - probably.

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With the type of control systems that we typically work with (large amounts of I/O) with alarms and control for nearly every I/O point, AND all specifications requiring updates to be no less than 0.5 sec on the HMI (with > 20 HMI PCs on our current project) there is certainly a bottleneck at the PLC 10/100 ethernet module. Sure we could introduce more plc 10/100 ethernet modules (but now we have to manage all these modules and create a more complicated communication network/config in the HMI application). We have been throttling this traffic into/out of these plc modules for years now but still do not get the thoughput you would expect. Perhaps some of these delays are a result of the protocol being used (Omron FINS Ethernet) but nevertheless, there are major delays at the HMI client-side.

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Have you thought about putting in an OPC server, having it collect all the data from the PLC, and then pass it amongst the PC HMIs without each of them asking the PLC for info? That would help speed up the PLC comms a bit I would think. Mitsubishi is releasing a gigabit PLC network called MELSECNET/G soon. This is fiber optic comms between PLCs, and I expect in the short term they will add it as an option on their HMI products and a PC board version as well.

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I second Crossbow here. Increasing concurrent clients on a system that polls the PLC hard is not a scalable model. I seriously doubt that your PLCs could process and deliver that much traffic even with a Gig E card. From a Computer Science perspective you need something to act as a cache. Most vendors distributed HMI systems have the clients talk to their server (which may be an application, web server, OPC server, or database) instead of all slamming the PLCs. In fact, sometimes there are several layers of abstraction there (one between client/server, one between server/OPC server, and between OPC Server/PLCs). You will either need to go with a more scalable architecture now, or will need one soon as you grow.

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I couldn't agree with you more. I have suggested going the route of an I/O server as the single client actually polling the PLC. Unfortunately the engineers/consultants have written their specifications such that each client will communicate to the PLC individually. (No one loss of a machine on the network will cause any other units to fail). I am aware of redundancy at the I/O server client level, and have again strived to make this happen... alas, here we are still fighting the same fight. Nathan, much like the Mitsubishi network you speak of, Omron has their own proprietary redundant fiber network utilizing a ring (CLK) that has fault tolerance built in. However, this is not gigabit ETHERNET as the specs require.

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Sounds like your 'engineers' wrote the perfect unattainable spec.

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Redundant rings take care of single failures of cabling. You will end up with redundant switches (and Ethernet ports) to take care of single failures of switches (unless you set up one switch per PLC and count it as part of the PLC). Either Kepware or Matrikon (forgot which) handles redundancy in terms of the PC (I/O server) level. In addition, at least Citect and Cimplicity allow you to have redundant HMI servers with automatic failover. With a little creativity depending on the operator interface, I could envision some easy ways to make off-the-shelf operator interface's failover too. The simplest is giving operators a "server A/server B" button on the screen and explaining that if all the tags suddenly come up blanks, hit that button. The automated version would monitor an OPC system status tag and switch screens automatically if the operator interface has that level of capability. Not that I want to promote their specific product, but Matrikon has been advertising using their specific OPC servers for a long time now specifically to deal with bottlenecks and redundancy at the PLC/HMI communication level and they heavily advertise solving these particular problems. It's probably worth a look, even if you go with someone else's product.

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Kepware has a product called Kepware Redundancy, priced around $1300.

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thanks everyone for the redundancy options... we are, however, off of the original topic... is everyone then in agreement with the following statement? At this time, there is not a single PLC manufacturer that provides a 1Gbps Ethernet Communication module.

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I do not know if there is one, but in all honesty, I cannot see a need for such bandwidth in a standard control network. I monitor all traffic on our control network daily and have traffic graphs for all devices going back several months. I have yet to see any sustained traffic over 1kps. I also have the system configured that the plant operators can pull up video surveillance over the network for various areas, and even with that running, we're not anywhere near using 100Mbs. If you like I'll post what some of my traffic graphs look like, but I cannot imagine a control network using enough bandwidth to warrant 1Gbs everywhere.

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thanks for your input; Even in our projects, the network itself will not be utilizing the bandwidth available for the 1Gbps... however the bottleneck is not the network, but the PLC ethernet module being polled by such a large amount of clients for a large amount of data at a pretty fast rate (0.5 secs). I agree with what you are saying for YOUR particular control network and others that are allowed to utilize a single I/O server machine that handles the requests of the clients (through pseudo-I/O tags to the associated clients). We are unfortunately not permitted to utilize this approach. Hopefully things will change and the specifications will follow suit. But until they do (meaning the group of consultants creating these specs will need to adopt a 'new' and 'foreign' topology) I am still searching. thanks

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That was my point. Interject a layer of PC's with OPC servers in between. This eliminates the PLC bandwidth issue. As to 1 Gbps, if you install one Ethernet switch per PLC, which I recommend doing anyway (isolation), if the switch is considered part of the "PLC", then it's 1 Gbps. Even if you had gigabit ports on the PLC Ethernet cards, you'd still saturate them with the amount of traffic. I haven't even gotten close to 100 Mbps on AB PLC's and it's pretty easy to run into bandwidth limitations (actually, traffic servicing limitations within the PLC, not the Ethernet capacity).

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To answer your question, I have not heard of a 1000Mbps connection for any brand of PLC. However, what I was trying to say earlier is that it wouldn't matter! PLCs weren't meant to handle that kind of bandwidth, from the processing/scantime/internal IO perspective. You could put a mega-mega-giga-giga-mega Ethernet controller on a PLC and it will still probably be able to serve out data somewhere in the sub-100Mbs data rate. Paul's a sharp dude - I'd pay special attention to what he says. At this point it looks to me like you're setting yourself up for failure. Edited by Nathan

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