Instrumentation & Measurement Magazine 25-2 - 38

Fig. 2. Schematic diagram of PE and IEPE accelerometers.
where ε is the dielectric constant of the piezoelectric crystal, A
is the area of the piezoelectric crystal patches, d is the thickness
of the crystal capacitor, and d33
is the piezoelectric coefficient.
To measure the acceleration of the structure, an inertial
mass has been placed on the piezoelectric patches (Fig. 2). The
inertial force produced by the inertial mass is proportional
to the acceleration of the structure. According to (1), the voltage
produced between the piezoelectric crystal patches is also
proportional to the acceleration of the structure. Piezoelectric
accelerometers can be classified into piezoelectric (PE) accelerometers
and piezoelectric accelerometers with Integral
Electronics (IEPE), whose structural principles are shown in
Fig. 2.
It can be seen from Fig. 2 that the biggest difference between
PE and IEPE accelerometers is whether electronics are
integrated into the sensor housing. The PE accelerometer directly
generates a high-impedance charge signal from the
piezoelectric patches, which is very sensitive to the environmental
and cable noise. A low-noise cable must be applied
and be connected to a charge amplifier to transfer the signal
to a low-impedance voltage signal. The PE accelerometer
has low failure rate, high reliability and high flexibility. The
IEPE accelerometer integrates the signal conditioning circuit
into the sensor housing, whose output is directly low-impedance
voltage signal. An IEPE accelerometer has strong
anti-interference ability and can use ordinary cables for signal
transmission. The drawback of an IEPE accelerometer is that
the integrated electronics and the sensor have the same working
environment, making a higher failure rate than that of the
PE accelerometer.
Piezoelectric accelerometers began to be mass-produced
in the 1940s and have been widely used in applications such
38
as vibration testing, signal analysis, vibration calibration, and
mechanical dynamic testing. The well-known global manufacturers
of vibration sensors include Danish B&K (1943),
Swiss Kistler (1944), and American PCB (1967). There are also
many piezoelectric accelerometers manufacturers in China,
among which the representative brands are DONGHUA and
FATRI. In the application of different fields, the piezoelectric
acceleration sensor has sensitivity from 0.5 to1000 mV/g,
measurement range from 0.001 to 10000g, and in-band resolution
from 0.0005 to 1g, where g means acceleration of gravity.
According to statistics, the global sensor market is mainly
occupied by American, Japanese, German, and Chinese companies.
They together account for 72% of the whole market, in
which China accounts for about 11%.
Control Algorithms and Controller
The control algorithm reflects the transfer relationship between
the controller inputs and outputs, which is the core of
AVC. The AVC algorithm can be classified into two categories.
One is the algorithm based on a mathematical model. The controller
is designed according to modern control theory, such
as direct feedback control, modal control, PID control, poles
assignment, optimal control, and robust control. The other
kind of algorithm is based on an identified model constructed
by the input and output data of the controlled structure. The
controller can be adaptively on-line designed by certain algorithm,
such as adaptive control, fuzzy control, or neural
network control, for example.
The classical feedback control is one of the most broadlyused
methods in the practices of AVC for its robustness and
simplicity. The diagram of the direct feedback control is shown
in Fig. 3, where C(s) is the transfer function of controller, G(s)
IEEE Instrumentation & Measurement Magazine
April 2022
Instrumentation & Measurement Magazine 25-2

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 25-2
