CVA Bearing Analysis & Fault Detection

Question 1

What are the four fundamental bearing defect frequencies for a rolling element bearing?

Accepted Answer

BPFO, BPFI, BSF, FTF

Answer

The four fundamental bearing defect frequencies are BPFO (Ball Pass Frequency Outer race), BPFI (Ball Pass Frequency Inner race), BSF (Ball Spin Frequency), and FTF (Fundamental Train Frequency or cage frequency).

Question 2

Which bearing defect frequency is typically the lowest and corresponds to cage rotation?

Accepted Answer

FTF

Answer

The Fundamental Train Frequency (FTF) represents the rotational speed of the cage and is typically 0.35–0.48× shaft speed, making it the lowest of the four bearing defect frequencies.

Question 3

In the early stages of rolling element bearing failure, defect-related energy typically appears first in which frequency range?

Accepted Answer

Ultrasonic frequencies (20 kHz and above), then high-frequency resonances

Answer

Early bearing defects generate very low-energy, high-frequency stress waves that first excite ultrasonic frequencies and bearing/structural natural frequencies; bearing defect frequencies in the low-frequency spectrum appear in later fault stages.

Question 4

What is the envelope (demodulation) technique used for in bearing analysis?

Accepted Answer

Detecting the repetitive impact pattern of a bearing defect by bandpass filtering and demodulating a high-frequency resonance

Answer

Envelope analysis bandpass filters the signal around a high-frequency resonance excited by bearing impacts, then demodulates (rectifies and low-pass filters) to extract the repetition rate of the impacts for bearing defect frequency identification.

Question 5

What does BPFO stand for, and what does it represent?

Accepted Answer

Ball Pass Frequency Outer race; the rate at which rolling elements pass a defect on the outer race

Answer

BPFO (Ball Pass Frequency Outer race) is the frequency at which rolling elements strike a defect on the outer ring, calculated as (N/2) × shaft speed × (1 - Bd/Pd × cos θ), where N is the number of rolling elements.

CVA - Certified Vibration Analyst Practice Test

CVA - Certified Vibration Analyst Practice Test

CVA Bearing Analysis & Fault Detection