Industrial Ethernet

Industrial Ethernet Hub

Industrial Ethernet (IE) refers to the use of the Ethernet family of computer network technologies in an industrial environment, for automation and process control. A number of techniques are used to adapt Ethernet for the needs of industrial processes, which require real time behavior. By using standard Ethernet, automation systems from different manufacturers can be interconnected throughout a process plant. Industrial Ethernet takes advantage of the relatively larger marketplace for computer interconnections using Ethernet to reduce cost and improve performance of communications between industrial controllers.

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 information technology equipment intended for installation in controlled environments.

Advantages and difficulties

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, interest increased to use Ethernet as the link-layer protocol, with one of the above protocols as the application-layer (as in the OSI model).

Some of the advantages are:

• Increased speed, up from 9.6 kbit/s with RS-232 to 1 Gbit/s with Gigabit Ethernet over Cat5e/Cat6 cables or optical fiber
• 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

Difficulties of using Industrial Ethernet include:

• 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.

Protocols

Although the use of Ethernet standardizes the physical transport of data in an industrial setting, multiple different incompatible protocols are used and encapsulated into Ethernet data frames. Intermediate network hardware such as routers and switches may be indifferent to the data protocol encapsulated in each Ethernet frame, but source and consumer devices must use the same protocol to allow communication to take place. Some standards, such as Modbus, have been adapted from their original versions and converted to a form that can be transmitted over an Ethernet network. For example, Profibus has been developed into an Ethernet compatible standard, PROFINET. Other protocols, such as EtherNet/IP have been developed only for the Ethernet transport layer. Industrial network protocols can be encapusulated inside TCP data frames, further standardizings their handling, but requiring a TCP-compatible protocol stack to be present at each end of a data connection.

See also

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