Condition monitoring
From symptom to root cause: a repeatable way to work a vibration problem
Quick answer
Cases from fans, pumps and gearboxes share a method: look at the pattern, check the cheap things first, confirm with a second source, and open the machine when you can.
The order that worked
| Step | Question | Tool | Example |
|---|---|---|---|
| 1 | Where is it highest, and in which direction? | Survey | 113 mm/s horizontal against 21 vertical: base looseness |
| 2 | Is it a wave or a shock? | Waveform | Shocks at 1X on a new pump: not unbalance |
| 3 | Which frequencies? | Spectrum, log scale | Harmonic ladder: looseness |
| 4 | Is something repeating at an exact rate? | Cursor spacing, autocorrelation | Shocks at 16.97 Hz: pinion shaft |
| 5 | Where on the shaft? | Circular plot | One angle: one tooth |
| 6 | Which parts move out of step? | Phase, motion video | Pedestal rocking |
| 7 | Is it heat? | Thermography | Hot bearing end cap |
| 8 | Does the cheap fix change the reading? | Bolt, foot or grease test | 6.2 to 1.2 mm/s by loosening one bolt |
| 9 | Does the machine agree? | Teardown | Inner race spall, load-zone line |
Habits that save time
- Check the cheap things first: bolts, soft foot, grease quantity, pipe strain.
- Ask two sources before a stop request: an automatic rating plus a spectrum or a waveform.
- Ask the operators. They know what changed.
- Compare identical machines: three new pumps, fifteen feed pumps.
- Keep before-and-after waveforms and temperatures. They are the evidence for the next decision.
- State the consequence in the plant's terms and put a date on it: a fan with a resonance warning failed ten days later.
Traps
- A high spectrum line is not a diagnosis. A line near 100 Hz can be electrical, mechanical or both.
- Overgreasing can imitate an inner race defect.
- Beating can look like an unstable machine.
- Low velocity does not clear a bearing.
- A thermal image shows surfaces, not temperatures.
Takeaway. Pattern, cheap checks, second source, teardown. The cases in this set follow that order.
Put it to work in the tool