How LVDT Works | Construction and Working
Summary
TLDRThis lecture delves into the workings of the Linear Variable Differential Transformer (LVDT), a device renowned for its precision in measuring linear displacement. It operates on the principle of mutual inductance, with a cylindrical former at its core, surrounded by a primary coil and two secondary coils. The movable ferromagnetic core's position relative to the coils determines the output voltage, indicating displacement direction and magnitude. The video explains the three core positions and the corresponding voltage outputs, highlighting the use of a phase-sensitive detector for direction sensitivity. Advantages include a wide measurement range, no frictional losses, high input sensitivity, low hysteresis, and direct conversion to electrical signals. However, the device's sensitivity to stray magnetic fields and environmental factors like vibrations and temperature are noted as drawbacks.
Takeaways
- 🌟 LVDT stands for Linear Variable Differential Transformer and operates on the principle of mutual inductance.
- 🔍 LVDTs are popular for measuring linear displacement with commercial models offering a range from plus/minus 0.25 millimeters to plus/minus 250 millimeters.
- 🏗️ The construction of an LVDT includes a cylindrical former, a primary coil, and two secondary coils, with a ferromagnetic core that moves freely within.
- 📍 The operation of LVDT is explained through three core positions: null (center), left of null, and right of null, affecting the output voltage.
- 🔧 A phase-sensitive detector is used with LVDT to determine the direction of core movement, as the output voltage alone cannot indicate direction.
- ⚙️ When the core moves left, the EMF in secondary coil 1 is greater than in coil 2, resulting in a net negative displacement.
- 🔄 Conversely, when the core moves right, the EMF in secondary coil 2 exceeds that in coil 1, leading to a net positive displacement.
- 📊 LVDTs offer several advantages, such as a wide measurement range, no frictional losses, high input and sensitivity, low hysteresis for excellent repeatability, and direct conversion to electrical signals.
- 🔌 They can also function as secondary transducers, converting other types of measurements, like pressure, into electrical signals after calibration.
- ⚠️ Disadvantages include sensitivity to stray magnetic fields and susceptibility to vibrations and temperature changes, necessitating protective setups.
Q & A
What does LVDT stand for?
-LVDT stands for Linear Variable Differential Transformer.
What is the principle on which LVDT operates?
-LVDT operates on the principle of variation of mutual inductance.
What is the full scale displacement range of commercial LVDTs?
-Commercial LVDTs are available with a full scale displacement range of plus minus 0.25 millimeters to plus minus 250 millimeters.
What are the main components of an LVDT?
-The main components of an LVDT are a cylindrical former, a primary coil, two secondary coils, and a movable ferromagnetic core.
What type of voltage source is used to excite the primary winding of an LVDT?
-The primary winding of an LVDT is excited by a 1 to 10 volts AC voltage source.
How are the secondary coils in an LVDT connected?
-The secondary coils in an LVDT are connected in series.
What is the null position in an LVDT?
-The null position in an LVDT is when the core is at the center, resulting in equal voltage induced in both secondary coils and a net output of zero.
What is the role of a phase sensitive detector in LVDT?
-A phase sensitive detector is used to make the measurement direction sensitive by comparing the phase of the secondary output with the primary signal to judge the direction of movement.
What happens when the core of an LVDT moves to the left-hand side?
-When the core moves to the left-hand side, the EMF voltage induced in secondary coil one is greater than in secondary coil two, resulting in a net negative displacement.
What are some advantages of using an LVDT?
-Advantages of using an LVDT include a wide range for measurement of displacement, no frictional losses, high input and sensitivity, low hysteresis for excellent repeatability, direct conversion to electrical signals, and the ability to act as secondary transducers.
What are the disadvantages of using an LVDT?
-Disadvantages of using an LVDT include sensitivity to stray magnetic fields and being affected by vibrations and temperature.
Outlines
🔍 Introduction to LVDT and Its Working Principle
This paragraph introduces the Linear Variable Differential Transformer (LVDT), a device used for measuring linear displacement based on the principle of mutual inductance. It discusses the construction of an LVDT, which includes a cylindrical former, a primary coil, and two secondary coils connected in series. The paragraph also explains the working of LVDT through three core positions: null (center), left, and right of the null position. The output voltage differences between the secondary coils indicate the direction and magnitude of displacement. A phase-sensitive detector is mentioned as a necessary component to make the measurement direction-sensitive.
🛠 Advantages and Disadvantages of LVDTs
The second paragraph delves into the advantages of LVDTs, such as their wide measurement range (from 0.25 mm to 250 mm), lack of frictional losses due to the core moving inside a hollow former, high input and sensitivity (producing an output that does not require amplification), low hysteresis for excellent repeatability, and direct conversion of linear displacement into electrical signals. It also mentions that LVDTs can act as secondary transducers, such as in the case of a LibDem tube that converts pressure into linear displacement. However, the paragraph also highlights the disadvantages, including sensitivity to stray magnetic fields and the impact of vibrations and temperature on their performance.
