How Linear Variable Differential Transformer works? Explain its three cases

The Linear Variable Differential Transformer is a passive transducer. It measures force in terms of displacement of ferromagnetic core of a transformer. It is based on the principle of magnetic induction or Faraday’s Law of Electromagnetic Induction.

Construction & Working

It consists of a primary winding and two secondary windings, which are placed on both sides of the core. The two secondaries Sec₁ and Sec₂ have equal number of turns but they are connected in series opposition.

Due to this connection, the e.m.f. induced in one coil opposes the e.m.f. induced in second coil and thus we get the difference of voltages.

A movable core, known as ferromagnetic rod or ferrite core, is inserted into the channel of LVDT. There are three possible positions of the core.

Case 1

When the core is in the middle or when there is no force acting on the core, then equal and opposite voltage is induced in both coils. Hence V₀ = e₂ – e₁ = 0.

Case 2

When the core is displaced on the left side, more flux is linked between the primary to Sec₁ rather than Sec₂. Hence e₂ < e₁. So the difference of output voltage is in phase with e₁.

Case 3

When the core is displaced on the right side, more flux is linked between the primary to Sec₂ rather than Sec₁. Hence e₂ > e₁. So the difference of output voltage is in phase with e₂.

Applications

1. Useful in accurate measurement of force, weight and pressure
2. Useful in automotive industries and in hydraulic machines
3. Used in Physics lab to measure displacement of objects

Advantages

1. It is very sensitive and can measure very small displacement
2. Smooth working with linear output
3. Low hysteresis
4. Low power consumption