测量基础

International System of Units (SI)

The principle behind the International System of Units is to provide the same values for measurements such as length, weight, and time no matter where in the world measurement is performed. The units used in this system are referred to as “SI units.” The system was established at the 1960 General Conferences on Weights and Measures (CGPM). The abbreviation “SI” stands for “Le Système International d'Unités.”

The International System of Units comprises the following three categories.

  • Base units
  • Supplementary units
  • 派生单位

Base Units

Amount Unit name Unit symbol Definition
Length Meter m The distance traveled by light in a vacuum in 1/299792458 second.
Weight Kilogram kg 这是重量的单位。国际原型千克的质量。
Time 第二 s The duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.
Current Ampere A 如果将恒定电流保持在两个无限长度的直接平行导体中，可忽略不计的圆形截面，并在真空中截至1 m，则将在这些导体之间产生等于2×10的力-7每米长度的纽顿。
Thermodynamic temperature Kelvin K 1/273.16 of the thermodynamic temperature of the triple point of water.
物质数量 Mole mol 在0.012千克碳12中包含与原子一样多的系统实质的物质量。
Luminosity Candela cd The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

补充单位

Amount Unit name Unit symbol Definition
平面角 Radian rad Radian describes the plane angle subtended by an arc of a circle with the same length as the radius of that circle corresponds to an angle of 1 radian.
Solid angle Steradian sr A steradian is a solid angle at the center of a sphere subtending a section on the surface equal in area to the square of the radius of the sphere.

派生单位

派生单位are a combination of base units and supplementary units and the mathematical symbols of multiplication and division.

Amount Unit name Unit symbol
Area Square meter m2
Volume 立方米 m3
Speed Meter per second m/s
Acceleration Meter per second squared m/s2
Wavenumber 倒数仪 m-1
Density Kilogram per cubic meter kg/m3
Current density 每平方米安培 A/m2
磁的field strength Ampere per meter A/m
Concentration (of amount of substance) Mole per cubic meter mol/m3
Specific volume 每公斤立方米 m3/公斤
Luminance Candela per square meter cd/m2

Some derived units are given unique names.

Amount Unit name Unit symbol Composition
Frequency Hertz Hz 1Hz=1s-1
Force Newton N 1N=1kg･m/s2
Pressure, stress Pascal Pa 1Pa=1N/m2
Energy, work, amount of heat Joule J 1J=1N･m
Power, radiant flux Watt W W=1J/s
Electric charge, amount of electricity Coulomb C 1C=1A･s
Electric potential/electric potential difference, voltage, electromotive force Volt V 1V=1J/C
Resistance (electrical) Ohm Ω 1Ω=1V/A
Conductance (electrical) Siemens S 1s =1Ω-1
磁的 Weber Wb 1Wb=1V･s
磁的flux density, magnetic induction Tesla T 1T=1Wb/m2
Inductance Henry H 1H=1Wb/A
Celsius temperature Degree Celsius ℃ 1t=T-To
光通量 流明 lm 1lm=1cd･sr
Illuminance 勒克斯 lx 1lx=1lm/m2

Reference Information

SI unit prefixes indicating integer powers of ten

Factor Prefix 象征 Factor Prefix 象征
1018 exa E 10-1 deci d
1015 peta P 10-2 centi c
1012 tera T 10-3 米利 m
109 giga G 10-6 micro µ
106 mega M 10-9 nano n
103 kilo k 10-12 pico p
102 公顷 h 10-15 femto f
10 Deka da 10-18 阿托 a

Non-SI units

Amount Unit name Unit symbol Definition
Time Minute min 1min=60s
Hour h 1h=60min
Day d 1d=24h
平面角 Degree ° 1°= (π/180) rad
Minute ′ 1′= (1/60) °
第二 ″ 1'=（1/60）''
Volume Liter l, L 1l=1dm3
Weight Metric ton t 1t=103kg

INDEX

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