Important concepts concerning calibration

Calibration
In measurement technology, calibration signifies the determination of the measurement error of the complete measuring instrument. No technical intervention takes place on the measuring instrument during calibration. On indicating measuring instruments, the measurement error is determined by calibration, comparing the value displayed with the correct value for the measurement in question.

Adjustment
A measuring instrument (or aggregate of mass) is set and adjusted in such a way that the measurement errors are as small as possible, or that the sum of the measurement errors does not exceed the error tolerances. Adjustment, therefore, requires an intervention that permanently changes the measuring instrument or aggregate of mass.

Official Verification
The official verification of a measuring instrument (or aggregate of mass) incorporates the tests to be carried out by the responsible verification authority, in accordance with the verification specifications, and the seal. By this testing, it is determined whether the measuring instrument submitted complies with the verification specifications, that is whether it satisfies the demands to be placed on it in terms of its qualities and technical measurement characteristics; and in particular it is verified that the sum of measurement errors does not exceed the error tolerances. By means of the seal it is certified that, at the time of testing, the measuring instrument satisfied these requirements and that, due to its qualities, it is to be expected that it will remain within the indicated tolerance range throughout the verification validity period, if operated in accordance with the rules of technology. Law regulates those measuring instruments that require compulsory verification and those that are exempt.

Traceability
A procedure to refer measurement results to national and international standards through an unbroken chain of calibrations.

National Standard
A Standard that, by national decree, is recognized in a country as the basis for determining the values of all other Standards of the measurement value in question.

Reference Standard
A Standard, generally of the highest available accuracy in a certain location or organization, from which measurements are derived.

Service Standard
A Standard that is routinely used to calibrate or test aggregates of mass, measuring instruments or reference materials.

Measurement Uncertainty
Parameter assigned to the measurement result that identifies the mean variation of the values that may reasonably be assigned to the measurement value.

Smallest Possible Measurement Uncertainty
The measurement uncertainty assigned to a laboratory as the smallest possible measurement uncertainty for each measurement value and determined measurement ranges, on the basis of the assessment of the measurement uncertainty budget and, if applicable, comparative measurements carried out.


For further information on the work of the PTB (Physikalisch-Technische Bundesanstalt) and the DAkkS (Deutsche Akkreditierungsstelle) see also www.ptb.de or www.dakks.de.