LVDT stands for Linear Variable Differential Transformer. It is an electromechanical transducer that converts linear motion to an electrical signal. LVDTs have advantages like friction-free operation, infinite resolution, and single axis sensitivity. They are used in applications like automation machinery, civil engineering, manufacturing, and testing. LVDTs work using electromagnetic induction - a ferrous core inside alters the magnetic flux in two coils, producing an output voltage proportional to displacement. Common manufacturers include RDP, Macro Sensors, and Honeywell, with LVDTs typically costing a few hundred dollars.

1. LVDT
LINEAR VARIABLE DISPLACEMENT
TRANSDUCER
-KUL BHUSHAN (45)
-MAYANK (46)
-MITHUN MOHANDAS(47)
-JITHIN P.(38)

2. OuTLine
 Definition of a Transducer
 Definition and Uses (4)
 Advantages & Disadvantages of LVDT
 Variety and Type (3)
 Underlying Principle (4)
 Manufacturers/Cost (1)

3. DeFiniTiOn OF TRAnSDuCeR
 Transducersareelectric or electronic devicesthat
transform energy from oneform to another. For
example, astereo speaker convertstheelectrical
signalsof recorded music into sound. Many
peoplethink of atransducer asbeing a
complicated, technical devicedesigned to gather
or transfer information. In reality, however,
anything that convertsenergy can beconsidered a
transducer.

4. 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

5. ADVANTAGESOF LVDT:-
 LINEARITY:-The output voltage of LVDT is
almost linear for displacement up to 5 mm.
 HIGH OUTPUT:-LVDT gives reasonably high
output and hence require less amplification
afterwards.
 HIGH SENSITIVITY:-LVDT has high
sensitivity of about 300mV/mm i.e. 1mm of
displacement of the core produces a output
voltage of300 mV,.

6. ADVANTAGESOF
LVDT(continue)
 LESS FRICTION:-Since there are no sliding
contacts, the friction is very less.
 LOW POWER CONSUMPTION:- Most
LVDT’s consume less than 1 W of power.

7. DISADVANTAGESOF LVDT:-
 Comparatively large displacements are
necessary for appreciable differential output.
 They are sensitive to stray magnetic fields.
However this interference can be reduced by
shielding.
 Temperature affects the transducer.

8. 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!!!

9. Uses
 Automation Machinery
 Civil/Structural Engineering
 Power Generation
 Manufacturing
 Metal Stamping/Forming
 OEM
 Pulp and Paper
 Industrial Valves
 R & D and Tests
 Automotive Racing
Source:http://www.rdpe.com/ex/tips.htm
LVDT accessories tips

10. Uses (cont.)
 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

11. Type of LVDT’s
 DC vs. AC Operated
 DC 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

12. Type of LVDT’s (cont.)
 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
 Suitability
 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
 Suitability
 Static – slow moving application (joint-opening in pavement slabs)

13. Type of LVDT’s (cont.)
Generic Schematic:
Source: http://www.daytronic.com/Products/trans/lvdt/default.htm#UNG
Examples:

14. LVDT Components
Signal conditioning circuitry
Primary coil
Secondary coil
Secondary coil
Bore shaft
Ferrous core
Source: http://www.macrosensors.com/lvdt_macro_sensors/lvdt_tutorial/lvdt_primer.pdf
Cross section of a DC-LVDT
Epoxy encapsulation
Stainless steel end caps
High density glass filled coil forms
Magnetic shielding

15. Underlying Principle
 Electromagnetic Induction:
L
i
Φ
=
Where: L= inductance
= magnetic flux
= electric currenti
Φ

16. Underlying Principle
 Electromagnetic Induction:
 Primary Coil (RED) is connected to power source
 Secondary Coils (BLUE) are connected in parallel but with opposing polarity
 Primary coil’s magnetic field (BLACK) induces a current in the secondary coils
 Ferro-Metallic core (BROWN) manipulates primary’s magnetic field

17. Underlying Principle
 In the null position, the magnetic field generates currents of equal magnitude in
both secondary coils.
 When the core is moved, there will be more magnetic flux in one coil than the
other resulting in different currents and therefore different voltages
 This variation in voltages is linearly proportional to displacement
Null position
Displaced
Source: http://www.macrosensors.com/lvdt_macro_sensors/lvdt_tutorial/lvdt_primer.pdf

18. Manufacturers/Cost
 Manufacturers:
 RDP group:
 http://www.rdpelectrosense.com/displacement/lvdt/menu-
lvdt.htm
 Macro Sensors:
 http://www.macrosensors.com/ms-lvdt_products.html
 Honeywell Sensing & Control:
 http://www.sensotec.com/lvdt.asp
 Costs:
Model Type Stroke Price
LAT 100-0.5 AC Unguided Armature 0.5 ± inch $270.00
LD200-10 AC Unguided Armature 0.5 ± inch $225.00
LAT 100-1 AC Unguided Armature 1.0 ± inch $305.00
LAT 101-0.5 Spring Return Armature 0.5 ± inch $410.00
LAT 101-1 Spring Return Armature 1.0 ± inch $470.00

19. Cited Sources
 Macro Sensors
 http://www.macrosensors.com/ms-lvdt_faq-
tutorial.html
 Daytronic Corporation
 http://www.daytronic.com/Products/trans/lvdt/de
fault.htm
 RDPE Group
 Source:http://www.rdpe.com/ex/tips.htm