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Encyclopedia > Allan variance

The Allan variance, named after David W. Allen, also known as two-sample variance, is a measurement of accuracy in clocks. It is defined as one half of the time average of the squares of the differences between successive readings of the frequency deviation sampled over the sampling period. For most real_world systems, the Allan variance depends on the time period used between samples: therefore it is a function of the sample period, as well as the distribution being measured. A low Allan variance is a characteristic of a clock with good stability over the measured period.


The Allan variance is given by

 sigma_y^2( tau) =  frac{1}{2}  langle(y_{n+1} - y_n)^2 rangle

where yn is the normalized frequency departure, averaged over sample period n, and τ is the time per sample period.


The samples are taken with no dead-time between them.


Source: from Federal Standard 1037C


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  Results from FactBites:
 
Allan variance - Wikipedia, the free encyclopedia (152 words)
The Allan variance, named after David W. Allan, is a measurement of accuracy in clocks.
For most real-world systems, the Allan variance depends on the time period used between samples: therefore it is a function of the sample period, as well as the distribution being measured.
A low Allan variance is a characteristic of a clock with good stability over the measured period.
Allan variance: Definition and Links by Encyclopedian.com - All about Allan variance (139 words)
The Allan variance is a measurement of accuracy in clocks.
For most real-world systems, the Allen variance depends on the time period used between samples: therefore it is a function of the sample period, as well as the distribution being measured.
Note: a low Allan variance is a characteristic of a clock with good stability over the measured period.
  More results at FactBites »

 

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