CVA Condition Monitoring & Diagnostics 2

Question 1

On a center-hung fan, horizontal 1x phase readings at the inboard and outboard bearings are nearly identical (within about 30°). Which fault does this most strongly suggest?

Accepted Answer

Static (force) imbalance

Answer

Static imbalance produces in-phase 1x radial motion at both bearings because the heavy spot pulls both ends in the same direction.

Question 2

Which spectral and phase pattern is most characteristic of angular misalignment across a flexible coupling?

Accepted Answer

High 1x axial with roughly 180° axial phase difference across the coupling

Answer

Angular misalignment creates a bending moment that drives strong 1x axial vibration out of phase across the coupling.

Question 3

A pump base shows many running-speed harmonics plus 0.5x subharmonics, and the time waveform is erratic and non-repeating. What is the most likely cause?

Accepted Answer

Rotating looseness (Type C) such as an oversized bearing bore fit

Answer

Type C rotating looseness produces truncated, non-linear response with many harmonics and half-order components.

Question 4

A machine with sleeve bearings shows a peak at 0.44x running speed that tracks speed as RPM changes. Which condition is indicated?

Accepted Answer

Oil whirl

Answer

Oil whirl occurs at roughly 0.40-0.48x shaft speed in fluid-film bearings and follows running speed.

Question 5

On an AC induction motor fed at 60 Hz, a dominant peak at 120 Hz that disappears instantly when power is cut points to what type of problem?

Accepted Answer

Electrical problem such as stator eccentricity or soft-foot-induced air gap variation

Answer

Vibration at twice line frequency that vanishes the instant power is removed is electromagnetic in origin.

CVA - Certified Vibration Analyst Practice Test

CVA - Certified Vibration Analyst Practice Test

CVA Condition Monitoring & Diagnostics 2