Industrial Ethernet: Powerlink, EtherNet/IP

At least eight organizations represent seven Ethernet protocols targeting industrial networking applications. Here are updates about two Ethernet protocols: Ethernet-Powerlink and EtherNet/IP. Information on other industrial Ethernet protocols can be viewed in the "Online Extra" addition

Marc Ostertag, vice president of B&R Industrial Automation, representing Ethernet-Powerlink, offers compelling reasons for using Ethernet for industrial automation. Ethernet is the most common network in IT; engineers are familiar with Ethernet, it offers transparent communication on all levels, it's an undisputed worldwide standard so it is "future-proof," it has compelling data rates, and offers a lot of software and many tools.

Ethernet Powerlink is a decentralized real-time communication system for automation and motion control, Ostertag says. Benefits are that it's an open protocol managed by the Ethernet Powerlink Service Group (EPSG), uses standard chips, has deterministic real-time data transfer, is easy to use for automation, allows any topology, and doesn't require a network guru, he says. Security is achieved via domain separation.

Ethernet Powerlink has been accepted by the IEC as a publicly available IEC specification (PAS), according to EPSG. The organization hopes EPL will become part of the IEC Standard IEC 61784-2 and IEC-61158—the fieldbus standard. Specifications were submitted by IAONA (Industrial Automation Open Network Association) to IEC SC65C as a real-time industrial Ethernet communication profile. IAONA, the platform organization for promotion of Ethernet in factory automation, works with ODVA (Open Device Vendor Association), EPSG, and three other groups to elaborate technical guidelines and recommendations in areas of mutual interest.

B&R resolves Ethernet's limitation for guaranteed data transmission by superimposing a "time slicing" method over the carrier-sense multiple access/collision detection mechanism of Ethernet. It cuts the transmission interval into numerous slots, making a time slot available for each device linked to a network segment. This ensures that no network collisions occur. Ostertag says cycle times down to 200 microseconds and jitter below 1 microsecond can be obtained.

Bystronic glass uses Ethernet Powerlink for fully automatic cutting, grinding, and drilling with 450 ft/min cutting speed, 2/1000 in. accuracy. The company moved away from proprietary electronics; has improved cutting accuracy, quality, and throughput by scoring at higher speeds; and has 800µs cycle time for 15 axes and more, Ostertag says. In all applications, more than 50,000 nodes are installed.

EtherNet/IP is a Common Industrial Protocol (CIP) supported by ODVA members, who also support the following CIP network technologies: DeviceNet, CIP Sync, CIP Safety, CIP Sync, and CIP Motion.

CIP Networks share a common, complete suite of services and device profiles plus seamless bridging and routing between multiple CIP sub-nets, says Katherine Voss, ODVA executive director. CIP and EtherNet/IP protocols are complementary to standard Ethernet technologies, she says, calling EtherNet/IP a pure Ethernet solution for control networks, enabling Internet and enterprise connectivity.

General Motors chose EtherNet/IP as its global standard for industrial Ethernet. With EtherNet/IP, General Motors expects to lower operating costs, leverage engineering resources, share information systems applications, and incorporate safety networks, according to Voss. EtherNet/IP is also in use at the CSIRO Exploration and Mining at the Queensland Centre for Advanced Technologies in Australia. Underground automation equipment, such as for coal mining, has similar concerns as factory automation and process control, Voss explains, such as:

1. Though application bandwidth requirements are modest, demands will increase, including addition of on-machine cameras.

2. Condition monitoring will collect vibration data, which involves large file transfers.

3. CSIRO plans to add wireless Ethernet for broadband communications with a 90-ton, 50-foot long automated coal shearer. Radio waves can withstand the environment better than cables.

4. CSIRO avoided a "home-spun simple protocol in TCP/IP," because of desire to keep the system open, expandable, and maintainable, Voss says.

Mark T. Hoske, mhoske@reedbusiness.com