Bilateral comparisons of hydrometer calibrations between the IMGC-LNE and the IMGC-MIKES

The Istituto di Metrologia "G. Colonnetti" (IMGC, Italy), the Laboratoire National d'Essais (LNE, France) and the Mittatekniikan Keskus (MIKES, Finland) support primary calibration facilities used both for liquid density measurements and for hydrometer calibrations. In 1998, two independent bilateral comparisons of the calibration of standard hydrometers were carried out between the IMGC and the LNE and between the IMGC and the MIKES, the main purpose being to assess the present state of mutual compatibility in the density range 600 kg/m³ to 2000 kg/m³ among the three laboratories. The results show agreement within the uncertainties declared by the laboratories, although the MIKES measurements are in general 0.2 kg/m³ lower than those of the IMGC and the LNE measurements are systematically 0.04 kg/m³ higher than those of the IMGC. Both differences are smaller than half of the least-scale division of the transfer hydrometer used.