Patent ID: 8036841

Claim:
Method for observing the condition of a measuring device having a potentiometric measuring probe which comprises at least two electrodes, each having a resistance, the method comprising: applying an alternating test voltage provided by a voltage source via a connecting cable to at least one of the electrodes; passing a combined signal containing a potentiometric voltage of the electrode and a signal that relates to the applied alternating test voltage to a processing unit; extracting from the combined signal the signal that relates to the applied alternating test voltage in the processing unit; and calculating from the signal that relates to the applied alternating test voltage a resistance of the at least one electrode, wherein the combined signal is processed in the processing unit by a transfer function unit, which substantially simultaneously extracts from the combined signal a measurement value which corresponds to the potentiometric signal of the at least one electrode and a test response that is used for calculating the resistance of the at least one electrode, and wherein the alternating test voltage comprises a sine shaped signal component with a base frequency at least during a calibration time period.