White paper Why metrology matters
Simply put, metrology is the science of measure- International System of Units—SI ment and its application. It includes all theoretical In the United States of America, there are two and practical aspects of measurement, at any measurement systems in use: the U. S. Custom- level of uncertainty in any field of application. We ary System and the International System of Units, all use metrology dozens of times a week. If you known as the SI. The U.S. Customary System is have measured cream in your coffee or used an used in mainly commercial and personal activities alarm clock or pumped gas into your car, you ap- (inch, ounce, cup, etc.), while the SI is used in sci- plied metrology principles. Metrology deals with ence, medicine, industry sectors and some areas making accurate, repeatable measurements with of government. The SI is used by most countries a known level of uncertainty. exclusively; indeed it is the foundation of our History worldwide measurement system. The SI has seven base units as defined in the chart below. The measurements we take for granted today started as far back as 3000 BC in ancient Egypt with the use of the Royal Cubit which was the Base quantity SI base unit SI symbol Length Meter m length of the pharaoh’s arm from bent elbow to Mass Kilogram kg the tip of his middle finger. A master cubit was Time Second s crafted in granite and subsequent tools cre- Electric current Ampere A ated from the master cubit. As you can imagine, Thermodynamic temperature Kelvin K this wasn’t a sustainable measurement system. Amount of substance Mole mol Which pharaoh created the tool? Did succeeding Luminous intensity Candela cd pharaoh’s change the measurement unit to match their forearms? Did measurement confusion reign As an evolving system, the SI is updated and with each new pharaoh? improved as technology permits. For example, up until 1960, the base unit meter was based on a Fast forward a couple of thousand years when platinum-iridium prototype rod cast in 1889. Now, seventeen nations met in Paris in 1875 for the it is defined as a constant of nature—the distance Metre Convention (Convention du Mètre), to light travels in a vacuum during one period of establish a permanent organizational structure radiation, corresponding to the transition be- to act in common accord on all matters relat- tween two hyperfine levels of the ground state of ing to units of measurement. The Treaty of 1875 the cesium-133 atom. This defines the meter as has some 58 government signatories today. The the distance light travels in 1/299 792 458th of a treaty established three essential organizations: second. CGPM—General Conference on Weights and Effective May 20, 2019, the CGPM passed a Measures: The main decision-making body com- resolution redefining the kilogram based on a posed of member states constant of nature, the Planck constant, which would remove the risk of referencing a single, CIPM—International Committee for Weights and delicate artifact. Measures: Advises the CGPM on technical mat- ters of metrology
BIPM—International Bureau of Weights and Measures: Operates under the CGPM and CIPM and maintains the SI—International System of Units Redefining the kilogram will have repercussions- measurement instruments. especially for derived units. Derived units are Applied, Technical or, Industrial metrology quantities we are all familiar with, use daily and, includes traceability to the SI to ensure confi- are made up of products and powers of SI units. dence in measurement. Measurement can be de- Looking at the last column in the chart below, one fined as the process of experimentally obtaining can appreciate how redefining the kilogram, or one or more quantity values that can reasonably any base unit for that matter, can have a ripple be attributed to another quantity. effect throughout the SI. Legal Metrology involves the technical and Derived quantity Name Symbol SI base unit administrative procedures established by law, Area Square meter m2 m2 by public authorities to guarantee the quality of Volume Cubic meter m3 m3 measurements. Statutory requirements come Velocity Meter per second m/s m · s-1 from: the need to protect health, public safety, Force Newton N m · kg · s-2 environmental concerns, enabling taxation, con- Pressure Pascal Pa m-1 · kg · s-2 sumer protection, fair trade and more. Electric resistance Ohm Ω m2 · kg · s-3 · A-2 Capacitance Farad F m2 · kg-1 · s4 · A2 Legal Metrology ensures that we maintain our EMF Volt V m2 · kg · s-3 · A-1 measurement systems. Manufacturers, hospitals Temperature Degree celsuis °C K and, medical facilities have a legal responsibil- ity to keep records to show that medical devices Why does metrology matter? and the test instruments used to calibrate them Metrology is born out of physics and is ubiqui- are accurate and traceable. There are number of tous; it underpins most other technologies to organizations that provide international support some degree. It has three primary and critical for legal metrology, including: subfields: • International Organization of Legal Metrology Scientific or Fundamental Metrology establishes (OIML) quantity systems and the development of new • European Cooperation in Legal Metrology measurement methods and standards. Handled (WELMEC) by the BIPM internationally, Fluke Biomedical, • Asia-Pacific Legal Metrology Forum (APLMF) RaySafe and its distributors also participate through committees established by the national measurement institutes (NMI) Why measurements matter Imagine the chaos if every country and state had The BIPM has several vital committees that a different measurement system. Our economy provide guidance documents for the metrology and our everyday lives rely on consistency and community and have a mission to harmonize trust in the goods we buy and sell. We also ex- worldwide metrological practices and dissemi- pect that the products we use must be capable nate scientific and technological knowledge of operating within their stated minimum perfor- mance standards. • Joint Committee for Guides in Metrology (JCGM) Interoperability is also crucial. In a global econ- – JCGM 100:2008 omy, we need measurements on components (GUM—Evaluation of Measurement Data) manufactured overseas to be as accurate as the – JCGM 200:2012 measurements we perform in the US. The reli- (VIM—International Vocabulary of Metrology) able quality of parts means we can trust that the • Joint Committee for Traceability in Laboratory individual pieces will fit together, physically and Medicine (JCTLM) electrically without effort. Adhering to standards and producing products Applied, Technical or, Industrial metrology is the that match measurement guidelines is a require- application of measurement science to manufac- ment for any manufacturer today. Metrology ac- turing and other industrial processes. It ensures curacy and traceability permeate every aspect of the suitability, calibration and, quality control of the industrial products built.
The pharaohs’ pyramids remind us that metrology has been understood for centuries and it
2 Fluke Biomedical Clinical importance of anesthesia machine testing: A review continues to evolve as devices, calibration and measurements become more and more sophisti- cated.
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