CEMB USA N500 - Manual (Page 33)

FFT analyzer mode 6 - 1
Chapter 6
FFT
(Fast Fourier Transform)
analyzer mode
A complete analysis of the vibration cannot fail to take into account the study of the
various factors contributing towards forming its overall value. Hence it is essential to be
able to carry out spectrum analysis with FFT (Fast Fourier Transform) algorithm.
Such technique allows splitting and memorizing a measured signal into its component
frequencies in a certain period of time, thus making it easier to discover their causes.
Analysis of the highest peaks in the spectrum, together with analysis of the frequencies to
which they correspond allows determining which are the principle sources of vibration and,
therefore, the aspects on which to act in order to reduce them.
Although a spectrum contains a series of very significant information, its interpretation
requires a certain amount of experience and attention; for this purpose, the material given
in Appendix C – A rapid guide to interpreting a spectrum could be useful.
FFT Setup
The choice of correct settings is vital in order to highlight the significant information in the
spectrum thus separating it from the inevitable background noise.
1. Unit of measurement
Select the unit of measurement in which the vibration is to be supplied; possibilities are as
follows:
–
acceleration (g) – enhances the higher frequencies and attenuates the lower ones
–
speed (mm/s or inch/s)
–
displacement (µm or mils) – enhances the lower frequencies and attenuates the
higher ones.