Standard Deviation

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, xnn = 1, …, N.

(1)   \begin{equation*} \sigma=(+)\sqrt{\sigma^2} \end{equation*}

Equation 6

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.