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3 Measuring Principle
Definition of Density
The density ρ of a sample is defined as its mass divided by its volume:
Density is a temperature-dependant measuring unit.
The Oscillating U-Tube Principle
The sample is introduced into a U-shaped borosilicate glass tube that is being excited to vibrate at its
characteristic frequency electronically. The characteristic frequency changes depending on the density
of the sample. Through determination of the characteristic frequency the density of the sample can be
calculated. Due to the temperature dependency of the density value, the temperature of the sample
has to be determined precisely.
Concentration Measurement
In binary mixtures, the density of the mixture is a function of its composition. Thus, by using
density/concentration tables, the density value of a binary mixture can be used to calculate its
composition.
This is also possible with so-called quasi binary mixtures. These are mixtures containing two major
components and some additional ones which are present in very small concentrations compared to the
two main components. Many decarbonated soft drinks, for example, can be considered to be quasi
binary mixtures of sugar in water because the concentration of flavors and acids are very small
compared to sugar and water. Thus, the sugar concentration can be measured with a density meter.
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