Monday, 18 July 2016

Industrial Automation in India | PLC SCADA DCS Training in Chennai

EtherCAT  :

Functional Principle

Protocol :

Short cycle times can be achieved since the host microprocessors in the slave devices are not involved in the processing of the Ethernet packets to transfer the process images. All process data communication is handled in the slave controller hardware. Combined with the functional principle this makes EtherCAT a high performance distributed I/O system: Process data exchange with 1000 distributed digital I/O takes about 30 µs, which is typical for a transfer of 125 byte over 100Mbit/s Ethernet. Data for and from 100 servo axis can be updated with up to 10 kHz. Typical network update rates are 1–30 kHz, but EtherCAT can be used with slower cycle times, too, if the DMA load is too high on your PC.  The bandwidth utilization is maximized, as each node and each date do not require a separate frame. Thus, extremely short cycle times of ≤ 100 µs are achievable. By using the full-duplex features of 100BASE-TX, effective data rates of more than 100 Mbit/s (> 90% user data rate of 2x100 Mbit/s) can be achieved.  The EtherCAT technology principle is scalable and not bound to 100 Mbit/s. A future extension to Gigabit Ethernet is possible, but is not in preparation at the moment since the EtherCAT performance is sufficient at 100 Mbit/s.

Using full-duplex Ethernet physical layers, the EtherCAT slave controllers close an open port automatically and return the Ethernet frame if no downstreamdevice is detected. Slave devices may have one, two, or more ports. Due to these features EtherCAT enables a multitude of network topologies, including line, tree, ring, star, or any combination thereof. The protocol also enables a multitude of communication features such as cable redundancy, Hot Connect of segments, change of devices during operation, or even master redundancy with Hot Standby.
Thus the combination of the topology variations and different network architectures, e.g. sub-ordinated or neighboring control systems with consistent synchronization, enables numerous possibilities. Additional switches are not required. The physics of Ethernet allow a cable length of up to 100 m (300 ft) between two nodes, so the E-bus (LVDS) is only intended for use as the physical layer for modular devices. For each cable path, the signal variant can be chosen individually. For higher distances, or the complete galvanic isolation between two slaves, fiber optic cables are used. With single-mode fiber, distances up to 20 km between two nodes can be bridged. Since a total of 65,535 nodes per network segment can be connected, the network extension is nearly unlimited.

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