What is traceability?
The term “traceability” describes the property of the indicated measured value of a measuring instrument (or a material measure) to be compared, by one or more steps, with the national standard for the related quantity.
These steps must form an unbroken chain of comparison measurements. For this purpose a measuring instrument or a material measure is compared with a standard, whose metrological characteristics were determined by a comparison with a higher ranking standard. Thus, a calibration hierarchy is set up, respectively, a hierarchy of test equipment. Laboratories making comparisons within this chain have to prove their technical competence, for example being accredited as calibration laboratory.
The measured value of every measuring instrument is connected with a (measuring) uncertainty. In the calibration hierarchy test equipment of a higher level has a smaller measurement uncertainty than the equipment of the level beneath. Every further comparison, that is each additional level, leads to an increased measurement uncertainty. Calibration alone of a measuring instrument does not ensure that the measurement uncertainty is small enough for the intended use of the measuring instrument. At the top of the hierarchy of national test equipment stand the “national standards”: These are the basis for the determination of the values of all subordinated standards for the relating quantities in each country. The national standards on their part have to be compared internationally with other national standards in „key comparisons“ to be recognized according to the CIPM-MRA (Mutual Recognition Arrangement for national measurement standards and for calibration and measurement certificates issued by National Metrology Institutes).
Calibration and Traceability in Austria
In Austria the BEV is assigned with the task to maintain the national standards or to designate other institutes to maintain them and to take care for the comparisons to the international standards.
Furthermore, BEV’s Physico-Technical Testing Service (PTP) has to test and calibrate measuring instruments by comparison with the national standards. A calibration certificate of the Physico-Technical Testing Service of BEV proves the traceability of a measuring instrument to the national standard and herewith to the highest level in the Austrian calibration hierarchy. This applies accordingly, in case BEV has designated another laboratory to maintain specified national standards. Another possibility to ensure traceability of test equipment is the calibration by an accredited calibration laboratory of the Austrian Calibration Service (ÖKD Österreichischer Kalibrierdienst). The competent authority for calibration is the Ministry of Economy, Family and Youth. The calibration laboratories of the ÖKD are the hierarchy level preceding the Physico-Technical Testing Service. Calibration certificates of the accredited calibration laboratories of other countries are considered equivalent if their calibration laboratories are part of a European multilateral agreement.
Also verification certificates of BEV, the verification offices and the verification bodies attest the traceability of measurement results to national standards. Calibrations by non-accredited laboratories are considered as not traceable according to the ISO 9000 and EN ISO/IEC 17025 series of standards since no evidence of technical competence was provided.
Links on this subject:
International Vocabulary of Metrology – VIM