Method and apparatus for metal target proximity detection at long distances

A sensor for detecting a position of a metallic object, the sensor comprising:

• a conductive coil;
• an oscillator connected to the conductive coil to:
• (1) drive the conductive coil with an oscillating current based upon an external control signal;
• (2) to receive feedback from the conductive coil and allow a frequency of the oscillating current to vary in accordance with a varying resonant frequency of the conductive coil as affected by the metallic object;
• an amplitude control circuit connected to the oscillator to provide the external control signal to adjust the oscillating current;
• an additional circuit coupled to the conductive coil, wherein the additional circuit operates to couple and decouple a resistive element in relation to the conductive coil at first and second times, respectively;
• and
• a processing circuit coupled to the amplitude control circuit,
• wherein the processing circuit derives an output signal based upon the external control signal, and
• wherein the output signal is derived, at least during some periods of operation of the sensor, based upon a difference between a first sample of at least one of the external control signal and an intermediate signal functionally related to the external control signal obtained at the first time and a second sample of at least one of the external control signal and the intermediate signal obtained at the second time.

A sensor for detecting a position of a metallic object, the sensor comprising:

• an antenna circuit capable of transmitting and receiving electromagnetic signals, wherein the antenna circuit further provides an intermediate signal indicative of a characteristic of operation of the antenna circuit;
• a secondary circuit capable of periodically adjusting an effective resistance of at least a portion of the antenna circuit;
• and
• a processing circuit capable of determining an output signal indicative of the position of the metallic object based upon the intermediate signal;
• wherein the processing circuit determines the output signal at least in part based upon differences that occur in the intermediate signal between first and second times at which the effective resistance is adjusted to first and second levels, respectively.