Patent ID: 8508234

Claim:
A method for detecting a failure of a measurement device for inductively measuring the electrical conductivity of a fluid medium with a sensor having at least two toroidal cores, wherein a first toroidal core carries an excitation coil and a second toroidal core carries an induction coil, the sensor is connected to a measuring device having an excitation driving circuit to supply an AC excitation voltage to the excitation coil inside the sensor so that a current or voltage, related to the conductivity of the measured liquid, is induced in the induction coil, said method comprising: applying an additional signal to terminals of at least one of the excitation coil and the induction coil, resulting in a derived signal from the coil having the additional signal; monitoring the derived signal to detect an open-circuit failure of the device; and monitoring an output swing of the excitation driving circuit in order to detect a short-circuit failure of the device.