Marc, Yuhang

Yesterday we wanted to check again QPD demodulations pahses before implementing the new driving matrix.

However, the BS pitch seemed to be totally out (180 offset required to get the beam on the end camera).

We had a look on one week data trend of every mirror oplev signal (attached pdf).

This large BS offset has 3 origins as indicated by the red arrows :

1. An earthquake not too far from Tokyo in March 3d caused a -500 pitch offset of BS (also visible on IN and slightly on END but not so evident effects on PR )

2. Switching the air conditioning to 'cold mode' cause a 1500 pitch offset of PR. Indeed, PR is located directly under the air conditioning.

3. Strong rain/storm on March 13th cause a further 500 pitch offset of PR

Therefore we decided to use PR pitch picomotors to move PR back to its previous good position (~300 steps).

But this made the required BS offset -180... This is quite close to coils saturation (it corresponds roughly to 20 000 counts) so we might have to move again BS picomotors...

After the movement of PR picomotor we took the oplev signals (fig 1) where green/brown are references and blue/red yesterday data.

We can see that PR seems fine. However, comparing the low frequency spectrum of BS and PR between reference and yesterday datas, PR low frequency spectrum changed quite more than BS one. It seems that PR is far more sensitive to seismic activities than BS?

We also found out that there is an air leakage on the BS gate valve. It might be due to a loose washer pointed by Yuhang in Fig 2. It might be another after effect of the large earthquake as the air leakage sound was not so easy to hear.