LVDT

• You’re expected to learn

– Linear Variable Differential Transformer

(LVDT)

• Architecture

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• Architecture

• Diagram

• Application

LVDTLVDT--Inductive TInductive 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

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electronics module. The

module is secured with a

potting compound that is not

shown in this drawing

Applications of LVDTsApplications of LVDTs

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Among the advantages of LVDT are as follows:

• It produces a higher output voltages for small

changes in core position.

• Low cost

LVDT

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• 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.

LVDTLVDT

Primary Secondary

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An inductor is basically a coil of wire

over a “core” (usually ferrous)

It responds to electric or magnetic

fields

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

BAoutVVV −=

EXAMPLES OF LVDT APPLICATIONEXAMPLES OF LVDT APPLICATION

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LVDT OperationLVDT 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

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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.

LVDT OperationLVDT 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

V .

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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.

LVDT OperationLVDT Operation

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ExampleExample

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

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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.

Student’s activity for next class

• Based on each measurement, I expect you to gather all the information in the following order– Type sensors

– Architecture

– Operation

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– 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)