Metrology Concepts PDF

I. METROLOGY CONCEPTS: I.1 FUNDAMENTAL or SCIENTIFIC: Scientific and fundamental metrology concerns the establishment of quantity systems, unit systems, units of measurement, the development of new measurement methods, realization of measurement standards and the transfer of traceability from these...

I. METROLOGY CONCEPTS: I.1 FUNDAMENTAL or SCIENTIFIC: Scientific and fundamental metrology concerns the establishment of quantity systems, unit systems, units of measurement, the development of new measurement methods, realization of measurement standards and the transfer of traceability from these standards to users in society. The field of metrology encompasses a multitude of disciplines: mathematics, statistics, physics, quality, chemistry, and certainly, computer science. Essential to metrology is an understanding of the fundamental methods by which objects and phenomena are measured. Also critical, an understanding of how values are assigned to these measurements and the certainty of these values. I.2 APPLIED, TECHNICAL OR INDUSTRIAL: Applied, technical or industrial metrology concerns the application of measurement science to manufacturing and other processes and their use in society, ensuring the suitability of measuring instruments, their calibration and the quality control of measurements. Although the emphasis in this area of metrology is on the measurements themselves, traceability of the calibration of the measurement devices is necessary to ensure confidence in the measurements. Traceability of calculated values is very important to metrology. I.3 Legal metrology Legal metrology is the system of laws and regulations that regulate measuring instruments used for measurements that are subject to legal control such as trade and law enforcement. Legal metrology also ensures the accuracy and reliability of measurements that affect health, safety, or the transparency of commercial transactions. 1 II. International system of units II.1 The meter (m) The meter (m) is the base unit of length in the International System of Units (SI). It is defined as the distance that light travels in a vacuum during a time interval of 1/299,792,458 of a second. This definition links the meter directly to the speed of light, which is a fundamental constant of nature. The speed of light in vacuum is exactly 299,792,458 meters per second. The definition was adopted in 1983 by the General Conference on Weights and Measures (CGPM), making the meter dependent on the precise measurement of time rather than relying on a physical artifact. This change ensures the meter's definition is both stable and reproducible anywhere in the world, as the speed of light is the same universally and can be measured with great accuracy. II.2 The kilogram (kg) The kilogram (kg) is the base unit of mass in the International System of Units (SI). Since May 20, 2019, it has been defined using the Planck constant (h), a fundamental constant of nature, rather than a physical object. The kilogram is defined by fixing the value of the Planck constant to exactly 6.62607015 × 10⁻³⁴ joule.seconds (J·s). Through this equation, the kilogram is now linked to the second (SI unit of time) and the meter (SI unit of length), ensuring that the kilogram can be measured in terms of fundamental constants rather than a physical artifact. Before this redefinition, the kilogram was defined by a physical object known as the International Prototype of the Kilogram (IPK), a platinum-iridium cylinder kept in France. The transition to using the Planck constant makes the definition of the kilogram more stable, reliable, and universally applicable. 2 II.3 The second (s) The second (s) is the base unit of time in the International System of Units (SI). It is defined based on the properties of the cesium-133 atom. Specifically, the second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom. In simpler terms:  The second is the time it takes for a cesium-133 electron to oscillate 9,192,631,770 times between its energy states.  This definition, adopted in 1967, is based on atomic clocks, which use cesium atoms to keep incredibly precise time. Atomic clocks measure these vibrations, making the second one of the most accurately measured units in the SI system. This definition of the second ensures that it is consistent and reproducible anywhere in the world. II.4 The ampere (A) The ampere (A), often shortened to "amp," is the base unit of electric current in the International System of Units (SI). Since May 20, 2019, the ampere has been defined using the elementary charge (e), which is the electric charge carried by a single proton or the magnitude of the charge on a single electron. The ampere is defined by taking the fixed numerical value of the elementary charge e as 1.602176634 × 10⁻¹⁹ coulombs (C), where one ampere corresponds to the flow of one coulomb of charge per second. In simpler terms:  1 ampere is the amount of current that results when 1 coulomb of electric charge passes through a conductor in 1 second. 3 This new definition ties the ampere to a fundamental constant of nature (the elementary charge), making it more stable and precise compared to the older, physical-based definitions. The relation is: 1 A=1 C/s II.5 The kelvin (K) : The kelvin (K) is the base unit of thermodynamic temperature in the International System of Units (SI). Since May 20, 2019, it has been defined using the Boltzmann constant (k). The kelvin is defined by fixing the value of the Boltzmann constant to exactly 1.380649 × 10⁻²³ joules per kelvin (J/K). This links the kelvin to energy, temperature, and the fundamental physical properties of particles. In simpler terms:  The kelvin measures the absolute temperature scale, where 0 K (absolute zero) is the point at which the thermal motion of particles theoretically ceases.  A temperature increase of 1 kelvin corresponds to an increase in the thermal energy of particles by exactly 1.380649 × 10⁻²³ joules. This definition ensures that the kelvin is universally accurate and can be measured based on fundamental physical constants, rather than relying on a physical object or substance like water, as in earlier definitions. II.6 The mole (mol): The mole (mol) is the base unit of the amount of substance in the International System of Units (SI). Since May 20, 2019, the mole has been defined based on the Avogadro constant (NA). The mole is defined by fixing the value of the Avogadro constant to exactly 6.02214076 × 10²³ entities (such as atoms, molecules, ions, or other particles). 4 This means that 1 mole of any substance contains exactly 6.02214076 × 10²³ individual entities. In simpler terms:  The mole is a counting unit, similar to a dozen, but instead of 12 items, a mole represents 6.02214076 × 10²³ entities.  This number is called Avogadro's number and is constant for all substances, regardless of their nature. For example, 1 mole of carbon atoms contains 6.02214076 × 10²³ carbon atoms, and 1 mole of water molecules contains 6.02214076 × 10²³ water molecules. The mole allows scientists to easily express amounts of a chemical substance in terms of its elementary particles. II.7 The candela (cd) The candela (cd) is the base unit of luminous intensity in the International System of Units (SI). It is defined based on the luminous efficacy of monochromatic light. It is now defined as the luminous intensity, in a given direction, of a monochromatic source that radiates at a frequency of 540 x 10^12 hertz with a power of 1/683 watts per steradian. The frequency chosen is that to which the eye is most sensitive. This definition ties the candela to human visual perception, making it relevant for measuring light sources in terms of how bright they appear to the human eye. 5