According to the OPLEV signal calibration value in elog1874, I plotted the four suspended mirrors drift during a time scale of one day(from 2021/05/12 1pm to 2021/05/13 1pm JST).
In figure 1, all four suspended mirrors are compared. It is very clear that PR pitch has a far larger angular drift compared with other mirrors.
The PR mirror changed by 100urad pk-pk during one day. Considering the distance from PR to END mirrors, the 1e-4*300 = 3e-2 m = 3cm.
Other mirrors other DOF changed by 10urad pk-pk during one day, which is ten times smaller than PR pitch.
Considering this measurement result, I think we should make beam pointing loop act on PR mirror.
Marc and Yuhang
We have also checked one week data (from 2021/04/25/3pm to 2021/05/01/3pm)
We made two plots, the first plot includes all the data in this week. But the second plot excluded the last part of the data. This is because an earthquake might happen around the end of the one week data. This makes we see a peak in the first plot.
To compare different mirrors angular drift, we calculated RMS value of data and summarized them as the attached table. [unit: urad]
|
|
PR pit |
PR yaw |
BS pit |
BS yaw |
INPUT pit |
INPUT yaw |
END pit |
END yaw |
|
angular drift RMS (including earthquake) |
59 |
4.5 |
14.35 |
8.85 |
31.24 |
15.81 |
9.81 |
2.86 |
|
angular drift RMS earthquake excluded |
62.46 |
3.98 |
10.39 |
9.07 |
29.42 |
15.49 |
9.08 |
2.66 |
From this table, we see PR pitch moved the most. But INPUT pitch also moved a lot. However, END pitch didn't move as large as PR and INPUT pitch. Since PR, INPUT and END have the same configuration, their difference in pitch drift indicates that this is not a design problem.
We know that temperature change influences mirrors drift. But PR, BS, and INPUT are all in the TAMA central room, they should have the same temperature change. But they didn't show the same drift. Form the airconditioner location, PR chamber is almost facing an air conditioner, which may cause temperature related problem. To confirm this is not the fault of air conditioner, we plan to switch off it for one or two days during weekends to check.