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{{Use British English|date=December 2013}} {{Use British English|date=December 2013}}


In ], the '''realisation''' of a ] is the conversion of its definition into reality.<ref name=OED>{{OED|Realise}}</ref> The ] identifies three distinct methods of realisation: In ], the '''realisation''' of a ] is the conversion of its definition into reality.<ref name=OED>{{OED|Realise}}</ref>
#Realisation of a measurement unit from its definition.
#Reproduction of ].
#Adopting a particular artefact as a standard.


An example of the concept of realisation, is the unit of length, the ]. The metre was originally defined in 1791 as one ten-millionth of the distance from the ] to the ] along a ]. To actually measure a length, this definition must be converted into a physical tool, which can be used to complete the measurement. The meter stick is the realisation of the meter.
The ] maintains the techniques for realisation of the ] in the ] (SI).<ref>{{cite web
|url = http://www.bipm.org/en/si/si_brochure/appendix2/
|title = Practical realization of the definitions of some important units
|author = ]
|page = 46
|year = 2012
|access-date = 23 April 2013}}</ref>


The ] maintains the techniques for realisation of the ] in the ] (SI), all seven of which are defined in terms of natural physical constants, rather than human artefacts such as the ].<ref name=SI-statement>
==Overview==
{{cite web
The Oxford English Dictionary defines the word "realise" (also spelt "realize") as "to convert (something imagined, planned, etc.) into real existence or fact."<ref name=OED/> The ] identifies three distinct ways in which this is done - the first being the realisation of a measurement unit from its definition, the second the reproduction of measurement standards and the third the process of actually adopting a particular artefact as a standard.<ref>{{cite book
|url = https://www.bipm.org/utils/common/pdf/SI-statement.pdf
|title = International vocabulary of metrology&mdash;Basic and general concepts and associated terms (VIM)
|title = BIPM statement: Information for users about the proposed revision of the SI
|edition = 3rd
|access-date = 5 May 2018
|year = 2012
|archive-url = https://web.archive.org/web/20180121160000/https://www.bipm.org/utils/common/pdf/SI-statement.pdf
|publisher = ] on behalf of the Joint Committee for Guides in Metrology.
|archive-date = 21 January 2018
|url = http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2012.pdf
|url-status = live
|accessdate = 26 April 2013}}</ref>
|df = dmy-all
<!--The term “realization” is used here in the most
}}
general meaning. It denotes three procedures of
</ref><ref>
“realization”. The first one consists in the physical
{{cite web
realization of the measurement unit from its definition
|url = http://www.bipm.org/en/committees/cipm/meeting/105.html
and is realization sensu stricto. The second, termed
|title = Decision CIPM/105-13 (October 2016)
“reproduction”, consists not in realizing the measurement
|access-date = 31 August 2017
unit from its definition but in setting up a highly
|archive-url = https://web.archive.org/web/20170824095943/http://www.bipm.org/en/committees/cipm/meeting/105.html
reproducible measurement standard based on a physical
|archive-date = 24 August 2017
phenomenon, as it happens, e.g. in case of use of
|url-status = live
frequency-stabilized lasers to establish a measurement
|df = dmy-all
standard for the metre, of the Josephson effect for the
}}</ref> Following the ] all fundamental units of metrology are now defined in terms of natural physical constants, rather than human artefacts. The realization of these units is also defined by a published "Practice for the Realization of the Unit", for each unit. This is a detailed set of technical instructions for the construction of a device that will produce a practical realization of each unit. Any competent person, who follows these instructions can realize any unit.
volt or of the quantum Hall effect for the ohm. The third
procedure consists in adopting a material measure as a
measurement standard. It occurs in the case of the measurement
standard of 1 kg. - VIM Page 46-->
==Techniques==


For example, the metre is defined as 1/{{val|299792458}} of the distance light travels in one second. The Practice for the Realization of the Metre describes how to build an apparatus to determine this distance. Using this aparatus it is possible to construct a ] which is the realization of the metre.<ref name="NewScientist">{{cite journal | last=Wilkie | first=Tom | title=Time to remeasure the metre | url=https://books.google.com/books?id=pKU5MXqo4UYC&pg=PA258 | journal=] | date=27 October 1983 | issue=27 October 1983 | pages=258–263}}</ref>
===Time===
The realisation of time has gone through three phases. During both the first and second phases, man used ]&mdash;during the first phase, realisation of time was by observing the ] using such devices as the ] or ]. During the second phase actual ] such as ]es or ]s were used. If the user needed to know ] rather than elapsed time, clocks were ] with ]. The third phase made use of clocks that were sufficiently accurate that they could measure variations in the earth's rotation&mdash;such clocks taking over from the rotation of the earth as the prime measure of time. <!--Early man measured two aspects of time - seasons and time of day. The seasons were measured by keeping a record on how many days had passed since an astronomical phenomena as is believed to have happened at ]. Time of day was measured using . One of the earliest time-measuring devices was the introduced into Europe by Luitprand, a monk at the cathedral in ], France in the 8th century AD.-->


