A symmetrically wired measurement device for measurement of the concentration of ions, especially hydrogen (H+) ions, in a measurement liquid, comprising:
- a pH-sensitive measurement electrode located in the measurement liquid;
- a reference electrode located in the measurement liquid;
- a comparison electrode located in the measurement liquid which places the measurement liquid at a definable ground reference;
- means for forming a difference signal referenced to the ground reference from the difference between a measurement signal (φpH) of said measurement electrode and the reference signal (φref) of said reference electrode, the difference signal being dependent on the ion concentration in the measurement liquid;
- and
- compensation means for compensation of the noise potential (φchem) which arises between said comparison electrode and the measurement liquid.