In vibration analysis, what is spectrum analysis and which fault signatures indicate bearing faults?

• A. Analysis of vibration frequency content; bearing faults show peaks at bearing cage, outer race, inner race defect frequencies.
• B. Analysis of time-domain signal; peaks at running speed indicate bearing faults.
• C. Analysis of thermal patterns; hotspots indicate bearing faults.
• D. Analysis of oil viscosity; high viscosity indicates bearing faults.

Answer: (A)

Spectrum analysis in vibration work means looking at the frequency content of a vibration signal, typically by converting the time signal with a Fourier transform. This lets you see periodic events as spikes at specific frequencies, rather than just how the signal changes over time.

Bearing faults create repetitive impacts as defects on inner race, outer race, or the cage pass by the load zone. Each type of defect generates energy at a characteristic frequency tied to the bearing’s geometry and rotation speed, so the spectrum will show peaks at the inner race fault frequency, the outer race fault frequency, and the cage (fundamental train) frequency, along with possible harmonics. That pattern is what makes spectrum analysis powerful for diagnosing bearing faults.

Options focusing on time-domain signals, thermal patterns, or oil viscosity don’t reveal these specific, defect-related frequencies in the spectrum, so they’re not as effective for identifying bearing faults.