Linear Variable Differential Transformer (LVDT)

LVDT Overview

• LVDT stands for Linear Variable Differential Transformer, a type of transformer and inductive transducer.
• Functions as a direct measurement device for physical quantities without requiring a primary transducer.

Construction and Components

• Features a primary coil that wraps around the length of a ferromagnetic cylinder.
• Contains electronic components for its operation.
• Housed in aluminum for protection against electrostatic and electromagnetic interference.

Operation Principles

• Operates using DC excitation rather than AC, which is connected to the primary winding.
• The core typically has low permeability, affecting the magnetic field interaction.
• Voltage output arises from the differential in primary voltages due to core position changes.

Output Characteristics

• The amplitude of the differential output voltage (Va - Vb) does not accurately represent core position.
• The phase shift of the output voltage (Va - Vb) relative to the excitation signal indicates the direction of movement toward the null position.
• Null position is defined where the phase shift between (Va - Vb) is 180 degrees.

Key Measurements

• At the null position, the output difference (Va - Vb) is termed Null Voltage.
• Quadrature voltage refers to the residual voltage at the null position and can be significant due to the LVDT's basic electrical design.

Excitation and Operating Conditions

• AC excitation voltage of 20-25 Volts, at frequencies between 40-350 Hz, is applied to the primary winding during operation.
• The working principle is anchored in Faraday's law of electromagnetic induction, highlighting the transformer’s reliance on electromagnetic principles.

Test your knowledge about the working principle and application of the Linear Variable Differential Transformer (LVDT) as an inductive transducer for measuring speed or position of an object.