Fieldbuses Adapt to Wireless World

Nov. 1, 2008
The success of wireless networks might be viewed as another nail in the coffin for fieldbuses. 

But many observers feel the wireless boom may breathe new life into some architectures. Though these fieldbuses have been around for a long time, they are adapting to the new world of wireless communications.

While fieldbuses are often phased out for newer technologies such as industrialized Ethernet, wireless is providing a new channel for the protocols. Many of the input/output (I/O) points that remain a bastion of fieldbus usage could benefit from the ease of installation provided by wireless technologies.

The organizations that oversee the various fieldbuses are moving to ensure that their technologies adapt to the rapidly expanding usage of wireless communications. “All the fieldbus consortia are looking at ways to ensure that their protocols operate over wireless networks,” says Cliff Whitehead, Mayfield Heights, Ohio-based strategic applications manager at vendor Rockwell Automation Inc..

Which wireless scheme they tap is an open question. A range of proprietary networks and standards such as ZigBee are vying for acceptance. Wi-Fi has gained acceptance because it’s compatible with Ethernet backbones. Even Bluetooth, normally associated with cell phones, is getting some interest.

“Wireless is not a solution, it’s a range of solutions,” says Greg Dixson, Automation Systems marketing manager at Phoenix Contact Inc., Middletown, Pa.-based automation supplier. “We can embed Bluetooth into the backplane along with a fieldbus and industrial Ethernet. Communications can occur in under 10 milliseconds. Bluetooth offers high speed, low costs and short range.”

Ease of installation is a key benefit of wireless links, which give engineers the ability to install sensors or other products in locations that would be difficult to wire. “A customer had a rotating table that made it impossible to connect though hard wires. We used a Wireless Adapter to connect a CPU (central processing unit) on the rotating table with the main CPU,” says Stephan Stricker, product manager at vendor B&R Industrial Automation Corp., in Roswell, Ga.

Suppliers also note that these links offer far higher bandwidth than conventional fieldbuses, giving users the ability to gather more data. “There are large numbers of Hart devices installed in the field, but a relatively small percentage are extracting all the rich Hart data because they’re tied to 4-to-20 milliAmp (mA) wiring,” Whitehead says. “People are putting wireless dongles on so they can get all the data that’s available.”

Though wireless links are easier to install in factories where it’s difficult to install new wiring, that doesn’t mean they’re easy. Reliability was a big question until the number of successful applications proved that wireless could be counted on even in the harsh, noisy world of factory automation. Understanding the environment and the capabilities of wireless technologies is one of the keys for successful deployment.

“You need to spend more time creating a good plan than if you’re doing a wired network,” Whitehead says.  “You need to understand that frequencies in the factory are dynamic. Walls move, equipment moves. You need a good plan and you need to ensure that everyone understands it.”

Once installations are up and running, they can usually be forgotten, much like wired networks are considered a basic infrastructure element that simply works. “Wireless nodes can be fairly low maintenance items. You just check them every four or five years to see if the battery is working OK,” Whitehead says.

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