The construction of LVDT is shown in figure. LVDT translates the linear motion into electrical signals.

The transformer consists of a single primary winding P & two secondary windings S1 & S2 wound on a cylindrical former. The secondary windings have equal number of turns and are identically placed on either sides of the primary winding. The primary winding is connected to an alternating current source. A movable soft iron core is placed inside the former. The displacement to be measured by is applied to the arm attached to the soft iron core. The core is made of high permeability, nickel iron which is hydrogen anneled. This gives low harmonics, low null voltage & a high sensitivity. This is slotted longitudinally to reduce eddy current losses. The assembly is placed in stainless steel housing and the end lids provide electrostatic and electromagnetic shield. The primary winding is excited by an alternating current source; it produces an alternating magnetic field which in turn induces alternating current voltages in the two secondary windings. When the core is at its normal (NULL) position, the flux linking with both the secondary windings is equal and hence equal emfs are induced in them. At null position voltages of both secondary windings ES1 and ES2 will be equal and the output voltage of Eo is zero at null position as the output voltage of the transducer is the difference of two voltages.

Advantages: 1. The LVDTs have a very high range for measurement of displacement. 2. The LVDT gives a high output and many a times there is no need for amplification. 3. These transducers can usually tolerate high degree of shock and vibrations especially when the core is spring loaded without any adverse effects. 4. Simple in construction, small and light in weight. 5. Low hysteresis and hence repeatability is excellent under all conditions. 6. It consumes power which is less than 1 W

Disadvantages: 1. Relatively large displacements are required for appreciable differential output. 2. They are sensitive to stray magnetic fields but shielding is possible. 3. The transducer performance is affected by vibrations.