Bilateral comparison of viscosity measurement standard system between KRISS and PTB

This study was conducted to compare the viscosity measurement standard systems of the KRISS and PTB, as well as to confirm the international equivalence of the standard viscosity measurement system built in the KRISS. The KRISS constructed a viscosity measurement standard system using an Ubbelohde-type capillary viscometer. In the KRISS, the viscometer was calibrated based on the water viscosity standard ISO TR 3666, and 16 viscometer coefficients were obtained using the step-up method. The measured viscosity was corrected by evaluating the surface tension, buoyancy, and kinetic energy. The uncertainty of the measurement system, including the temperature and measurement time, was evaluated. The measurement range of the viscosity measurement standard system was 0.3 to 100000 mm 2 /s, with 0.13%–0.5 % uncertainty (U, k = 2). A bilateral comparison of the viscosity measurement standard system between KRISS and PTB was conducted using three different viscosity standard liquids (5A, 2000A, and 50000A) synthesized by the PTB. The viscosity of the standard liquid was measured at three different temperatures (15 °C, 20 °C, and 40 °C), and comparisons were performed under all six experimental conditions (5A/15 °C, 5A/20 °C, 2000A/20 °C, 2000A/40 °C, 50000A/20 °C, and 50000A/40 °C). By considering the uncertainty, the calculated En was less than 1 (0.17–0.72) for all experimental cases. Therefore, it was confirmed that the recently constructed viscosity standard system of the KRISS exhibits mutual equivalence with the viscosity measurement standard system of the PTB. In the future, KRISS will register the viscosity measurement standard system in a CMC based on the results of this bilateral comparison.