The ] identifies three distinct methods of realisation:
====Direct measurement of solar time====
# Realisation of a measurement unit from its definition.
*]s and ]s
# Reproduction of ].
# Adopting a particular artefact as a standard.<ref>
{{cite web
|url = http://www.bipm.org/en/si/si_brochure/appendix2/
|title = Practical realization of the definitions of some important units
|author = ]
|page = 46
|year = 2012
|access-date = 23 April 2013
}}</ref>


====Timekeepers==== == Overview ==
The Oxford English Dictionary defines the word "realise" (also spelt "realize") as "to convert (something imagined, planned, etc.) into real existence or fact".<ref name=OED/> The ] identifies three distinct ways in which this is done – the first being the realisation of a measurement unit from its definition, the second the reproduction of measurement standards and the third the process of actually adopting a particular artefact as a standard.<ref>
*Accuracy of clocks
{{cite book
|title = International vocabulary of metrology&mdash;Basic and general concepts and associated terms (VIM)
|edition = 3rd
|year = 2012
|publisher = ] on behalf of the Joint Committee for Guides in Metrology.
|url = http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2012.pdf
|accessdate = 26 April 2013
}}</ref>
<!-- The term "realization" is used here in the most general meaning. It denotes three procedures of "realization". The first one consists in the physical realization of the measurement unit from its definition
and is realization sensu stricto. The second, termed “reproduction”, consists not in realizing the measurement unit from its definition but in setting up a highly reproducible measurement standard based on a physical phenomenon, as it happens, e.g. in case of use of frequency-stabilized lasers to establish a measurement standard for the metre, of the Josephson effect for the volt or of the quantum Hall effect for the ohm. The third procedure consists in adopting a material measure as a measurement standard. It occurs in the case of the measurement standard of 1 kg. – VIM Page 46 -->


====Time generators==== == Techniques==
*Radiation frequency & SI


===Length=== === Time ===
The realisation of time has gone through three phases. During both the first and second phases, man used ] – during the first phase, realisation of time was by observing the ] using such devices as the ] or ]. During the second phase actual ] such as ]es or ]s were used. If the user needed to know ] rather than elapsed time, clocks were ] with ]. The third phase made use of clocks that were sufficiently accurate that they could measure variations in the Earth's rotation – such clocks taking over from the rotation of the earth as the prime measure of time. <!-- Early man measured two aspects of time – seasons and time of day. The seasons were measured by keeping a record on how many days had passed since an astronomical phenomena as is believed to have happened at ]. Time of day was measured using . One of the earliest time-measuring devices was the introduced into Europe by Luitprand, a monk at the cathedral in ], France in the 8th century AD. -->
Units of length, along with mass (or weight) and time, are one of the earliest quantities that was measured by man. Historically two distinct approaches were used - one was to use a naturally occurring phenomenon such as a particular seed or part of the human body, the other was to use a standard length that was held by a community leader.
*] - barleycorn, feet
*Regal units - measures held by ruler
*Using speed of light
An example of a modern realisation is the realisation of the ] in terms of optical frequency standards.<ref name=Quinn2003>{{cite journal|last=Quinn|first=T. J.|title=Practical realisation of the definition of the metre, including recommended radiations of other optical frequency standards (2001)|journal=Metrologia|year=2003|volume=40|pages=103–133|url=http://www.bipm.org/utils/common/pdf/mise_en_pratique_2001.pdf|accessdate=6 December 2013|doi=10.1088/0026-1394/40/2/316|bibcode=2003Metro..40..103Q}}</ref>


==== Direct measurement of solar time ====
===Volume===
* ]s and ]s
*Jugs etc. in ancient times
*Not a base unit in SI


===Mass=== ==== Timekeepers ====
* Accuracy of clocks
*grains
*artefacts held by governments
*Kibble balance & Avogadro experiment


===Electric charge=== ==== Time generators ====
* Radiation frequency and SI
*Silver Nitrate deposits
*Force between conductors
*charge on the electron


===Temperature=== === Length ===
Units of length, along with mass (or weight) and time, are one of the earliest quantities that was measured by man. Historically two distinct approaches were used – one was to use a naturally occurring phenomenon such as a particular seed or part of the human body, the other was to use a standard length that was held by a community leader.
*freezing & boiling water
* ] – ], ]
*non-linearity etc.
* Regal units – measures held by ruler
*]
* Using ]
An example of a modern realisation is the realisation of the ] in terms of optical frequency standards.<ref name=Quinn2003>{{cite journal|last=Quinn|first=T. J.|title=Practical realisation of the definition of the metre, including recommended radiations of other optical frequency standards (2001)|journal=Metrologia|year=2003|volume=40|pages=103–133|url=http://www.bipm.org/utils/common/pdf/mise_en_pratique_2001.pdf|accessdate=6 December 2013|doi=10.1088/0026-1394/40/2/316|bibcode=2003Metro..40..103Q}}</ref>


