Structural Health Monitoring Using Smart Sensors - ideals ...

Figure 7.11. The Imote2s on a truss node.
Figure 7.12. Accelerometer: model 353B33 and magnetic base.
of the Imote2 nodes, while noise common to both Imote2 nodes needs to be detected in
comparison with reference sensors.
PCB high-sensitivity piezotronics accelerometers (see Figure 7.12.) are used as
reference accelerometers. These accelerometers have a sensitivity of approximately 100
mV/g, a frequency range of 1 to 4,000 Hz, and a measurement range of ±50g. These
accelerometers are mounted on the structure through a magnetic base. These magnetic
bases facilitate easy relocation of the accelerometers between tests.
Four PCB accelerometers are attached on the same structural node as the one that the
Imote2s are attached to. Two of them measure acceleration in the longitudinal direction,
while the others measure acceleration in the transverse direction. To investigate vertical
acceleration measurements, the two accelerometers used in longitudinal acceleration
measurement are relocated so that these sensors measure vertical acceleration. Thus, at
least two reference accelerometers measure acceleration in one direction; differences in
signals from these two sensors indicate noise components that are not common to both of
them.
A four-channel 20-42 Siglab spectrum analyzer (Spectral Dynamics, Inc., 2007)
provides the signal to the shaker and measures the inputs or reference sensor signals.
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