[EtherCAT Feature Packs]
EtherCAT Cable Redundancy refers to the capability of the EtherCAT communication system to maintain continuous and reliable communication even in the event of a cable failure. Cable Redundancy employs a ring topology, which is operated in both directions. If one cable fails or is disconnected, another cable path still works to ensure uninterrupted communication. Cable Redundancy enhances the fault tolerance of the EtherCAT network, minimizing downtime and improving overall system reliability.
Three scenarios are listed as below regarding whether the cable is broken or not in Cable Redundancy. The following you will see how to work for Cable Redundancy, and the differences for the EtherCAT Master Controller between these scenarios.
- Without Cable Broken
- Cable Broken between two slaves
- Cable broken between master and slave
For ease of explanation, some assumptions will be made here:
- Assume Cycle Time is set to 125 µs.
- Assume all slaves only with input PDO (without output PDO), the working counter (WKC) in process data frame will increase 1 when passing through every slaves.
- Assume only have 6 slaves on EtherCAT network, and the expected working counter (EWKC) is 6.
- Primary Port and Secondary Port send process data frames in every cycle at the same time.
Without Cable Broken
Without Cable Broken:
- Primary frame from primary port will be received by secondary port, which frame with WKC = 6.
- Secondary frame from secondary port will be received by primary port, which frame with WKC = 0.
- Master will discard the secondary frame because primary frame’s WKC equals to EWKC and secondary frame’s WKC equals to 0, it means that without cable broken.
Cable Broken between two slaves
Unplug the cable between Slave 3 and Slave 4:
- If you unplug the cable manually, it might with some interference which last several cycles. (N = 0 ~ more)
- If the interference continues for a period of time, some slaves will enter the SAFEOP state due to SyncManager Watchdog.
Cable broken between Slave 3 and Slave 4:
- Primary frame from primary port will be received by primary port, which frame with WKC = 3.
- Secondary frame from secondary port will be received by secondary port, which frame with WKC = 3.
- Primary frame and secondary frame will be combined by Master, because primary frame’s WKC is less than EWKC and secondary frame’s WKC is greater than 0, it means that the cable broken event is happened between two slaves.
Cable broken between master and slave
Unplug the cable between Master and Slave 1:
- If you unplug the cable manually, it might with some interference which last several cycles. (N = 0 ~ more)
- If the interference continues for a period of time, some slaves will enter the SAFEOP state due to SyncManager Watchdog.
Cable broken between Master and Slave 1:
- Primary frame from primary port will lost.
- Secondary frame from secondary port will be received by secondary port, which frame with WKC = 6.
- Master will ignore the primary frame because primary frame was lost and secondary frame’s WKC equals to EWKC, it means that the cable broken event is happened between Master and Slave 1.
Stay tuned for more projects on QEC!
Feel free to comment if you have any doubts/queries!
For more details, please refer to the EtherCAT Library API User Manual.
