The Linear Variable Differential Transformer(LVDT) is a device used to measure linear displacement. The LVDT has 3 coils-one primary and two secondary, and an armature. The armature is basically a ferromagnetic core such as iron. An AC voltage is applied to the primary coil.
The two secondary coils are connected in opposite such that the output voltage is the difference of the individual voltages of the secondary coils. When the core is at the centre both the secondary coils produces equal and opposite voltage. Hence the output voltage(Vout) is zero.
When the core moves in left or right direction the output voltage of one secondary coil decreases and the output voltage from the other secondary coil increases. The output voltage is proportional to the distance travelled by the armature. This output voltage is used to determine the displacement.
The advantages of a LVDT are
- Non contact-There is no contact between the armature and the primary or secondary coils. Hence there is no friction and wear.
- Accurate
- Can be totally sealed and can be made to work in harsh conditions
- Less sensitive to vibrations
- Internally non contact but externally has to be connected where the measurement has to be made
- Not feasible for very long range measurements
- Linear displacement measurement
- Position sensing
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