Craig, Stefan, Danny

• While updating the MICHFF we noticed that there was a drop in coherence between MICH and DARM that couldn't be accounted for by any notch filters in the MICH loop
• Discovered a notch/resonance feature in the MICH OLTF between 17 and 18 Hz.
• Using /opt/rtcds/userapps/release/lsc/h1/scripts/MICH_OLTF_fit.ipynb we use IIRational which gives us the following zpk fit of the notch/resonance with frequencies in rad/s:

  • zpk(
    [
    -4.727413e-02+i*1.115585e+02; 
    -4.727413e-02-i*1.115585e+02; 
    ],
    [
    -2.325583e-02+i*1.118566e+02; 
    -2.325583e-02-i*1.118566e+02; 
    ],
    4.596248e-01
    )

• We will be adding a filter to the MICH loop to mitigate its effects.