Patent ID: 6150811
Filing Date: 2000-11-21
Classification: G01R

Abstract:
A magnetic field sensor comprising:an oscillator comprising an oscillation circuit, and a first coil with a ferromagnetic metal core, inductance of said first coil being responsive to the earth magnetic field, said oscillator providing a frequency of oscillation determined by a permanent self-magnetization of the metal core of said first coil;a second coil, and a regulator circuit applying current to said second coil for establishing a magnetic field in said second coil, the magnetic field of said second coil coupling said first coil and summing with a magnetic field established in said first coil by said oscillator circuit;switch means interconnecting said regulator circuit with said second coil for receiving a direction of current flow in said second coil;a control unit for operating said switch means to reverse current flow in said second coil at a switching frequency greater than a frequency of change of direction of the earth magnetic field within said first coil; andmeans for measuring the current in said second coil to output a current measurement for each direction of the current flow, said measurement being suitable for operation of a computer for determining a difference between a current measurement for a first direction of the current flow and a current measurement for a second direction of the current flow, said difference in current measurements being proportional to the strength of the earth magnetic field;whereby said regulator circuit compensates for variations in said oscillator frequency resulting from the presence of the earth magnetic field within said first coil in order to establish a set value of working frequency for said oscillator, said set value being the value of the absence of influence of the earth magnetic field.