Viscometers measure the viscosity of a liquid, usually under one flow condition. In general, the fluid remains stationary and an object moves through it or the object remains stationary and a fluid moves past it. The drag caused by the relative motion of the fluid and a surface is measured. They can be classified as direct or reverse flow. There are various kinds of viscometer. The ones used in laboratories are often the capillary versions when the container is a vertical or U-shaped glass tube known as the Ostwald and Ubbelohde viscometers after their inventors. The falling sphere type has a sphere of known size/density descend through a stationary fluid. The Norcross viscometer is made up of a piston and cylinder assembly whilst the oscillating piston design uses a magnetically-influenced piston. Other types include the vibrational, quartz and rotational viscometers. Viscometers are an important piece of apparatus in laboratories which do quality and efficiency testing of fluids in areas such as the effects of a process, changes to formulas and ageing phenomena especially for food, beverage and personal care products. As viscosity affects coating performance, they are used in the paint industry to check batch consistency and quality control.

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