In the last posting we took the 5000 foot view of industrial Ethernet and examined why using it for industrial networks is such a good idea. In this posting we want to zoom in and drill down into what makes Ethernet devices play nice together on an industrial network: Protocols.
These protocols all share one commonality: the use of standard Ethernet network topologies and equipment. In most cases, that is where the similarities end. While there are a number of industrial Ethernet protocols, we will only examine briefly the top five used, listed from least used to most used:
- Ethernet Powerlink
EtherCAT, or Ethernet for Control Automation Technology is an Ethernet Master/Slave fieldbus system developed for networks requiring very short cycle times. It is able to achieve very high speed because much of the message processing time is eliminated as devices capture only the data addressed to them as the message frame passes through the node. A special EtherCAT slave chip is required In order to perform this processing. EtherCAT is extremely flexible with regard to network topology in that switches are not required. EtherCAT is used in 4% of industrial Ethernet networks.
Managing group: EtherCAT Technology Group
Ethernet Powerlink is a safety oriented open protocol developed by B&R Automation in 2001 as a proprietary networking protocol. Powerlink is essentially CANopen over Ethernet using a recently developed custom stack which allows for realtime capabilities. Ethernet Powerlink comprises 11% of industrial networks.
Managing group: Ethernet Powerlink Standardization Group (EPSG)
The MODBUS protocol was originally developed in 1979 by Modicon to be used to communicate over RS232 and RS485. MODBUS/TCP is a TCP/IP adaptation of the MODBUS-RTU protocol using the standard TCP/IP stack. MODBUS is a client/server protocol. Services are provided via function codes to read or write data in bit or word form. MODBUS/TCP is used in 22% of industrial Ethernet networks, making it compatible with a large array of devices.
Managing group: Modbus-IDA
ProfiNet is a scalable, open networking standard developed by Siemens. The performance of ProfiNet allows it to work on three levels: TCP/IP for non-real-time application, real-time for time critical process data and isosynchronous real-time for motion control. The ProfiNet IO stack is optimized to achieve high performance. 28% of industrial Ethernet networks use ProfiNet.
Managed by: Profibus International
The Industrial Ethernet Protocol (Ethernet/IP) was originally developed by Rockwell Automation and is a well-established industrial Ethernet communications system with good real-time capabilities. EtherNet/IP is an Ethernet extension of the Common Industrial Protocol (CIP), which is the same upper layer protocol and object model used in DeviceNet and ControlNet utilizing the standard TCP/IP stack. This means the EtherNet/IP, DeviceNet and ControlNet devices can all play in the same sandbox without conflict. EtherNet/IP is used in 30% of the industrial Ethernet world. This massive presence is due to both to the availability of compatible devices and the extensive use of Rockwell Automation/Allen-Bradley PLCs and HMI’s.
Managing group: Open DeviceNet User Organization (ODVA)
All of these protocols have advantages for use in industrial automation applications. Some are more specialized such as EtherCAT and Powerlink while others, such as ProfiNet and EtherNet/IP have a higher number of available devices as well as vendors such as Siemens and Rockwell, who are the major players in the factory automation industry.
Which is your choice?