LVDT is an acronym for Linear Variable Differential Transformer. It is a common type of electromechanical transducer that can convert the rectilinear motion of an object to which it is coupled mechanically into a corresponding electrical signal

1. .
LVDT
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2. OuTLine
 Definition of a Transducer

3. TRAnSDuCeR
 Transducersareelectric or electronic
devicesthat transform energy from one
form to another.
 In reality, however, anything that
convertsenergy can beconsidered a
transducer.
 . For example, astereo speaker converts
theelectrical signalsof recorded music
into sound

4. 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. L?V?D?T?
Linear Variable Differential Transformer
 Transformer: AC Input / AC Output
 Differential: Natural Null Point in
Middle
 Variable: Movable Core, Fixed Coil
 Linear: Measures Linear Position

6. Why 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. Definition of LVDT.
 The term LVDT stands for theLinear Variable
Differential Transformer. It is the most widely used
inductive transducer that covert the linear motion
into the electrical signals . The output across
secondary of this transformer is the differential so
it is called so.

8. construction
 Main Features of Construction are as, The
transformer consists of a primary winding P
and two secondary winding S1 and S2 wound
on a cylindrical former (which is hollow in
nature and will contain core).
 Both the secondary windings have equal
number of turns and are identically placed
on the either side of primary winding
 The primary winding is connected to an AC
source which produces a flux in the air gap
and voltages are induced in secondary
windings.

9. 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

10.  A movable soft iron core is placed inside
the former and displacement to be
measured is connected to the iron core.
 The iron core is generally of high
permeability which helps in reducing
harmonics and high sensitivity of LVDT.


11.  The LVDT is placed inside a stainless steel
housing because it will provide
electrostatic and electromagnetic
shielding.
 The both the secondary windings are
connected in such a way that resulted
output is the difference of the voltages of
two windings.

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

13. 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

14. Working in lvdt
 As the primary is connected to an AC source
so alternating current and voltages are
produced in the secondary of the LVDT.
 output in secondary S1 is e1 &in S2 is e2.
 So the differential output
is, eout = e1 - e2
This equation explains the principle of Operation
of LVDT

15.  CASE I When the core is at null position (for no
displacement) When the core is at null position then the
flux linking with both the secondary windings is equal so
the induced emf is equal in both the windings. So for no
displacement the value of output eout is zero as e1 and e2
both are equal. So it shows that no displacement took
place.
 CASE II When the core is moved to upward of null
position (For displacement to the upward of reference
point) In the this case the flux linking with secondary
winding S1 is more as compared to flux linking with S2.
Due to this e1 will be more as that of e2. Due to this
output voltage eout is positive.

16. CASE III When the core is moved to downward of Null position (for
displacement to the downward of reference point) In this case magnitude of
e2 will be more as that of e1. Due to this output eout will be negative and
shows the output to downward of reference point.

17. Analytic view

18. Tyes of lvdt
 Unguided Armature
 Captive Armature
 Spring-extended Armature

19. Unguided Armature
Measured
Object
Armature fits loosely
Armature must be attached to the
specimen
Body must be separately
supported & properly aligned
Elevation/Cross-Section
View

20. 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”).
Elevation/Cross-Section
View
Measured Motion

21. Captive Armature
Body must be separately supported
Measured
Object
Armature must be attached to
the specimen
Armature is both guided and restrained by
a low friction assembly

22. Captive Armature
Advantages compared to unguided armature:
► Better for longer working rangesBetter for longer working ranges
►Preferred when misalignment may occurPreferred when misalignment may occur

23. Spring-Extended Armature
Elevation/Cross-Section
View
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

24. ADVANTAGESOF LVDT:-
Robust; LVDT’s are robust equipment for measuring
deflection
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,.
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.

25. 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.

26. 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

27. web Sourcesweb Sources
 http://www.macrosensors.com/ms-lvdt_faq-tutorial.html
 http://www.electrical4u.com/linear-variable-
differential-transformer/
 Source:http://www.rdpe.com/ex/tips.htm
 https://en.wikipedia.org/wiki/Linear_variable_differe
ntial_transformer

28. conclusion