Air-gap flux sensors observe magnetic behaviour close to the machine. Their value is in repeatable trending, not automatic naming of faults from a single spectrum.
Decide whether a change is actionable
- Confirm the sensor, channel, mounting and acquisition configuration match the baseline.
- Normalize the comparison for speed, load, voltage, frequency and VFD operating point.
- Check whether maintenance, rewinding, rotor work or sensor movement created a new baseline.
- Escalate only after corroborating the pattern with current signature, vibration, air-gap measurements or inspection.
| Evidence | Question it answers | Limitation |
|---|---|---|
| Flux trend | Has magnetic asymmetry changed? | Sensitive to operating point and sensor position |
| Phase current | Is electrical loading balanced? | Supply effects can resemble machine effects |
| Vibration | Is a mechanical response present? | Does not identify magnetic cause alone |
| Air-gap/inspection | Is geometry or damage visible? | Often requires outage access |
Record raw data, analysis settings, load, speed, temperature, supply and alarm rationale. Avoid universal amplitude thresholds unless the monitoring system and motor supplier define them for the installation.
Related reading: motor current signature analysis boundaries and motor air-gap inspection.