Measurement & Calibration of Displacement Using LVDT

1
1. MEASUREMENT & CALIBRATION OF DISPLACEMENT

USING LVDT
AIM: To measure the displacement using LVDT.
APPARATUS:
1. LVDT Setup
2. Resistors – 4.7K-3, 10K
3. Signal generators
4. Digital multi- meter
DESCRIPTION:
The linear variable differential transformer is an inductance variable

type displacement transducer. It consists of three coils, one primary and two
secondary, all in a linear arrangement, with a magnetic core free to move
inside the coils. The core is normally made of nickel iron alloy and has a
longitudinal slot for reducing eddy currents. Ferrite cores are also being used
now for less loss and larger sensitivity. The core is positioned with a non-
magnetic rod. The primary is supplied with an alternating voltage of
amplitude between 5 and 25 volts and frequency 50Hz to 20 KHz. The
secondary are connected in phase opposition, so that the output is zero. This
assumes that there is no transverse displacement also of the core. The output
is linear with core displacement over a wide range but under goes a phase
shift of 180˚ when the core passes through the zero displacement position
i.e.; the central location. There is a residual voltage of 1% or less of the
maximum linear voltage at zero displacement. This in complete imbalance is
attributes to the stray magnetic and capacitive coupling between the primary
and the secondary and presence of harmonic components.
2
CIRCUIT DIAGRAM:
PROCEDURE:
1. Connection are made as per circuit diagram
2. Initially setup core of LVDT at center
3. Minimize the residual voltage with external balance circuit
4. Change the core displacement 1 mm in one direction and
observe the corresponding output voltage in DMM/CRO
5. Repeat the step 4 until then displacement is 10 mm and
observe the corresponding voltage for various displacement
in steps
6. The core is moved forwards in other direction and take the
reading for various displacements in steps
A) Measurement:
Residual voltage - 3.2mv
Minimum voltage - 0.7mv
3
Color code:
Red & green / shield: Primary
Yellow & green, center black: Secondary
MODEL OF EXPERIMENTAL RESULTS:
DISPLACEMENT
S.NO O/P VOLTAGE (mv)
(mm)
1 0 0.7
2 1 9.1
3 2 17.9
4 3 26.3
5 4 35.4
6 5 44.6
7 6 33.7
8 7 63.3
9 8 72.8
10 9 81.8
11 10 91.0
12 1 8.3
13 2 16.9
14 3 23.5
15 4 34.4
16 5 42.8
17 6 52.4
18 7 62.48
19 8 71.5
20 9 80.5
21 10 90.2
4
B) CALIBRATION:
a) Initially set the core of an LVDT at center position and observe the
residual voltage at null position.
b) Now rotate the 10Kohm pot and observe the voltage in DMM such
that it should be lowest reading which is approximately ( 0.6mv to
1.3mv)
TABULAR FORM:
DISPLACEMENT O/P VOLTAGE

S.NO in mm LEFT RIGHT
MODEL GRAPH:
RESULT:
Residual voltage = -------mv
Minimum voltage = --------mv
Linear displacement range =------mm
5
PRE EXPERIMENTAL QUESTIONS:

1. What are the different types of transducers used for displacement
measurements?
2. What is the difference between variable resistance and variable
inductance displacement transducer?
3. Explain about synchros and resolvers?
4. Explain about LVDT basic construction and connection of secondary
winding?
5. List few advantages of the LVDT type of displacement sensors?
6. Define the term residual voltage?
7. Define the characteristics of LVDT (such as Range, Linearity,
Temperature range etc)?
8. What is the i/p voltage applied for the LVDT?
9. How can you measure the angular displacement?
10.How can you measure the displacement by using Hall effect?
POST-EXPERIMENTAL QUESTIONS:
1. What is residual voltage applied from your experiment?
2. How can you identify the center of LVDT?
3. What is the min voltage you can obtain by adjusting the null balancing
circuit?
4. Define the range of displacement and range of voltage of your
experiment?
5. How can you obtain the Ac signal w3ith different frequencies such as
2 K Hz –10 K Hz with different amplifiers?
6. Describe the color code of LVDT?
7. What is the linear displacement range of LVDT?
8. What is the difference between LVDT and RVDT?
9. Is it possible to measure stress by using LVDT?
10.Analyze the results.

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1

1. MEASUREMENT & CALIBRATION OF DISPLACEMENT

AIM: To measure the displacement using LVDT.

The linear variable differential transformer is an inductance variable

DISPLACEMENT O/P VOLTAGE

PRE EXPERIMENTAL QUESTIONS:

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