Question

30. The linear variable differential transformer (LVDT) is an accurate and reliable transducer for measurement of

• A. Voltage
• B. Current
• C. Displacement
• D. Temperature

Hint:

LVDT is a non-contact type displacement transducer with high sensitivity, low friction, and high resolution.
Always remember that it requires AC excitation and its output voltage is zero at the null position.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The Linear Variable Differential Transformer (LVDT) is a highly reliable passive inductive transducer that converts linear mechanical motion or displacement into a proportional electrical signal.
It operates on the principle of mutual induction between primary and secondary windings, which is modulated by the movement of a ferromagnetic core.

Step 2: Detailed Explanation:
An LVDT consists of a single primary winding wound on a cylindrical former and two identical secondary windings placed symmetrically on either side of the primary winding.
A movable, high-permeability soft iron core is placed inside the hollow passage of the former, and is mechanically linked to the object whose displacement is to be measured.
The primary winding is excited by an alternating current (AC) source, which induces alternating voltages \(E_1\) and \(E_2\) in the two secondary windings.
The secondary windings are connected in series-opposition, so the net output voltage (\(E_0\)) of the LVDT is the difference between the two induced secondary voltages:
\[ E_0 = E_1 - E_2 \]
When the core is at the exact center (known as the null position), the magnetic flux linking both secondary windings is equal, resulting in \(E_1 = E_2\) and a net output voltage of zero.
When the core is displaced in either direction from the null position, the magnetic coupling with one secondary winding increases while the other decreases, producing a differential output voltage (\(E_0\)) that is directly proportional to the magnitude of the displacement.
The phase of the output voltage relative to the primary excitation indicates the direction of displacement.
Therefore, the primary parameter measured by an LVDT is linear displacement.

Step 3: Final Answer:
The LVDT is used for the measurement of displacement.