What is Linear Variable Differential Transformers(LVDT)

Introduction

Linear Variable Differential Transformers, LVDT, are the most commonly used passive type transducers. They work under the principle of a mutual inductance change due to the movement of a magnetic core. This movement produces an electrical output proportional to the displacement of the core. The transformer has three solenoid coils placed end to end around a tube. The central coil is the primary coil, and the two external coils are the secondary coils. A cylindrical ferromagnetic core, attached to the object whose position is to be measured, slides along the axis of the tube. An alternating current is driven through the primary, causing the induction of a voltage in each secondary proportional to its mutual inductance with the primary. The frequency is generally in the range of 1 to 10 kHz.
We can see the LVDT’s application in displacer type level  measurment

Advantages of LVDT are-

1. High range: the LVDT has a very high range for displacement measurement. This can be used to measure the displacement from 1.25 mm to 250 mm.

2. There is no physical contact between the mobile core and the coil structure, which means that the LVDT is a frictionless device.

3. High input and high sensitivity: the LVDT provides a high input and many times it is not necessary to amplify.

4. LVDT has low hysteresis and, therefore, the repeatability is excellent.

5. The fact that LVDT is a transformer means that there is complete isolation between the excitation voltage given to the primary winding and the output produced by the secondary windings. This makes the LVDT an effective analogue computing element without the need for protection amplifiers.

Disadvantages of LVDT

1. They are sensitive to a stray magnetic field.

2. Many times the performance of the transducer is affected by vibrations.

3. The temperature affects the performance of the transducer.

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