need much onboard intelligence. Many sensors, valves and other low-cost products don’t have Ethernet compatibility, so these lower-level architectures won’t fade away any time soon.

Another downside for Ethernet is that many factory-floor personnel are more comfortable with established industrial networks than with Ethernet. “One of the biggest issues is still that a lot of control engineers don’t have Ethernet backgrounds, so they’re not sure how to lay out networks to get the best performance,” Daudt says.

Fieldbuses such as Profibus, Modbus and DeviceNet have been upgraded with Ethernet versions, but the original versions are still seeing widespread usage. Low-cost solutions such as AS-Interface, which offers simplified wiring, are also maintaining solid market acceptance.

Another alternative comes from the personal computer world that made Ethernet a high-volume standard technology. Some vendors are starting to use the Universal Serial Bus (USB) to link sensors and other gear to controllers. The simplicity that made it sell at a clip of two billion units per year in the consumer world is also its lure in industrial environments.

USB 3.0, which is now shipping in consumer markets, pushes the data rate up to 3.2 Gbits per second. That’s far above the 480 Mbits/second for USB 2.0, which dominates current shipments. The slower rate will often be sufficient for industrial products, while the higher speed provides a path to the future. “USB’s data rates are increasing, and it has much better plug-and-play characteristics than Ethernet,” Holste says. “There’s a lot of confusion about getting Ethernet installed, there’s confusion about hubs, gateways and IP addresses. With USB, you just plug it in.”

Holste predicts that USB will see growing acceptance for sensor configuration, with less usage for communications. However, he notes that one limitation for USB is its cable lengths.

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