Capacitive sensing system with hardware diagnostics concept for detection of sensor interruption

1. A capacitance measurement circuit for determining a sense current of a capacitive sensor including at least one electrically conductive sense electrode and at least one electrically conductive guard electrode that are proximally arranged and mutually galvanically separated from each other, the capacitance measurement circuit comprising

a periodic signal voltage source that is configured for providing an alternating measurement voltage with reference to a reference potential, wherein at least one of the at least one electrically conductive sense electrode and the at least one electrically conductive guard electrode is electrically connectable to the periodic signal voltage source for receiving the periodic measurement voltage,

a sense current measurement circuit that is configured to determine the sense current that is indicative of a position of an object relative to the capacitive sensor, and

at least one switch member that is remotely controllable by a switch remote control unit and has an open circuit state and at least one closed state, wherein the at least one switch member, in the at least one closed state, is configured to provide an additional electrical path between the at least one guard electrode and the reference potential.

2. The capacitance measurement circuit as claimed in claim 1 , wherein the switch remote control unit is formed by a microcontroller.

3. The capacitance measurement circuit as claimed in claim 1 , wherein the switch remote control unit is configured to periodically switch the remotely-controllable switch member from the open circuit state to the closed state for a predetermined time period and back to the open circuit state after the time period has elapsed.

4. The capacitance measurement circuit as claimed in claim 1 , further comprising a test capacitor that forms part of the additional electrical path between the at least one guard electrode and the reference potential.

5. A capacitive sensing system including

a capacitance measurement circuit as claimed in claim 1 ,

a switch remote control unit, and

at least one capacitive sensor that is electrically connected to the periodic signal voltage source, wherein the at least one capacitive sensor includes at least one electrically conductive sense electrode and at least one electrically conductive guard electrode that are proximally arranged and mutually galvanically separated from each other.

6. The capacitive sensing system as claimed in claim 5 , wherein the switch remote control unit is formed as a microcontroller.

7. The capacitive sensing system as claimed in claim 5 , wherein a capacitor formed by the at least one electrically conductive sense electrode and the at least one electrically conductive guard electrode has a capacitance value of at least 3 nF.

8. A method of operating the capacitive sensing system as claimed in claim 5 with regard to capacitive sensor interruption diagnosis, the method comprising steps of

controlling the at least one switch member to be in the open circuit state,

determining a first sense current value of the capacitive sensor,

controlling the at least one switch member to be in the at least one closed state,

determining a second sense current of the capacitive sensor,

determining an absolute difference between the first sense current and the second sense current,

comparing the determined absolute difference with a predetermined threshold value for the absolute difference of sense current, and

generating an output signal that is indicative of a sensor interruption if the determined absolute difference is smaller than the predefined threshold value.

9. The method as claimed in claim 8 , further comprising steps that are to be executed if the determined absolute difference is equal to or larger than the predefined threshold value, of

controlling the at least one switch member to be in the open circuit state, and

resuming determining sense current values of the capacitive sensor.

10. The method as claimed in claim 8 , wherein the steps are executed in a periodic manner.