Mechanical Engineering - 22.302 ME Lab I
ME 22.302
Mechanical Lab I
Displacement Measurements LVDT
Linear Variable Differential Transformer
Dr. Peter Avitabile
University of Massachusetts Lowell
LVDT - 122601 - 1
Copyright © 2001
Mechanical Engineering - 22.302 ME Lab I
A “transducer” is a device that converts some mechanical quantity
into some measurable electrical quantity.
Through a calibration procedure, the “sensitivity” of the
transducer can be obtained
OUTPUT
INPUT
transducer
Physical Phenomenon
Pressure, Temperature,
Strain, Displacement,
Velocity, Acceleration,
etc
Dr. Peter Avitabile
Volts
per
Engineering
Unit
University of Massachusetts Lowell
Electrical Signal related
to Physical Phenomenon
DC voltage, AC voltage,
current, resistance, etc
V/EU
LVDT - 122601 - 2
Copyright © 2001
Mechanical Engineering - 22.302 ME Lab I
There are a wide variety of devices used to measure displacement
Potentiometer
Linear and Rotary Variable Differential Transformers
Capacitive Displacement Sensors
Linear Velocity Transducers
Angular Displacement and Velocity Devices
Only the LVDT will be considered here
Dr. Peter Avitabile
University of Massachusetts Lowell
LVDT - 122601 - 3
Copyright © 2001
Mechanical Engineering - 22.302 ME Lab I
An LVDT works on the principle of modifying the spatial
distribution of an alternating magnetic field. The LVDT consists
of a primary coil and two secondary coils.
The primary core tends to concentrate
the field in its vicinity.
Animate LVDT
This induces alternating currents in the
secondary coils.
As the primary is displaced, the voltage
in the closest secondary increases.
The difference in the two secondary
coils is proportional to the displacement
of the primary coil. The direction of the
motion is obtained from the phase of
the secondary coil AC voltages
Dr. Peter Avitabile
University of Massachusetts Lowell
LVDT - 122601 - 4
Copyright © 2001
Mechanical Engineering - 22.302 ME Lab I
LVDTs can be obtained to
measure thousands of an
inch up to several inches.
However, their frequency
response characteristics
are limited. They can be
used up to 100 to 200 Hz
depending on the excitation
frequency for the coil.
(They are “self” filtering
low pass filters.)
They are also very linear
over their designed linear
range and then become
highly non-linear.
Dr. Peter Avitabile
University of Massachusetts Lowell
LVDT - 122601 - 5
Copyright © 2001
Mechanical Engineering - 22.302 ME Lab I
Dr. Peter Avitabile
University of Massachusetts Lowell
LVDT - 122601 - 6
Copyright © 2001