[Tamaki, Ushiba, Nakano]

We found we can't lock the IFO due to the 0.6Hz oscillation of ETMX. So, we adjusted the ETMX MN damping loop. 

We just compensate the damping loop gain so that all the loops are identical to the damping loop when we can lock the FPMI at 30K. The tricky part is the pitch and yaw loop. Maybe due to the sensor or actuator diagonalization, the coupling with the other DoFs is larger. We adjusted it so that the single loop has the same gain as before (turned the other loops off and engaged and measured only the target loop).

Unfortunately, this doesn't solve the issue of locking. We will keep the investigation.

1324 Request LOCK_ACQUISITION to the ETMX guardian
1335 Start to measure the OLG of the MN damping loop. Templates can be opened by the medm execute function (olg slow). 
         Make a new filter named gain_220K to compensate for the gain difference between the newly measured curve (red) and the reference (blue).
1501 Find that the pitch OLG seems totally different at low frequencies as shown in the attached plot. We were wondering if the ETMX is robbing due to the height drift.
1503 Ushiba-san adjusted the height by changing the F1 GAS filter offset
1506 Re-measured but no difference has been made. 
1535 We found that the difference is caused by the damping loop of the other damping loop. The OLG was measured only with the pitch loop, then, no overdamping shape appeared. We decided to adjust the gain only with the pitch loop.
1545 Yaw loop was the same situation as the pitch.
1600 Tried to lock the FPMI with the new damping loop, but the situation didn't change.