Measurement of density

In considering the measurement and control of density or relative density of liquids, the units used in the two factors are borne in mind. Density is defined as the mass per unit volume of a liquid. Relative density, on the other hand, is the ratio of the mass of a volume of liquid to the mass of an equal volume of water at 4°C (or some other specified temperature), the relative density of water being taken as 1.0. Both density and relative density are temperature-dependent and, for high precision, the temperature at which a measurement is made is known so that any necessary compensation can be introduced. The majority of industrial liquid-density instruments are based on the measurement of weight, buoyancy, or hydrostatic head, but measuring systems based on resonant elements or radiation techniques are also used. Various methods for continuous density weighing have been devised, but the most successful involves the use of a horizontal U-shaped tube with flexible couplings at a pivot point. In addition, measurement of density using weight is also explained.