Patent ID: 7724002

Claim:
Capacitive sensor, comprising: at least one reference impedance, at least one measuring condenser, at least one electrical alternating signal source, a current supply network, and an analysis unit, wherein the reference impedance and the measuring condenser are connected via the current supply network with the at least one electrical alternating signal source and the analysis unit in such a way that the charge and discharge currents of the reference impedance and the measuring condenser are able to be at least partially analyzed the analysis unit, and wherein the reference impedance is a tunable reference impedance, wherein a first connection and a second connection with the analysis unit are provided, wherein a diode ring is provided that is formed of at least first, second, third and fourth diodes that are connected one behind the other in series and in the same direction, wherein the diode ring has a first connection between the first diode and the second diode, a second connection between the second diode and the third diode, a third connection between the third diode and the fourth diode, and a fourth connection between the fourth diode and the first diode, wherein a first electrode of the at least one reference impedance is connected to the fourth connection of the diode ring, a second electrode of the at least one reference impedance is connected to a reference potential, wherein a first electrode of the at least one measuring condenser is connected to the second connection of the diode ring, wherein the first connection with the analysis unit is connected to the first connection of the diode ring, and the second connection with the analysis unit is connected to the third connection of the diode ring, and wherein an electrical alternating signal from the at least one electrical alternating signal source is fed to the first connection of the diode ring and the third connection of the diode ring, wherein a switch is provided for switching the reference impedance, at least one of the connection of the second electrode of the reference impedance with the reference potential and the connection of the first electrode of the reference impedance with the first connection of the diode ring.