A linear variable differential transformer (LVDT) consists of a primary winding and two secondary windings symmetrically spaced on a cylindrical form. A movable magnetic core inside the coil assembly provides a path for the magnetic flux linking the windings.

When an AC carrier excitation is applied to the primary winding, voltages are induced in the two secondary windings. These are connected in opposition, so that the two voltages are 180° out-of-phase. If the core is centered between the secondary windings, the net output of the transducer is zero. When the core is moved off center, the induced voltage in the secondary winding toward which the core is moved increases, while the induced voltage in the opposite winding decreases.

For off-center displacements within the range of operation, differential voltage output varies Iinearly with the changes in the core position. The phase of this output voltage is reversed as the core is moved from one side of the electrical center to the other.

Because there is no physical contact between the core and coil assembly, the mechanical components of the LVDT do not wear out or deteriorate. The corresponding absence of friction gives truly infinite resolution and no hysteresis.

The small core mass and the lack of friction enhance response capabilities for dynamic measurements. Since the LVDT is not affected by any mechanical overload, its reliability is can be very high.