linear variable displacement transducer (sensor) (LVDT)

A differential transformer, Linear Variable Differential Transformer (LVDT), is an electromechanical displacement sensor that converts linear motion into an electrical signal. They can detect the smallest distances from less than one micrometer up to many centimeters as measured values.

In terms of construction, LVDT sensors consist of three coils: a primary winding and two secondary windings. The secondary windings are arranged symmetrically around the primary winding. The primary winding forms the excitation coil and is supplied with a constant frequency of several kilohertz.

The secondary coils are electrically wired so that their voltages subtract. As a moving part, the LVDT sensor contains a soft iron core that changes the coupling between the coils when the position is changed. If the soft iron core is symmetrical between the coils, the resulting voltage is zero. If the coils deviate from the symmetrical arrangement, a voltage is generated from whose magnitude and polarity the asymmetry can be derived.