CMRT Predictive Maintenance Technologies 2 — Questions and Answers
Question 1: In vibration analysis, what does a high amplitude peak at exactly 1× running speed (1X) typically indicate?
- Bearing defect
- Unbalance (Correct answer)
- Gear mesh frequency
- Looseness
Correct answer: Unbalance
A dominant 1X peak in the vibration spectrum is the classic signature of mechanical unbalance in rotating equipment.
Question 2: Which FFT window function is best suited for detecting closely spaced frequency components with similar amplitudes?
- Hanning (Correct answer)
- Flat Top
- Rectangular
- Exponential
Correct answer: Hanning
The Hanning window provides good frequency resolution and reduces spectral leakage, making it ideal for detecting closely spaced peaks.
Question 3: A vibration spectrum shows peaks at 0.5X, 1X, and 1.5X running speed. This pattern is most consistent with:
- Unbalance
- Misalignment
- Fluid-film bearing instability (oil whirl) (Correct answer)
- Looseness
Correct answer: Fluid-film bearing instability (oil whirl)
Sub-synchronous peaks near 0.5X are the hallmark of oil whirl instability in fluid-film bearings.
Question 4: When using an accelerometer for high-frequency vibration measurement, what mounting method provides the widest usable frequency range?
- Magnet mount
- Adhesive stud mount
- Stud mount (Correct answer)
- Hand-held probe
Correct answer: Stud mount
Stud mounting provides the most rigid coupling, extending the usable frequency range up to the sensor's full specification.
Question 5: The kurtosis value of a vibration signal is most useful for:
- Identifying resonance frequencies
- Detecting early-stage bearing defects (Correct answer)
- Measuring overall vibration severity
- Diagnosing misalignment
Correct answer: Detecting early-stage bearing defects
Kurtosis measures impulsiveness in a signal; a rising kurtosis value (above ~4) indicates early-stage bearing defects before they appear in the spectrum.
Question 6: In rolling element bearing analysis, the Ball Pass Frequency Outer race (BPFO) is calculated using:
- Number of balls, ball diameter, pitch diameter, and shaft speed (Correct answer)
- Shaft speed and number of blades
- Gear tooth count and shaft speed
- Rolling element diameter and shaft speed only
Correct answer: Number of balls, ball diameter, pitch diameter, and shaft speed
BPFO = (N/2) × (1 − Bd/Pd × cos θ) × RPM/60, requiring the number of balls, ball diameter, pitch diameter, and contact angle.
Question 7: When performing route-based vibration data collection, measurements should ideally be taken:
- At random intervals throughout the shift
- Under consistent load and speed conditions (Correct answer)
- Only during equipment startup
- While the equipment is being lubricated
Correct answer: Under consistent load and speed conditions
Consistent operating conditions (load and speed) are essential for valid trend comparisons between data collection routes.
CMRT Predictive Maintenance Technologies 2
In vibration analysis, what does a high amplitude peak at exactly 1× running speed (1X) typically indicate?