serve to detect electric conductibility, which is also termed as conductivity. They function by applying an AC power source to one electrode which is placed in the solution to measure. The electricity runs through the solution and to a second electrode. By determining the currency and the voltage drop between the electrodes, the resistance of the solution can be calculated using Ohm’s law. As the resistance and the conductivity directly correlate, the latter can be deducted from the first. The system needs calibration before it can be used as geometry, surface and material of the electrodes play an essential role. Measuring cells consisting of 2 and 4 electrodes are available, whereby 4-electrode measuring cells are able to cover a larger measuring range. In contrast to the 2-electrode cells, the measurement is not disturbed by polarization effects or impurities at the electrodes 41.