[time-nuts] Allan deviation vs standard deviation

Rick Karlquist richard at karlquist.com
Wed Sep 7 23:16:42 UTC 2011

I was playing with an Agilent 53132 counter, and noticed that
it measures "standard deviation" but doesn't seem to offer
what everyone really wants, ie, Allan deviation.  According
to the textbooks, standard deviation won't work for oscillators
because the mean is not fixed and the deviation goes to infinity.
However, I tried it anyway on a high quality oscillator for
100 measurements of one second each (N=100) and it seemed to
basically work, giving 2E-11 for the deviation.  The drift
over 100 seconds may be small enough that the mean didn't
move significantly.  I have a 53230 on order that does
actually measure Allan deviation, but am trying to get some
work done in the mean time with what I currently have.

Can anyone comment on the relationship between the two
types of measurements in the lab?  (We know how they
differ mathematically, but what is the practical implication).


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