Etherbus: One company says industrial PoE is indeed ready to go

-- Control Engineering, 4/4/2007

In the February issue of Control Engineering, we said that Ethernet is not likely to replace fieldbus technology anytime soon due to impractical wiring topology and powering issues. Well, one company says that isn't true anymore and wants to prove it. Sixnet is launching a new line of networking equipment under the banner Etherbus that claims to be the best of the worlds of Ethernet, PoE, and fieldbus technology.

This is an ambitious launch in that it involves a whole range of products, and the larger implications are certainly interesting. Information is available now on the company Website, and products are expected to begin shipping by mid-April.

Sixnet says its technology offers the following:

• PoE using standard cable and RJ 45 connectors;
• PoE at 24 V dc, or 14 V dc;
• All the necessary hardware (switches, splitters, injectors) to support power distribution (including non-PoE devices);
• Units feature industrial toughened connectors and cabling;
• Ethernet switches to support any desired wiring topology, including daisy chain (ala fieldbus); and,
• While PoE use is possible, it is not required. Devices can still be externally powered when desired.

The hardware can support any commercial Ethernet protocol (e.g., EtherNet/IP, ProfiNet, etc.) but doesn't have to use any of them because standard TCP/IP works fine. As Sixnet says in its product data, "Etherbus is 'every bus' because it passes any and all Ethernet message packets regardless of origin or protocol."

Some strategic limitations could still dampen the enthusiasm a little, at least for a while:

• PoE is limited in this context to 15.4 W using current cables and connectors. 30- and 60- W circuits are coming, but these will need heavier cable and larger connectors.
• End devices have to be Ethernet enabled. Availabilities of Ethernet instruments and sensors are increasing, but still limited. There are very few bit-level devices.

Sixnet's offering promises to be one of the most comprehensive campaigns so far to push Ethernet below the PLC barrier. This larger effort has been going on for some time from different directions but never made much headway due to technical issues. For example, daisy chain wiring topology for instruments with Ethernet can be done with generic equipment by adding a switch to each device and daisy chaining the switches. (This does add latency to long chains and unmanaged switches can make troubleshooting troublesome.) Some protocols already support Ethernet daisy chains (ProfiNet for one) if the devices have appropriate connectivity built in. (Siemens, Phoenix Contact, et. al., have it on some devices, however these need external powering.)

It will be interesting to see how this fares. Fieldbus technology has been around for well over a decade and many companies still consider it new. But Ethernet is everywhere (84% of companies responding to our recent networking poll say they have it in their plants.) so this could grow in new directions. Device availability will be critical, and this may push more vendors to increase Ethernet and PoE enabled offerings. The ultimate indicator of success will be if other networking hardware vendors follow suit.

—Edited by Peter Welander, process industries editor,
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