Method and apparatus for determining the rotational position of a magnetic rotor relative to current carrying coils utilizing magnetic coupling between coils

An Apparatus comprising:

• a rotatably mounted magnetic rotor formed from a permanent magnet;
• a first coil mounted in proximity of the magnetic rotor, the first coil mounted such that, if the first coil is flowing with electric current, the magnetic rotor is within immediate proximity of at least part of a magnetic field created by the first coil;
• a second coil mounted in proximity of the magnetic rotor, the second coil mounted such that, if the second coil is flowing with electric current, the magnetic rotor is within immediate proximity of at least part of a magnetic field created by the second coil;
• means, coupled to the first coil, for generating an AC input signal and applying the AC input signal across the first coil to develop an AC output signal across the second coil, the AC output signal having a magnitude that varies in relation to the rotational position of the rotor;
• means coupled to the second coil for detecting the magnitude of the AC output signal and for determining the rotational position of the rotor based upon the magnitude of the AC output signal;
• and
• wherein the AC input signal has a magnitude and the means for determining the rotational position of the rotor further includes means coupled to the first toil for detecting the magnitude of the AC input signal, with the rotational position of the rotor being determined based upon a ratio of the magnitude of the AC output signal to the magnitude of the AC input signal.

A method of operating an air core gauge having a permanent magnet rotor and coils for receiving signals to rotatably position the rotor relative to the coils, comprising the steps of:

• applying a first DC signal to a first coil and a second DC signal to a second coil to rotate the permanent magnet rotor to an actual rotational position in response to an input signal, the input signal representing a desired rotational of the permanent magnet rotor;
• superimposing an AC input signal with the first DC signal applied to the first coil;
• detecting an AC output signal developed across the second coil in response to the AC input signal and the actual rotational position of the permanent magnet rotor;
• and
• generating a measured position signal in response to the detected AC output signal, the measured position signal representing the actual rotational position of the permanent magnet rotor.