LVDT Transducer Type Explained

The LVDT, which stands for Linear Variable Differential Transformer, is a widely used electromechanical transducer. Its primary function is to convert linear displacement or position into an electrical signal.

Inductive Nature of LVDT

The LVDT operates on the principle of mutual inductance. This makes it an inductive transducer. Here's how it works:

• The LVDT consists of a single primary winding and two secondary windings wound on a cylindrical former. These secondary windings are identical and are connected in series opposition.
• A movable soft iron core, typically made of a high-permeability material, slides freely within the former, inside the coils.
• When an AC excitation voltage is applied to the primary winding, it induces voltages in the two secondary windings.
• The position of the movable core determines the magnetic coupling between the primary and each secondary winding.
• When the core is at the central or null position, the induced voltages in the two secondary windings are equal in magnitude but 180 degrees out of phase, resulting in a net output voltage of zero.
• As the core moves from the null position, the coupling with one secondary winding increases while it decreases with the other. This causes a difference in the induced voltages, creating a differential output voltage.
• The magnitude of this differential output voltage is proportional to the displacement of the core, and its phase indicates the direction of displacement.

Why LVDT is an Inductive Transducer

The classification of LVDT as an inductive transducer is due to its reliance on changes in inductance (specifically, mutual inductance) to sense and measure displacement. The movement of the core alters the magnetic flux linkage, which directly affects the induced voltages in the secondary coils, hence changing the output signal based on inductive principles.

Distinguishing LVDT from Other Transducer Types

Let's briefly consider why other options are not appropriate for LVDT:

• Eddy current transducers: These transducers typically work on the principle of generating eddy currents in a conductive target and sensing the change in coil impedance due to the proximity of the target. While also inductive in a broader sense, LVDT's specific configuration and operation on mutual inductance for linear displacement set it apart.
• Resistance transducers: These devices measure physical quantities by converting them into a change in electrical resistance. Examples include strain gauges (resistance changes with deformation) and potentiometers (resistance changes with position). LVDT does not rely on resistance changes.
• Magnetostriction transducers: These transducers utilize the magnetostrictive effect, where certain materials change shape or magnetic properties when subjected to a magnetic field or mechanical stress. LVDT's principle is not based on this effect.

Therefore, based on its fundamental operating principle involving varying mutual inductance with linear core movement, the LVDT is definitively an inductive transducer.