Viscosity

Viscosity is a physical property of liquids and describes the force, which is necessary for its agitation (shearing). A special case are Newtonian liquids, whose viscosity is independent on shear conditions. The most accurate instruments – and therefore the reference technique – to determine the viscosity of such Newtonian liquids are glass capillary viscometers. Some advantages are the high chemical resistance and low thermal expansion of the DURAN® glass, which results in a calibration valid for years and nearly independent on temperature.
As viscosity depends strongly on temperature, precise viscosity measurement always requires precise temperature control ±0,02°C. Capillary viscometer are especially used for petrochemical products, in polymer analytics (viscosity number, intrinsic viscosity) and in pharmacy.

National metrology institutes play a decisive role in the definition and dissemination of standards for physical quantities. The Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig is the national metrology institute in Germany and is responsible for realizing and disseminating the units of physical quantities.

In fact, PTB operates atomic clocks to provide high-precision time standards. Atomic clocks are based on the property of atoms to change between different energy states and use this to measure time accurately. The internationally accepted unit for time is the second, which is defined based on atomic clocks.

Close cooperation and comparison of atomic clocks at the international level, as you mentioned, is critical to ensure accuracy and consistency of time standards worldwide. This is done within the framework of organizations such as the International Bureau of Weights and Measures (BIPM), which is responsible for the international coordination of metrology.

The aforementioned quantities of mass, length and time are fundamental physical quantities, and the accurate measurement of these quantities is of great importance in many scientific, technological and industrial applications. Metrological institutes help to ensure that these measurements are performed at the highest levels of precision and reliability.