scholarly journals How to Define the Units of the Revised SI Starting from Seven Constants with Fixed Numerical Values

2018 ◽  
Vol 123 ◽  
Author(s):  
Richard S. Davis
Keyword(s):  
International System ◽  
International System Of Units ◽  
System Of Units ◽  
Revised Si ◽  
Base Units

As part of a revision to the International System of Units (SI) approved in2018 and to take effect in May 2019, the seven base units will be defined bygiving fixed numerical values to seven defining constants. This article shows howthe definitions of all seven base units can be derived efficiently from thedefining constants, with the result appearing as a table. The table’s form makesevident a number of connections between the defining constants and the base units.Appendices show how the same methodology could have been used to define the samebase units in the present SI, as well as the mathematics that underpins themethodology. Since the base units are now defined in terms of constants, then allunits in the SI are now defined in terms of those constants.

scholarly journals Quantity Calculus, Fundamental Constants, and SI Units

2018 ◽  
Vol 123 ◽  
Author(s):  
Barry N. Taylor
Keyword(s):  
International System ◽  
Fundamental Constants ◽  
Weights And Measures ◽  
International System Of Units ◽  
Si Units ◽  
System Of Units ◽  
Revised Si ◽  
Base Units ◽  
New Si

A revised International System of Units (SI) is expected to be established by the 26th General Conference on Weights and Measures when it convenes in November 2018 and to be put into practice starting on 20 May 2019, World Metrology Day. In consequence, the article published in this journal in 2011, “The Current SI Seen from the Perspective of the Proposed New SI,” is updated in this paper, which provides an opportunity to again demonstrate the usefulness of the quantity calculus in dealing with quantities and units. The quantity calculus and the seven defining constants of the current and revised SI are reviewed, and expressions for the seven current and revised SI base units are given. Relationships between the magnitudes of revised and current SI units and expressions for the numerical values of current SI defining constants expressed in revised SI units are also obtained using the quantity calculus.

scholarly journals Adapting the International System of Units to the twenty-first century

2011 ◽  
Vol 369 (1953) ◽  
pp. 3907-3924 ◽  
Author(s):  
Ian M. Mills ◽  
Peter J. Mohr ◽  
Terry J. Quinn ◽  
Barry N. Taylor ◽  
Edwin R. Williams
Keyword(s):  
International System ◽  
International Committee ◽  
First Century ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
Elementary Charge ◽  
Magnetic Constant ◽  
Base Units ◽  
New Si

We review the proposal of the International Committee for Weights and Measures (Comité International des Poids et Mesures, CIPM), currently being considered by the General Conference on Weights and Measures (Conférences Générales des Poids et Mesures, CGPM), to revise the International System of Units (Le Système International d'Unitès, SI). The proposal includes new definitions for four of the seven base units of the SI, and a new form of words to present the definitions of all the units. The objective of the proposed changes is to adopt definitions referenced to constants of nature, taken in the widest sense, so that the definitions may be based on what are believed to be true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and mole are linked to exact numerical values of the mass of the international prototype of the kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature of water and the molar mass of carbon-12, respectively, in the new SI these units are linked to exact numerical values of the Planck constant, the elementary charge, the Boltzmann constant and the Avogadro constant, respectively. The new wording used expresses the definitions in a simple and unambiguous manner without the need for the distinction between base and derived units. The importance of relations among the fundamental constants to the definitions, and the importance of establishing a mise en pratique for the realization of each definition, are also discussed.

scholarly journals Changing the status of mmHg

2019 ◽  
Vol 25 (1) ◽  
pp. 81-82 ◽  
Author(s):  
Dominik Pražák ◽  
Václav Sedlák ◽  
Ekrem Sınır ◽  
František Pluháček
Keyword(s):  
International System ◽  
Medical Doctor ◽  
Public Attention ◽  
International System Of Units ◽  
System Of Units ◽  
The Status ◽  
User Groups ◽  
The Media ◽  
Base Units

AbstractThe new International System of Units (SI) came into force this May, and while the media and public attention are focused on the changes in the base units, there are also other changes introduced. One of them is the abolition of millimetre of mercury (mmHg). This simplifies the SI but also can cause problems to the patients which are extremely conservative user groups (although this unit is still supported by some other authoritative documents). Hence, it is necessary to increase awareness of both the medical doctor and the patients.

scholarly journals SI-2019 and prospects for improving the accuracy of electrical measurements

2021 ◽  
pp. 35-39
Author(s):  
Iurii Pavlenko ◽  
Alexander Kolbasin ◽  
Olena Vаsileva
Keyword(s):  
International System ◽  
Fundamental Constants ◽  
Electrical Measurements ◽  
International System Of Units ◽  
Si Units ◽  
Accuracy Of Measurements ◽  
System Of Units ◽  
Measurement Units ◽  
Physical Laws ◽  
Base Units

Increasing requirements for the accuracy of measurements have led to the need to revise the existing International System of Units (SI). The important element of the SI-2019 reform is “the establishment of the SI base units through seven defining constants, the numerical values of which are fixed”. The approach to the establishment of the measurement units has fundamentally changed. If earlier a definition was given of how the unit is realized, now only the exact numerical values of the fundamental constants are fixed, and their values are expressed in the corresponding SI units. Measurement units are determined on the basis of known physical laws, which include certain fundamental constants. The article analyzes the changes in SI-2019 related to electrical measurements, and also discusses the prospects for the development of accurate electrical measurements.

Dimensions of plane and solid angles and their units in the International System of Units (SI)

2020 ◽  
pp. 26-32
Author(s):  
M. I. Kalinin ◽  
L. K. Isaev ◽  
F. V. Bulygin
Keyword(s):  
Solid Angle ◽  
International System ◽  
International Committee ◽  
Plane Angle ◽  
Arc Length ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
In Series ◽  
Solid Angles

The situation that has developed in the International System of Units (SI) as a result of adopting the recommendation of the International Committee of Weights and Measures (CIPM) in 1980, which proposed to consider plane and solid angles as dimensionless derived quantities, is analyzed. It is shown that the basis for such a solution was a misunderstanding of the mathematical formula relating the arc length of a circle with its radius and corresponding central angle, as well as of the expansions of trigonometric functions in series. From the analysis presented in the article, it follows that a plane angle does not depend on any of the SI quantities and should be assigned to the base quantities, and its unit, the radian, should be added to the base SI units. A solid angle, in this case, turns out to be a derived quantity of a plane angle. Its unit, the steradian, is a coherent derived unit equal to the square radian.

scholarly journals A quantum ampere

2020 ◽  
Vol 87 (4) ◽  
pp. 258-265
Author(s):  
Luca Callegaro
Keyword(s):  
Electric Current ◽  
International System ◽  
International System Of Units ◽  
System Of Units ◽  
Elementary Charge ◽  
User Friendly

AbstractThe revision of the International System of Units (SI), implemented since 20 May 2019, has redefined the unit of electric current, the ampere ( A), linking it to a fixed value of the elementary charge. This paper discusses the new definition and the realisation of the electrical units by quantum electrical metrology standards, which every year become more and more accessible, reliable and user friendly.

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