The digital density meter DMA 5000 M from Anton Paar can be used for measurements of the density of a liquid sample, and its related variables like relative density and concentration.
To determine the density of a sample, at least 1 mL of the liquid sample has to be injected in the hollow, U-shaped glass tube, which is electronically excited into undamped oscillation. The eigenfrequency of such a mechanic oscillator is influenced by the oscillating mass, which is, at a constant volume, dependent on the density of the sample. The frequency of the mechanical oscillation is electromagnetically transformed into an alternating voltage with the same frequency. The period τ which is defined as the reciprocal frequency is measured with a high resolution and is related to the density ρ by the following formula:
KA and KB are the respective instrument constants of the oscillator. For calibration, the constants can be determined by measuring the well-known densities of water and air, and are saved by the DMA 5000 M for the following measurements. f1 and f2 are correcting factors for temperature, viscosity and non-linearity .
As the temperature has a large influence on the density of the sample and on the mechanic properties of the oscillator, the DMA 5000 M shows an accuracy of temperature of 0.01 °C. Concerning the density, the DMA 5000 M gives an accuracy of 0.5·10-5 g/cm3 and a reproducibility of 0.1·10-5 g/cm3 .