User Manual
Slam Stick User Manual
Version No. 2.0
51
Figure 25: The Fourier Transform plots vibration amplitude as a function of frequency.
Render PSD
Power spectral densities (PSD) are used to characterize random vibration signals. A PSD is
computed by multiplying each frequency bin in an FFT by its complex conjugate which results in
the real only spectrum of amplitude in g
2
. The key aspect of a PSD which makes it more useful
than a FFT for random vibration analysis is that this amplitude value is then normalized to the
frequency bin width to get units of g
2
/Hz. By normalizing the result we reduce the dependency
on the number of samples in the original acquisition. The area under the curve in a PSD
represents the RMS vibration energy in that frequency range. This area can be calculated
precisely by exporting the PSD into a CSV file, summing the data in the desired frequency range,
and multiplying by the frequency bin width, or the space between adjacent frequencies. Slam
Stick Lab filters the three lowest frequencies to 0 to remove the DC component. For more
information, visit our