Abstract: A variable inductor wherein two closed magnetic circuits each having a predetermined gap in one place are constructed of a movable magnetic core and a fixed magnetic core. When the movable magnetic core is moved, the opposite area between both the magnetic cores in one of the closed magnetic circuits increases, while the opposite area between both the magnetic cores in the other closed magnetic circuit decreases. Thus, the inductances of coils wound around parts of the respective closed magnetic circuits vary complementarily.

Abstract: A displacement - electricity transducer contains a movable magnetic core and a fixed magnetic core oppositely arranged so as to have predetermined gaps or clearances in at least two places. Two substantially closed magnetic circuits, each including one of the gaps, are formed by both magnetic cores, so that when the movable magnetic core is displaced relative to the fixed magnetic core while maintaining a predetermined spacing therefrom, the substantially opposite area of the gap portion in one of the magnetic circuits increases, while the substantially opposite area of the gap portion in the other magnetic circuit decreases. A first coil is wound around a part common to the two magnetic circuits, while a second coil is wound around a part not common thereto. By applying an alternating current to the first coil, an output responsive to the displacement of the movable magnetic core is derived from the second coil.

Abstract: A digital displacement sensor includes a plurality of zigzag coils provided with projecting or convex portions having different pitches and arranged on the surface of a flat plate. A magnetic head consisting of a magnetic body and a coil is wound around part of the magnetic body, the magnetic head being supported so as to be moved, while maintaining a given gap from the surface of the flat plate, whereby a digital signal corresponding to the displacement of the magnetic head is sensed by means of a plurality of zigzag coils.