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DKD Masse & Waagen

Mass and Weighing Instruments

Norbert Schnell

This technical committee was founded in 1995 and brings together the DAkkS-accredited calibration laboratories for the mechanical measurand mass. Currently, it represents 23 laboratories for the calibration of weights and 59 laboratories for the calibration of weighing instruments. By ensuring the traceability of their calibration results, the calibration laboratories for weights guarantee that all weighing results in the range from milligrams to tonnes are comparable with the definition of the kilogram in the International System of Units (SI).

 

The replacement of the international kilogram prototype (original kilogram) by a new definition of the embodied standard of mass (Avogadro project or Watt scale projects) came into force on 20 May 2019.  Further information can be found on the PTB website.

 

The requirements for weights are comprehensively described in the "International Recommendation OIML R 111" of the International Organization of Legal Metrology (Organisation Internationale de Metrologie Légale). It regulates, among other things, specifications for accuracy classes (permissible errors and measurement uncertainties), design and configuration, surface quality and material (density and magnetic properties).

Classes E1 and E2 represent the highest accuracies that can only be achieved under very demanding measurement conditions in special laboratories. For this purpose, mass comparators are used. These comparators are capable, for example, of calibrating one kilogram to an accuracy of 1 µg.

Usually, the calibration of weighing instruments is carried out at the customers' premises (location of the device) in order to take account of the ambient and installation conditions.

The smallest relative measurement uncertainty that can be achieved under very good conditions and with high-precision test weights for analytical and microbalances is 1 ∙ 10–6.

The Technical Committee played a decisive role in the development of the Guideline on the Calibration of Non-Automatic Weighing Instruments (EURAMET cg 18) which is the standard guideline used for the calibration of weighing instruments in Germany. The German translation was published in 2018 as Guideline DKD-R-7-2.

 

If required, the Technical Committee organizes interlaboratory comparisons for weighing instruments and weights.A group of experts is currently working on a DKD Expert Report on the calibration of non-automatic weighing instruments (NAWI) by means of substitution procedures.

 

Norbert Schnell im Mai 2019