Standards provide people and organizations a basis for mutual understanding, and these are utilized as tools to facilitate communication, measurement, commerce and manufacturing. Standards are generated by bringing together all groups involved such as manufacturers, consumers and regulators with reference to a particular material, product, process or service.
Standards are available all over and have an important role in the economy by facilitating business interactions between various entities. It helps people from different parts of the globe to compare results of their experiments on a reliable basis. Therefore it becomes all the more necessary to establish certain standards for length, mass, time, temperature, pressure, etc.
A Dimension defines a physical variable that is used to describe some aspect of a physical system. The fundamental value associated with any dimension is expressed as a Unit.
A Unit defines the measure of a dimension.
Fundamental Dimensions are: Length, Mass, Time, Temperature, Electrical Current, and Luminous Intensity.
Derived Dimension are: Acceleration, Area, Density, Velocity and Force.
A Primary Standard defines the value of a unit. It also provides the means to describe the unit with a unique number that can be understood anywhere in the world. The primary standard therefore assigns a unique value to the unit by definition.
Dimension Unit
Length Meter
Mass Kilogram
Time Second
The standard of length:
A meter is the base unit of length in the metric system and can easily be converted to other units in the metric system. In 1983 the meter was re-defined in terms of speed of light according to which one meter is the distance travelled by light in 1/299,792,458 of a second in air or vacuum.
1 foot = 0.30480060 meters. 1 inch = 0.02540005 meters.
The standard of Mass:
The gram was defined as a unit equal to the mass of one cubic centimeter of pure water at 4°C (the temperature at which water has maximum density).
The Planck constant is set as 6.62607015 × 10-34 m2 kg/s. And from this fixed value of the Planck constant, scientists derive the mass of a kilogram.
Now a gram is defined by the International Bureau of Weights and Measures, not in terms of grams, but by taking the fixed numerical value of the Planck constant.
1 Pound = 0.45359237 Kg.
The standard of time:
Nowadays, Cesium-133 is used to define one second due to the reliable frequency of microwave it emits. The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.
One second can also be defined as, the cesium frequency ∆ν, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9,192,631,770 when expressed in the unit Hz, which is equal to s−1. The wording of the definition was updated in 2019.
The standard of Temperature:
Temperature, similar to pressure or density, is called an intensive property—one that is independent of the quantity of matter being considered. Three temperature scales are generally in use today. Fahrenheit (°F), Celsius (°C) and Kelvin (K) scale. Kelvin scale is an absolute temperature scale that is recognized as the international standard for scientific temperature measurement.
Standard temperature is defined as zero degrees Celsius (0 C), which translates to 32 degrees, Fahrenheit (32 F) or 273.15 degrees kelvin (273.15 K).
Standard temperature and pressure, abbreviated STP, refers to nominal conditions in the atmosphere at sea level. Since 1982 the standard has been set at 273.15K (0ºC) and a pressure of 100kPa (1bar).
°C = K – 273.15 °F = °R – 459.67 °F = 1.8 °C + 32
Electrical Standards
All electrical units originate from the definition of the Ampere. An “amp”, short for ampere, is a unit of electrical current which is defined in terms of other base units by measuring the electromagnetic force between electrical conductors carrying electric current.
Ampere is the constant current which if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed one meter apart in vacuum, would produce between these conductors a force equal to 2 × 10−7newton per metre of length. The remaining electrical units, such as volts and ohms, can all be derived from the value of the ampere and the basic units of mass, length and time.
