LVDT - Linear Variable Differential Transformer or Transducer Working

The Linear Variable Differential Transformer (LVDT) is an electromechanical sensor that converts linear motion into a proportional electrical signal. It provides high accuracy, excellent resolution, and sensitivity with minimal mechanical friction. These qualities make it ideal for measuring linear displacement in various applications.

An LVDT (Linear Variable Differential Transformer) consists of a cylindrical transformer with three coils: one primary coil at the center and two secondary coils on either side. The secondary coils have equal turns but are oppositely wound. A movable soft iron core within the cylinder alters magnetic coupling between these coils as it slides, enabling displacement measurement when connected to an object via its projecting arm.

The Linear Variable Differential Transformer (LVDT) operates on the principle of electromagnetic induction. When an AC supply is applied to its primary coil, it induces currents in two secondary coils arranged oppositely. The resulting electromotive forces (emf), E1 and E2, are generated in these coils, with their net emf calculated as E1-E2 due to their opposing configurations.

The Linear Variable Differential Transformer (LVDT) operates by detecting the position of a soft iron core within its coils. When the core is centered, equal but opposite voltages are induced in secondary coils S1 and S2, canceling each other out to produce zero net output voltage—this is called the null position. If the core shifts leftward closer to coil S1, more flux links with it than with coil S2, resulting in a positive net output voltage proportional to displacement. Conversely, when shifted right toward coil S2, greater flux linkage occurs there compared to coil S1; this produces a negative net output voltage also proportional to displacement. The measured emf indicates both direction and magnitude of core movement.

LVDTs provide a linear relationship between output voltage and core displacement, ensuring precise measurements. They offer a high range for displacement measurement without frictional losses, enhancing accuracy. With high sensitivity and output levels, no additional amplification is needed. Low hysteresis ensures excellent repeatability while their rugged construction guarantees durability.

LVDTs are highly sensitive to stray magnetic fields, necessitating protective measures during operation. They require significant displacement to generate a noticeable differential output. Additionally, their performance is influenced by temperature variations and vibrations.

LVDTs serve as secondary transducers for measuring force, weight, and pressure. They are utilized in medical applications like brain probing and provide displacement feedback in hydraulic systems. Additionally, they measure distances between metals during friction welding.