10
Method of measurement
The concentration, valence and mobility of the ions dissolved in the liquid indicates its
composition, for example the salt content. The electric conductivity of the liquid is
proportional to the aforementioned ion properties, with their mobility depending on the
temperature of the liquid. The conductivity is measured with a high degree of accuracy by
applying an AC voltage to a cuvette (either filled with the liquid or subjected to a flow of the
liquid) of known measurements (cross-sectional area, separation of the electrodes) via the
zero voltage point (
U
W
= 0) of a Wien bridge.
2
3
1
1 measuring cell
2 electrode
3 sample
A
cross-section
l
distance
G
conductance
Z
impedance
U
q~
source voltage
U
W
Wien voltage
l
G
cell
σ
=
R
1
Z
3
Fig. 2: Using a Wien measurement bridge for measuring electrical conductivity
[
σ
]
= S/m
A
l
2
2
Z
cell
U
R
2
Z
cell
q~
U
q~
U
W
V
3
A
