Condition Monitoring & Diagnostics Flashcards

A pinion with 23 teeth runs at 1,800 RPM. What is the gear mesh frequency?

Answer: 690 Hz

GMF = 23 teeth × 30 Hz (1,800 RPM) = 690 Hz.

Sidebands around gear mesh frequency spaced at the output shaft speed most likely indicate what?

Answer: Eccentricity or a problem on the output gear

Sideband spacing identifies the shaft whose gear is modulating the mesh, here the output gear.

A single cracked tooth on a gear is best confirmed by which observation?

Answer: One distinct impact per revolution of that gear in the time waveform

A cracked or broken tooth produces a once-per-revolution impact that is clearest in the time waveform.

A centrifugal pump shows high vibration at vane pass frequency. Which cause is most likely?

Answer: Insufficient gap between impeller vanes and the cutwater/diffuser

Vane pass amplitude rises when the impeller-to-cutwater clearance is too small or the impeller is off-center.

Which signature is most typical of pump cavitation?

Answer: Random, broadband high-frequency energy, often with a gravel-like sound

Collapsing vapor bubbles generate random impacts that show as broadband high-frequency energy.

During a coastdown, phase shifts by about 180° while amplitude peaks then falls. What does this indicate?

Answer: The machine passed through a resonance (natural frequency)

Passing through a natural frequency produces an amplitude peak with a 90° shift at resonance and about 180° total.

Worn or defective drive belts typically produce vibration at which frequencies?

Answer: Belt frequency and its harmonics, often below running speed, with 2x belt frequency common

Belt defects appear at subsynchronous belt pass frequency and its harmonics, with 2x often dominant.