7
Traceable Calibration
An instrument has a traceable calibration if the measurement instrument used for
performing the calibration is traceable to national or international institutes / standards
through an unbroken chain of comparisons all having stated uncertainties.
Accredited Calibration
An instrument has an accredited calibration if the calibration is performed by an
approved accredited calibration laboratory. Approval for accredited calibration is granted
by a national metrology institute after careful evaluation and inspection of the laboratory
in question.
Secondary Calibration
The secondary calibration has the next highest metrological quality in an area. The cali-
bration value is assigned by comparison with a primary standard of the same quantity.
Primary Standard
The primary calibration (reference standard) has the highest metrological quality avail-
able at a given location or in a given organization. Its value is accepted without reference
to other standards of the same quantity.
In many countries, a body has been established to maintain primary standards of
measurements that will be used to provide traceability to customers’ instruments. The
national metrology institute supports the metrological infrastructure in that country by
establishing an unbroken chain from the top level of standards to an instrument used for
measurement.
National Metrology Institute
Country
DANAK
Denmark
PTB
Germany
NPL
UK
NIST
USA
Fig. 2.
Examples of national metrology institutes
Which type of Calibration do I need?
For performing a quality measurement, you must keep these factors in mind:
1.
Resolution:
Does the measurement meet the requirements of the application?
2.
Accuracy:
Does the measurement reflect the true characteristics of what is
measured?
3.
Precision:
Do you get the same result each time you measure the same quantity?
The accuracy of the calibration needed is directly dependent on these considerations.