Condition Monitoring & Diagnostics Flashcards

Which approximation is commonly used to estimate ball pass frequency outer race (BPFO) when bearing geometry is unknown?

Answer: 0.4 × number of rolling elements × shaft speed

BPFO is roughly 40% of the number of rolling elements times shaft speed, while BPFI is roughly 60%.

Why are inner race defect frequencies (BPFI) typically surrounded by 1x running speed sidebands?

Answer: The defect rotates with the shaft, moving in and out of the load zone each revolution

The rotating inner race carries the defect through the load zone once per revolution, amplitude-modulating impacts at 1x.

Fundamental train frequency (FTF) of a rolling-element bearing typically falls at approximately what fraction of shaft speed?

Answer: 0.4x

The cage rotates at slightly less than half shaft speed, typically around 0.38-0.45x.

In the earliest stage of rolling-element bearing failure, where is evidence most likely to first appear?

Answer: In the ultrasonic/high-frequency range (roughly 20-60 kHz) via spike energy, HFD, or PeakVue-type measurements

Stage 1 defects generate low-energy stress waves detectable only by high-frequency techniques before discrete defect peaks emerge.

A rolling element (ball) spin defect frequency is most often accompanied by sidebands spaced at which frequency?

Answer: Fundamental train frequency (FTF)

Balls travel with the cage, so a ball defect is modulated as it moves through the load zone at the cage rate.

What is the primary purpose of envelope (demodulation) analysis in bearing diagnostics?

Answer: To extract the repetition rate of impacts that excite high-frequency structural resonances

Enveloping high-pass filters and rectifies the signal so the repetition rate of defect impacts appears as clear peaks in a low-frequency spectrum.

In late-stage (Stage 4) bearing failure, what typically happens to the vibration spectrum?

Answer: Discrete defect frequencies may diminish while broadband noise floor and 1x amplitude rise

As defects spread and clearances grow, discrete peaks merge into a raised 'haystack' noise floor and running speed amplitude increases.