Industrial Ethernet
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Industrial Ethernet is the name given to the use of the Ethernet protocol in an industrial environment, for automation and production machine control.
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.
[edit] 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 | by 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.)
[edit] 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.
