Hirata, Dan, Ikeda, Komori, Takidera, Aso

We started the recovery work of the PR3 suspension.

The current state:

• OpLev is centered
• Horizontal OSEMs are around 6000 counts (middle of the linear range)
• Vertical OSEMs are out of the linear range (need adjustment)
• No OSEM flag seems to touch the coil

Fixing the suspended table

Before fixing the table, we measured the height of the table from the nominal height of the PR3 mirror marked on a pillar near the chamber.
The numbers should be reported separately.

OSEM flag rotation

We fixed the IM and IRM, then rotated the IM OSEM flags to the nominal orientation.

After releasing the IM and IRM, we confirmed that none of the flags are rubbing.

OpLev centering

The tilt OpLev beam was missing the QPD on the upper side.
We moved the IM moving mass in -pitch to move the center the OpLev beam on the QPD.
Along the way, we checked the IM OSEM flangs. None of them touched the coils.

OSEM adjustment

After the OpLev is centered, we fixed the IRM and adjusted the position of the OSEMs to be the center of the linear range.
The adjustment required several rounds of iteration.
While adjusting the vertical OSEMs, the IM suddenly moved in tilt changing the OSEM outputs by roughly 2000 counts.
We don't know exactly what happened but Hirata-san reported that he touched a cable during the adjustment.

After all the adjustments are done and released the IRM, we found that the OpLev is largely miscentered in pitch, this time in the downward direction.
We don't know if this is related to the sudden move of the IM during the OSEM adjustment.
The shift of the OpLev beam spot (>1cm) is too large compared with the 2000 count change (~0.1mm) of the OSEMs.

Re-centering of the OpLev

We moved the IM moving mass to center the OpLev again.
During this adjustment, the V3 OSEM showed a strange behavior.

When the IM is moved in pitch V2 and V3 OSEMs should move in the opposite direction as V1. Indeed, the V1 and V2 OSEMs showed opposite change. However, V3 OSEM did not move at all.
Initially, we suspected that V3 might be touching. However, it did not seem so from the visual inspection.
As a check, we moved the BF fishing rod to move the IM vertically. In this case, V3 OSEM responded exactly the same as the other vertical OSEMs. 
We also moved the roll moving mass of the IM. Again, the V3 OSEM responded in the expected way (opposite sign as the V2).

We decided to continue the pitch adjustment to center the OpLev. As we moved the IM pitch by a few tens of thousands of counts, V3 started to move in the expected direction.

When we completely centered the OpLev on the QPD, all the vertical OSEMs became out of linear range.
We will adjust the vertical OSEMs again tomorrow.