Spider DSA User’s Manual
270
Figure 180:3D Color map of an FFT spectrum
With a 3D RPM frequency spectrum, the variation of components of frequency
with respect to the RPM can be clearly observed. A clear differentiation of the
spectral components that depend on the rotational speed (forcing orders) and the
spectral components that do not (resonances) is clearly shown.
Band RMS Spectrum
In order tracking, it is also important to monitor the overall RMS level or signal
power level of the measurement versus RPM. The overall level is a good tool to
rapidly identify critical bands of operating RPM. Overall level can be in unit of
RMS (EU
rms
) or power (EU
rms
2
). The horizontal axis is RPM. Below is a typical
overall level display.
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