Practical
Definition:
-
The 'Overall'
Amplitude is the sum of all of the vibration energy occurring between 0
cpm and the data collector's maximum frequency (its "Fmax" - well over
1,000kcpm). In other words, if you were to collect a spectrum over a frequency
range of 0 - collector's Fmax and added all of the amplitude peaks together,
that would be your 'overall' amplitude. Although not technically correct,
that is one way to look at it.
Technical Definition:
-
Consider again
collecting a spectrum from 0 - the collector's Fmax. Take every amplitude
value, square it, add them together and take the square root of that sum.
Although not exactly perfectly accurate, that is closer to what actually
goes into calculating an 'overall' amplitude. That is known as a "Root
Mean Square", or RMS, value.
-
All data is collected
as an "RMS" value. That is an ISO convention and applies no matter what
collector you may have.
-
The RMS value
was settled on in order to guard against a transient spike in the signal
distorting the true value significantly.
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