17. Calibration – Introduction & Metrological Traceability
Calibration is an act which establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties. Then refers to the relation from the indication before establishing a confirmed measurement result.
Calibration shall not be confused with adjustment of a measuring system, often mistakenly called self calibration nor with verification of calibration.
Also, 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 should be referenced before establish a finalized calibration statement.
The diagram below shows traceability chart regarding calibration laboratory references (where SI unit will always be on the top of the metrological traceability chain)
International Laboratory Accreditation Cooperation (ILAC) considers the elements for confirming metrological traceability to be
- An unbroken metrological traceability chain (see above) to an international measurement standard or a national measurement standard
- A documented measurement uncertainty
- A documented measurement procedure
- Accredited technical competence
- Metrological traceability to the SI
- Calibration intervals.
Standard metrological traceability realization
Lastly, in order to satisfy metrological traceability chain, there are 4 options to maintain the traceability chain.
- Option 1: Calibration service from National Measurement Institute (NMI) with CIPM Mutual Recognition Arrangement (MRA) scope, the calibration service shall include the calibration range and uncertainty.
- Option 2: Calibration service from certified calibration laboratory (with certification logo on the report). If the laboratory has the ILAC’s dimension measurement approval while providing measurement results with uncertainty can also be considered.
- Option 3:
- a. Calibration service from National Measurement Institute (NMI) but without CIPM MRA scope, the calibration service shall include the calibration range and uncertainty.
- b. Calibration service which complies with requirement, but does not include in ILAC agreement or ILAC MRA scope.
- Option 4:
- a. Use reference materials or certified reference materials for traceability references, although the laboratory shall be in compliance with reference material policy.
- b. Use official procedure and/or including a agreed standard specification with relative organizations. Laboratory shall provide relative document approval.