Bearing Analysis & Fault Detection Flashcards

What is the crest factor of a vibration signal?

Answer: The ratio of peak amplitude to RMS amplitude

Crest factor is the ratio of peak to RMS amplitude; for a pure sine wave it equals √2 (≈1.414), while impulsive bearing faults increase the peak without proportionally increasing RMS, raising the crest factor.

What does a 'sideband' pattern around BPFI indicate in bearing diagnostics?

Answer: Modulation of the inner race defect frequency by shaft speed, confirming an inner race defect

Because the inner race rotates with the shaft, an inner race defect produces sidebands spaced at shaft speed around BPFI harmonics, which confirms the inner race as the defect location.

What is the ISO 10816 standard's primary concern regarding bearing vibration?

Answer: Setting velocity-based vibration severity limits for overall machine vibration assessment

ISO 10816 (now ISO 20816) establishes overall vibration velocity severity limits for evaluating machine condition, providing zone classifications that guide maintenance decisions based on RMS velocity.

What is the Spike Energy (gSE) measurement, and what makes it useful for bearing analysis?

Answer: A high-frequency (5–50 kHz) energy measurement sensitive to very early-stage impacting from bearing and gear defects

Spike Energy measures the energy content of high-frequency stress waves (typically 5–50 kHz) generated by bearing or gear impacting, and its trend over time provides early warning of developing defects before they appear in normal velocity spectra.

In which bearing failure stage would you expect to see harmonics of bearing defect frequencies clearly visible in the low-frequency velocity spectrum?

Answer: Stage 3 (intermediate)

In Stage 3 of bearing failure, distinct harmonics of bearing defect frequencies (BPFO, BPFI, BSF) appear clearly in the normal velocity spectrum along with sideband development, indicating significant bearing damage.

What type of bearing fault is indicated by a non-synchronous frequency at approximately 0.4–0.5× shaft speed with harmonics?

Answer: Cage defect (FTF harmonics)

FTF (cage frequency) at approximately 0.4–0.45× shaft speed with multiple harmonics indicates cage damage or defect; cage faults are often related to lubrication failure or contamination.