Difference between revisions of "Realization"
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There are three general methods of realizing a unit or a scale. The first and most obvious is simply to follow the definition of the unit or scale, for example by measuring the [[distance]] travelled by [[light]] in [[vacuum]] in {{frac|299,792,458}} of a [[second]] to realize the [[metre]]. The second method is to use a physical phenomenon which is accepted to be equivalent to the definition, for example realizing the metre by laser [[interferometry]] with a measured [[frequency]] of light. The third method is to have a physical standard, for example the now-obsolete [[International Prototype Metre]].<ref name="VIM"/> | There are three general methods of realizing a unit or a scale. The first and most obvious is simply to follow the definition of the unit or scale, for example by measuring the [[distance]] travelled by [[light]] in [[vacuum]] in {{frac|299,792,458}} of a [[second]] to realize the [[metre]]. The second method is to use a physical phenomenon which is accepted to be equivalent to the definition, for example realizing the metre by laser [[interferometry]] with a measured [[frequency]] of light. The third method is to have a physical standard, for example the now-obsolete [[International Prototype Metre]].<ref name="VIM"/> | ||
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| + | As a realization is a measurement, it is associated with a [[measurement uncertainty]], which is called the '''standard measurement uncertainty'''. The standard measurement uncertainty is a component of the uncertainty in any measurement result which relies on the measurement standard, although it is often (indeed usually) negligeable compared to other components of the uncertainty.<ref name="VIM"/> | ||
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| + | ==History== | ||
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| + | ==International System of Units== | ||
==References== | ==References== | ||
Revision as of 18:49, 29 July 2010
In metrology, the realization (or embodiment) of a measurement unit or a measurement scale is the practical method by which the unit can be measured (or the scale put into practice). The realization of a unit or of a scale creates one or more measurement standards against which an unknown physical quantity of the same kind can be compared.[1]
There are three general methods of realizing a unit or a scale. The first and most obvious is simply to follow the definition of the unit or scale, for example by measuring the distance travelled by light in vacuum in 1⁄299,792,458 of a second to realize the metre. The second method is to use a physical phenomenon which is accepted to be equivalent to the definition, for example realizing the metre by laser interferometry with a measured frequency of light. The third method is to have a physical standard, for example the now-obsolete International Prototype Metre.[1]
As a realization is a measurement, it is associated with a measurement uncertainty, which is called the standard measurement uncertainty. The standard measurement uncertainty is a component of the uncertainty in any measurement result which relies on the measurement standard, although it is often (indeed usually) negligeable compared to other components of the uncertainty.[1]
History
International System of Units
References
- ↑ 1.0 1.1 1.2 International vocabulary of metrology — Basic and general concepts and associated terms (VIM), 3rd ed.; International Bureau of Weights and Measures: Sèvres, France, 2008; pp 46–47, <http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf>.
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