Viscometers generally work by measuring the force and displacement of a device inside the instrument. They are either placed in a fluid or have fluids injected to perform measurement. When a fluid exerts stress on the instrument's displacement, the fluid's viscosity can be determined.
Viscosity is inversely proportional to force and displacement. High force with a low displacement results in a high viscosity measurement, and vice versa. For an appropriate reference point, scientists usually calibrate their instrument to the viscosity of water. However, depending on the purpose of the experiment, calibrations may vary. Other viscometers are designed to measure the viscosity of other forms of fluids, such as semi-solids and gases.
Viscosity lies within the scope of rheology, the change in form and flow of matter, elasticity, viscosity and plasticity. Since viscosity is the measurement of the internal friction within a fluid, viscometers function as a tool within rheology.
Viscometers have their place in many industries. These instruments are tested on liquids, such as sauces, oils and creams. Viscometers are used for the quality and efficiency testing of fluids in areas such as the effects of processing, changes to formulas and aging phenomena. A common standard in many industries is assessing flow behavior, which indirectly reflects quality and consistency.