'Ethernet' isn't a protocol; something needs to run in the wire

Installing industrial Ethernet requires selecting one or more protocols. Because application requirements differ and because vendors invest more in one technology than others, multiple protocols have emerged to operate through the Ethernet physical media. Using an Ethernet protocol in a manufacturing setting—often with rugged components—is called, generically, industrial Ethernet.

05/01/2006


Installing industrial Ethernet requires selecting one or more protocols. Because application requirements differ and because vendors invest more in one technology than others, multiple protocols have emerged to operate through the Ethernet physical media. Using an Ethernet protocol in a manufacturing setting—often with rugged components—is called, generically, industrial Ethernet.

To help subscribers match protocols to their applications, Control Engineering invited seven industrial Ethernet protocol organizations to a day-long Industrial Ethernet conference session at National Industrial Automation Show and Conference at National Manufacturing Week. The protocols are EtherCat, EtherNet/IP, Ethernet-Powerlink, High Speed Ethernet (HSE), Modbus TCP/IP, Profinet, and SERCOS III.

Unlike most industrial networks (except those within the same family), these protocols can co-exist on the same physical media (Ethernet). However, because application layers for each differ, devices using these Ethernet-based protocols cannot interoperate or exchange information without translations. The protocols are part of the IEC SC 65C project, due for August 2007 ratification. Organizations that sent a delegate to speak at the conference follow.

EtherCat by EtherCat Technology Group offers real-time performance by processing 1,000 digital I/O communications in 30are about $7. www.ethercat.org

Ethernet Powerlink by Ethernet Powerlink Standardization Group (EPSG) is an ISO/OSI level 2 protocol enabling deterministic, isochronous, real-time data exchange via standard Fast Ethernet (IEEE 802.3 u), according to Bill Seitz, Ixxat president. It allows high precision data communication with cycle times as low as 100 www.ethernet-powerlink.org

High Speed Ethernet (HSE) by Fieldbus Foundation specifications were released in March 2000; linking device test and registration program followed in May 2001, says David Glanzer, director of technology development. Multiple vendors provide Foundation-registered linking devices. HSE uses the same standard and flexible function blocks for distributed control within instrumentation, including IEC 61804 Electronic Device Description Language (EDDL), as the 31.25 kb/s H1 protocol, but at 100 megabits/s with commercial off-the-shelf Ethernet equipment. HSE integrates system architectures for continuous process, hybrid, and batch applications. www.fieldbus.org

Profinet by Profibus Trade Organization (PTO), supports advanced plant automation strategies and helps them merge with the enterprise and beyond, says Carl Henning, deputy director. It also can embrace other fieldbuses. Profinet IO has similarities to Profibus DP; Profinet CBA (modular, component-based approach) simplifies design, engineering, and commissioning for larger systems. Profinet uses Ethernet, TCP, UDP, and IP. Application areas can use non-time-critical (IEEE 802.3) services through real-time-capable, synchronized isochronous real time, to synchronize 150 axes in less than 1 ms with jitter of &1 www.us.profibus.com

SERCOS III by SERCOS N.A. is based on real time mechanisms of the original SERCOS interface, with cycle times down to 31.25) can be transmitted in non-real time slots, parallel to real-time processing. It can exchange telegrams with super-ordinate networked devices, and can hot-swap, without switches or hubs; controllers are available. www.sercos.org

Mark T. Hoske, Control Engineering, MHoske@cfemedia.com


Online Extra

More protocols, organizations
Two other Ethernet protocols are governed by industry groups.

IEEE 1588 is the Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems Sponsored by the Technical Committee on Sensor Technology TC-9. IEEE 1588

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