When it comes to implementing new Industrial Ethernet technology, manufacturers have a lot of choices. There are upwards of 30 different protocols that can be used, each with their own options that make them more ideal for certain applications.
These are five of the most common Industrial Ethernet technologies on the market today.
PROFINET RT and PROFINET IRT
Process Field Network (PROFINET) is divided into two classes: PROFINET RT (real-time) and PROFINET IRT (isochronous real time). PROFINET RT allows manufacturers to increase production speed by enhancing data communication between their devices. It is ideal for applications like packaging machines or those whose production cycles require precise digital and analog I/O control. PROFINET RT sends high priority payload data (in Ethernet frames) directly via Ethernet protocols with VLAN prioritization. At the same time, diagnostics and configuration data is sent using UDP/IP. This separation allows for systems to achieve cycle times between one to 10 milliseconds for I/O applications.
PROFINET IRT is required for systems that operate below one millisecond, such as motion control applications. PROFINET IRT operates in a time multiplex mode that is based on specially managed, hardware-synchronized switches. The communication system is also able to reserve bandwidth so that critical data messages are always able to be delivered quickly and successfully.
POWERLINK is an open-source, software-based communication system that employs timeslot and polling procedures to maintain isochronous data transmission among devices. Its hot-plugging capabilities allow users to add, remove or swap devices on the fly, and it can be deployed to any desired network topology.
POWERLINK works by designating a Managing Node (usually a PLC or Industrial PC) that synchronizes a number of devices that operate as Controlled Nodes. The Managing Node polls the Controlled Nodes in a fixed sequence over the course of a clock cycle.
There are three phases in POWERLINK:
- Start of Cycle: the Managing Node synchronizes all Controlled Nodes
- Isochronous Phase: the Managing Node conducts a data exchange with all Controlled Nodes
- Asynchronous Phase: the Managing Node allows a single Controlled Node to send a larger amount of ad-hoc data.
POWERLINK can distinguish between real-time and non-real-time domains and is suitable for many automation applications.
EtherNet/IP Protocol adapts the Common Industrial Protocol (CIP) to standard Ethernet. It transfers data using TCP/IP and UDP/IP and uses many communication mechanisms:
- Cyclic polling
- Time triggers
- Event triggers
- Point-to-point connections
EtherNet/IP is widely used in many controllers and automation equipment and can achieve soft real-time performance with 10 millisecond cycle times. Its main feature is its ability to differentiate between implicit (data only) and explicit (requests and denies) messaging. Implicit I/O messages are sent via UDP, while explicit messages are reserved for TCP/IP, and switches prevent the data from colliding.
Ethernet for Control Automation Technology (EtherCAT) has a “logical ring” network topology. It is based on the summation frame network, which sends a frame through all connected nodes in a sequence. The frame travels through each node, exchanging and collecting data with them before reaching the final node and turning back. The frame will also be able to traverse back and forth on any branching sections it encounters.
Every EtherCAT frame consists of a header and several commands for slave nodes, and every slave node provides a real-time clock. This clock is synchronized by the master using a process similar to IEEE 1588. Because EtherCAT only extends to the first three layers of the Open Systems Interconnection model, extra protocols must be added in order to achieve full functionality.
- CAN application protocol over EtherCAT (CoE) – CANopen has a wide selection of device categories and applications: I/O modules, drives, encoders, and more. This protocol is being widely adopted industrywide.
- Servodrive-Profile over EtherCAT (SoE) – SERCOS s a powerful real-time communication interface, as with CoE, very good for demanding motion control applications.
- Ethernet over EtherCAT (EoE) – Though not advisable unless necessary, any Ethernet device can be connected on an EtherCAT network. The EtherCAT network is fully transparent for the Ethernet devices, and the real-time features of EtherCAT are not disrupted.
- Functional Safety: Safety over EtherCAT (FSoE) – A field bus safety protocol was developed in parallel with EtherCAT; “Safety over EtherCAT” (FSoE = Fail Safe over EtherCAT). FSoE allows for functional safety. Certified by TÜV, FSoE meets the requirements of the Safety Integrity Level 3 (IEC 61508).
SERCOS III Communication
SERCOS III is an open digital interface that is primarily used in motion control systems. It operates in a master/slave arrangement where data exchange between nodes occurs during a real-time cycle. Users can choose the cycle time for applications, and the there is also an optional non-real-time channel that can be used.
Like EtherCAT, SERCOS III is based on the summation frame network, however the network nodes must be arranged in a daisy chain (a single ring) or closed ring. Data is exchanged using Master Data Telegrams (MDT) and Acknowledge Telegrams (AT), both of which are issued by the Master Node. The telegrams pass through each node twice, once on the way out and once on the way back, making communication possible within one cycle without having to route back through the master.
Choosing the Right Protocol
While these five industrial Ethernet technologies are some of the most common, there are up to 30 different protocols worldwide. To find out which is right for your system, contact the automation experts at AMMC.