Viscometer

A viscometer (also called viscosimeter) is an instrument used to measure the viscosity of a fluid. Viscometers can only measure constant viscosity, that is, viscosity that does not change with flow conditions. For liquids with viscosities which vary with flow conditions, an instrument called a rheometer is used. Thus, a rheometer can be considered as a special type of viscometer.

In general, either the fluid remains stationary and an object moves through it, or the object is stationary and the fluid moves past it. The drag caused by relative motion of the fluid and a surface is a measure of the viscosity. The flow conditions must have a sufficiently small value of Reynolds number for there to be laminar flow.

At 20°C, the dynamic viscosity (kinematic viscosity × density) of water is 1.0038mPa·s and its kinematic viscosity (product of flow time × factor) is 1.0022mm/s. These values are used for calibrating certain types of viscometers.