sentiment is echoed by others.

“We don’t condone using Ethernet for everything. CAN (Controller Area Network) is good for products with small pieces of data like sensors,” says Hougland, of Opto 22. ARC’s Forbes notes that simple products such as proximity switches that don’t have diagnostics are another application where Ethernet may be too costly.

Another potential reason for avoiding Ethernet is its openness to viruses and hacker attacks. But for the most part, that’s a higher-level issue that doesn’t go down to the fieldbus level. That’s because it is not generally desirable to have equipment on a fieldbus communicating freely with any other device on the network. “You can configure the I/O so it only listens to communications from defined addresses,” Hougland says.

Though there are solid reasons for not using Ethernet everywhere today, that may not remain the case. Some observers feel that the semiconductor industry’s continuing drive to integrate more peripherals onto chips that cost less may eventually make Ethernet suitable in those low-performance applications. “When you can buy a microcontroller that has everything for under $5, Ethernet becomes basically free,” says NI’s Walters.

The low cost of microcontrollers is already making it easy for design engineers to include Ethernet on a growing number of products that tie into fieldbuses. As with many electronic technologies, once a couple of high end products incorporate a feature or function, it rapidly becomes a common attribute on many of the emerging new products.

“Many motor controllers have Ethernet now; they didn’t a couple years ago,” Hougland says.

For more information, search keyword “Ethernet” at www.automationworld.com.