With Fujii-kun.

This post is related with entry 7066. Is related to the investigation of the large drift of the suspension, especially in F0.

Fujii-kun notifed that the calibration factor of the F0 LVDT seemed unusual. I checked the original Excel file and I have found the factor (2.174 µm/cnt) to be incorrect. I have the following comments:

1. The plot was made with the keystone position data formated as text not as numbers. That's the reason the data in the horizontal axis does not show the correct data.
2. It also happens that the axes labels are the other way around. Nevertheless, the calibration factor which was written in the medm screen was calculated considering the keystone position in the horizontal axis and the LVDT output in the vertical one.

After the correction I got a calibration factor of 1.1285 cnt/µm, which becomes 0.8861 µm/count for the medm screen. This value has been corrected in the medm screen already. On December we will have access to the suspension and we should double check the offset value.

On 2018-12-19 I found that the gain in the BS F0 LVDTINF filter had reverted to the old, incorrect value of 2.174 µm/ct, presumably because a safe.snap had not been done after it was corrected and there had been at least one reboot since. I reentered the corrected gain of 0.8861 µm/ct and did a new safe.snap.

With  Hirata-san

F0  LVDT  calibration

Summary:  we  calibrated  the  F0  LVDT after  we  replaced  the  LVDT  driver  card.

Because we replaced the LVDT card (see 18933 and related entries) due to the problem with the F1 LVDT, we calibrated the F0 LVDT again. The following are the highlights:

• The 3D CAD nominal position of the keystone is 16.5 mm below the upper plate. See  entry  5314  for details (the  entry  is  for  SR3,  but  it  applies  to the  BS  also).
• Because  the  reference  point,  from  which  we  measured  the  position  of  the  keystone,  is  above  the  keystone,  the  calibration factor  calculated  with  this  data  is  negative.  Nevertheless,  we  when  did  installation,  we set the polarities in hardware such  that an upward displacement produces a positive LVDT output. Therefore, the calibration factor that should be written in the medm screen should be positive.
• I was able to move the keystone below the nominal position 3 mm only because the RM came very close to the security structure below. See pitcures.
• The directory where the data is stored is: /kagra/Dropbox/Subsystems/VIS/TypeBData/BS/F0_calibration/
• The result of the fit is:
  • Slope: -1348.1 cnt/mm (with the sign given by the plot).
  • Linear range: 6 mm in total (from 12.5 to 18.5 mm in the plot); with respect to the nominal position, and with the correct sign, it is [-2 , 4] mm.

Summary: After the calibration of the F0 LVDT, I wrote the appropriate calibration factor and offset in the medm screen.

• The slope from the plot is 1348.1 cnt/mm, which becomes 0.7418 um/cnt for the medm screen.
• The LVDT output at the 3D CAD nominal position of the keystone (16.5 mm) is -1461.438 cnt, therefore, the offset to write in the medm screen is 1461.438 cnt.
• After the change I accepted the new values in the SDF.