Industrial Ethernet

Industrial Ethernet is the name given to the use of the Ethernet network protocol in an industrial environment, for automation and process control. A number of techniques are used to adapt the Ethernet protocol for the needs of industrial processes, which must provide real time behavior. By using non-proprietary protocols, automation systems from different manufacturers can be interconnected throughout a process plant. Industrial Ethernet takes advantage of the relatively larger marketplace for computer interconnections to reduce cost and improve performance of communications between industrial controller.Hi ?

Industrial Ethernet (IE) components used in plant process areas must be designed to work in harsh environments of temperature extremes, humidity, and vibration that exceed the ranges for IT equipment intended for installation in controlled environments.

A Production Ethernet example (beer production)

Beer takes several days to weeks to produce and requires the monitoring and management of temperature, pressure, liquid flow, stirring, adding ingredients and much more that is handled by the Production IE network. This is commonly referred to as ICT or Industrial Control Technology that is connected through the IE.

A major beer brewer once had his Production Network (IE) go down for a period of several hours and during that time they could not be sure that the brew was being kept at the correct temperature and that the correct items had been added on time and given the correct time to mix or cure. The result was that the brew had to be dumped. Not only did this result in a lot of non productive work, the cost of a lost brew of several thousand bottles of beer but the clean up and loss of all the ingredients and the time lost. If this beer had been bottled and it was bad or spoiled it would have resulted in lawsuits and loss of market share another major cost. This is a simple but powerful example of the need for IE and that it cannot be managed as the best effort, user focused IT world of today. If this had been a chemical plant the results could have been deadly and an even more expensive cost/loss.

Advantages and difficulties

Industrial Ethernet Protocols - Until recently, a PLC (Programmable logic controller) would communicate with a slave machine using one of several possible open or proprietary protocols, such as Modbus, Sinec H1, Profibus, CANopen, DeviceNet or FOUNDATION Fieldbus. However, there is now increasing interest in the use of Ethernet as the link-layer protocol, with one of the above protocols as the application-layer (see OSI model).

Some of the advantages are:

• Increased speed, up from 9.6 kbit/s with RS-232 to 1 Gbit/s with IEEE 802 over Cat5e/Cat6 cables or optical fiber
• Increased overall performance
• Increased distance
• Ability to use standard access points, routers, switches, hubs, cables and optical fiber, which are immensely cheaper than the equivalent serial-port devices
• Ability to have more than two nodes on link, which was possible with RS-485 but not with RS-232
• Peer-to-peer architectures may replace master-slave ones
• Better interoperability

The difficulties of using Industrial Ethernet are:

• Migrating existing systems to a new protocol (however, many adapters are available)
• Real-time uses may suffer for protocols using TCP (but some use UDP and layer 2 protocols for this reason)
• Managing a whole TCP/IP stack is more complex than just receiving serial data
• The minimum Fast Ethernet frame size including inter-frame spacing is about 80 bytes, while typical industrial communication data sizes can be closer to 1-8 bytes. This often results in a data transmission efficiency of less than 5%, negating any advantages of the higher bitrate.
  • On Gigabit Ethernet the minimum frame size is 512Bytes, reducing the typical efficiency to less than 1%.
  • Some of the Industrial Ethernet protocols introduce modifications to the Ethernet protocol to improve efficiency.

Main protocols

Serial	Ethernet	Protocol	Network	Standards
Modbus-RTU	Modbus-TCP	TCP/IP		IEC 61158 and IEC 61784
Profibus	PROFINET IO	Isochronous real time protocol (IRT), Real time protocol (RT), Real time over UDP protocol (RTU)	Switches, router and wireless, from 100 Mbit/s up to 1 Gbit/s	IEC 61158 and IEC 61784
DeviceNet (CIP); ControlNet (CIP)	Ethernet/IP (CIP)	TCP/IP; UDP/IP	Switches, router and wireless, from 100 Mbit/s up to 1 Gbit/s	IEC 61158 and IEC 61784; ODVA EtherNet/IP standard
Foundation Fieldbus H1	Foundation Fieldbus High Speed Ethernet (HSE)
CANopen	Ethernet Powerlink		Ethernet 100Mbit/s	IEC 61158, EPSG (Ethernet Powerlink Standardization Group)
CANopen	EtherCAT	EtherCAT, EtherCAT/UDP	Ethernet 100Mbit/s	IEC 61158, IEC/PAS 62407, IEC 61784-3, ISO 15745-4
	VARAN Versatile Automation Random Access Network	VARAN, TCP/IP, Safety	Ethernet 100Mbit/s	VARAN-BUS USER GROUP - VNO
SERCOS I / II	SERCOS III		Ethernet 100Mbit/s	IEC 61491, merged into IEC 61158
	FL-Net (OPCN-2)	UDP/IP	Ethernet 10Mbit/s	by JEMA (Japan Electrical Manufacturers' Association)

(Note the highly ambiguous name given the Ethernet version of DeviceNet. The "IP" in Ethernet/IP stands for Industrial Protocol.)

See also

• Fieldbus
• Modbus
• Computer network
• Process control
• Programmable logic controller
• Distributed control system
• Human-machine interface
• SCADA

References

• Arndt Lüder, Kai Lorentz (Editor), IAONA Handbook Industrial Ethernet, Industrial Automation Open Networking Alliance e.V., 150 S., Magdeburg (Germany), 2005, ISBN 3-00-016934-2, free copy at handbook(at)iaona.org.

External links

• Industrial Ethernet Advisory Group
• Lammermann.eu: Ethernet as a Real-Time Technology