March 29, 2018
The standard deviation measures a signal’s variability about its mean value. Equation 6 gives the standard deviation of a set of numbers, xn, n = 1, …, N.
A vibration signal with a mean value of zero has a standard deviation equal to the signal’s RMS value. For the vibration signal Figures 3.1 and 3.2, the standard deviation and RMS level have a value of 0.073 G.
The variance and standard deviation play an important role in determining the confidence interval—or, conversely, the uncertainty—of a statistical measure. This is discussed further in the lesson on confidence intervals.