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Today

Today. International System of Units Measurement process. International System of Units. Measurement result = ESTIMATE + UNCERTAINTY + U.M. Best assessment of the property being quantified. Spread indicator of the values reasonably associated with the property being quantified.

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Today

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  1. Today • International System of Units • Measurement process

  2. International System of Units Measurement result = ESTIMATE + UNCERTAINTY + U.M. Best assessment of the property being quantified Spread indicator of the values reasonably associated with the property being quantified Reference to a system of units enabling the comparison of different measurements

  3. International System of Units (SI) Homogeneous: secondary units can be derived by primary ones Coherent: conversion factors between units products shall be unary Uniform: an interval shall be evaluated from its extremes Complete: allows for a quantitative evaluation of every phenomenon Universal: shall not be specific to a place or a culture in particular Stable: standard prototypes shall not be time variant Accurate: shall allow for accurate measurements

  4. International System of Units (SI) • Started as a cause for the French revolution in 1789, has evolved becoming a continuously updated system now lawful worldwide, maintained by an international body. • Created in 1875 with the Meter Convention • Revised in 1960 with the General Conference • Adopted by Italy in 1978 • Adopted by European countries in 1996 only US, Liberia and Burma do not recognize the SI as the only system of measurement unit.

  5. International System of Units (SI) The International System of Units (SI) is the modern form of the metric system. The Bureau international des poids et mesures (BIPM) is tasked with ensuring worldwide uniformity of measurements and their traceability to the International System of Units (SI)

  6. International System of Units (SI) All unit of measurements are to be referred as multipliers of seven base reference prototypes*. * only the mass has an actual physical sample

  7. International System of Units (SI) A system of multiples and subdivisions is enacted, with no combination allowed and a base 10 power scale

  8. International System of Units (SI) HOW DO I COMPARE MY MEASUREMENT RESULT WITH THE INTERNATIONAL REFERENCE PROTOTYPE? The task of the BIPM is to ensure world-wide uniformity of measurements and their traceability to the International System of Units (SI) AN UNBROKEN CHAIN OF TRACEABILITY HAS BEEN ESTABLISHED LINKING EACH TRANSDUCER TO THE SI

  9. International System of Units (SI) BIPM prototypes (implementation of SI definitions) National Metrology Institute(INRIM in Italy) National standards Accredited calibration laboratory (SIT laboratories in Italy) company calibration centre Company reference standards Reference standards in-house calibration section Working factory standards company measuring equipment

  10. Norms and directives The Measuring Instruments Directive (2004/22/EC) is a directive by the European Union, which intends to create a common market for measuring instruments across the 27 countries of the EU.(Before uniforming meters standards there will be a 10 year transition period. National implementations of the new legislation are currently in the works) UNI ISO 9000:2000 and connected norms require measurement coherency, therefore adherence to the SI traceability chain. ISO 17025:2000 rules about the accreditation of laboratories of test and calibration of measurement devices EA ILAC-G2:1994 Traceability of Measurements

  11. Measurement process Measurement Informations model measurement result Output Data PhysicalPhenomenon input MeasurementSystem A measurement system quantifies a property of the physical phenomenon under scrutiny thanks to a mathematical model based on a physical relation. But every model is a simplification of reality itself, therefore inaccuracies need to be taken into account.

  12. Parameters which are not subject of measurement and which can interfere with the measurand or the transducer are to be taken into account! Measurement process Measurement Informations model measurement result Output Data PhysicalPhenomenon input MeasurementSystem InterferingParameters InfluencingParameters

  13. Uncertainty sources are also to be taken into account, adding up to the result Measurement process Model uncertainty Measurement Informations model measurement result phenomenon uncertainty Reading uncertainty Output Data PhysicalPhenomenon input MeasurementSystem Parameters uncertainty InterferingParameters InfluencingParameters Parameters uncertainty

  14. Accuracy vs Precision: a note Although commonly used as synonims precision and accuracy yield a very different meaning in metrology. When referring to a measurement process or transducer affected by a low degree of uncertainty ACCURACY is the correct term, while PRECISION has come to be replaced by the more specialist term REPEATABILITY to avoid confusion

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