A VFD on a screw conveyor begins tripping on acceleration after a product change. Someone increases acceleration time and the trips become less frequent. At 3 AM the fault returns. Rather than increasing the ramp again, the technician compares motor current with an identical conveyor and inspects the process. The screw is packed with sticky product, and the product recipe introduced higher moisture than normal.
Cleaning the screw and correcting the process condition return current to normal. The acceleration parameter is restored to its documented value. The temporary parameter change was not inherently unreasonable as a diagnostic clue, but it became dangerous when it was allowed to substitute for root-cause work. The drive was telling the team that torque demand was abnormal.
What Mattered
- Parameter changes can mask process or mechanical problems.
- Always record original settings before adjustment.
- Compare against healthy reference equipment when possible.
- Restore design settings after the cause is corrected.
Questions to Ask Yourself
- Which early clue had the highest information value?
- What tempting but unsupported action could have wasted time?
- Which measurement or observation moved the diagnosis across a system boundary?
- What should be changed so the same failure is detected earlier next time?