Basic Principle of Strain Gauge Accelerometer
When a cantilever beam attached with a mass at its free end is subjected to vibration,
vibrational displacement of the mass takes place. Depending on the displacement of the
mass, the beam deflects and hence the beam is strained. The resulting strain is proportional
to the vibration displacement of the mass and hence the vibration/acceleration being
measured when calibrated.
Description of Strain Gauge Accelerometer
The main parts of a strain gauge accelerometer are as follows:
A cantilever beam fixed to the housing of the instrument.
A mass is fixed to the free end of the cantilever beam.
Two bounded strain gauges are mounted on the cantilever beam as shown in
Damping is provided by a viscous fluid filled inside the housing.
Operation of Strain Gauge Accelerometer
The accelerometer is fitted on to the structure whose acceleration is to be measured.
Due to the vibration, vibrational displacement of the mass occurs, causing the
cantilever beam to be strained.
Hence the strain gauges mounted on the cantilever beam are also strained and due
to this their resistance change.
Hence a measure of this change in resistance of the strain gauge becomes a
measure of the extent to which the cantilever beam is strained.
But the resulting strain of the cantilever beam is proportional to the
vibration/acceleration and hence a measure of the change in resistance of the strain gauges
becomes a measure of vibration/acceleration.
The leads of the strain gauges are connected to a wheat stone bridge whose output
is calibrated in terms of vibration/acceleration.
A piezoelectric accelerometer utilizes the piezoelectric effect of certain materials to
measure dynamic changes in mechanical variables, such as mechanical shock,
vibration and acceleration. Like other transducers, piezoelectric accelerometers convert
one form of energy into another and provide an electrical signal in response to the
condition, property or quantity. Acceleration acts upon a seismic mass that is restrained
by a spring or suspended on a cantilever beam, and converts a physical force into an
There are two types of piezoelectric accelerometers: high and low impedance. High
impedance accelerometers have a charge output that is converted into a voltage using
a charge amplifier or external impedance converter. Low impedance units use the same
piezoelectric sensing element as high-impedance units, and incorporate a miniaturized
built-in charge-to-voltage converter and an external power supply coupler to energize
the electronics and decouple the subsequent DC bias voltage from the output signal.
Working Principle of Piezoelectric Accelerometer
A piezoelectric accelerometer consists of a mass attached to a piezoelectric crystal
which is mounted on a case. When the accelerometer body is subjected to vibration, the
mass on the crystal remains undisturbed in space due to inertia. As a result, the mass
compresses and stretches the piezoelectric crystal. This force is proportional to
acceleration in accordance with Newton’s second law, F = ma, and generates a charge.
The charge output is then converted into low impedance voltage output with the help of
Benefits of Piezoelectric Accelerometer
The key benefits of piezoelectric accelerometers are:
Wide frequency range
No moving parts
Excellent linearity over their dynamic range
Low output noise
Self-generating - no external power required
Acceleration signal can be integrated to provide velocity and displacement
Major applications of piezoelectric accelerometers include:
Engine testing - Combustion and dynamic stressing
Ballistics - Combustion, explosion, and detonation
Industrial/factory - Machining systems, metal cutting, and machine health monitoring
Original equipment manufacturer - Transportation systems, rockets, machine tools,
engines, flexible structures, and shock/vibration testers
Engineering - Dynamic response testing, shock and vibration isolation, auto chassis
structural testing, structural analysis, reactors, control systems and materials evaluation
Aerospace - Ejection systems, rocketry, landing gear hydraulics, shock tube
instrumentation, wind tunnel and modal testing.