Transcript CHAPTER 2

Today’s class
• By the end of this class, you’re expected
to learn
– Linear Variable Differential Transformer
(LVDT)
• Architecture
• Diagram
• Application
– Discussion on student’s activity
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LVDT-Inductive T
A reliable and accurate sensing
device that converts linear position
or motion to a proportional
electrical output.
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LVDT
The cross sectional view of
the DC LVDT at left shows the
built-in signal conditioning
electronics module. The
module is secured with a
potting compound that is not
shown in this drawing
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Applications of LVDTs
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LVDT
Among the advantages of LVDT are as follows:
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•
It produces a higher output voltages for small
changes in core position.
Low cost
Solid and robust -capable of working in a wide
variety of environments.
No permanent damage to the LVDT if
measurements exceed the designed range.
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LVDT
Primary
Secondary
A
A
B
B
An inductor is basically a coil of wire
over a “core” (usually ferrous)
It responds to electric or magnetic
fields
Vout  VA  VB
A transformer is made of at
least two coils wound over the
core: one is primary and
another is secondary
Inductors and tranformers work only for ac signals
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EXAMPLES OF LVDT APPLICATION
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LVDT Operation
Windings are connected “series
opposing” polarities of V1 and V2
oppose each other if we trace through
the circuit from terminal A to B.
If the core at the center, V1=V2, Vo=0
When the core is away from center
toward S1, V1 is greater than V2 and
the output voltage Vo will have the
polarity V1.
When the core is away from center
toward S2, V2 is greater than V1 and
the output voltage Vo will have the
polarity V2.
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LVDT Operation
That is, the output ac voltage inverts
as the core passes the center position
The farther the core moves from
center, the greater the difference in
value between V1 and V2,
consequently the greater the value of
Vo.
Thus, the amplitude of Vo is a function
of the distance the core has moved,
and the polarity or phase indicates
which direction is has moved.
If the core is attached to a moving
object, the LVDT output voltage can be
a measure of the position of the
object.
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LVDT Operation
Please read the supplementary lecture note on LVDT:
http://notes.ump.edu.my/fkee/BEE1313/SYAKIRIN/slide/lvdt_primer.pdf
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Example
An ac LVDT has the following data; input 6.3V,
output 5.2V, range ±0.50 cm. Determine:
a) Plot of output voltage versus core position for a
core movement going from +0.45cm to -0.03cm?
b) The output voltage when the core is -0.35cm from
the center?
c) The core movement from center when the output
voltage is -3V?
d) The plot of core position versus output voltages
varying from +4V to -2.5V.
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Student’s activity for next class
• Based on each measurement, I expect you to
gather all the information in the following order
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–
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Type sensors
Architecture
Operation
Application
Diagram
• You will need to prepare study materials/notes
based on the information above
• I will collect them by the end of next class (soft
copy)
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