CE738_Lecture_02_Standards_5281fc4b-c232-4ff0-bd9b-bb26398a60d5.pdf

CE 738A : Hydrometry Standards  Recap Measurement : Process of associating numbers with physical quantities and phenomenon – Comparison with standards Metrology and Hydrometry Importance of measurements Four scales / levels...

CE 738A : Hydrometry Standards  Recap Measurement : Process of associating numbers with physical quantities and phenomenon – Comparison with standards Metrology and Hydrometry Importance of measurements Four scales / levels of measurements: Nominal, Ordinal, Interval and Ratio  Standards for Measurements An established reference point or unit against which other measurements can be compared or calibrated A quantity with stated value and associated measurement uncertainty, used as a reference Desired characteristics: o Definability o Reproducibility o Accessibility o Stability o Universality o Comparability  Standards for Measurements Which standard to follow and who decides the standard? French Revolution (1789) and Metric system (1799) Treaty of the Metre or Metre Convention (1875) – 17 nations Conference on Weights and Measures (Conférence générale des poids et mesures – CGPM) International Committee for Weights and Measures (Comité international des poids et mesures or CIPM) International Bureau of Weights and Measures (Bureau international des poids et mesures, BIPM) National standards laboratories International System of Units (Le Système international d'unités, SI - 1960) Source: xDevs.com  National Standards Laboratory - India National Physical Laboratory of India (Jan 4th, 1947)  Standard for Length - metre What is a metre? One ten-millionth of the distance from the equator to the North Pole (1791) A prototype metre bar (1799 and1889) Metre Bar No. 57, made by BIPM for India 1650763.73 wavelengths of an emission line of the krypton-86 atom in vacuum (1960) Length of the path travelled by light in vacuum in 1/299 792 458 of a second (1983 and 2002)  Standard for Time - second What is a second? Egyptian and Mesopotamian civilizations 1/86,400 of the mean solar day 1/31556925.9747 of the tropical year for 1900 (1960) Duration of 9 192 631 770 periods of the radiation of the caesium 133 atom (1967 & 2019)  Standard for Weight - kilogram What is a kilogram? The mass of 1 dm3 of water at the temperature of its maximum density, i.e. at approximately 4 °C (1799) The mass of International Prototype of the Kilogram (1889) Defined in terms of the Planck constant, the speed of light and radiation frequency of 133Cs (2018)  SI : Base Units 7 base units SI : Derived Units SI : Prefixes Non-SI units