Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT fault NC 0x4550: Position lag monitoring (following error) (17744)
Beckhoff: while position lag monitoring was active, the lag error (set position minus actual position) exceeded the Maximum Position Lag Value for longer than the Maximum Position Lag Filter Time. The NC axis is stopped immediately by direct shutdown and set to the logical state "Error".
Diagnose this with AI
Try Free PLC Fault Diagnostic Upload a keypad photo, the fault history or a parameter export from your Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT. InduQT compares the evidence and suggests the next useful checks.
When it happens
- During acceleration or at high speed
- When the axis meets a mechanical obstruction or load change
- At first moves after commissioning or a drive change
Likely causes and checks
1Mechanical: obstruction, brake not released, binding or a crash
- Points to it
- Lag grows while actual velocity drops; torque at its limit in the drive.
- Check
- Trace set/actual position, lag and torque in Scope View; inspect the axis mechanics and brake.
2Motion profile beyond what the drive/motor can follow
- Points to it
- Lag peaks at acceleration ramps; drive at current limit.
- Check
- Compare commanded acceleration/velocity with motor and drive capacity.
3Scaling, encoder or tuning error
- Points to it
- Lag grows steadily even with slow moves, or the axis runs the wrong way.
- Check
- Check encoder scaling, direction and the position controller settings against commissioning values.
Telling it apart
- 0x4551 is the velocity lag counterpart.
- A larger lag window or filter time only delays the stop; on a machine that ran before, find what changed instead of widening the limits.
- If the encoder lost data (WcState error), 0x4655 or encoder errors come first; read the logger order.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| Position Lag Monitoring | Position lag monitoring enable | TRUE enables monitoring. |
| Maximum Position Lag Value | Maximum position lag | Upper limit that must not be exceeded for longer than the filter time. |
| Maximum Position Lag Filter Time | Lag filter time | How long the limit may be exceeded before 0x4550. |
Evidence to collect
- Axis online tab (error, set/actual position, lag)
- Scope View trace of set position, actual position, lag and drive torque
- Axis parameter export (lag monitoring, scaling, controller)
- Logger export
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Related
- Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT WcState: Working counter error (WcState = 1, FrmXWcState ≠ 0)
- Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT NC 0x4260: Controller enable missing (16992)
- Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT NC 0x4650: Drive hardware not ready to operate (18000)
- All Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT fault codes