Mindmap
Keywords
💡LVDT
💡Mutual Inductance
💡Cylindrical Former
💡Primary Coil
💡Secondary Coils
💡Ferromagnetic Core
💡Null Position
💡Phase Sensitive Detector
💡Displacement Range
💡Advantages and Disadvantages
Highlights
LVDT stands for Linear Variable Differential Transformer and operates on the principle of mutual inductance variation.
It is a popular device for measuring linear displacement with commercial models offering a range from plus/minus 0.25 mm to plus/minus 250 mm.
The construction of an LVDT includes a cylindrical former, a primary coil, and two secondary coils with equal turns connected in series.
A ferromagnetic core within the LVDT is movable and can freely slide through the former.
LVDT operation is explained through three core positions: null (center), left of null, and right of null.
At the null position, the induced voltage in both secondary coils is equal, resulting in a net output of zero.
A phase-sensitive detector is used with LVDT to determine the direction of core movement due to equal induced voltages at the null position.
When the core moves left, the induced EMF in secondary coil 1 is greater than in secondary coil 2, resulting in negative displacement.
Conversely, when the core moves right, the induced EMF in secondary coil 2 exceeds that of coil 1, indicating positive displacement.
LVDTs have a wide measurement range, capable of measuring displacements from 0.25 mm to 250 mm.
They have no frictional losses as the core moves inside a hollow former, ensuring accurate displacement measurement.
LVDTs exhibit high input and sensitivity, producing an output that does not require amplification.
Low hysteresis in LVDTs ensures excellent repeatability under all conditions.
LVDTs provide direct conversion of linear displacement to electrical voltage signals.
They can also function as secondary transducers, converting other types of measurements into electrical signals.
LVDTs are sensitive to stray magnetic fields and require protection setups to prevent interference.
They are also affected by vibrations and temperature, which can impact their performance.
The lecture concludes with a teaser for the next video on the calibration of LVDT.
Transcripts
hello friends in this lecture I am going
to explain about how LVDT means linear
variable differential transformer works
LVDT works on the principle of variation
of mutual inductance it is one of the
most popular type of device for
measurement of linear displacement
commercial LVD tees are available having
full scale displacement range of plus
minus 0.25 millimeters to plus minus 250
millimeters now look at construction of
LVDT it consists of a cylindrical former
it is surrounded by one primary winning
called as primary coil at the center of
the former the primary winding is
excited by 1 to 10 volts AC voltage
source and the 2 secondary windings are
at both sides of primary coil are fixed
called as secondary coil 1 and secondary
coil 2 the number of terms in both
secondary coils are equal and they are
connected in series it consists of
movable a ferromagnetic core which is
freely moves through the former now see
how LVDT works Here I am going to
explain three positions for LVDT first
condition core at null position that is
at center
second condition is core at left side of
null position and third condition core
ax right side of null position now let
us see first case in details that is
core at naught position the voltage
induced in both for secondary coils are
equal as EMF induced is same in both
coils which results in net output is
equal to zero thus from the measurement
of the output voltage only one cannot
predict the direction of the core
movement so a phase sensitive detector
is a useful circuit to make the
measurement Direction sensitive it is
connected at the output of the LVDT and
compares the phase of the secondary
output with the primary signal to judge
the direction of movement case second
when an external force is applied and if
the iron core tends to move in the
left-hand side direction then the EMF
voltage induced in the secondary coil
one is greater when compared to the EMF
induced in the secondary coil two
therefore the net output will give
negative displacement case 3 when an
external force is applied and if the
iron core moves in the right hand-side
direction then the EMF induced in the
secondary coil 2 is greater when
compared to the EMF voltage induced in
the secondary coil first therefore the
net output will give positive
displacement LVDT having many advantages
like one pad range the LVDT s have a
very high range for measurement of
displacement they can used for
measurement of displacements ranging
from 0.25 millimeters to 250 millimeters
to no frictional losses as the core
moves inside a hollow former so there is
no loss of displacement input as
frictional loss so it makes LVDT as very
accurate device 3 high input and high
sensitivity the output of LVDT is so
high that it doesn't need any
amplification the transducer possesses a
high sensitivity which is typically
about 40 volts per millimeter for low
hysteresis LVDT s show a low hysteresis
and hence repeatability is excellent
under all conditions five direct
conversion to electrical signals 6 they
convert the linear displacement to
electrical voltage which are easy 7 they
can also acts as the secondary
transducers for example LibDem tube
which acts as
a primary transducer and covered
pressure into linear displacement then
LVDT covers this displacement into
electrical signal which after
calibration gives the ideas of the
pressure of fluid disadvantages of LVDT
one LVDT is sensitive to stray magnetic
fields so they always require a set up
to protect them from stray magnetic
fields to they are affected by
vibrations and temperature thank you for
listening carefully watch my next video
on calibration of LVDT
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