The functionality and/or calibration of any measuring instrument should be checked regularly. Checking a rheometer or viscometer is usually done by measuring a standard liquid with a certified viscosity value.
A standard liquid is a Newtonian fluid for which the viscosity value is certified for one or several temperature values.
A wide range of standard liquids with different viscosity values and uncertainties as well as different reference temperatures and chemical structures (mineral oils, synthetic oils) are available.
Standard liquids from Thermo Fisher Scientific are delivered with a certified viscosity at 20°C and an uncertainty of ±2% (±4% for E7). Standard liquids with viscosity values between 5 mPas and 40000 mPas are available in 100ml or 500 ml containers.
Standard liquids with other viscosity values or other reference temperatures as well as the delivery in other containers (e.g. 1.0 l) are available from Rheology Solutions on request.
Standard liquids with a lower uncertainty of the viscosity (±0.4%) and/or certified viscosity values at other temperatures between 20°C and 100°C are available from the German calibration service (DKD – Deutscher Kalibrierdienst).
Because of their lower viscosity – temperature dependence silicon oils are often used for checking simple viscometers which do not provide any means of temperature control. For this application the slight shear thinning behaviour of silicone oils (decreasing of the viscosity with increasing shear rate) should be neglected.
For checking a specific viscometer or rheometer configuration it is important to use a standard liquid that matches the parameters (temperature, viscosity, etc.) of the routine measurements normally run on that instrument.
When comparing the measured viscosity value with the standard liquid's certified value it is important to take the instruments uncertainty into account also.