hang.yu@LIGO.ORG - posted 16:59, Monday 22 October 2018 - last comment - 23:15, Monday 22 October 2018(44739)
Lowered MICH P ASC loop to 0.7 Hz UGF to avoid the 1.1 Hz oscillation
Sheila, Gabriele, Hang
We saw some ASC oscillations at 1.1 Hz, corresponding to the secondary BS pitch resonance. This might be due to imperfect plant inversion or some cross-couplings between MICH and DH/DS. For now we just took the simple solution to avoid it by reducing the MICH P UGF to 0.7 Hz.
Please see the attached plot for comparisons between the original (pink; UGF 1 Hz) and new (red; UGF 0.7 Hz) MICH OLTFs.
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This instability was caused by the SRCL FF we realized later, but we have left the MICH gain as Hang set it.