Calibration of Measuring Instruments

What is calibration and why do we need it at all?

Calibration is a set of operations that under certain conditions establish relations between values indicated by a measuring instrument or system, or values represented by a materialised measure or reference material, and values realised by measurement standards (VIM 1993*, 6.11).

*VIM 1993: Vocabulaire international des termes fondamentaux et généraux de métrologie, joint issue ISO/IEC/OIML/BIPM, 1993.

It is clear to everybody that a car has to be regularly maintained and brought in for roadworthiness test at least once a year. It is the law. We are also aware that this ensures our safety and that the car will serve us throughout its lifecycle.

It is, however, less clear to everyone that a measuring instrument, too, needs maintenance, servicing, technical examination, etc., even if it is not broken. But still...

As is the case with the usual wear and tear of the car's brakes, spark plugs and other parts, components of measuring instruments also age. With time and use, especially incorrect use or misuse, the capabilities of instruments deteriorate.

These time-induced changes (drift) diminish the reliability of measurement results. This applies especially to complex electronic measuring instruments where individual measurement parameters can be interrelated (mutually dependent) in a completely unpredictable manner.

This means that the expected accuracy of a measuring instrument is limited to a certain time period. This is why almost all manufacturers of electronic measuring instruments limit the validity of specified limit values (accuracy of measurements for individual parameters) to a period of one year, and only exceptionally to two years, and often even to only a few months.

Although these time-induced changes (drift) cannot be avoided, they can be detected in time, corrected mathematically, or adjusted by calibration.

Correctly performed calibration increases productivity, optimises resources, and assures consistency, comparability and compatibility of products and services, as well as their acceptability anywhere in the world.

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