Common Sense? EXACTLY!
Peter, I'll admit that my experience is limited to the single industry (cotton ginning) and I know from reading your other posts that you have much broader knowledge and much more experience than I do, but...
Peter Nachtwey said:
GIVE ME A BREAK. THE WORLD WILL COME TO AN END TOO. SO?
BOGUS argument.
I've been in the situation where a data logging computer with two network cards (one for computer network, one for control network) got a virus and started broadcast storming the control network. The computer was running anti-virus when it got infected, anti-virus software is not perfect. A network switch with broadcast storm protection saved my control equipment from having problems, but it was a common control network throughout the plant and not all other vendors used switches with broadcast storm protection; some of the equipment from the other vendors got quite upset at the network conditions. This was one of my first experiences with Ethernet and PLCs.
Peter Nachtwey said:
I have never heard of a broadcast storm with industrial devices.
OK, here's one for your list...
I know of only one HMI that for a
FACT creates a broadcast storm when talking to a PLC (or PLCs) via Ethernet. The AVG (also sold by AD) EZ-Touch
WILL create a broadcast storm and use 100% of the network if it can. Obviously when there is only one EZ-Touch talking to one PLC on the network this is not an issue because, as you pointed out, Ethernet is faster than the PLC will respond anyway, but what if you have 7-8 PLCs, 3-4 HMIs all on the same network and all moving data between each other? I know that a broadcast storm that brings network response time from milliseconds to several seconds
can happen; been there and done that.
Peter Nachtwey said:
Most of the Ethernet projects I am involved with use our motion controllers and Rockwell PLCs.
If I ever come across a project where the only things that will ever be connected to the Ethernet network is your motion controllers and Rockwell PLCs then I guess I'll defer to your judgment that everything will be ok and I can use whatever network gear is cheapest and go on with life... I've never used your motion controllers (though I hear they are quite good) nor a Rockwell PLC so I can't speak to their reliability on a network.
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With my last post I was simply trying to point out that in the real world things happen. Some idiot will connect an infected notebook to the control network, or some such stupid thing, and its better if the whole system doesn't come crashing down when things like that happen.
I guess my point was that while Ethernet is a wonderful communications network (I use it very expensively) you must put some careful thought and planning into what happens if (really more like when) the network bogs down AND what can you do to keep the network from bogging down.