1. LVDT Linear Variable Displacement Transducers/Transformers
Government College of Engineering Palanpur
Prepared by:-
Subject:- Analog Electronics( )
Department :- Electrical Engineering
Faculty Name:- N. A. Mistri &
S.Swami
LVDT Linear Variable Displacement Transducers/Transformers

2. LVDT:-
Linear Variable Displacement Transducers/Transformers

3. Definition – What is a LVDT?
Electromechanical transducer
Coupled to any type of object/structure
Converts the rectilinear motion of an object into a corresponding electrical signal
Measures Displacement!!!!!!!!
Precision of LVDT
Movements as small as a few millionths of an inch
Usually measurements are taken on the order of ±12 inches
Some LVDT’s have capabilities to measure up to ±20 inches

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It consists basically of a primary winding and two secondary windings, wound over a hollow tube and positioned so the primary winding is between two secondaries. In figure shows the construction of the LVDT

5. An iron core slides within the tube and therefore affects the magnet coupling between the primary and the two secondaries. When the core is in the centre, voltage induced in the two secondaries is equal.

6. Definition – Why use a LVDT?
Friction – Free Operation
NO mechanical contact between core and coil (usually)
Infinite Mechanical Life
Infinite Resolution
Electromagnetic coupling
Limited only by electrical noise
Low risk of damage
Most LVDT’s have open bore holes
Null Point Repeatability
Zero displacement can be measured
Single Axis Sensitivity
Effects of other axes are not felt on the axis of interest
Environmentally Robust
Stable/Strong sensors – good for structural engineering tests!!!

7. Uses Automation Machinery Civil/Structural Engineering
Power Generation
Manufacturing
Metal Stamping/Forming
OEM
Pulp and Paper
Industrial Valves
R & D and Tests
Automotive Racing
LVDT accessories tips

8. Uses Civil/Structural Engineering Examples
Displacement measurement of imbedded concrete anchors tested for tensile, compression, bending strength and crack growth in concrete
Deformation and creep of concrete wall used for retaining wall in large gas pipe installation
Dynamic measurement of fatigue in large structural components used in suspension bridges
Down-hole application: measuring displacement (creep) of bedrock

9. Type of LVDT’s DC vs. AC Operated DC Operated AC Operated
Ease of installation
Simpler data conditioning
Operate from dry cell batteries (remote locations)
Lower System Cost
AC Operated
Smaller than DC
More accurate than DC
Operate well at high temperatures

10. Type of LVDT’s Armature Types Unguided Armature
Fits loosely in bore hole
LVDT body and armature are separately mounted – must ensure alignment
Frictionless movement
Suitability
Short-range high speed applications
High number of cycles
Captive (Guided) Armature
Restrained and guided by a low-friction bearing assembly
Longer working range
Alignment is a potential problem
Spring Extended Armature
Restrained and guided by a low-friction bearing assembly (again!)
Internal spring pushes armature to max. extension
Maintains reliable contact with body to be measured
Static – slow moving application (joint-opening in pavement slabs)

11. Type of LVDT’s
Generic Schematic:
Examples:

12. 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
Cross section of a DC-LVDT

13. Advantages The output of LVDT is displacement upto 5 mm.
The change in output voltage is continuous and stepless.
High output
Low hysteresis

14. THANK YOU