Sunday, 16 July 2017

LVDT - Advantages and Disadvantages


As shown in figure, LVDT consists of a transformer with one primary winding and two secondary windings. Here the secondary windings are connected in such a way that their induced voltages oppose each other. An alternating current is driven through the primary, causing a voltage to be induced in each secondary proportional to its mutual inductance with the primary. An iron core is located in between the primary and secondary windings.If the core is at the central position, the voltages in the two secondary windings are equal and hence the output is cancelled. When the core is displaced in one direction, the voltage in one coin increase as the other decreases causing the output voltage to increase from zero to maximum. This voltage is in phase with the primary voltage. When the core moves in the other direction, the output voltage also increases from zero to maximum, but its phase is opposite to that of primary. Thus the magnitude of the output voltage will be proportional to the distance moved by the core and it is why the device is called linear. The phase of the voltage indicates the direction of the displacement.

Advantages of LVDTs

1. The sliding core does not touch inside the tube and hence it can  move without friction.
2. As friction is avoided, the output will be accurate in almost all cases.
3. There is no sliding or rotating contacts which improves the efficiency.
4. Very high resolution
5. Simple in construction
6. Easy to align and maintain
7. Light in weight

Disadvantages of LVDTs

1. Large displacements are required for differential output
2. Sensitive to stray magnetic field
3. It is sensitive to temperature variations.

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