Title: Piezoelectric Accelerometer
1Piezoelectric Accelerometer
ECE 5320 MECHATRONICSSensor Tutorial
- Prepared by Jaime Fernandez
- Department of Electrical and Computer Engineering
- Utah State University
Robert H. Bishop, Mechatronics Handbook, figure
19.3
2Outline
- Reference List
- History
- Piezoelectric Notions
- Acceleration Sensing Notions
- Major Applications
- Basics Principles
- Piezoelectric Accelerometer Design
- Major specifications
3Reference List
- Robert H. Bishop, Mechatronics Handbook, 2002,
CRC Press LLC - Wikipedia, http//en.wikipedia.org/wiki/Piezoel
ectricity - Alexander D. Khazan, Transducers and Their
Elements, Prentice Hall PTR - Robert H. Bishop, Mechatronics Handbook,
section 19.2 - Curtis D. Johnson, Process Control
Instrumentation Technology, Prentice Hall PTR,
National Instruments.
4History
- A related property known as pyroelectricity, the
ability of certain mineral crystals to generate
electrical charge when heated, was known of as
early as the 19th century, and was named by David
Brewster in 1824. In 1880, the brothers Pierre
Curie and Jacques Curie predicted and
demonstrated piezoelectricity using tinfoil,
glue, wire, magnets, and a jeweler's saw. - They showed that crystals of tourmaline, quartz,
topaz, cane sugar, and Rochelle salt (sodium
potassium tartrate tetrahydrate) generate
electrical polarization from mechanical stress.
Wikipedia, http//en.wikipedia.org/wiki/Piezoe
lectricity
5- Quartz and Rochelle salt exhibited the most
piezoelectricity. Converse piezoelectricity was
mathematically deduced from fundamental
thermodynamic principles by Lippmann in 1881. - The Curies immediately confirmed the existence of
the "converse effect," and went on to obtain
quantitative proof of the complete reversibility
of electro-elasto-mechanical deformations in
piezoelectric crystals. (1)
Wikipedia, http//en.wikipedia.org/wiki/Piezoe
lectricity
6Piezoelectric Notions
- Piezoelectricity is the ability of certain
crystals to generate a voltage in response to
applied mechanical stress. The word is derived
from the Greek piezein, which means to squeeze or
press. The piezoelectric effect is reversible in
that piezoelectric crystals, when subjected to an
externally applied voltage, can change shape by a
small amount. The deformation, about 0.1 of the
original dimension in PZT, is of the order of
nanometers, but nevertheless finds useful
applications such as the production and detection
of sound, generation of high voltages, electronic
frequency generation, and ultra fine focusing of
optical assemblies. (1) - In a piezoelectric transducer, the acceleration
acts on the seismic mass that develops a force on
piezoelectric quartz, or ceramic crystal, or on
several crystals. The force causes charges on the
crystals proportional to the acceleration. (2)
Wikipedia, http//en.wikipedia.org/wiki/Piezoel
ectricity Alexander D. Khazan, Transducers and
Their Elements, Prentice Hall PTR Robert H.
Bishop, Mechatronics Handbook, section 19.2
7 Acceleration Sensing Notions
- Direct measurement this is done by sensing the
acceleration directly. - Indirect measurement this is done
differentiating the velocity. In the real world
is more common integrating a measurement than
differentiating it. - The applicability of these techniques depends on
the type of motion (rectilinear, angular, or
curvilinear motion) or equilibrium centered
vibration. For rectilinear and curvilinear
motions, the direct measurement accelerometers
are preferred. However, the angular acceleration
is usually measured by indirect methods. (3)
Robert H. Bishop, Mechatronics Handbook,
section 19.2 Curtis D. Johnson, Process Control
Instrumentation Technology, Prentice Hall PTR,
National Instruments
8Major Applications
- Piezoelectric accelerometer are good sensing
device for the application were is needed - high bandwidth
- low power consumption
- ruggedness
As acceleration acts on the mounting surface of
a flat plate shear sensing configuration, the
piezoelectric ceramic element is put into shear
relative to the attached mass.
Robert Shear, Endevco Kavlico Corporation
Piezoelectric Sensors for OEM Applications,
figure 3
9- Applications
- Machine Monitoring. Bearing and gear mesh wear
typically have characteristic frequencies in the
210 kHz range. - Shock Detection. For applications such as
shipment monitoring, impact detection, or drop
testing. - Vehicle Dynamics. handling parameters such as
ride smoothness, vehicle performance, cargo
transport, and asset tracking in vehicle. - Structural Dynamics detect fatigue, resonance,
and response to load.
10Basics Principles
- These devices utilize a mass in direct contact
with the piezoelectric component or crystal as
shown in When a varying motion is applied to the
accelerometer, the crystal experiences a varying
force excitation (F ma), causing a proportional
electric charge q to be developed across it. - So, where q is the charge developed and dij is
the piezoelectric coefficient of the material. As
this equation shows, the output from the
piezoelectric material is dependent on its
mechanical properties, dij.
11- These accelerometers are useful for
high-frequency applications. The roll-off
typically starts near 100 Hz. These active
devices have no DC response. Since piezoelectric
accelerometers have comparatively low mechanical
impedances, their effect on the motion of most
structures is negligible.
12- Mathematically, their transfer function
approximates a third-order system that can be
expressed as where Kq is the piezoelectric
constant related to charge (C cm), t is the time
constant of the crystal, and s is the Laplace
variable. It is worth noting that the crystal
itself does not have a time constant t, but the
time constant is observed when the accelerometer
is connected to an electric circuit, for example,
an RC circuit.
Robert H. Bishop, Mechatronics Handbook,
Robert H. Bishop, Mechatronics Handbook, fig
19.22
13- The low-frequency response is limited by the
piezoelectric characteristic ts / (ts 1), while
the high frequency response is related to
mechanical response. The damping factor ? is very
small, usually less than 0.01 or near zero.
Accurate low-frequency response requires large t,
which is usually achieved by use of
high-impedance voltage amplifiers. At very low
frequencies thermal effects can have severe
influences on the operation characteristics.
Robert H. Bishop, Mechatronics Handbook,
14Piezoelectric Accelerometer Design
Manfred Weber, http//www.mmf.de/
15 Manfred Weber, http//www.mmf.de/
16Major specifications
Endevco Piezoelectric accelerometer, model
22, lthttp//www.bksv.com/pdf/22.pdfgt
17Endevco Piezoelectric accelerometer, model
22, lthttp//www.bksv.com/pdf/22.pdfgt
18Endevco Piezoelectric accelerometer, model
22, lthttp//www.bksv.com/pdf/22.pdfgt
19Advantages of piezoelectric accelerometer
20Suppliers Information
- http//www.columbiaresearchlab.com/index.asp/
- http//www.endevco.com/
- http//www.meas-spec.com/myMeas/default/index.asp/
- http//www.summitinstruments.com/
- http//www.ferroperm-piezo.com
- http//www.matsysinc.com/
- http//www.piezosolutions.net/
- http//www.sensortech.ca/
- http//www.vfultrasound.com/
- http//www.xinetics.com/home.html/