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Ethernet in Automation and Control

Posted May 01, 2007 9:43 AM

According to this article in Control Design, a University of Limerick, UK researcher says that Gigabit Ethernet holds out much promise for factory networks. Operating systems, protocol stacks, and device drivers all add to the processing time. The author also feels that finely tuned software will remain a big contributor to overall latency. Of course, many factory operations demand deterministic, real-time communications links with iron-clad guarantees on latency and 'jitter' (short-term variations in latency). Although Gig-E is technically non-deterministic, the article describes how latency can be minimized, making this high-speed off-the-shelf networking technology suitable for real-time networks. How do you plan to use Gigabit Ethernet?

The preceding article is a "sneak peek" from Data Acquisition, a newsletter from GlobalSpec. To stay up-to-date and informed on industry trends, products, and technologies, subscribe to Data Acquisition today.

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#1

Re: Ethernet in Automation and Control

05/02/2007 12:20 AM

Talking historically, Ethernet wasn't acceptable for machine control because of its CSMACD nature. One had to know when one would have control back. This meant some sort of token-based protocol, such as Token Ring or FDDI. However, the bandwidth of gig Ethernet has become so wide that CSMACD is moot. No matter how many machines you have to talk to, you're almost guaranteed instant connectivity.

Does this make any sense?

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#2
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Re: Ethernet in Automation and Control

05/02/2007 9:31 PM

Vermin--

Yes, but no. Lets assume that the network uses distributed intelligence, so each node is doing its own work and communicating to other nodes as needed to pass data and conditions. In an ideal world, this would be great. However, you need to have an architecture and components which are all built to provide redundant data pathways and fail-safe types of logic. I don't think this type of design is widely taught or understood at present.

Also, I am concerned about the types of operating systems which may be used in the different nodes or locations. A crash or hang would need to be detectable and recoverable.

The design of all the parts and integration of them together is possible, but I would be very cautious in making promises.

--jmueller

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#3
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Re: Ethernet in Automation and Control

05/02/2007 11:22 PM

If you have multiple computers sharing tasks, then your computers should be large, powerful servers that have access to RAID disk arrays. Next, you run InfiniBand in the server room. InfiniBand bypasses the network adapter card, and will eventually bypass the PCI bus altogether. InfiniBand cards allow each server to do remote DMA to every other server - this is done at about 300 Mbits/sec, and is climbing to 1000 Mbits/sec.

Not only do you not have to worry about Ethernet adapters, PCI bus timing, and latency, InfiniBand allows each computer to talk to each other on their own level.

Have you heard of this? I think it's on Wikipedia, and I know it's on the web. If you don't know about it, check it out. It pretty cool!

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#4
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Re: Ethernet in Automation and Control

05/03/2007 7:39 AM

Thanks, Vermin, for the heads up. I have not done anything at that level of communication, but am always interested in learning what is "out there". --jmm

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Re: Ethernet in Automation and Control

05/03/2007 11:40 PM

It's cool. I just learned about it myself. Wow! computers being able to do remote DMA's that blew me away!!!

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#6
In reply to #2

Re: Ethernet in Automation and Control

08/21/2014 8:03 AM

Sounds like CANbus. Have you investigated that. Distributed low level computing and a co-ordinator that doesn't have to be huge.

Look also at LINbus and FLEXray.

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