Working of LVDT- Linear Variable Differential Transducer & its advantages and disadvantages


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Linear Variable Differential Transformers (LVDTs) measure linear displacements over a limited range. LVDT works under the principle of mutual induction and the displacement a non-electrical energy is converted into an electrical energy. It is a passive inductive transducer.

##Construction of LVDT:

LVDT

LVDT consists of a cylindrical transformer where it is surrounded by a primary winding and two secondary winding. The primary winding is placed in the middle of the two secondary winding. Both secondary windings have the same number of windings and opposite to each other.

The primary winding is connected to the AC input line and the output is taken across the secondary lines. A sliding core is placed at the centre of the cylindrical transformer.

##Working:

High-frequency alternating current (AC) is applied to the centre coil. This generates a magnetic field that induces a current in the two outside coils. The core will pull the magnetic field towards it, so in the figure more current will be induced in the left-hand coil. The outside coils are wound in opposite directions so that when the core is in the centre the induced currents cancel, and the signal out is zero (0Vac). The magnitude of the signal out voltage on either line indicates the position of the core. Near the centre of motion, the change in voltage is proportional to the displacement. But, further, from the centre the relationship becomes nonlinear.

If the core moves to any of the directions the flux linkage with any of the secondary coil increases. As the two secondary windings are connected in opposite direction, change in magnitude represents the direction of the core moved. The amount of voltage change in either secondary winding is proportional to the amount of movement of core.

##Advantages:

  • High sensitivity

  • Linearity, output of the LVDT is linear

  • LVDT produce high output signal, so no need of amplification

  • This transducer can usually tolerate a high degree of vibration and shock

  • There is no sliding contact so no friction

  • No hysteresis

  • Low power consuption

##Disadvantages:

  • High cost

  • Large displacement is needed to get an appreciable output

  • Sensitive to stray magnetic field

  • Temperature can affect the transducer


Position and Motion Measurement