What is Ethercat | Ethercat vs Ethernet/IP | Ethercat Cables

EtherCAT known as Ethernet for Control Automation Technology, developed by Beckhoff Automation. Also known as beckhoff ethercat .

What is ethercat ?

Same as Ethernet, EtherCAT is also a real-time protocol which relies on Ethernet as physical carrier and thus it is dependent on long-term stable operation of the Ethernet connection.

Ethercat configuration

EtherCAT uses standard data frames as well as the physical layer characterized in IEEE 802.3 and no special hardware is required to implement the EtherCAT network.

This protocol is standardized in IEC 61158 and IEC 61784-2 and also included in ISO 15745-4 published standard. It was developed for applications requiring cycle time’s ≤ 100 μs and for precise synchronization purposes and to reduce the hardware costs and it gives nanosecond accuracy.If we use an EtherCAT system architecture the processor load is reduced to 25-30 % compared to other bus systems with the same cycle time.

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Ethercat Protocol

Ethernet Protocol cannot be considered as a practical solution for many industrial applications as it routes data frames to and from a vast number of separate addresses, individually, where the data can be something considered as simple a single register to obtain a real-time analog reading.

In comparison to EtherCAT, Ethernet requires a huge bandwidth for the packets been moved between master and client (which requests the data).Whereas EtherCAT works on the principle of pass-through reading, which means that the messages are not only for a single node and consumed by that node.

Instead, they are transmitted to the following node in a string as they are processed. The input data at a node is read as the message is processed and output data is inserted in the message to the next node.

A single message is passed by the EtherCAT masters with data for all nodes. The messages are passed around a ring, each nodes reads its input and adds its output to the message and goes back to the master which means that now every node has a new input data received from the master and master has a new output data received from different nodes.

As the messages are targeted to a specific nodes without deficiency of small payloads, an EtherCAT network can achieve maximum bandwidth utilization.

The EtherCAT master uses a standard Ethernet Media Access Controller (MAC) without an additional processor for communication.

Ethernet Media Access Controller allows a master to be implemented on any hardware platform with an available Ethernet port, regardless of which real-time operating system or application software is used.

EtherCAT Slave devices use an EtherCAT Slave Controller (ESC) to process frames on the fly and entirely in hardware, which makes network performance predictable and independent of the individual slave device implementation

EtherCAT uses a self-terminating technology which means that if any node does not detect a next node in the string it automatically terminates the network at that particular point and terminating nodes copy the message from master’s transmit path to the master’s receive path. EtherCAT devices has a switch embedded in it, so external switches are not required in EtherCAT network.

EtherCAT devices has two RJ45 ports, one for the previous node and one for the next node connected in the network.

If the master device has two Ethernet ports than the EtherCAT networks can be connected in a ring topology, which will also facilitates with redundancy.

The breaks in cable can easily be detected by master and can send messages out to both of the new sub-segments. As EtherCAT facilitates with self-terminating feature, it can also be connected in star, line or tree topologies.

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EtherCAT Cable and Connectors

Ethercat is used Ethernet Cable.Ethernet cable can be used between two nodes up to range of 100m (100BASE-TX mode.) Furthermore,the protocol addition EtherCAT P enables the transmission of data and power via one cable. This type of connection used enables the connection of devices such as sensors with a single line.if node distance is more than 100m then used Fiber Optics Cable(Such as 100BASE-FX).The complete range of Ethernet wiring is also available for EtherCAT.

EtherCAT Cable

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EtherCAT frame

EtherCAT uses a standard Ethernet frame with an addition of its payload. The use of TCP/IP or UDP/IP, can be eliminated as EtherCAT protocol is optimized for short cyclic process data.

The EtherCAT frame contains one or more datagrams. The datagram header in the frame will indicate what type of access the master device would like to execute:

  • Read, write, read-write.
  • Access to a specific slave device through direct addressing, or access to multiple slave devices through logical addressing (implicit addressing).

For cyclic exchange of process data logical addressing is used in which each Datagram addresses a specific part of the process image in the EtherCAT segment, for which 4GBytes of address space is available.

Each slave device is assigned with one or more addresses in this global address space during the network startup. A single Datagram is considered if multiple slave devices are assigned addresses in the same area.

The Datagrams in EtherCAT contains all the data access related information, so the master device decides which and when to access the data.

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Ethercat utilizes Protocol Safety

In today’s world safety is one of the key feature even in case of automation world for communication and data transfer, EtherCAT utilizes the protocol Safety over EtherCAT for safety purpose and allows a single communication system for both control and safety data, the ability to flexibly modify and expand the safety system architecture, pre-certified solutions to simplify safety applications.

The EtherCAT safety technology is TÜV certified and was developed according to IEC 61508, and is standardized in IEC 61784-3. The protocol is suitable for safety applications with a Safety Integrity Level up to SIL 3.

Ethercat vs Ethernet/IP

Parameters Ethercat Ethernet/IP
Company/association Beckhoff Rockell Automation
Real time approach Standard Software
Standard Etherneet
Open Software
Modified Ethernet
Centralized Control Yes Yes
Decentralized Control Yes Not avilable
Tree Yes Not avilable
Star Yes Not avilable
Ring Yes Yes
Daisy-chain Yes Yes

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Ethercat Protocol Advantage

One of the main advantage of EtherCAT is the principle which it is using i.e. “processing on the fly”. Ethernet network gives a more delay in a message compared to EtherCAT and the reason for delay in EtherCAT is due to its frame cannot move continuously.

We can also manage the speed of EtherCAT networks as the computers may have difficulties to handle the increased quantity of cycles, so the optimization in EtherCAT is possible.

EtherCAT also facilitates with a distributed clock system which meets the synchronization need in the industrial automation. Timestamping facility is also provided in EtherCAT each node adds the timestamp as the message is received and then, each node again attaches a timestamp as the frame returns back through the nodes, then back to the master. Due to it the master has an accurate delay for each nodes as the timestamp data is calculated with every frame transmission.

EtherCAT redundancy is also possible using a ring topology.EtherCAT also uses star, tree, line, bus topology.

EtherCAT provides drastically high speed, reduced data traffic, decreased hardware cost and more accuracy and clock synchronization mechanism compared to Ethernet.

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