Linear variable differential transformer
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LINEAR VARIABLE DIFFERENTIAL TRANSFORMER. VISHAL VASISTHA ASSISTANT PROFESSOR (ME) DRONACHARYA COLLEGE, GURGAON. LVDT WORKING. +. (50-20K Hz). E1. E2. (E1-E2). -. LVDT WORKING. LVDT WORKING. LVDT OPERATION. INTRODUCTION.

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LINEAR VARIABLE DIFFERENTIAL TRANSFORMER

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Linear variable differential transformer

LINEAR VARIABLE DIFFERENTIAL TRANSFORMER

VISHAL VASISTHA

ASSISTANT PROFESSOR (ME)

DRONACHARYA COLLEGE, GURGAON


Lvdt working

LVDT WORKING

+

(50-20K Hz)

E1

E2

(E1-E2)

-


Lvdt working1

LVDT WORKING


Lvdt working2

LVDT WORKING


Linear variable differential transformer

LVDT OPERATION


Introduction

INTRODUCTION

  • A transformer with variable secondary coupling dependent upon the core position (linear movement)

  • position-to-electrical sensor whose output is linearly proportional to the position of a movable magnetic core

  • Core moves linearly inside a transformer consisting of a primary coil and two secondary coils

  • Primary winding is excited with an ac voltage source(50-20K Hz)


Introduction1

INTRODUCTION

  • Voltage is induced by mutual induction principle (same as transformer) in secondary coils that vary with the position of the magnetic core within the assembly

  • Core is attached to the object whose movement or displacement is being measured

  • Core is not in contact with primary and secondary coils.

  • Secondary windings are wound out of phase with each other


Lvdt components

LVDT COMPONENTS

Ferrous core

Epoxy encapsulation

Primary coil

Secondary coil

Bore shaft

Magnetic shielding

Stainless steel end caps

Secondary coil

High density glass filled coil forms

Signal conditioning circuitry


Advantages

ADVANTAGES

  • Frictionless Measurement

  • Infinite Mechanical Life

  • Infinite Resolution

  • Null Position Repeatability

  • Cheap, easy to use way of measuring deflection


Advantages1

ADVANTAGES

  • Low risk of damage

  • Core and Coil Separation

  • Environmental Compatibility


Types of lvdt s

TYPES OF LVDT’S

AC

DC

Ease of installation

Can operate from dry cell batteries

Usually lower system cost

  • Smaller size

  • More accurate

  • Can operate within a wide temperature range

  • Lower unit cost.


Disadvantages

DISADVANTAGES

  • Area of dynamic measurement due to appreciable mass of core itself

  • Very high displacement is required for generating high voltages

  • Shielding is required since it is sensitive to magnetic field

  • The performance of the transducer gets affected by vibrations

  • Requires alignment to be correct

  • The range of measurement is limited to 12 in.


Applications

APPLICATIONS

  • Measure displacement of thermostat valve stem for diesel truck engine monitoring system

  • Blood-testing device measuring the displacement of blood cells as they contract

  • Measuring displacement of diamond tip to determine material hardness


Lvdt accelerometer

LVDT ACCELEROMETER


Lvdt accelerometer1

LVDT ACCELEROMETER


Lvdt accelerometer2

LVDT ACCELEROMETER


Lvdt accelerometer3

LVDT ACCELEROMETER

  • LVDT core acts as a seismic mass

  • Core is attached with two spring steels with the help of rods

  • Spring steels are attached to the case firmly

  • Spring steels provide spring action

  • As instrument is subjected to vibration, core moves up and down and induces resultant output in secondary coils


Types of lvdt s1

TYPES OF LVDT’S

  • Unguided Armature

  • Captive (Constrained) Armature

  • Spring-extended Armature


Unguided armature

UNGUIDED ARMATURE

Measured Object

Armature must be attached to the specimen

Armature fits loosely in the bore

Body must be separately supported & properly aligned


Unguided armature1

UNGUIDED ARMATURE

  • There is no wear on the LVDT because no contact is made between armature and bore.

  • LVDT does not restrict the resolution of measured data (“infinite resolution”).

Measured Motion


Unguided armature2

UNGUIDED ARMATURE

  • Well-suited for short-range, high-speed applications (vibration)

Measured Motion

time

displ.


Captive armature

CAPTIVE ARMATURE

Measured Object

Armature must be attached to the specimen

Armature is both guided and restrained by a low friction assembly

Body must be separately supported


Captive armature1

CAPTIVE ARMATURE

Advantages compared to unguided armature:

  • Better for longer working ranges

  • Preferred when misalignment may occur


Spring extended armature

Spring-Extended Armature

Measured Object

Like the captive armature, it has a low-friction bearing assembly

Internal spring to continuously push the armature to its fullest possible extension


Spring extended armature1

Spring-Extended Armature

  • The spring-extended armature is best suited for slow-moving applications.

  • Attachment between armature and specimen is not required.


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