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Institute for Measurement Technology
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Measurement of the electrolytic conductivity

Birgit Pühringer


Electrolytes are substances, which dissociate to free ions, if put into water. If they are placed in an electrical field, the ions move and current flows. It is possible to measure current and voltage and calculate the specific conductivity with knowing the dimensions of the cell the specific conductivity. The specific conductivity is the conductance of a cube with a side length of 1 m.

At the interface between elctrode and liquid an electric double layer is formed. Water molecules and ions place themselves on the electrode.

To avoid the influences of the nonlinear charge transfer resistance alternating current voltage is used for measure. This approach is used because of the capacity of the electrolytic double layer.

In this bachelor thesis the behavior of the conductivity at a large range of frequencies and different temperatures is measured. The result is that at low frequencies the admittance is capacitive due to the capacity of the electric double layer, at higher frequencies the magnitude is almost independent of frequency. The conductivity also rises with the temperature of the liquid.

The mesasurement of conductivity can be utilized to test the cleaness of water or determine the concentration of the ions in a known solution.

Keywords: accelerometer, real-time-processing, servo-motor

August 01 , 2011

Figure 1: This picture shows the setup for measuring the specific conductivity.