Allen-Bradley Kinetix 5700 servo drive alarm FLT S54: POSN ERROR (Excessive Position Error Fault)
Fault FLT S54 – POSN ERROR on an Allen-Bradley Kinetix 5700 is Excessive Position Error: the position error of the position control loop exceeded Position Error Tolerance for longer than Position Error Tolerance Time. It does not apply to induction motors in frequency control mode.
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When it happens
- During acceleration or deceleration when the axis cannot follow the motion profile
- When the load jams or hits a mechanical stop
- On the first moves after commissioning, with untuned loops or wrong motor wiring
Likely causes and checks
1Position loop poorly tuned or feedforward too low
- Points to it
- Error peaks during acceleration and settles at constant speed.
- Check
- Trend position error against the command in Studio 5000; check position loop tuning and increase the feedforward gain.
2Drive or motor undersized for the move, or load blocked
- Points to it
- Torque reaches its limit during the move; error grows until the fault.
- Check
- Verify the sizing of the drive and motor against the motion profile; check the mechanism turns freely.
3Motor power wiring fault
- Points to it
- Fault on the first motion after wiring work; poor torque.
- Check
- Check the motor power wiring (phase order and connections).
4Tolerance set too tight for the application
- Points to it
- Motion is good but the error at peak acceleration is just over the setting.
- Check
- Compare Position Error Tolerance and Position Error Tolerance Time with the trended error; increase them only after the mechanics and tuning are confirmed.
Telling it apart
- FLT S55 – VEL ERROR is the velocity-loop equivalent (velocity error over Velocity Error Tolerance for the tolerance time).
- If FLT S07/S08 (motor overload) or FLT S13 (inverter overload) appear around the same time, the axis is working too hard; S54 alone during acceleration usually means tuning or profile.
- S54 is the drive-side following-error fault; Rockwell does not have software overtravel fault codes in the drive (those are handled in the controller).
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| Position Error Tolerance | Axis attribute | Position error limit used for FLT S54. |
| Position Error Tolerance Time | Axis attribute | Time the error must exceed the tolerance before FLT S54 is raised. |
Evidence to collect
- Full LCD text and fault log time stamp
- Trend of position error, command and torque for the failing move
- Position Error Tolerance and Position Error Tolerance Time values
- Loop gains and feedforward settings
- Drive and motor catalog numbers
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