Linear variable differential transformer with improved secondary windings

Abstract

A linear variable differential transformer (LVDT), includes a hollow bobbin with first and second ends, a ferromagnetic core adapted for linear movement within the bobbin, a primary coil wound around the exterior of the bobbin, and first and second secondary coils wound around the primary coil. The first and second secondary coils are wound from starting points at the first and second bobbin ends, respectively. The seconardy coils are then wound continuously and simultaneously toward the opposite bobbin ends, so that the two secondary coils cross over each other at a cross-over point approximately halfway between the bobbin ends. The second secondary coil thus overlaps the first secondary coil between the cross-over point and the first bobbin end, and the first secondary coil overlaps the second secondary coil between the cross-over point and the second bobbin end. Each of the secondary coils has a sufficient continuous length to overlay substantially the entire length of the primary coil. The average distance of the first secondary coil from the primary coil is approximately equal to the average distance between the second secondary coil and the primary coil, thereby equalizing the flux densities in the two secondaries. The result is a substantially equal transfer function between the primary coil and each secondary coil, with well-balanced output characteristics.