comm check

[automatic2]

I'm digging deeper into this PLC thing and reading about various serial busses. DeviceNet, ControlNet, /IP. Which is leading the way and which has better performance under remote I/O connections. Anyone offer a generalization where one exceeds over the other.

 

[dV8r]

Profinet will out perform all of those mentioned. In ease of use, cost of implementation, speed and ability to add/change the configuration in the future.

 

[CREED01]

This may give a little help:

http://www.weighing-systems.com/TechnologyCentre/fieldbus1.html

 

[automatic2]

Nice overview, thanks.

would not all protocols improve in a TC/IP wrapper?

 

[dV8r]

No!
TCP/IP is only part of Ethernet and is not as fast and efficient as you may think. The reason that Profibus is more efficient is that it minimizes the use of TCP/IP and uses mostly UDP. Do the research and compare on your own along with some of these others that you may discover on the 'net.

Oh, I keep forgetting "You can't put anything on the internet that isn't true."

 

[djs]

You have to separate the protocol from the medium. Ethernet is not generally considered a "serial" communications link. Along with the medium is whether the link is half duplex (one way at a time) or full duplex (two way). Also of consideration often ignored is the available bandwidth. For example Ethernet over radio on licensed bands is very bandwidth limited. The radio link usually only supports 9600 baud, and then the Ethernet imposes a communications overhead on that. So your effective throughput will only be 7000 baud or so. If you went pure serial over that same link you would get the full 9600 baud bandwidth.

Many of the Ethernet based protocols were designed to be used on high bandwidth channels. For example AB Ethernet/IP usually takes at least four exchanges for each operation. When the bandwidth in 100 Mbps this is not a problem. But when the available bandwidth is 7000 bps it is. The use of UDP by some protocols helps with this issue, but at the price od data integrity. So at this point there is really no one "best" protocol.

 

[controlsdude]

Devicenet is solid but old in the tooth, solid address recovery feature, but has noise issues if doing welding.
Ethernet IP growing leaps and bounds, alot more devices on this network but watch out on how IT views the use of switches and your control.
ControlNet very fast but the media is high dollar and difficult to install.
Profibus very fast and reliable but make sure you have the right connectors if doing high speed baud rates.
ASI is new and the media for this is cheap and more idiot proof and the setup is easier than most networks.
RIO/DH legacy but be aware of it if you doing retrofits.