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frequency and harmonic would be maintained, and trends represent-
ing statistically significant increases would be identified by threshold
detection and indicated graphically.
By using algorithms based partly on analyses of data from prior
tests, the results of both keratosis and power spectrum calculations
would be processed onto predictions of the remaining operating time
until failure. All the results would then be processed by an expert
system. The final output would be a graphical display and text that
would describe the condition of the bearings.

6.18 Sensors for Vibration Measurement
of a Structure
An advanced sensor was developed to gauge structure excitations
and measurements that yield data for design of robust stabilizing
control systems (Fig. 6.20).
An automated method for characterizing the dynamic properties
of a large flexible structure estimates model parameters that can be
used by a robust control system to stabilize the structure and mini-
mize undesired motions. Although it was developed for the control
of large flexible structures in outer space, the method is also applica-
ble to terrestrial structures in which vibrations are important—
especially aircraft, buildings, bridges, cranes, and drill rigs.

FIGURE 6.20 Automated characterization of vibrations of a structure.