Many demanding industrial applications require millisecond updates and jitter at a microsecond or less. High-speed protocols and appropriate network design can deliver determinism.

Brian Oulton

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Manufacturers and machine builders use EtherNet/IP Ethernet protocol for motion applications with more than 100 axes of coordinated motion control, without special hardware, complex designs, or proprietary technologies. Also, they can combine motion control with other industrial communications needed on one network, helping to simplify design and make it more cost-effective.

When Rockwell Automation designed EtherNet/IP more than 10 years ago, ControlNet already was, arguably, the most deterministic, high-performance industrial network of its time. Network designers had to choose whether to port the ControlNet “scheduled” approach to Ethernet wire or use standard Ethernet and TCP/IP and its collision-based hubs running at 10 MB. Designers envisioned EtherNet/IP’s future, when collisions in hubs would be replaced with switches, with later network speeds of 100 MB, 1 GB, and beyond.

Within two years, those technology advances became common, making EtherNet/IP faster and more deterministic than ControlNet, enabling industrial devices to be commonly updated in 1 ms or less. The capacity, performance, and determinism available in EtherNet/IP have made it the appropriate for the broadest set of applications, replacing fieldbuses, I/O networks, safety networks, and process control networks.

A few years later, ODVA (the governing organization that owns EtherNet/IP technology) extended that protocol with CIP Sync and CIP Motion technologies, enabling the same standard Ethernet network to provide additional precision and accuracy needed for the most demanding coordinated motion control applications. It uses the IEEE-1588 standard to keep the internal clocks precisely synchronized in all devices within synchronization accuracy of 100 nanoseconds, while effectively neutralizing any effects of “jitter.”

Principal members of ODVA (the independent organization that owns EtherNet/IP technology) are Bosch Rexroth, Cisco, Omron, Rockwell Automation, and Schneider Electric. The ODVA member roster numbers more than 275 companies. EtherNet/IP is the most widely used network, according to an Aberdeen report. The standard, open network’s capacity, performance, and determinism enables users to deploy EtherNet/IP for the broadest set of applications, replacing fieldbuses, I/O networks, safety networks and process control networks.

How to select, apply

Inquire carefully. Network technology capabilities differ. When selecting an industrial network:

1. Ensure the network can do what the application requires, including real-time I/O and drive control, safety, motion, process, human-machine interface (HMI), machine-to-machine interlocking, and integration with the enterprise. EtherNet/IP does all of these well; older fieldbuses meet some, but not all, of these application needs.
2. Determine how the preferred devices and preferred vendors can connect. Devices with built-in network ports or choices for option cards are better than those that must be connected to I/O or through a network converter. That’s because connecting devices directly to the network, in this case EtherNet/IP, provides real time connection to the device. This means data flows in real time with less jitter and latency. Wiring that occurs via I/O or using network converters, on the other hand, adds a delay to the data flow. For example, wiring via I/O requires that the programmable logic controller (PLC) read and write code to pass data, meaning it no longer occurs in real-time. Using network converters adds latency, and in some cases it requires the PLC to read and write the data – incurring additional lags in data transmission. EtherNet/IP delivers interoperable Ethernet products from more than 300 vendors providing more than 1,000 product lines.
3. Ensure the performance, capacity, topology, and segmentation characteristics of the network meet the possible range of applications. EtherNet/IP characteristics follow the latest commercial Ethernet capabilities, and support line and ring topologies standardized through IEC and ODVA.
4. Ensure the network technology will meet future needs. EtherNet/IP inherits the technology advances from, and compatibility with standard commercial Ethernet.
5. Ensure the technology is easy enough to live with. EtherNet/IP simplifies automation architectures by providing one network technology that leverages the skills and features of commercial Ethernet.

Brian Oulton is networks business director, Rockwell Automation. Edited by Mark T. Hoske, CFE Media, Control Engineering, www.controleng.com 

www.rockwellautomation.com 

www.odva.org

www.controleng.com/networks

High Performance Industrial Networks: research and discussion 

Table of High-performance Industrial Networks

Courtesy of Control Engineering

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