Inductive Transducers with Focus on LVDT
Principles, Construction, and Applications
Academic Exploration Structured Content Visual Approach
Comprehensive study of Covers principles, construction, Illustrated with schematics,
inductive transducers with working mechanism, diagrams, and vector-based
detailed focus on LVDT, the characteristics, advantages, academic visuals for clarity and
most widely used variant. limitations, and applications. engagement.
Introduction to Transducers
Role in Measurement Systems
Definition Role in Measurements Classification Basis
A transducer is a device that Essential for sensing, Classified by operating principle
converts one form of energy monitoring, and control in (active/passive), output nature
into another, often translating engineering and scientific (analog/digital), and parameter
physical parameters into applications, enabling precise measured (displacement,
electrical signals. data acquisition. pressure, etc.).
Classification of Transducers
Different Perspectives of Categorization
Active vs. Passive Analog vs. Digital Primary vs. Secondary
Active transducers generate Analog transducers provide Primary transducers sense the
output directly (e.g., continuous output signals, while parameter directly, while
thermocouples), while passive digital transducers generate secondary transducers convert
require external power (e.g., discrete or binary outputs. it into measurable signals.
LVDT).
Inductive Transducers
Definition and Concept
Basic Idea Passive Nature Common Usage
Inductive transducers work on They require external AC Widely used for displacement,
the principle that inductance of excitation and produce an vibration, and pressure
a coil changes with the position output proportional to measurement in engineering
or motion of a magnetic core. displacement or related applications.
parameters.
Principle of Inductance
Physics Behind Inductive Transducers
Flux Linkage Dependence on Core Mathematical Relation
Inductance is proportional to the Position and permeability of the L = N²μA / l, where N is turns, μ
number of turns and magnetic core material directly influence is permeability, A is area, and l
flux linkage with the coil. the inductance value. is length of coil path.
Types of Inductive Transducers
Different Configurations
Reluctance-based Mutual Inductance Type Differential Transformer
Use changes in reluctance Work on the principle of Type
caused by motion of a variation in mutual inductance Include LVDT and RVDT, widely
ferromagnetic element. between two coils due to used for precise linear and
displacement. angular displacement
measurement.
Introduction to LVDT
Linear Variable Differential Transformer
Definition Operating Principle Significance
An LVDT is an electromechanical Based on differential voltages Most widely used inductive
device that converts linear induced in secondary coils due transducer due to accuracy,
displacement into an electrical to movement of a ferromagnetic linearity, and durability.
signal. core.
Construction of LVDT
Components and Design
Primary Coil Secondary Coils Movable Core
Single primary winding excited Two identical secondary coils Ferromagnetic core moves
by an AC source, generating placed symmetrically and linearly inside the coils, altering
alternating magnetic flux. connected in series opposition. flux linkage.
Working Principle of LVDT
How Displacement Becomes Voltage
Null Position Core Displacement Differential Output
At central core position, Movement of the core towards The net differential voltage is
voltages in both secondary coils one coil increases its voltage proportional to core
are equal and opposite, giving while decreasing the opposite displacement and indicates
zero output. coil's voltage. direction as well as magnitude.
Output Characteristics of LVDT
Response and Sensitivity
Linear Region Null Point Phase Sensitivity
In the central range of core At core center, output is zero; Direction of displacement
displacement, output voltage is provides a stable reference determined by phase of output
highly linear with position. point for calibration. voltage relative to input.
Mathematical Model of LVDT
Equations Relating Displacement to Output
Induced Voltages Differential Output Linear Relation
e1 ∝ N dΦ1/dt and e2 ∝ N Eout = e1 – e2, proportional to For small displacements: Eout ≈
dΦ2/dt, where Φ1 and Φ2 are displacement and phase k·x, where k is sensitivity
flux linkages to secondary coils. indicating direction. constant and x is displacement.
Performance Characteristics of LVDT
Key Parameters
Linearity Sensitivity Frequency Response
Excellent linearity over a wide High sensitivity, typically Capable of operating across a
displacement range, crucial for several mV per micrometer of wide frequency range, suitable
precision applications. displacement. for dynamic measurements.
Advantages of LVDT
Why It Is Widely Used
High Accuracy Durability Infinite Resolution
Provides precise displacement Rugged design, long operational Theoretically unlimited
measurements with excellent life, and resistance to wear resolution as output changes
linearity. since no physical contact is smoothly with displacement.
required.
Limitations of LVDT
Practical Constraints
Temperature Sensitivity Electronics Requirement Size Constraints
Performance may degrade at Requires AC excitation and Bulkier compared to some
high temperatures due to coil signal conditioning circuits for modern displacement sensors,
resistance changes. proper operation. limiting miniaturization.
Applications of LVDT
Engineering and Industrial Uses
Aerospace Robotics & Automation Civil & Mechanical
Used for flight control systems, Provides precise displacement Engineering
landing gear monitoring, and feedback for robotic arms and Employed in vibration analysis,
structural testing. automated machinery. bridge monitoring, and precision
machine tools.
