JNTU B.Tech II TRANSDUCERS ENGINEERING Previous Question Paper (March - 2022 - R18)

Variable parameter transducers convert physical displacement into changes in electrical parameters. Variable Capacitance transducers operate on the principle of a parallel plate capacitor where capacitance C = εA/d. By varying the distance (d) between plates, the overlapping area (A), or the dielectric constant (ε), the capacitance changes proportionally to the displacement. Variable Inductance transducers function by changing the self-inductance of a coil. This is achieved by moving a ferromagnetic core within a coil, which alters the magnetic flux linkage and thus the inductance. Variable Reluctance transducers operate by varying the reluctance of a magnetic circuit. A common configuration involves a stationary coil and a movable ferromagnetic armature. As the armature moves, the air gap in the magnetic path changes, altering the total reluctance of the circuit and consequently the inductance of the coil.

The LVDT (Linear Variable Differential Transformer) consists of a primary winding and two secondary windings wound on a hollow cylindrical former. A movable soft-iron core is placed inside. When an AC excitation is applied to the primary, the magnetic coupling induces voltages in the secondaries. When the core is at the center (null position), the induced voltages are equal and opposite, resulting in zero output. Displacement of the core increases the coupling in one secondary and decreases it in the other, producing a differential output voltage proportional to the displacement. Magneto-elastic sensors operate on the principle of the Villari effect, where the magnetic permeability of a ferromagnetic material changes under mechanical stress. The sensor typically consists of a core made of a magneto-elastic material surrounded by a coil. When an external force is applied, the stress alters the permeability of the core, which in turn changes the inductance of the coil. This change in inductance is measured using an AC bridge circuit, providing an electrical signal proportional to the applied force or pressure.