Multiple flavors of Ethernet
Although Ethernet in and of itself isn’t interoperable, its evolution and proliferation has smoothed the path to integrating the automation space, enabling open protocols such as OPC to function optimally. A number of Ethernet network variations are available today, among them Ether- Net/IP and EtherCAT.
Applying a standard Ethernet technology such as EtherNet/IP lets facilities unite disparate batch, continuous process, discrete, safety, motion, and drive control industrial network technologies into a multidisciplinary industrial network. EtherNet/IP, a network technology built on the common industrial protocol, or CIP, is managed by ODVA (www.odva.org). It can coexist with an IT Ethernet network, and is described by Rockwell Automation’s Mike Hannah as an enabler. “It is more or less the piping that allows data to move from one point to another,” he added. “Because it uses the same TCP/IP protocol stack that Ethernet uses for data, no special switches or gateways are needed when data are required to move between VLANs and subnets. This means that EtherNet/IP can be more than a fieldbus network; it can be the automation network as well, simplifying the network infrastructure.”
Another Ethernet variation, EtherCAT is an open, real-time network intended for control automation technology. This fieldbus protocol was among the innovative technologies adopted by a photovoltaic and automotive supplier recently to meet communication needs. In this case, EtherCAT acts as the primary fieldbus system and a Beckhoff Automation terminal system allows integration of peripheral devices and subsystems.
“EtherCAT is able to communicate effectively with hardware in the field unencumbered by multiple software suites and works well as a gateway to other fieldbus protocols, including the associated legacy devices,” explained EtherCAT Technology Group representative Stubbs. “It can be used for motion, complex CNC machines, and robotics, with a flexible topology that allows advanced data acquisition and high-speed performance. EtherCAT uses the controller efficiently, sorting data ahead of time, eliminating the need to map data with every I/O scan. Its use of Ethernet bandwidth efficiently translates into speed. Benefits trickle down, creating a simpler system overall.”
– Jeanine Katzel for Control Engineering, as part of the December 2010 Cover story: Integrating Disparate Control Systems.