Non-contacting electromagnetic thickness gauge for sheet measurement having improved small distance sensitivity

An apparatus for non-contacting measurement of the thickness of a sheet of a non-magnetic material comprising:

• a first body of a magnetically susceptible material, substantially cylindrical in shape, to one side of said sheet;
• said first body aligned such that the axis of the cylinder is substantially perpendicular to said sheet;
• a first electrical wire wound a plurality of times about said first body, capable of being energized to produce a magnetic field;
• means for holding said first body at a constant distance apart from said sheet;
• a second body of a magnetically susceptible material, substantially cylindrical in shape, having a diameter less than the diameter of the first body, to other side of said sheet;
• said second body positioned such that the axis of the cylinder is substantially aligned with the axis of the first body;
• a member of magnetically susceptible material, substantially disk shaped, attached to said second body with said second body between said member and said sheet and with the center of said member substantially aligned with the axis of said second body and having a diameter larger than that of the second body;
• a second electrical wire wound a plurality of times about said second body, said second wire capable of detecting the amplitude of said magnetic field, said field detected determinative of the thickness of said sheet;
• and
• means for maintaining said second body at a constant distance apart from said sheet.