Method for determining a conductivity (σ) of a medium with a controller and a measuring cell, wherein the measuring cell has a cell constant (k), a first electrode and a second electrode, wherein the first electrode and the second electrode are in direct contact with the medium, and wherein the controller carries out the following steps: - generating a signal with a first frequency (f 1) and a second frequency (f 2) and feeding the signal to the first electrode and the second electrode, - determining a first voltage (U 1) between the first electrode and the second electrode and a first current (I 1) through the medium for the first frequency (f 1) of the signal and a first impedance (Z 1) from the first voltage (U 1) and the first current (I 1) - determining a second voltage (U 2) between the first electrode and the second electrode and a second current (I 2) through the medium for the second frequency (f 2) of the signal and a second impedance from the second voltage (U 2) and the second current (U 2) - determining and comparing a phase (φ 1) of the first impedance(Z 1) with a phase (φ 2) of the second impedance (Z 2), - determining, when the phase (φ 1) of the first impedance (Z 1) is smaller than the phase (φ 2) of the second impedance (Z 2), a resistance of the medium according to a first formula R = Re Z 2 − Im Z 2 ⋅ Re Z 2 − Re Z 1 Im Z 2 − Im Z 1, - determining, when the phase (φ 1) of the first impedance (Z 1) is equal to or greater than the phase (φ 2) of the second impedance (Z 2), the resistance according to a second formula R = Z 1 cos φ 1 and - determining a conductivity (σ) of the medium using the resistance and the cell constant (k). wherein the measuring cell has a cell constant (k), a first electrode and a second electrode, wherein the first electrode and the second electrode are in direct contact with the medium, and wherein the controller carries out the following steps: - generating a signal with a first frequency (f 1) and a second frequency (f 2) and feeding the signal to the first electrode and the second electrode, - determining a first voltage (U 1) between the first electrode and the second electrode and a first current (I 1) through the medium for the first frequency (f 1) of the signal and a first impedance (Z 1) from the first voltage (U 1) and the first current (I 1) - determining a second voltage (U 2) between the first electrode and the second electrode and a second current (I 2) through the medium for the second frequency (f 2) of the signal and a second impedance from the second voltage (U 2) and the second current (U 2) - determining and comparing a phase (φ 1) of the first impedance(Z 1) with a phase (φ 2) of the second impedance (Z 2), - determining, when the phase (φ 1) of the first impedance (Z 1) is smaller than the phase (φ 2) of the second impedance (Z 2), a resistance of the medium according to a first formula R = Re Z 2 − Im Z 2 ⋅ Re Z 2 − Re Z 1 Im Z 2 − Im Z 1, - determining, when the phase (φ 1) of the first impedance (Z 1) is equal to or greater than the phase (φ 2) of the second impedance (Z 2), the resistance according to a second formula R = Z 1 cos φ 1 and - determining a conductivity (σ) of the medium using the resistance and the cell constant (k). - generating a signal with a first frequency (f 1) and a second frequency (f 2) and feeding the signal to the first electrode and the second electrode, - determining a first voltage (U 1) between the first electrode and the second electrode and a first current (I 1) through the medium for the first frequency (f 1) of the signal and a first impedance (Z 1) from the first voltage (U 1) and the first current (I 1) - determining a second voltage (U 2) between the first electrode and the second electrode and a second current (I 2) through the medium for the second frequency (f 2) of the signal and a second impedance from the second voltage (U 2) and the second current (U 2) - determining and comparing a phase (φ 1) of the first impedance(Z 1) with a phase (φ 2) of the second impedance (Z 2), - determining, when the phase (φ 1) of the first impedance (Z 1) is smaller than the phase (φ 2) of the second impedance (Z 2), a resistance of the medium according to a first formula R = Re Z 2 − Im Z 2 ⋅ Re Z 2 − Re Z 1 Im Z 2 − Im Z 1, - determining, when the phase (φ 1) of the first impedance (Z 1) is equal to or greater than the phase (φ 2) of the second impedance (Z 2), the resistance according to a second formula R = Z 1 cos φ 1 and - determining a conductivity (σ) of the medium using the resistance and the cell constant (k).