Campbell CR6 Series, Operator'S Manual

Page: 455 / 690

Section 8. Operation
455
FIGURE 105: Wide Sweep, High Noise
Minimize Resonant Decay
A narrow-swept range ensures minimal decay of the resonant response prior to
measurement. Gage response starts to decay as soon as the frequency sweep
moves past the resonant frequency. Observing this decay is difficult because the
swept frequency overwhelms the resonant-frequency response while excitation is
still active. Because wider excitation sweeps take longer, the resonant response
decays for a longer time before the CR6 can measure it. The resulting resonant
amplitude is smaller. The figure
Wide Sweep, High Noise
(p. 453)
shows this effect,
with the resonant frequency response decreased by about a factor of two when
compared with the narrow sweep.
Prevent Spectral Leakage
Matching the swept excitation to the expected resonant frequency range prevents
spectral leakage
(p. 602)
from complicating the spectral analysis. Vibrating wire
sensors are usually optimized for a single resonant frequency to overwhelm
harmonic and sub-harmonic responses, so spectral leakage usually has little