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SBS-3510 User’s Manual
2.1 Measuring Principle
Definition of density
The density (ρ) of a sample is defined as its mass (m) divided by its volume (V):
ρ
= m
----
V
As the volume changes with temperature, density is a temperature-
dependent measuring unit.
The oscillating U-tube method
The sample is introduced into a U-shaped borosilicate glass tube that is being
excited to vibrate at its characteristic frequency. The characteristic frequency
changes depending on the density of the sample. With the 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, with the aid of density/concentration tables, the density value of a
binary mixture can be used to calculate its composition.
This procedure is also applicable for so-called quasi-binary mixtures. These
mixtures contain two major components and some additional ones 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 and water because the concentrations of flavors and
acids are very small compared to those of sugar and water. Hence, the sugar
concentration can be determined with a density meter.
The same holds for the determination of the alcohol concentration in distilled
spirits that can be considered to be quasi-binary mixtures of ethanol and
water.
