Evaluation of uncertainty in viscosity measurements by capillary master viscometers

Uncertainty evaluations for kinematic viscosity measurements using a series of capillary master viscometers are given, based on model equations considering precise corrections for the U-tube-type viscometers used at the National Metrology Institute of Japan (NMIJ). Results of viscometer constant calibrations for the NMIJ viscosity scale calibrated by stepping up to high viscosities, and the kinematic viscosity measurements of standard liquids with master viscometers at temperatures from −40 °C up to 100 °C, are evaluated in detail. The relative expanded uncertainties at k = 2 for kinematic viscosity measurements of standard liquids are 0.04% to 0.17% in the viscosity range up to 160 000 mm2 s−1.