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  3. Calibrate, adjust, verify or legally verify?

Calibrate, adjust, verify or legally verify?

What does "calibration" actually mean?

Calibration is the act of determining and documenting, in a traceable manner, the deviations between a measuring instrument called device under test (DUT) and a reference device called reference standard.

The result of this comparison shows the measuring deviations at different measurement points and can be provided in absolute or relative form. The regular calibration of measurement instruments ensures the precision and reproducibility of the measurement data. The reference measurement is made with a reference device.

Traceability refers to the uninterrupted chain of comparative measurements related to the measuring results of a measuring instrument and the specific, higher-ranking national standard.

Metrological traceability

The resulting hierarchy is based on accreditation, i.e. the calibrating authorities have been assessed for their technical competence and thus formally recognised. The Physikalisch-Technische Bundesanstalt (PTB) is the highest-ranking national authority for metrology, providing reference standards of the highest accuracy, such as the standard meter, for all physical and legally required quantities for use in calibration.

What is meant by "adjustment"?

As opposed to calibration, adjustment is the act of setting a measuring instrument to a measurement deviation that is reduced as much as possible in order for the deviations to stay within the limits of error. Thus, adjustment requires an intervention on the measuring instrument, which usually results in permanent changes to the device.

What is "Verification"?

Verification is about providing objective proof that a measuring instrument meets specific requirements.

As opposed to calibration, uncertainty of measurement is not indicated, only a pass or fail statement is made. Verification can cover secondary measurands such as the sensor, the transducer or I/O modules via test signals.

What is meant by "legal verification"?

Legal verification means performing legally required checks of measuring instruments, e.g. scales used in food retailing, that are subject to public interest and are used to set prices. Legal verification is performed by specific authorities and is thus governed by severe regulations.

Measuring and testing technology in comparison

  Calibration Adjustment Verification Legal verification
Certificate with accuracy
Yes, documents the deviation from the data sheet specification

Yes, by an accredited certification body
Measurement uncertainty documented
Yes, including information on traceability

No, as there is no documentation

No, only qualitative statement on functionality

Yes, within legally prescribed tolerances
Traceability to standards
Yes, to national or international standards

Possible through subsequent calibration

Possible if reference device is traceable

Yes, certified by the state
Typical measuring instruments Sensors, scales, pressure/temperature measuring devices Sensors, laboratory equipment, production machines Test devices, sensors Scales, petrol pumps, measuring instruments used for billing purposes (gas/water/electricity)
Typical application Quality assurance in industrial environments, laboratories
(pharmaceuticals, food, automotive)
Optimisation of measurement accuracy in production and development Quick check in production or in the incoming goods department Measurement technology used for trade and billing (e.g. scales, petrol pumps)
Required according to standard ISO 9001, IFS, GMP, HACCP, ISO/TS 16949, ISO 50001 etc. Not required, but often necessary for compliance with specifications Depending on the respective standard
(e.g. ISO 10012)
Regulated by law for measuring instruments subject to legal verification
Audit-compliant
Yes, calibration certificate serves as proof

No, only through subsequent calibration

Partially, depending on standard requirements

Yes, verification mark or official certificate are recognised forms of proof
Executing service provider Accredited and non-accredited calibration laboratories Manufacturers, maintenance service providers, service technicians Internal quality assurance or external certification bodies Measurement offices or accredited certification bodies
Advantages Objective assessment of the measurement deviation, traceability, basis for quality assurance Optimisation of measurement accuracy Quick check with little effort Legally recognised, required for billing-related measurements
Particularities Only shows the deviation - no interference with the device Recalibration is necessary after each adjustment Check only, no interference with the device Required by law for certain use cases
Costs (approximate)
(depending on required accuracy and calibration standard)

(depending on the type and complexity of the adjustment)

(low to medium, depending on testing effort)

(statutory testing fees)