Calibration & traceability
The basic concept behind calibration is that measuring equipment should be periodically compared against a standard of higher accuracy. If this reveals errors, then corrections can be evaluated and applied.
The outcome of a calibration is often a certificate. This reports errors or corrections for an instrument or artefact, and the uncertainties in these. During a calibration an instrument may also be adjusted so that its output is more accurate.
In order for a calibration to be considered traceable, there must be an unbroken chain of measurements, relating the calibration result to a national or international standard (such as the metre); and the calibration result must be accompanied by a statement of uncertainty. The uncertainty of the calibration is evaluated through careful uncertainty analysis.
Theoretically anyone who can read and follow directions of a calibration procedure can perform the work. To improve the quality of the calibration and have the results accepted by outside organisations it is desirable for the calibration and subsequent measurements to be traceable to the internationally defined SI measurement units as this ensures consistency between measurements made all around the world.
Un-calibrated instruments may be used where the un-calibrated accuracy is already sufficient or where calibration errors will cancel due to the procedure being used. These instruments might have a sticker saying ‘calibration not required’.
1 of 3