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DKD Masse & Waagen

Mass and Weighing Instruments

Norbert Schnell

This Technical Committee was established in 1995 and brings together the DAkkS-accredited calibration laboratories for the mechanical measurand mass. It currently represents 23 laboratories for the calibration of weights and 38 laboratories for the calibration of weighing instruments. Through the traceability of their calibration results, the calibration laboratories for weights guarantee that all weighing results within the range from milligram to tonne are comparable to the prototype kilogram. The requirements for weights are extensively described in the “International Recommendation OIML R 111” of the International Organization of Legal Metrology.

It contains, inter alia, requirements for accuracy classes (permissible errors and measurement uncertainties), configurations, surface quality and material (density and magnetic properties). The classes E1 and E2 represent the highest accuracies which can only be achieved under very demanding measurement conditions in special laboratories. For this purpose, mass comparators that, for example, can calibrate one kilogram up to 1 µg accuracy are used. The calibration of balances is usually carried out at the customers premises (location of the device), in order to take into account the installation and ambient conditions. The smallest achievable relative measurement uncertainty, that can be attained for analytical balances and high precision scales under very good conditions and with higly accurate test weights, amounts to 1 ∙ 10–6.  The Technical Committee has played a major part in the elaboration of the  Guideline EURAMET cg-18 (Guideline on the Calibration of NonAutomatic Weighing Instruments) which is generally used for the calibration of balances in Germany. The guideline is currently being revised with regard to the practice-oriented requirements  by an international group of experts of the EURAMET TC-Mass and with the support of German experts (including the Committee‘s chairperson).

In doing so, special emphasis is placed on supporting the users of weighing instruments in order to meet the process requirements. Besides the official results, the calculation of uncertainties in everyday use of the weighing instrument and the resultant minimum sample weights will be explained. Currently, the Technical Committee deals with the organization  of interlaboratory comparisons for balances and E1 weights. Moreover, an interlaboratory comparison to determine the magnetic properties of weights has been carried out.

The replacement of the prototype kilogram by redefining the material measure mass (Avogadro Project as well as watt balance) has been discussed by the Technical Committee and, with regard to the achieved uncertainties, has been judged as being conservative.It is planned to publish the German translation of the rev. 4 of the  Guideline EURAMET cg-18 as a DKD Guideline.