1. Department of Mechanical Engineering, Institute of Process Measurement and Sensor Technology , Technische Universität Ilmenau , Gustav-Kirchhoff-Str. 1, 98693 Ilmenau , Germany
2. Department of Mass Comparators , Sartorius Lab Instruments GmbH & Co. KG , Otto-Brenner-Str. 20, 37079 Göttingen , Germany