During today's lock we did a quick MICH PITCH OLTF measurement after the 'ENGAGE_REFL_POP_WFS' state.
Please see the first image for the OLTF with UGF ~ . The blue trace is predicted OLTF based on the SUS model and the ctrl filter banks. The orange trace is the measured data. There seems to be some small discrepancies at the sus resonances at 0.47 Hz and 1.1 Hz. Other than that the model matched to the measurement pretty well. We might need to compensate for the 1.1 Hz peak better if we want to increase the MICH loop BW.
In the second plot we show the same OLTF model (blue), and the M1 (orange) and M2 (yellow) stages' contribution. The crossover freq ( using the convention that |M1_P2P| = |M2_P2P|) happens at ~ 0.03 Hz.
We took another measurement of MICH ASC OLTFs. This time we shape the excitation to focus on the 0.7-2 Hz band. It turned out that we actually had a good inversion of the BS SUS TF and we were nicely sitting on a phase bubble with plenty of margin there. We should be able to increase the MICH ASC gain by 3dB at least.
