EtherCAT Commissioning and Diagnostics in TwinCAT 3

Prepare the engineering baseline

• Record the TwinCAT build, EtherCAT master hardware, slave order and device revisions.
• Use approved EtherCAT Slave Information files and retain them with the project or controlled build environment.
• Define expected device identity, optional stations and replacement policy.
• Document network cycle time, task relationship and Distributed Clocks requirements.
• Allocate named PLC structures for process data rather than scattering links across unrelated variables.

Commission in controlled stages

1. Inspect power, protective earth, connectors, cable routes and port sequence before scanning.
2. Compare the discovered topology with the electrical design and approved configuration.
3. Confirm each slave moves through INIT, PREOP, SAFEOP and OP without unexplained delay.
4. Validate PDO selection, scaling, data type and byte order at the application boundary.
5. Check Distributed Clocks reference, synchronisation error and task timing where motion or time-aligned sampling depends on it.
6. Exercise every field point and retain the result as I/O test evidence.

Diagnose from topology to application

When a slave will not reach OP, first locate the earliest device or link at which the state diverges. Inspect the EtherCAT state and AL status code, link status, working counter, device identity and mailbox communication before changing PLC logic. A fault downstream of one lost link may make many slaves appear missing.

For intermittent problems, trend CRC errors, lost frames, working-counter changes and cycle-time excursions. Compare them with machine events such as drive enable, contactor switching, welding, laser operation or cable-chain movement. Physical-layer evidence matters as much as configuration.

Make diagnostics available to the machine

Expose a concise fieldbus health structure to the PLC and HMI: master state, expected and responding slave counts, first affected station, working-counter status and relevant device diagnostics. The Beckhoff EtherCAT diagnostics library can support PLC-level reading of supported diagnostic histories.

Do not automatically reset or reconfigure a failed bus without a documented equipment-level risk assessment. Communications recovery can re-enable outputs and motion; the machine state model must decide whether recovery is permitted.

Commissioning record

Retain the approved topology, device list, ESI set, I/O mapping report, cycle and DC settings, error-counter baseline, point-to-point test, known optional devices and replacement procedure. This package turns a future EtherCAT incident from exploratory troubleshooting into a controlled comparison with a known-good state.