Domaine technique
Laboratoires d’étalonnage
Calibration establishes the relation between values indicated by an instrument, or represented by a material measure, and the corresponding values realised by a measurement standard. The result is incomplete without a stated uncertainty.
ISO/IEC 17025
Calibration laboratories serve the chain of measurement on which testing, inspection and manufacturing depend. The work may concern dimensional, electrical, mechanical, thermal or other quantities. The common requirement is metrological traceability to a stated reference, through an unbroken chain of calibrations, each contributing to the measurement uncertainty.
ISO/IEC 17025 is also the standard ordinarily applied to calibration laboratories. In this use, particular weight falls on traceability, uncertainty, the suitability of the method and the competence of the people who perform and authorise the calibration.
A scope of calibration accreditation identifies the quantity, the instrument or artefact, the range and the calibration and measurement capability or an equivalent statement of performance. A broad phrase such as “electrical calibration” is not, by itself, a scope.
A calibration certificate reports the result for an identified item. It is not a statement that every future reading of that item will remain within the same limits. The user of the instrument remains responsible for its subsequent use and for any interval between calibrations, unless a published scheme says otherwise.
Points ordinairement examinés
- The quantity, range and method are defined.
- Traceability of measurement is demonstrated to a stated reference.
- Uncertainty is estimated and reported in a way a competent user can understand.
- Environmental conditions that affect the result are known and controlled.
- The certificate identifies the item calibrated and the conditions of the calibration.
Questions
Why is measurement uncertainty part of a calibration?
A calibration result is a measured relation. Without an estimate of uncertainty, a user cannot judge whether the result is close enough for the decision they need to make. Uncertainty is therefore part of the reported result, not an optional comment.
Does accreditation fix the interval between calibrations?
Accreditation attests the competence of the laboratory to calibrate as described in the scope. The interval at which an instrument is later submitted for calibration is a decision for the user, or for a scheme that regulates that user, unless a published requirement says otherwise. No interval is set by this website.