Ethernet continues to expand its role in the factory, but it’s facing some stiff competitors as it stretches down to the input/output (I/O) level. When engineers need to connect sensors and other simple components, they’ve got a number of alternatives that are often more cost-effective than Ethernet.

A range of architectures provide the low cost and performance needed for I/O connections. At the same time, wireless technologies are addressing ease of use, eliminating the difficulty of routing wires every time equipment is moved or new gear is added. Though skeptics scorn the reliability of sending signals through the air of a noisy factory, there’s little doubt that wireless is going to play a solid role in the factory of the future.

Ethernet will also hold a significant role in data gathering. It’s dominating as a central network when production facilities are upgraded, bringing compatibility with the front office. A number of companies are now eyeing the large number of I/O nodes that fill today’s factories, hoping to displace the fieldbuses often used to link these nodes to Ethernet or other factory-wide backbones. Speed is a key weapon in their arsenals.

“We’re betting the farm that Ethernet to remote I/O is the way to go. With today’s switched networks, speed is not an issue. It takes less than a millisecond to send a message,” says Tom Edwards, senior technical advisor at Opto 22, a Temecula, Calif.-based vendor.

Pick your flavor

Other companies and technology groups are promoting various flavors of Ethernet, using different approaches to keep performance high without pushing costs up. For example, the EtherCat architecture keeps costs down by using an application-specific integrated circuit, or ASIC, to handle network communications, making it possible to use less powerful, less expensive central processing units (CPUs) in equipment. “Our ASICs or FPGA (field programmable gate array) implementations are typically cheaper than what competitors use for the underlying fieldbus applications,” argues Joey Stubbs, North American representative for the EtherCat Technology Group, based in Nuremberg, Germany.

Without that capability, Ethernet may not be effective for I/O. “Cost prohibits going down to the [sensor] level. Implementing Ethernet still requires a small computer with a software stack and maybe some extra code to handle standard communications,” Stubbs says.

Others eschew extra hardware, instead using software techniques to give Ethernet the speed that’s needed in applications with strict timing requirements. “Ethernet Powerlink can run on any Ethernet board, because it’s only software. We add the Powerlink stack to assure that messages arrive on time,” says Markus Sandhoefner, sales manager at automation vendor B&R Industrial Automation Corp., of Roswell, Ga.

“At very high speeds on equipment for jobs like carpet making, each I/O node has to operate at 300 to 400 microseconds. If you did that with Modbus, you’d have latency, and with IEEE 1588 (a standard of the Institute of Electrical and Electronics Engineers) you couldn’t rely on an action occurring, though you would know how much a knot might be off,” Sandhoefner says.

Though variations of Ethernet bring real-time capabilities, others note that Ethernet’s speed continues to increase, making the basic network suitable for I/O jobs in which speed is critical. “Fieldbuses have always been deterministic. Ethernet has gotten so refined that that’s usually not a problem now,” says Jeff Blyther, systems engineer at Lantronix Inc., an Irvine, Calif.-based vendor.

Proponents of basic Ethernet also note that pricing premiums over alternative buses are fading as volumes continue upward. “As Ethernet’s usage becomes bigger and bigger, cost issues are disappearing, though for sensors, you still need an alternative,” says Sylain Olier, distributed I/O marketing manager at automation supplier Schneider Electric, in North Andover, Mass.

Product developers also note that Ethernet is addressing ease-of-use by simplifying cabling. With Power-over-Ethernet, engineers don’t have to route power to I/O nodes. “Power-over-Ethernet will help drive application to these types of jobs,” says Bill Black, controllers product manager at GE Fanuc Intelligent Platforms, another automation supplier based in Charlottesville, Va.

But here again, the additional cost of delivering power takes Ethernet away from its high-volume niche. Connectors and cables will be a bit more expensive than those for conventional network products. “It boils down to cost. If you have modular I/O and want to use only Ethernet, you may need to go to Power-over-Ethernet, which raises the price,” Olier says.

Expansion blockers

Ethernet is very cost effective for equipment that has a fair amount of computing power, which earned it the role of standard backbone technology throughout most factories and front ...