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basic principle of transduction that occurs in a piezoelectric element may best be thought of as a charge
generator and a capacitor. The frequency response of piezoelectric transducers is very high, since the
frequency response is determined primarily by the size and material properties of the quartz crystal. The
modulus of elasticity of quartz is approximately 85 GPa, yielding load cells with typical static sensitivities
ranging from 0.05 to 10 mV/N, and a frequency response up to 15,000 Hz. A typical piezoelectric load cell
construction is shown in Figure 12.24.
Proving Ring A ring-type load cell can be employed as a local force standard. Such a ring-type
load cell, as shown in Figure 12.25, is often employed in the calibration of materials testing
machines because of the high degree of precision and accuracy possible with this arrangement of
Applied
load
Strain
gauge locations
Shear stress
Shear stress in I-beam
y
Center line of web
Figure 12.22 Shear beam load cell and shear stress distribution.
Figure 12.23 Typical
load cells. (Courtesy of
Transducer Techniques, Inc.)
12.2 Sensors 527
13:54:11 Page 527
basic principle of transduction that occurs in a piezoelectric element may best be thought of as a charge
generator and a capacitor. The frequency response of piezoelectric transducers is very high, since the
frequency response is determined primarily by the size and material properties of the quartz crystal. The
modulus of elasticity of quartz is approximately 85 GPa, yielding load cells with typical static sensitivities
ranging from 0.05 to 10 mV/N, and a frequency response up to 15,000 Hz. A typical piezoelectric load cell
construction is shown in Figure 12.24.
Proving Ring A ring-type load cell can be employed as a local force standard. Such a ring-type
load cell, as shown in Figure 12.25, is often employed in the calibration of materials testing
machines because of the high degree of precision and accuracy possible with this arrangement of
Applied
load
Strain
gauge locations
Shear stress
Shear stress in I-beam
y
Center line of web
Figure 12.22 Shear beam load cell and shear stress distribution.
Figure 12.23 Typical
load cells. (Courtesy of
Transducer Techniques, Inc.)
12.2 Sensors 527