Fluke PM6690 - Statistics; Allan Deviation Vs. Standard Deviation; Selecting Sampling Parameters

Statistics
Statistics can be applied to all measuring func
-
tions and can also be applied to the result from
Mathematics.
The available statistics functions are as fol
-
lows:
X MAX: Displays the maximum value
within a sampled population of N
x
i
-values.
X MIN: Displays the minimum value within
a sampled population of N x
i
-values.
X P-P: Displays the peak-to-peak deviation
within a sampled population of N
x
i
-values.
MEAN: Displays the arithmetic mean
value (x
) of a sampled population of N
x
i
-values and is calculated as:
x
N
x
i
i
N
=
=
å
1
1
ST DEV: Displays the standard deviation
(s) of a sampled population of N x
i
-val-
ues and is calculated as:
s
xx
N
i
i
N
=
-
-
=
å
()
2
1
1
It is defined as the square root of the
variance.
A DEV: Displays the Allan deviation (s)ofa
sampled population of N x
i
-values and
is calculated as:
s=
-
-
+
=
-
å
()
()
xx
N
ii
i
N
1
2
1
1
21
It is defined as the square root of the
Allan variance.
The number N in the expressions above can
assume any value between 2 and 2
*
10
9
.
Allan Deviation vs. Standard
Deviation
The Allan Deviation is a statistic used for
characterizing short-term instability (e.g.
caused by jitter and flutter) by means of sam
-
ples (measurements) taken at short intervals.
The fundamental idea is to eliminate the influ
-
ence of long-term drift due to aging, tempera
-
ture or wander. This is done by making con
-
secutive comparisons of adjacent samples.
The S tandard Deviation, which is probably a
more familiar statistic, considers the effects of
all types of deviation, as all samples in the
population are compared with the total mean
value.
As you can see, both the Allan Deviation and
the S tandard Deviation are expressed in the
same units as the main parameter, e.g. Hz or s.
Selecting Sampling
Parameters
–
Press SETTINGS ® Stat..
–
Press No. of samples and enter a new
value by means of the numerical keys or
the UP/DOWN arrow keys, if you want to
change the default value of 100.
–
Proceed in the same way for No. of bins,
if you want to present the measurement re
-
sults graphically in a histogram.
+
Note that the six statistic
measures are calculated and dis
-
played simultaneously only in the
non-graphic presentation mode
under STAT/PLOT.
Use the same key for toggling
between the three modes Nu
-
merical - Histogram - Trend.
Statistics 6-3
Process