Aim

To determine the characteristics of LVDT.

Apparatus Required

LVDT kit

Theory

LVDT is basically a mutual inductance type of transformer with variable coupling between primary and secondary two coupling coils.

LVDT (Linear Variable Differential Transformer) is used to measure displacement. It operates on the principle of a transformer; it consists of a coil assembly and a core. The coil assembly is typically mounted to a stationary form while the core is secured to the object whose position is being measured.

The coil assembly consists of three coils of wire wound on a hollow form. A core of permeable material can slide freely through the centre of the form. The inner coil is the primary, which is excited by an AC source. Magnetic flux produced by the primary is coupled to the two secondary coils, inducing an AC voltage in each coil.

When the core is at the central (null) position, the voltages induced in both secondary coils are equal and opposite, resulting in zero output voltage. When the core is displaced, the output voltage is proportional to the displacement within a specific linear range.

Procedure

1. Connect the multimeter to the output of the kit.
2. Set the range to a maximum value of 10 mm.
3. Move the screw gauge from zero to maximum of 10 mm.
4. Note the corresponding voltage values in the multimeter.
5. Plot the graph between the voltage and displacement on graph paper.

Observation

Result

LVDT was studied and the graph of displacement was linear for a particular range.

Precautions

• The values on the multimeter should be carefully noted.
• The core should be set to a maximum value of 10 mm.
• To get good performance from the kit, maintain room temperature.