What is "rheometer"

Hydrometer \Hy*drom"e*ter\, n. [Hydro-, 1 + -meter: cf. F. hydrom[`e]tre.]

1. (Physics) An instrument for determining the specific gravities of liquids, and thence the strength spirituous liquors, saline solutions, etc.

   Note: It is usually made of glass with a graduated stem, and indicates the specific gravity of a liquid by the depth to which it sinks in it, the zero of the scale marking the depth to which it sinks in pure water. Extra weights are sometimes used to adapt the scale to liquids of different densities.

2. An instrument, variously constructed, used for measuring the velocity or discharge of water, as in rivers, from reservoirs, etc., and called by various specific names according to its construction or use, as tachometer, rheometer, hydrometer, pendulum, etc.; a current gauge.

n. 1 A device used to measure the flow properties of fluids with variable viscosity. 2 (context obsolete English) A device used to measure the flow of electric current: an ammeter. 3 (context now rare English) A flowmeter, especially for water or blood.

A rheometer is a laboratory device used to measure the way in which a liquid, suspension or slurry flows in response to applied forces. It is used for those fluids which cannot be defined by a single value of viscosity and therefore require more parameters to be set and measured than is the case for a viscometer. It measures the rheology of the fluid.

There are two distinctively different types of rheometers. Rheometers that control the applied shear stress or shear strain are called rotational or shear rheometers, whereas rheometers that apply extensional stress or extensional strain are extensional rheometers. Rotational or shear type rheometers are usually designed as either a native strain-controlled instrument (control and apply a user-defined shear strain which can then measure the resulting shear stress) or a native stress-controlled instrument (control and apply a user-defined shear stress and measure the resulting shear strain).