In case you don't see the plots attached please click here: 10823.

Summary in the context of the commented entry

• The reported problem with the filter bank was solved.
• I compared the transfer functions from the seismometer on the ground to the IP-LVDT.

Transfer function: measurement and prediction

The plot attached shows the comparison between a measured transfer function and the model prediction. A second plot shows the coherence of the measurement.

• DoF: from seismometer-on-ground-Y-arm to IP-L
• The coherence is larger than 0.5 between 100 mHz and 515 mHz and from 515 mHz to 615 mHz it's intermittently larger than 0.5.
• There's a pendulum mode resonance at 405 mHz properly predicted by the model.

The Matlab model used does't properly take into account structural damping and a suitable improvisation or fix has not been implemented. Therefore it's not surprising that the predicted amplitude of the large peak below 100 mHz does not coincide wih the measurement. In any case, below 100 mHz the coherence is low. Nevertheless, the general features of the model do coincide with the measurement, including the shape of the transer function when going from the IP resonance below 100 mHz to the pendulum mode resonance at 405 mHz.