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why do we use piezo ?

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mohammad hasan

on 6 July 2015

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Transcript of why do we use piezo ?

Accelerometer on smartphones
why do we use piezo ?
there is many reasons to use piezo such as :

-small size
-light weight
-wide dynamic range
-wide temperature range
-ultra low noise
-broad frequency range
-simple signal conditioning

common uses for piezoelectric
- Modal analysis
- Health and usage monitoring systems
- Aircraft flight test
- Preventative maintinance

There is many types of accelerometer
1- isolated compression
Single ended compression accelerometers can be susceptible to base strain and so to alleviate this problem the crystal is isolated from the base by mounting on an isolation washer or by reducing the mounting area by which the crystal is mounted to the base.

why do we need accelerometer ?
Vibration and shock are present in all areas of our daily lives. They may
be generated and transmitted by motors, turbines, machine-tools,
bridges, towers, and even by the human body.

While some vibrations are desirable, others may be disturbing or even
destructive. Consequently, there is often a need to understand the
causes of vibrations and to develop methods to measure and prevent
them. The sensors we manufacture serve as a link between vibrating
structures and electronic measurement equipment.

How does a piezo-electric accelerometer work?
Piezo-electric crystals are man-made or naturally occurring crystals that produce a charge output when they are compressed, flexed or subjected to shear forces. In a piezo-electric accelerometer a
mass is attached to a piezo-electric crystal which is in turn mounted to the case of the accelerometer. When the body of the accelerometer is subjected to vibration the mass mounted on the crystal wants to stay still in space due to inertia and so compresses and
stretches the piezo electric crystal. This force causes a charge to be generated and due to Newton law F=ma this force is in turn proportional to acceleration. The charge output is either is converted to a low impedance voltage output by the use of integral electronics
in a charge output piezo-electric accelerometer.

Piezoelectric Application
what is an accelerometer ?
- A sensor that measures acceleration

- Based on Newton’s second law of motion

-The acceleration of an object as produced by a net force is
directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

2- Shear type accelerometer

A shear type accelerometer is where the seismic mass is attached to the crystal so that it exerts a shear load on the crystal rather than a compressive load.
Shear type accelerometers are designed for applications that are likely to encounter significant base distortion from thermal transients or where they are mounted onto flexible structures.

3- Strain-gage based accelerometer

A strain gauged based accelerometer is based on detecting the deflection of a seismic mass by using a silicon or foil strain gauge element. A whetstone bridge network detects
the deflection. The deflection is directly proportional to the acceleration applied to the sensor and it has a frequency response down to zero Hz.

The reason for using different piezoelectric systems is their individual
suitability for various measurement tasks and varying sensitivity to
environmental influences. The following table shows advantages and
drawbacks of the 3 designs:

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