Look PA, No Wires

While many engineers tout the benefits of using Ethernet cables to replace hard wiring or multiple networking cable styles throughout a plant, others say that completely eliminating wiring is a far more efficient installation technique.

Wireless networks are seeing solid growth in factories. Many vendors and consumers no longer fear the uncertainty that comes when signals travel through the air in noisy industrial environments. Ruggedized Wi-Fi (wireless fidelity, based on the 802.11 standard of the Institute of Electrical and Electronics Engineers) is making solid inroads, and a number of proprietary industrial networks are also seeing success. Another challenger is ZigBee, an industry standard based on IEEE 802.15.4 that’s starting to see usage in utility metering and consumer applications.

Together, they’re building solid market growth. Wireless is ideal for mobile equipment, many contend. “There are already a number of wireless applications using wireless for guided vehicles that run long distances in SCADA (supervisory control and data acquistion) applications, for example,” says Brian Oulton, network marketing manager at automation vendor Rockwell Automation Inc., in Mayfield Heights, Ohio.{mosimage}

As companies consolidate and create larger factories, wireless makes it simpler to add equipment that is far from a central hub. Petroleum processors and others feels that the larger the space, the greater the benefits.
“Wireless is especially popular for sensors, especially in the processing space where you might have long distances between tanks. You can install wireless sensors without running any wire,” says Carl Henning, deputy director of the Profibus Trade Organization, in Scottsdale, Ariz.

Challenges remain

Though wireless is seeing rapid growth, observers caution that it’s not a technology that fits all applications. As when they deploy any new technology, users will find a number of issues that must be addressed. One of the first involves a basic issue that comes when wires are unplugged.

Many products will operate well on batteries. But in hard-to-reach places, or those where unexpected downtime could cause major problems, designers are looking at techniques that create power using vibration, temperature variations or other changes. “One of the challenges is that you still need power. There are energy harvesting technologies that can solve that, but in many applications the costs are prohibitive,” Oulton says.

Another key factor is that factories are noisy environments. Interference that blocks wireless connections may not matter much in a Starbucks coffee shop, but if signal strength falls below specified levels for even a few milliseconds, industrial operations can suffer major consequences. “Customers are taking a risk if they implement wireless to get determinism. Lost packets are not good, seeing a hiccup due to something like RF (radio frequency) interference is a huge concern,” says Skip Hansen, I/O systems product manager at Beckhoff Automation LLC, in Burnsville, Minn.
Correct placement of hubs and repeater nodes can alleviate this problem. But in the ever-changing industrial world, plant managers must remain constantly vigilant. Every time new equipment is installed, its impact on wireless local area networks should be considered. “Sometimes you have to do a site survey to figure out where to put devices and antennae and see where you need to block noise that may impact the wireless net. Then if you put a new welder in a plant, the whole noise situation changes,” Oulton observes.

For more on wireless, see "Weighing Wireless Benefits."

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