Linear Variable Differential Transformer

This type of pressure measurement relies on the movement of a high permeability core within transformer coils. The movement is transferred from the process medium to the core by use of a diaphragm, bellows or bourdon tube. The LVDT operates on the inductance ratio between the coils. Three coils are wound onto the same insulating tube containing the high permeability iron core. The primary coil is located between the two secondary coils and is energised with an alternating current. Equal voltages are induced in the secondary coils if the core is in the centre.

The voltages are induced by the magnetic flux. When the core is moved from the centre position, the result of the voltages in the secondary windings will be different. The secondary coils are usually wired in series.

LVDT’s are sensitive to vibration and are subject to mechanical wear.

Disadvantages

- Mechanical wear

- Vibration