Newtonian viscosity standards are samples of Newtonian fluids that are traceable to the national standard of the unit of viscosity. They therefore represent viscosity standards and are used to calibrate viscosity measuring devices. Viscosity measuring devices that are calibrated with these standard samples according to device-specific procedures and conditions are traceable to the national standard of the unit of viscosity for measurements of the viscosity of Newtonian liquids and fulfil the requirements of DIN EN ISO 9001 and DIN EN ISO/IEC 17025.
The national standard of the unit of viscosity is maintained by the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany, in accordance with the Law on Units in Metrology.
The liquids used for standard samples meet special requirements, e.g. for flow behaviour and long-term constancy of viscosity. They are in equilibrium with the atmosphere with regard to dissolved gases.
The standards for determining the kinematic viscosity are Ubbelohde viscometers with hanging level, which are traceable to the national standard. The viscosity specifications are based on the viscosity value of water at 20 °C ( = 1.0034 mm²/s). This value is an internationally agreed value in accordance with ISO/TR 3666-1998, taking into account the international temperature scale ITS-90.
The exact values of the kinematic and dynamic viscosity as well as the viscosity-temperature coefficient are specified for each standard sample at the standard temperatures 20°C, 23°C, 25°C, 30°C, 40°C, 100°C in the DAkkS calibration certificate.
