BEE1313 – CHAPTER 4 1

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

BEE1313 – CHAPTER 4 2

LVDT-Inductive TLVDT-Inductive T

A reliable and accurate sensing device that converts linear position or motion to a proportional electrical output.

BEE1313 – CHAPTER 4 3

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

BEE1313 – CHAPTER 4 4

Applications of LVDTsApplications of LVDTs

BEE1313 – CHAPTER 4 5

Among the advantages of LVDT are as follows:

• 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.

LVDT

BEE1313 – CHAPTER 4 6

LVDTLVDT

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

Primary Secondary

Inductors and tranformers work only for ac signals

A

B

A

B

BAout VVV

BEE1313 – CHAPTER 4 7

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

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.

BEE1313 – CHAPTER 4 9

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 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.

BEE1313 – CHAPTER 4 10

LVDT OperationLVDT Operation

Please read the supplementary lecture note on LVDT:http://notes.ump.edu.my/fkee/BEE1313/SYAKIRIN/slide/lvdt_primer.pdf

BEE1313 – CHAPTER 4 11

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 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.

BEE1313 – CHAPTER 4 12

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– 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)