Calibration (based on the English word calibration, also calibration ) in metrology is a measurement process for determining and documenting the deviation of a measuring device or a measuring standard compared to another device or another measuring standard , which in this case are referred to as normal . In the definition of the VIM by JCGM 2008, calibration includes a second step, namely taking into account the determined deviation when using the measuring device to correct the readings. The calibration takes place without intervention that changes the measuring device.
The term calibration is often confused with the non-synonymous words calibration , statement of conformity , specification test, comparison, adjustment or certification , see below for differentiation .
In a metrologically traceable calibration, a standard is used, the value of which is also traceably determined: Such a standard itself has a calibration that has a relationship to the definitions of the SI units through an uninterrupted chain of calibrations . This relationship is expressed by the two parameters deviation and calibration uncertainty . If the result of the calibration is again expressed with deviation and uncertainty, then this calibration result is also traceable . Traceability is therefore the property of a result and not of a device.
Increase in uncertainty in a calibration
With each calibration along the traceability chain, the uncertainty increases. The calibrated objects are therefore always of lower value (of lower order) than the normals with which they were calibrated.
Calibration is a snapshot
Statements about the behavior over time (drift, shift) of a measuring device can only be made after a few calibrations have been carried out. Only through these considerations and corresponding additional uncertainty contributions do measurement results retain their traceability for the duration between two calibration intervals.
Procedure for a calibration
Part of a calibration
- the definition of the measurement process
- Environmental conditions
- required standards
- Creation of a mathematical model for evaluating the calibration including its uncertainty
- Performing the calibration
- Creation of a result report, also known as a calibration certificate or calibration certificate, with details of a complete result, i.e. deviation and calibration uncertainty.
Differentiation from other terms
- A calibration is the confirmation of the conformity of a measuring device that is legally subject to calibration with a statutory national regulation.
- A declaration of conformity or a specification test can follow a calibration, but is not a mandatory part.
- A calibration must take place after each adjustment, because a change in the measuring device invalidates a previously performed calibration.
- A certification is the confirmation from an independent certification body that a thing (product, person, system) fulfills all requirements of a list of requirements.
A clear example is the calibration of a self-indicating balance by placing weights on it as standards. Taking into account systematic influences (measurement deviations of the weights previously determined by calibration; air pressure, temperature, buoyancy forces) and random influences, the display of the balance is compared with the applied mass and the uncertainty of this deviation is estimated. A simple calibration result is therefore: The balance display has a deviation of +0.12 g with a load of 200 g; this result has an uncertainty of 0.20 g with a confidence interval of 95%.
Guidelines and standards
DIN EN ISO 9001: 2015 : This set of rules for the certification of quality management systems requires that quality-relevant characteristic data for the manufactured product be measured with calibrated measuring devices.
In addition to the requirements and technical measures of quality assurance and quality management, such as test equipment monitoring and traceable calibration of measuring equipment, the calibration guideline 2622 from VDI , VDE , DGQ and DKD or DAkkS contains general calibration instructions, models for the calculation of measurement uncertainty and the traceability of measured variables for most electrical and electronic measuring devices.
- Joint Committee for Guides in Metrology: International vocabulary of metrology - Basic and general concepts and associated terms (VIM): Definition 2.39 .
- DIN 1319-1: 1995 Fundamentals of measurement technology; Part 1: Basic Concepts ; No. 4.10