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Piezo transducers
Piezoelectric accelerometer
Dynamic range: 108 : 1 (160 dB)
Advantages:
Wide frequency range
Compact, often low weight
High stability
Can be mounted with any orientation
Self generating High impedance output
No moving parts, no wear No true DC response
Rugged
Very large dynamic range
Limitations:
High impedance output
No true DC response
Piezoelectric materials
When a force is applied to a piezoelectric material in the direction of its
polarization an electric charge is developed between its surfaces, giving rise
to a potential difference on the output terminals. The charge (and voltage) is
proportional to the force applied. The same phenomenon will occur if the
force is applied to the material in the shear mode. Both modes are used in
practical accelerometer design.
Compression type design
This traditional, simple construction gives a moderately high sensitivity-tomass
ratio. In the Centre-mounted configuration shown, the piezoelectric
element-spring-mass system is mounted by means of a cylindrical centre
post attached to the base of the accelerometer.
The design is very stable, but even with careful design the influence from
environmental parameters is higher than for the other construction types.
Therefore this design is especially used for accelerometers which are
intended for measurement of very high shock levels and special purpose
accelerometers.
Shear type design
Shear type accelerometers have the advantage that they intrinsically are
rather insensitive to environmental parameters like temperature transients
and base strain. A high sensitivity-to-mass ratio can be obtained, and this
helps to create miniature accelerometers as well as high performance
general purpose accelerometers. The piezoelectric elements are arranged in
such a way that they are subjected to shear forces from the seismic mass
when accelerated.
Choosing an accelerometer
The range of operation is the first to be considered when selecting an
accelerometer.
General Purpose Type Accelerometers
Small (miniature) Accelerometers
Accelerometer Calibration
Setups similar to the setup shown above are used to calibrate
accelerometers with very high accuracy (1%) at a reference frequency
(normally 160 or 80 Hz) and also over wider frequency ranges with slightly
less accuracy. This method, using a Reference Standard Accelerometer in a
so called Back-to-back configuration or in a fixture, is widely
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