Page 40 - Shock and Vibration Overview

Analysis Overview

the result we get rid of the dependency on bin width so that we can compare vibration
levels in signals of different lengths.

PSDs are powerful because the area under the curve (or integral) in the frequency
domain represents the RMS vibration level for that frequency range. And RMS vibration
is related to the energy in the environment. PSDs are also often used in test standards
because of how they cancel out the effect of bandwidth of a frequency spectrum. Let’s
go through an example from MIL-STD-810G. Figure 514.6C-5 (page 312 from the
standard) describes the typical acceleration levels that jet aircraft cargo are exposed to

as shown below.

Figure 22: Typical vibration levels that jet aircraft cargo will be exposed to.

If you were developing something for the government that was going to be transported
with a jet aircraft, you would be required to do some testing on your device/equipment
to prove it can survive prolonged exposure to those vibration levels. Most shaker
control systems will have these exposure profiles built in but they can also be
constructed easily given some known PSD levels and rise/decline rates. Let’s take a look

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