Omron CJ1W-FLN22, Руководство по эксплуатации, Страница: 271 / 277

245
Appendix G
International System of Units
The International System of Units (SI) consists of base units, supplementary units, and derived units. SI is
founded on the seven base units, which have been used historically and technically, and are used to define the
other quantities. The base units include the meter (m) to express length, kilogram (kg) to express mass, sec-
ond (s) to express time, Ampere (A) to express current, Kelvin (K) to express thermodynamic temperature,
mole (mol) for expressing amount of substance, and the candela (cd) for expressing luminous intensity.
SI Base Units and Definitions
Note The triple point of water is the point at which the water can coexist in equilibrium in all three phases, i.e.,
liquid, solid (ice), and gas (water vapor).
Units that are expressed as products or divisions of powers of basic units are called derived units, such as
square meters (m
2
) and meters per second (m/s). When many base units are used to express a derived unit,
resulting in a complicated expression, special names are sometimes used, e.g, Hertz (Hz) = 1/s is used to
express frequency and Newton (N) = kg·m/s
2
is used to express force. The Newton (N) is used to express the
amount of force required to accelerate a mass of one kilogram at a rate of one meter per second squared. Sim-
ilarly, the SI unit of pressure is the Pascal (Pa).
A new concept established supplementary units as a separate class from base units including the radian for
plane angles and the steradian for solid angles. These units can also be considered as derived units, but in
mathematics and other specific fields, they are used as if they were base units. Therefore, the General Confer-
ence on Weights and Measures designated these units as supplementary units to base units. Whether these
are designated as supplementary units or derived units is left to the discretion of each country. Japan’s Mea-
surement Law defines these units as derived units.
Quantity Unit name Unit
symbol
Definition
Unit of length Meter m The meter is the length of the path travelled by light in vacuum dur-
ing a time interval of 1/299 792 458 of a second.
Unit of mass Kilogram kg The kilogram is the unit of mass. It is equal to the mass of the inter-
national prototype of the kilogram.
Unit of time Second s The second is the duration of 9 192 631 770 periods of the radia-
tion corresponding to the transition between the two hyperfine lev-
els of the ground state of the cesium 133 atom.
Unit of electric current Ampere A The ampere is that constant current which, if maintained in two
straight parallel conductors of infinite length, of negligible circular
cross-section, and placed 1 meter apart in vacuum, would produce
between these conductors a force equal to 2 x 10
-7
newton per
meter of length.
Unit of thermodynamic
temperature Kelvin K The kelvin, unit of thermodynamic temperature, is the fraction
1/273.16 of the thermodynamic temperature of the triple point of
water (see note).
Unit of amount of matter Mole mol The mole is the amount of matter of a system which contains as
many elementary entities as there are atoms in 0.012 kilogram of
carbon 12. When the mole is used, the elementary entities must be
specified and may be atoms, molecules, ions, electrons, other par-
ticles, or specified groups of such particles.
Unit of luminous intensity Candela cd The candela is the luminous intensity, in a given direction, of a
source that emits monochromatic radiation of frequency 540 ×
10
12
hertz and that has a radiant intensity in that direction of 1/683
Watt per steradian.