Signal Processing & FFT Analysis Flashcards

What does FFT stand for in vibration analysis?

Answer: Fast Fourier Transform

FFT stands for Fast Fourier Transform, a mathematical algorithm that converts a time-domain signal into its frequency-domain components.

What is aliasing in digital signal processing?

Answer: False frequencies appearing when the sampling rate is too low

Aliasing occurs when the sampling rate is insufficient (below twice the highest frequency of interest), causing high-frequency signals to appear as false low-frequency components.

What is spectral leakage in FFT analysis?

Answer: Spreading of energy into adjacent frequency bins caused by non-integer cycles in the time record

Spectral leakage occurs when a signal's frequency does not fall exactly on an FFT bin, causing energy to spread into neighboring bins and masking nearby peaks.

Which windowing function is most appropriate for analyzing synchronous (shaft-speed) vibration components?

Answer: Hanning window

The Hanning window is the most common general-purpose window for rotating machinery analysis as it provides a good balance between frequency resolution and leakage reduction.

What is the frequency resolution of an FFT spectrum?

Answer: 1 divided by the time record length

Frequency resolution equals 1 divided by the time record length (in seconds), so longer time records provide finer frequency resolution.

What is the purpose of averaging multiple FFT spectra?

Answer: To reduce random noise and improve the signal-to-noise ratio

Averaging multiple FFT spectra reduces random noise by a factor proportional to the square root of the number of averages, improving the visibility of true vibration components.