LINEAR VARIABLE DISPLACEMENT TRANSDUCER (LVDT)LINEAR VARIABLE DISPLACEMENT TRANSDUCER (LVDT)

A basic transducer which is always useful in the field ofinstrumentation

Principle of LVDT:

LVDT works under the principle of mutualinduction, and the displacement which is a non-electrical energy is converted into an electrical energy.

And the way how the energy is gettingconverted is described in working of LVDT in a detailedmanner.

Construction of LVDT:

LVDT consists of a cylindrical transformer where it issurrounded by one primary winding in the centre of theformer and the two secondary windings at the sides.

The number of turns inboth the secondarywindings are equal, butthey are opposite to eachother.

i.e., if the left secondary windings is in the clockwisedirection, the right secondary windings will be in theanti-clockwise direction, hence the net outputvoltages will be the difference in voltages betweenthe two secondary coil.

The two secondary coil is represented as S1 andS2. Esteem iron core is placed in the centre ofthe cylindrical former which can move in to andfro motion as shown in the figure.

Working of LVDT:

On applying an external force which is the displacement, ifthe core reminds in the null position itself withoutproviding any movement then the voltage induced in boththe secondary windings are equal which results in netoutput is equal to zero Esec1-Esec2=0

Working of LVDT:When an external force is applied and if the steel iron coretends to move in the left hand side direction then the emfvoltage induced in the secondary coil is greater whencompared to the emf induced in the secondary coil 2.Therefore the net output will be Esec1-Esec2

Working of LVDTWhen an external force is applied and if the steel iron coremoves in the right hand side direction then the emfinduced in the secondary coil 2 is greater when comparedto the emf voltage induced in the secondary coil 1.The net output voltage will be E0 = Es2-Es1

Advantages of LVDT:1) Infinite resolution is present in LVDT2) High output3) LVDT gives High sensitivity4) Very good linearity5) Ruggedness6) LVDT Provides Less friction7) Low hysteresis8) LVDT gives Low power consumption.

Applications of LVDT:

1)LVDT is used to measure displacement ranging from fraction millimeter to centimeter.

2)Acting as a secondary transducer, LVDT can be used as a device to measure force, weight and pressure, etc..

RVDT – Rotary Variable Diff Transformer

Construction of RVDT and Working Principle

Basic RVDT construction and operation is provided by rotating an

iron-core bearing supported within a housed stator assembly.

The stator consists of a primary excitation coil and a pair of

secondary output coils.

A Rotary Variable Differential Transformer (RVDT) is an

electromechanical transducer that provides a variable alternating

current (AC) output voltage that is linearly proportional to the

angular displacement of its input shaft.

LINEAR POTENTIOMETER

Potentiometers are electrical devices which are a form of variable resistance.

It consists of a sliding contact which moves over the

length of a resistance element.

This sliding contact connects to a plunger, which

links to the object whose displacement is to be

measured.

Referring to the electrical circuit shownhere, An input voltage Xt is applied acrossthe whole resistance element, at pointsA and C. The output voltage, Xi , is measuredbetween the sliding contact at point Band the end of the resistance elementat point C. A linear relationship exists betweenthe input voltage Xt, output voltage Xiand the distance BC.

ANGULAR POTENTIOMETER Rotary or angular potentiometers measure angular displacement .

FLAPPER NOZZLE SYSTEM

A pneumatic control system operates with air. The signal is transmitted in form of variable air pressure (often in the range 3-15 psi, i.e. 0.2 to 1.0 bar) that initiates the control action.

It converts very small displacement signal (in order of microns) to variation of airpressure.