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If we compare this peak value with the LSB for the 16-bit A/D with gain 100 and full-scale +/-0.1V
we can reach the conclusion that there is enough resolution for this type of measurements.
Figure 2.1.1 shows the time series and the corresponding FFT for a signal generated by a Force
Balance type accelerometer with a dynamic range >120dB and a full-scale of +/-lg, recorded with 16-
bit resolution, gain 100, full-scale 4-/-0.1V. The sensor was located in Pasadena, on a quiet street, at
the ground level, and oriented horizontal.
Figure 2.1.2 shows a detail of the time series to underline the resolution of the signal
In both figures time series traces from top down are:
Ground acceleration in um/s"
Integrated Velocity in um/s
Reference velocity in um/s provided by a seismometer with T n = 3 sec and S= lOOV/m/s.
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Time series Acceleration Velocity Reference Velocity
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FFTforRef VotandVtf
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FFT for Acceleration
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Noise signal recorded at ground level
Figure 2.1.1 City noise recorded at ground level