Method of determining a remaining operating time of a potentiometric measuring probe, apparatus for performing the method, and use of the apparatus

A method of determining a remaining operating time of a potentiometric measuring probe containing an electrolyte, wherein a primary reference element and a secondary reference element are arranged so that an electrolyte deficiency advancing from an opening of the measuring probe arrives at the secondary reference element before it arrives at the primary reference element, the method comprising the steps of:

• monitoring a potential difference (V12) existing between respective electrical potentials of the primary reference element and the secondary reference element for conformance to a predefined tolerance criterion;
• when the tolerance criterion is found to be violated, determining the elapsed operating time from when the measuring probe was put into operation and retaining said elapsed operating time as a base time period (tG);
• calculating a remaining operating time (ΔtR) of the measuring probe from the base time period (tG).