Patent ID: 7839282

Claim:
An apparatus for the inspection of a length of a dielectric material using a capacitive sensor comprising: the capacitive sensor, where the capacitive sensor is comprised of a driven electrode, a ground electrode, and a guard electrode, where the guard electrode is between the driven electrode and the ground electrode such that a position vector from a first point on the driven capacitor to a second point on the ground capacitor crosses or intersects the guard capacitor, such that when a constant voltage not equal to a voltage of the ground electrode is supplied to the driven electrode and the guard electrode, a fringing electric field is established between at least the driven electrode and the ground electrode; a capacitance measurement device, the capacitance measurement device electrically connected to the driven electrode, and the capacitance measurement device electrically connected to the ground electrode, such that the capacitance measurement device forms an RC circuit with the driven electrode and the ground electrode and such that the capacitance measurement device may determine a capacitance between the driven electrode and the ground electrode based on a time constant of the RC circuit, and the capacitance measurement device in data communication with a processor; a shield driver electrically connected to the driven electrode and electrically connected to the guard electrode, such that the shield driver senses a voltage supplied to the driven electrode and provides an equivalent voltage to the guard electrode; a power supply electrically connected to the capacitance measurement device; a location device maintained at a fixed distance from the capacitive sensor, and the location device in data communication with the processor; and the processor, the processor programmed to receive a location signal via data communication with the location device, where the location signal is representative of a location of the location device, and the processor programmed to receive a capacitance signal from the capacitance measurement device, where the capacitance signal is representative of the capacitance between the driven electrode and the ground electrode, and the processor programmed to correlate the capacitance signal and the location signal to provide an output indicating the capacitance signal and the location signal.