Vibration Measurement & Analysis Techniques Flashcards

What does time synchronous averaging (TSA) require, and what does it do to the signal?

Answer: A tachometer trigger; it keeps components synchronous with the shaft and averages out non-synchronous ones

Triggering each block from a once-per-revolution tach makes shaft-synchronous signals add coherently while random and non-synchronous content averages toward zero.

A pure sine wave has a peak amplitude of 1.0 in/s. What is its RMS value?

Answer: 0.707 in/s

For a pure sinusoid, RMS = 0.707 × peak.

What is the crest factor of a pure sine wave, and what does a rising crest factor usually mean on a rolling element bearing?

Answer: 1.414; impacting from developing defects

Sine crest factor (peak/RMS) is 1.414, and early bearing defects add short impacts that raise the peak more than the RMS.

A machine has 2 mils peak-to-peak displacement at 30 Hz. What is the approximate velocity in in/s peak?

Answer: 0.188 in/s

V = 2πfD = 6.283 × 30 × 0.001 in (1 mil peak) ≈ 0.188 in/s peak.

How does envelope demodulation (enveloping) detect early bearing faults?

Answer: It high-pass/band-pass filters around excited resonances, rectifies, and finds the repetition rate of the impacts

Enveloping pulls out the high-frequency ringing caused by impacts and shows how often it repeats, which lines up with defect frequencies such as BPFO.

Which mounting method gives an accelerometer the highest usable frequency range?

Answer: Stud mount on a flat, spot-faced surface

A stiff stud mount keeps the mounted resonance highest, so the flat frequency response reaches furthest up.

A 16-bit analog-to-digital converter provides a theoretical dynamic range of roughly:

Answer: 96 dB

Each bit adds about 6 dB, so 16 bits × 6 dB ≈ 96 dB.