Making Measurements 5
6000 Series Oscilloscope User’s Guide 245
Peak-Peak
The peak-to-peak value is the difference between Maximum
and Minimum values. The Y cursors show the values being
measured.
RMS
RMS (DC) is the root-mean-square value of the waveform
over one or more full periods. If less than one period is
displayed, RMS (DC) average is calculated on the full width
of the display. The X cursors show what interval of the
waveform is being measured.
Std Deviation
The Std Deviation measurement shows the standard
deviation of the displayed voltage values. It is an RMS
measurement across the full screen with the DC component
removed. It is useful, for example, for measuring power
supply noise.
The standard deviation of a measurement is the amount that
a measurement varies from the mean value. The Mean value
of a measurement is the statistical average of the
measurement.
The following figure graphically shows the mean and
standard deviation. Standard deviation is represented by the
Greek letter sigma: σ. For a Gaussian distribution, two sigma
(± 1σ) from the mean, is where 68.3 percent of the
measurement results reside. Six sigma (± 3σ) from is where
99.7 percent of the measurement results reside.
RMS (dc) =
x
i
2
i 1=
n
∑
n
----------------
where x
i
= value at ith point being measured
n = number of points in measurement interval
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