Densimeters for very accurate density measurements of fluids over large ranges of temperature, pressure, and density

This paper comprehensively describes those types of densimeters that allow very accurate density measurements of fluid substances over large ranges of temperature and for high pressures and that also cover the entire density range from low gas densities up to high densities of compressed liquids. Densimeters meeting these requirements are based on special applications of hydrostatic balances in combination with magnetic suspension couplings. These densimeters can be subdivided into two-sinker densimeters, and single-sinker densimeters which allow pρT measurements with total uncertainties in density of about 0.01% to 0.02% (level of confidence 95%) depending on their individual design. Besides a discussion of the design of such densimeters, it is also shown which substances in which ranges of the fluid state have been investigated with these instruments. Using nitrogen as an example, the experimental results obtained with these densimeters are discussed and compared with the pρT data obtained with other types of densimeters. A description of the features of other types of densimeters is outside the scope of this paper, but they are briefly summarized at the beginning of this paper.