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Research cooperation between Sartorius AG and PTB in the field of 1 kg vacuum mass comparators

31.01.2007

Within the scope of a scientific cooperation between Sartorius AG and PTB a 1 kg vacuum mass comparator developed by Sartorius AG in cooperation with the Bureau International des Poids et Mesures (BIPM) and the Technische Universität Ilmenau was installed at PTB. As a result of first measurements standard deviations of < 0.2 µg in air and < 0.1 µg in vacuum could be achieved for the mass comparison of 1 kg stainless steel weights.

Within the scope of a scientific cooperation between Sartorius AG and PTB a new 1 kg vacuum mass comparator (Figure 1) developed by Sartorius AG in cooperation with the Bureau International des Poids et Mesures (BIPM) and the Technische Universität Ilmenau was installed at PTB.

Set-up of the 1 kg vacuum mass comparator Sartorius CCL1007 at PTB

Figure 1: Set-up of the 1 kg vacuum mass comparator Sartorius CCL1007 at PTB

The aim of this scientific cooperation is the investigation and improvement of the performance of the new mass comparator with respect to applications of highest requirements in mass metrology and mass-related research projects taking acount of the effects in air and in vacuum. The system consists of a mass comparator with a load alternator for eight mass standards inside a pressure-tight enclosure, the drive and control units with a PC and an oil-free vacuum pumping system with a turbo-molecular and a membrane pump. The comparator is equipped with a monolithic weighing cell with a resolution of 0.1 µg. The loading of the weights using a carousel-shaped turntable is performed fully automated by an external load device. During the loading procedure the centre of gravity of the mass standard is determined and the eccentricity of the weights is corrected automatically if necessary. Construction and functionality of the 8-position carousel are based on the known BIPM FB2-technology. The diameter of the carousel was increased to 555 mm in order to meet the requirement that spherical weights up to a diameter of 100 mm, i. e. also 1 kg silicon spheres, can be carried on each position. The 8-positions provide sufficient space for simultaneously weighing reference weights, sorption artefacts, buoyancy artefacts and test weights. First results give an impression of the performance and the potential of this new mass comparator. For 1 kg stainless steel weights pooled standard deviations of < 0.2 µg in air and of < 0.1 µg in vacuum (Figure 2) could be achieved. Measurements in air indicated a sensitivity of the system with respect to short-time temperature variations in the measuring room. In order to reduce this sensitivity modifications of the thermal insulation are planned.

Results of a comparison of two cylindrical stainless steel weights (1 kg) in vacuum

Figure 2: Results of a comparison of two cylindrical stainless steel weights (1 kg) in vacuum

Contact person:

Michael Borys, FB 1.1, AG 1.11, E-Mail: Michael.Borys@ptb.de