===Photometry=== === Volume ===
* Jugs etc. in ancient times
*sensitivity of the eye
* Not a base unit in SI


===Amount of substance=== === Mass ===
* Grains
*development of the mole
* Artefacts held by governments (e.g. the ])
* ] and Avogadro experiment


=== Electric charge ===
==References==
* ] deposits
{{Reflist}}
* ]
* ]


=== Temperature ===
{{systems of measurement}}
* ] & ] water
* Non-linearity etc.
* ]

=== Photometry ===
* Sensitivity of the eye

=== Amount of substance ===
* ]

== References ==
{{reflist}}

{{Systems of measurement}}
{{systems}} {{systems}}


Latest revision as of 03:48, 10 December 2024

Conversion of the definition of a unit of measure into reality

In metrology, the realisation of a unit of measure is the conversion of its definition into reality.

An example of the concept of realisation, is the unit of length, the meter. The metre was originally defined in 1791 as one ten-millionth of the distance from the equator to the North Pole along a great circle. To actually measure a length, this definition must be converted into a physical tool, which can be used to complete the measurement. The meter stick is the realisation of the meter.

The International Bureau of Weights and Measures maintains the techniques for realisation of the base units in the International System of Units (SI), all seven of which are defined in terms of natural physical constants, rather than human artefacts such as the standard kilogram. Following the 2019 revision of the SI all fundamental units of metrology are now defined in terms of natural physical constants, rather than human artefacts. The realization of these units is also defined by a published "Practice for the Realization of the Unit", for each unit. This is a detailed set of technical instructions for the construction of a device that will produce a practical realization of each unit. Any competent person, who follows these instructions can realize any unit.

For example, the metre is defined as 1/299792458 of the distance light travels in one second. The Practice for the Realization of the Metre describes how to build an apparatus to determine this distance. Using this aparatus it is possible to construct a metre stick which is the realization of the metre.

The International vocabulary of metrology identifies three distinct methods of realisation:

  1. Realisation of a measurement unit from its definition.
  2. Reproduction of measurement standards.
  3. Adopting a particular artefact as a standard.

Overview

The Oxford English Dictionary defines the word "realise" (also spelt "realize") as "to convert (something imagined, planned, etc.) into real existence or fact". The International vocabulary of metrology identifies three distinct ways in which this is done – the first being the realisation of a measurement unit from its definition, the second the reproduction of measurement standards and the third the process of actually adopting a particular artefact as a standard.

Techniques

Time

The realisation of time has gone through three phases. During both the first and second phases, man used solar time – during the first phase, realisation of time was by observing the Earth's rotation using such devices as the sundial or astrolabe. During the second phase actual timing devices such as hourglasses or clocks were used. If the user needed to know time-of-day rather than elapsed time, clocks were synchronised with astronomical time. The third phase made use of clocks that were sufficiently accurate that they could measure variations in the Earth's rotation – such clocks taking over from the rotation of the earth as the prime measure of time.

Direct measurement of solar time

Timekeepers

  • Accuracy of clocks

Time generators

  • Radiation frequency and SI

Length

Units of length, along with mass (or weight) and time, are one of the earliest quantities that was measured by man. Historically two distinct approaches were used – one was to use a naturally occurring phenomenon such as a particular seed or part of the human body, the other was to use a standard length that was held by a community leader.

An example of a modern realisation is the realisation of the metre in terms of optical frequency standards.

Volume

  • Jugs etc. in ancient times
  • Not a base unit in SI

Mass

Electric charge

Temperature

Photometry

  • Sensitivity of the eye

Amount of substance

References

  1. ^ "Realise". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  2. "BIPM statement: Information for users about the proposed revision of the SI" (PDF). Archived (PDF) from the original on 21 January 2018. Retrieved 5 May 2018.
  3. "Decision CIPM/105-13 (October 2016)". Archived from the original on 24 August 2017. Retrieved 31 August 2017.
  4. Wilkie, Tom (27 October 1983). "Time to remeasure the metre". New Scientist (27 October 1983): 258–263.
  5. International Bureau of Weights and Measures (2012). "Practical realization of the definitions of some important units". p. 46. Retrieved 23 April 2013.
  6. International vocabulary of metrology—Basic and general concepts and associated terms (VIM) (PDF) (3rd ed.). International Bureau of Weights and Measures on behalf of the Joint Committee for Guides in Metrology. 2012. Retrieved 26 April 2013.
  7. Quinn, T. J. (2003). "Practical realisation of the definition of the metre, including recommended radiations of other optical frequency standards (2001)" (PDF). Metrologia. 40: 103–133. Bibcode:2003Metro..40..103Q. doi:10.1088/0026-1394/40/2/316. Retrieved 6 December 2013.
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