CVA Signal Processing & FFT Analysis 2

Question 1

What does the Nyquist frequency represent?

Accepted Answer

Half the sampling rate, above which aliasing occurs

Answer

The Nyquist frequency is half the digital sampling rate and represents the highest frequency that can be accurately captured without aliasing.

Question 2

In a vibration spectrum, what is a sideband?

Accepted Answer

A frequency peak located a fixed interval above or below a carrier frequency

Answer

Sidebands are spectral peaks spaced symmetrically around a carrier frequency and indicate amplitude or frequency modulation, commonly associated with gear mesh or bearing faults.

Question 3

What is the purpose of a Flat Top window in FFT analysis?

Accepted Answer

To provide accurate amplitude measurements at the cost of frequency resolution

Answer

The Flat Top window provides the most accurate amplitude readings because it has a very flat passband in the frequency domain, making it ideal for calibration and amplitude-critical measurements.

Question 4

What is cepstrum analysis primarily used for in machinery diagnostics?

Accepted Answer

Detecting families of equally spaced harmonics or sidebands

Answer

Cepstrum analysis is particularly useful for identifying regularly spaced harmonics or sidebands in a spectrum, which are characteristic of gear defects and bearing faults.

Question 5

What does 'overlap processing' refer to in FFT averaging?

Accepted Answer

Reusing a portion of each time record in the next record to improve averaging efficiency

Answer

Overlap processing reuses a percentage (typically 50–75%) of each time block in the subsequent block, allowing more averages to be computed from the same total data length.

CVA - Certified Vibration Analyst Practice Test

CVA - Certified Vibration Analyst Practice Test

CVA Signal Processing & FFT Analysis 2