Linear variable displacement transformer

The term “LVDT” are known as “linear Variable Displacement Transformer”. This is a common type   of electromechanical transducer. It converts the rectilinear motion of an object couples as in mechanical linkages into signals.

PRINCIPLE:-

                           LVDT is a popular transducer which is based on a “variable inductance principle” for displacement measurement. It is based on changing the intensity of signal.

CONSTRUCTION:-

  In this three coils are arranged as shown in fig. (a) Between which magnetic core are moves freely. The construction of LVDT is as shown in fig. (b) The central coil (primary) energized from an external AC supply & the two end coils (secondary) are pick up coils. The core passing through the primary and & secondary coils.  

   

 WORKING:-         

                           In operation an AC input is impressed on the primary coil, and an AC output voltage, depending on magnetic coupling between the core and the coils, is obtained at the secondary coils.

                           The magnetic coupling, hence the output depends upon the position of the core. usually a linear range is specified for a differential transformer , and when the core is operated within this range ,it is called “linear variable displacement transformer” (LVDT)

  Theoretically, there should be a core position for which the voltage induced in the secondary coils will be the same as that of the input and resulting output should be zero. This position is called as null position and is difficult to obtain in practice.

                       The difference of the two voltages across the output terminals of (LVDT) gives a measure of the physical position of the center core. By comparing the magnitude and the phase of output voltage, the amount and direction of the moment of core can be determined

Advantages of LVDT:-

1.      It serves as primary detector transducers, it converts mechanical displacement into proportional electrical voltage without the assistance of any elastic number.

2.      It cannot be overloaded, since the core is completely separable from the device.

3.      It is insensitive to temperature changes.

4.      It gives high output without any intermediate amplification.

5.      It is an economical device.

Disadvantages of LVDT:-

1.        When used with strain gauge, the core is appreciable mass,compared to the bonded strain gauge.

2.        It is designed for specific input frequency.

3.        The device becomes complicated, is the direction of null is also required.

 Application:-

1.        It is used as transduction element.

2.        It is used in CNG machine for displacement measurement

3.        In creep testing machine, it is used for deflection measurement.

4.      It is used for different measurements like pressure, force, thickness, etc.also in the control system.