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Metrological traceability

According to the International Vocabulary of Metrology – Basic and General Concepts and Associated Terms:

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

NOTES
  1. For this definition, a 'reference' can be a definition of a measurement unit through its practical realization, or a measurement procedure including the measurement unit for a non-ordinal quantity, or a measurement standard.

  2. Metrological traceability requires an established calibration hierarchy.

  3. Specification of the reference must include the time at which this reference was used in establishing the calibration hierarchy, along with any other relevant metrological information about the reference, such as when the first calibration in the calibration hierarchy was performed.

  4. For measurements with more than one input quantity in the measurement model, each of the input quantity values should itself be metrologically traceable and the calibration hierarchy involved may form a branched structure or a network. The effort involved in establishing metrological traceability for each input quantity value should be commensurate with its relative contribution to the measurement result.

  5. Metrological traceability of a measurement result does not ensure that the measurement uncertainty is adequate for a given purpose or that there is an absence of mistakes.

  6. 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.

  7. The BIPM, OIML, ILAC, and ISO endorse the following recommendations on metrological traceability:

    - in order to be able to rely on their international acceptability, calibrations should be performed;
    • in National Metrology Institutes which should normally be signatories to the CIPM MRA and have CMCs published in the relevant areas of the KCDB or
    • in laboratories accredited to ISO/IEC 17025 by accreditation bodies that are signatories to the ILAC Arrangement;
    - measurement uncertainty should follow the principles established in the GUM;
    - the results of the measurements made in accredited laboratories should be traceable to the SI;
    - NMIs providing metrological traceability for accredited laboratories should normally be signatories to the CIPM MRA and have CMCs published in the relevant areas of the KCDB;
    - within the OIML-CS, accreditation should be provided by bodies which are signatories to the ILAC Arrangement and the above policies on metrological traceability to the SI should be followed.

    The above principles should be used whenever there is a need to demonstrate metrological traceability for international acceptability (Joint BIPM, OIML, ILAC and ISO declaration on metrological traceability).

  8. The abbreviated term "traceability" is sometimes used to mean 'metrological traceability' as well as other concepts, such as 'sample traceability' or 'document traceability' or 'instrument traceability' or 'material traceability', where the history ("trace") of an item is meant. Therefore, the full term of "metrological traceability" is preferred if there is any risk of confusion.


Annotated VIM3:



Traceability to the SI through the BIPM
Subject area:
What is traceability?
BIPM policy on stating uncertainties
Summary charts: Technical services per Member State
Chemistry
Electricity
Ionizing Radiation
Mass
Time
Related articles:
Comparisons piloted by the BIPM
BIPM calibration and measurement services
BIPM work programme
Joint BIPM, OIML, ILAC and ISO declaration on metrological traceability