By definition, Ethernet technology does not allow any physical loop structures and, due to the broadcast characteristics of Ethernet, no redundant communication paths are possible. However, the reliability and the use of redundant architectures are fundamental requirements of many automation systems. Industrial Ethernet protocols such as EtherCAT deliver redundancy methods to realize more robust and fail-safe networks.
Redundancy in automation
In today’s Industrial Ethernet networks, the requirements for availability and reliability are growing steadily. This is because the complexity of the automation processes is increasing. If a single point of failure exists, the communication network of an automated production line, for example, could potentially stop working. This can lead to high follow-up costs. If redundant structures are used, the network simply reverts to a fail-safe state in the event of a single error. Communication over the network is still possible and the redundant system enables repairs to restore the original fault-free state.
How it works
A typical network structure is the daisy chain, where the master sends all frames in summation down the chain. The last member in the chain returns the frames back to the master via all other members of the chain. If a single fault occurs, the components behind that fault are unreachable. In the worst-case scenario in a production line, this would lead to the entire process collapsing. To overcome this weak link, the EtherCAT Technology Group (ETG), the global organization in which OEM, End Users and Technology Providers join forces to support and promote the further technology development, defined the EtherCAT cable redundancy mechanism. Cable redundancy is used to compensate for the failure of a communication cable section in the EtherCAT system.
To set up a ring topology, an additional cable connects the last member of the daisy chain with the master. The master, in turn, now transmits the same frames over both ports. If a single error occurs in the chain, it still remains possible to reach all participants. The master correlates the received data within the frames and can therefore access all necessary process data and statuses. As a result, the communication between the master and the slaves can be maintained, even if the cable is physically interrupted at one point. When a proper functioning communication is restored, the original communication path is also reestablished. If the communication is interrupted at more than one point, all connections must be restored before the redundancy mechanism can intervene again.
What are the benefits of using redundancy in your EtherCAT network?
- Increasing the robustness of the networks
- Protection against loss of runtimes and single points of failure
- Works with standard EtherCAT Slave devices
- Hilschers EtherCAT Master stacks supporting this feature since version V4.4.0.0
The following products are also capable of using redundancy:
