Realization of the unit of density
The density is defined as the ratio of the mass of a material and its volume. The SI unit is kg/m3.
According to the definition the density for a material is given, when its mass as well as its volume is known. Since the mass can be determined by a smaller relative uncertainty than the volume, to realize a density measurement is mostly a problem of the determination of the volume.
The following methods of the determination of density are applied at BEV:
- Geometrical determination of volume and weighing: optical measurement and weighing in air
- Flexural resonator measuring instruments: do not give a connection between “heavy” mass and the volume, but use the “inert” mass by bringing a sample to free vibrations
- Hydrostatic procedure: according to Archimedes’ principle a body immersed in a liquid loses apparently as much weight as the displaced amount of liquid weighs; the density is determined by this apparent loss of weight
- Pycnometric weighing procedure: the density is determined using volume standards (with known inner volume).