LVDT is the short form of Linear Variable Differential Transformer. It is a type of electromechanical transducer that converts the rectilinear motion of a given object into a corresponding electrical signal. LVDT linear position sensors are capable of measuring positions of up to ±20 inches (±0.5 m) as well as small movements of about a millionth of an inch.
The internal structure of transformers comprise of a primary winding, centred between a couple of identically wound secondary windings that are symmetrically spaced near the primary. These coils are generally wound on a piece of hollow, thermally stable glass durable polymer. They are also wrapped inside a high permeability magnetic shield and en-capsulated against moisture. This type of coil assembly is generally an immobile element of the position sensor.
On the other hand, the moving element of an LVDT is a detached tubular armature of a magnetically permeable substance known as the core. It is free to move axially within the hollow bore of the coil and is mechanically coupled with the object whose position is to be measured.
The bore of the coil is usually large enough to offer a considerable radial clearance between the bore and the coil, without any physical contact between them. In operation the primary winding of the LVDT is energised by an alternating current of a suitable frequency and amplitude, known as the primary excitation. The electrical output signal of the LVDT is basically the differential AC voltage between the two windings.
Generally the AC output voltage of an LVDT is converted using appropriate electronic circuitry to a high level DC current or voltage that is convenient to use.
