Realisation (metrology)
In
- Realisation of a measurement unit from its definition.
- Reproduction of measurement standards.
- Adopting a particular artefact as a standard.
The International Bureau of Weights and Measures maintains the techniques for realisation of the base units in the International System of Units (SI).[2]
Overview
The Oxford English Dictionary defines the word "realise" (also spelt "realize") as "to convert (something imagined, planned, etc.) into real existence or fact."
Techniques
Time
The realisation of time has gone through three phases. During both the first and second phases, man used
Direct measurement of solar time
- Sundials and astrolabes
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.
- natural units - barleycorn, feet
- regal units - measures held by ruler
- using speed of light
An example of a modern realisation is the realisation of the
Volume
- Jugs etc. in ancient times
- Not a base unit in SI
Mass
- Grains
- Artefacts held by governments (e.g. the IPK)
- Kibble balance and Avogadro experiment
Electric charge
Temperature
Photometry
- Sensitivity of the eye
Amount of substance
References
- ^ a b "Realise". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
- ^ International Bureau of Weights and Measures (2012). "Practical realization of the definitions of some important units". p. 46. Retrieved 23 April 2013.
- ^ 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.
- . Retrieved 6 December 2013.