Time-Synchronized Ethernet

As Ethernet penetrates the factory floor, at least two issues regarding connectivity and devices are active—and both pertain to time.

Aw 3155 0903 Infrast
One is continued implementation of the Institute of Electrical and Electronics Engineers’ IEEE 1588: Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems. The other is convergence of manufacturing and enterprise networks, using new IEEE 1588-supporting switches.

The most important recent development in Ethernet connectivity devices, according to Brian Tutor, product marketing manager in the industrial-networking group within Moxa Americas Inc. (www.moxa.com), a Brea, Calif.-based automation vendor, is continued IEEE 1588 implementation. “Timing control between devices is becoming more sensitive as new technologies emerge to improve monitoring and control of devices related to industrial automation.”

Under a microsecond

But Tutor quickly notes that even though IEEE 1588 was published in late 2002, “vendors are still integrating the required hardware and protocols, especially in Ethernet networking equipment.” And although there are other timing/synchronization standards, “IEEE 1588 is needed to bring synchronization down to the sub-microsecond range.” That’s done by integrating real-time clocks and IEEE 1588’s protocol into Ethernet devices, he explains.

Doing that requires a network time server, network switches and end devices with 1588 support to allow latency to be determined and passed to the end device, Tutor states. “With this support, deterministic control and monitoring of factory automation equipment can be achieved in an Ethernet environment.

“This technology is needed in factories that need precise control of equipment such as motor starters, actuators, I/O (input/output) points and any device instrumental in controlling and monitoring mission-critical equipment designed to start/stop/monitor a production line,” Tutor states. One mission-critical use he mentions is determining failures so that immediate remedial action can be taken.

Driving this development is the need to avoid the mistakes of fieldbus technologies, in which interoperability was difficult, creating pricing, innovation and obsolescence/retrofit problems, Tutor says. But with Ethernet, companies can “future proof” their equipment and take advantage of multiple vendors’ technologies to get the best available solution, he thinks. “Since Ethernet is not a deterministic solution like fieldbus technologies, a new method for increasing determinism became necessary. Using advanced network technologies such as Layer 2 and Layer 3 switches along with IEEE 1588, companies can now standardize on Ethernet as their network of choice.”

Designing and deploying a robust, secure network infrastructure requires a well-planned, well-executed strategy, remarks Mike Hannah, NetLinx product business manager for vendor Rockwell Automation Inc. (www.rockwellautomation.com), in Mayfield Heights, Ohio. But the demarcation between manufacturing and information technology (IT) engineers is cloudy. “Manufacturing engineers know how to program controllers for their applications; IT engineers know how to program Ethernet switches to control and monitor information flow at the enterprise level,” he says.

To achieve success, those groups must work together. To help bridge the gap between them, Rockwell and San Jose, Calif.-based network equipment supplier Cisco Systems Inc. (www.cisco.com) delivered last July an industrial Ethernet switch, the Stratix 8000. It contains Cisco technology, including the Command Line Interface, which provides programming and configuration tools familiar to IT engineers. Hannah adds that the new switch is best suited for connecting machines on the plant floor with a company’s enterprise resource planning system.

As of February 2009, the Rockwell switch supports IEEE 1588’s time-synchronization standard. “With IEEE 1588 Precision Time Protocol, the same Ethernet network used for control and information can be used for time synchronization and coordinated motion-control applications,” Hannah comments. Later in 2009, Moxa will be introducing new Layer 2 and 3 switches with support for IEEE 1588, Tutor adds.

C. Kenna Amos, ckamosjr@earthlink.net, is an Automation World Contributing Editor.

Moxa Americas Inc.

Rockwell Automation Inc.

Cisco Systems Inc.
More in Control