Metrology definitions and nomenclature

International vocabulary of metrology – Basic and general concepts and associated terms (VIM) 3rd edition

Metrological traceability property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty

metrological traceability chain traceability chain sequence of measurement standards and calibrations that is used to relate a measurement result to a reference

  • NOTE 1 A metrological traceability chain is defined through a calibration hierarchy.
  • NOTE 2 A metrological traceability chain is used to establish metrological traceability of a measurement result.
  • NOTE 3 A comparison between two measurement standards may be viewed as a calibration if the comparison is used to check and, if necessary, correct the quantity value and measurement uncertainty attributed to one of the measurement standards.

metrological traceability to a measurement unit metrological traceability to a unit metrological traceability where the reference is the definition of a measurement unit through its practical realization

NOTE The expression “traceability to the SI” means ‘metrological traceability to a measurement unit of the International System of Units’.

Verification - in terms of legal metrology - certification that the scale has been tested to ensure accuracy in terms of compliance. UUT has all the prescribed markings etc.

Accreditation is the process in which certification of competency, authority, or credibility is presented.

International measurement standard measurement standard recognized by signatories to an international agreement and intended to serve worldwide

Resolution smallest change in a quantity being measured that causes a perceptible change in the corresponding indication

ILAC International Laboratory Accreditation Cooperation

ISO International Organization for Standardization SANAS The South African National Accreditation System

NMISA National Metrology Institute of South Africa

BIPM The International Bureau of Weights and Measures

DTI The department of trade and industry

NLA National Metrology Association

The International System of Units (SI)

Accreditation vs traceability - Recently, the question of traceability and accreditation have been confusing to some.

Your system could be traceable to national and international standard, by being able to prove the unbroken chain to the international standard. correction factors can be taken into account when adjusting during calibration. Accreditation is when competency, credibility and authority is certified by a body that is recognized as the national accreditation body, in our case, this is SANAS.

By Means of the unbroken chain of traceability we are able to prove that the calibrations that we perform are linked to those of the national standard. Our measurement capability is outlined on our schedule of accreditation for each lab and clearly defined as our accredited scope.

For Force Calibrations we are not accredited by SANAS, but traceble to national and international standard through the unbroken chain of traceability to the National Metrology Institute of South Africa (NMISA)