1. Basic Construction: An LVDT consists of a single primary winding and two secondary windings wound on a cylindrical former. A movable soft iron core is placed inside this former. The two secondary windings are identical and symmetrically placed on either side of the primary winding.
2. Principle of Mutual Induction: When the primary winding is excited by an alternating current source, it produces an alternating magnetic field. This field induces voltages in the two secondary windings through
mutual inductance.
3. Core Position and Output:
• When the core is at its central (null) position, the mutual inductance between the primary and each secondary winding is equal, resulting in equal induced voltages. Since the secondaries are connected in series opposition, the net output is zero.
• As the core moves, the mutual inductance of one secondary increases while the other decreases. This change in mutual inductance leads to a differential output voltage that is linearly proportional to the core's displacement.
Therefore, the variation of mutual inductance between the primary and secondary windings is the fundamental operating principle of the LVDT.