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Densitometers are most commonly required to indicate a change in density of the oil passing through a pipeline, for example at an interface. Normally they are not used to measure density to a high degree of precision.

There are a variety of densitometers in use.

• “Balanced flowâ€� type. A sample of the liquid flows through a fixed volume chamber where it is weighed or compared with a predetermined weight.
• “Displacerâ€� type. A float or plummet is immersed in the liquid and the density of the liquid determined from the effect on its buoyancy.
• “Gamma-rayâ€� type. A source of gamma radiation and a radiation detector are mounted to measure the degree to which the radiation is absorbed by the liquid. Absorption depends upon the density of the liquid.
• “Vibratingâ€� type. Mechanical energy, usually produced by electromagnetic apparatus is used to set up vibrations in the liquid. The density, or change in the density, of a liquid can be determined from the amplitude or frequency of the vibrations which vary with the density of the liquid.