The Mass Laboratory's Activities

The priority activities of the Mass Laboratory, which operates within the framework of the Metrology Institute, are ensuring measuring traceability to the international level for the physical quantity of mass, and value transfer to the mass standards of lower hierarchical level in Slovenia. In order to obtain international recognition as holder of the national standard of mass, the Laboratory places the key stress on inter-laboratory comparisons within the framework of the EUROMET organisation, as well as with other national institutions. The R & D work in the field of the physical quantity of mass allows the Laboratory to meet the national needs and to maintain the adequate proficiency.

Ensuring traceability of the national standard of mass to the international level

At the moment, the Laboratory is ensuring traceability of the national standard of mass to the international level through direct comparison with the German national standard in the primary laboratory of the Physikalisch-Technische Bundesanstalt (PTB), Germany, which holds copy no. 52 of the international prototype of kilogram in Paris. The traceability thus ensured corresponds to the accuracy class E1. However, since measurement uncertainty can also be reduced by making various international comparisons of equal measurement standards, the Mass Laboratory takes part in various EUROMET and other international projects, whereby it makes possible, through research work, a reduction of uncertainty of the national standard.

Dissemination of the value of the national standard to the lower hierarchical levels in Slovenia

The dissemination of the value is conducted following the accredited procedures for comparison calibration, to own working standards, which are used in calibration of standards of the Slovenian users. The Mass Laboratory can, through dissemination procedures, provide for traceability of all standards in the Republic of Slovenia. The measuring principle is based on comparison measurement of weights, which is performed on one of the four comparator weighing instruments. On the comparator, the mass of the calibrated standard/weight is compared with the mass of the reference standard/weight. The comaprator weighing instruments operate on the principle of incorporated counter-weights and on the basis of an electromagnetic compensation system. The differences between the forces caused by different masses are measured as the difference in electric current, which is proportional to the weight's force of weight. According to the procedures, the mass and the measurement uncertainty are evaluated for the calibrated standard.

Scientific research work in the field of the quantity of mass

Besides maintaining the standard and its traceability, the Laboratory is also dealing with the project of dissemination of the 1 kg mass by making a national mass scale - which will be carried out for the first time in Slovenia - and with the project of automation of measurements. These two projects are extremely important for the mass measurement field in Slovenia, since through controlling the dissemination procedure, they will provide for a reduction of measurement uncertainty. This goal is also important from the international point of view, because we will be able to participate with the 1 kg standard in international comparisons, and thereby switch to a higher level of inter-laboratory comparisons.

Standard equipment

The national standard of mass consists in two sets of weights of the E1 accuracy class, with masses ranging from 1 mg to 10 kg, namely: (1, 2, 5, 10, 20, 50, 100, 200, 500) mg, (1, 2, 5, 10, 20, 50, 100, 200, 500) g and (1, 2, 5, 10) kg. Measurement uncertainties range between ( 0,0006 mg per 1 mg weight and ( 1,5 mg per 10 kg weight, while the relative uncertainty in the range between 100 g and 10 kg is 0.15 ppm. As a function of their nominal mass, the weights are made of stainless steel, aluminium or brass-nickel alloy. Their shape, density, roughness and magnetic properties are within the limits prescribed for the weights of the E1 accuracy class by the international OIML Recommendation 111, edition1994. The two sets of weights are alternatively in use one year each, with a re-calibration interval of two years for individual set. The standards are traceable to the primary standard of mass at the international level. Calibration of these weights is performed in a foreign institution by disseminating, through the primary standard of one kilogram, the 1 kg mass to weights ranging from 1 mg to 10 kg with uncertainty equal to maximum 1/10 of the maximum permitted errors for the E1 accuracy class, upon which the Slovenian national standard is calibrated according to the direct comparison method.