Continued from LHO alog 84128.
RM1 (Tip Tilt suspension)
Last week Daniel and I replaced the original TT bosem cable (with a new 25in long, D2100049 S/N 2200358) since the original cable was having issues with grounding. However, Betsy informed us that the new cable might have pin 1 missing (and should be sent back to CIT for repair). I inspected the cable in-chamber and found pin1 missing.
Hence, I replaced the 25in long D2100049 S/N 2200358 (missing pin 1) with 54in long D2100049 s/n S2100426 cable. However, the ground loop issues has now returned (shorting with the chamber itself) and it looks like the culprit is not the cable but the bosem itself (despite having kapton tape for shielding, clearly its not enough). I am still considering to slide a kapton sheet underneath RM1.
Also, I measured the Open light counts of all four bosems for RM1 and they are listed below,
| OLC for RM1 bosems | offsets | gain |
| UL = 21613 | -10806 | 1.38 |
| LL = 22400 | -11200 | 1.33 |
| UR = 12380 | -6190 | 2.42 |
| LR = 16473 | -8236 | 1.82 |
RM2 (Tip Tilt suspension)
Kissel, Betsy, Rahul
Here, Jeff suspects that the bosem magnet polarity is incorrect (i.e is not as per E1400316) which was recorded in his LHO alog from 2018. To verify Jeff's claim we went back into the chamber to check the polarity of RM2 magnets. However we faced two problems over here. At first I looked into the Tip Tilt assembly drawing and then the Tip Tilt PEEK flags in Triples lab to locate the magnet inside the flag. It turns out that the magnet is buried deep inside the PEEK flag, such that my polarity tester cannot detect its presence. Hence, I took another strong magnet to check if its pulling or repelling it - which worked fine. The second problem we faced was that the PEEK flag are a very tight fit inside the TT mirror holder (in-chamber) and despite our best efforts (both Betsy and I tried unscrewing it) we couldn't remove it for checking. Hence, we were unsuccessful in measuring the magnet polarity and after some discussion we decided to move ahead and reset RM2 (digitally) to how it was before this vent. Jeff will file an FRS ticket regarding this issue.
The Open light counts for RM2 is given below,
| OLC for RM2 bosems | offsets | gain |
| UL = 15800 | -7900 | 1.89 |
| LL = 20048 | -10024 | 1.49 |
| UR = 16753 | -8376 | 1.79 |
| LR = 21173 | -10586 | 1.41 |
I have accepted the SDFs for both RM1 and RM2 and three screenshots are attached below.
RM1 still needs a cable table bracket.
The first set of transfer function measurement results for both RM1 and RM2 are shown in the attachments below (screenshots for all three L, P, Y degrees of freedom). I am not happy with the coherence in RM1 and still working on improving it. I am also planning on taking osem spectra to analyze the noise levels in bosems (considering that their OLC have degraded considerably).
RM1 Transfer function templates:-
/ligo/svncommon/SusSVN/sus/trunk/HTTS/H1/RM1/SAGM1/Data
2025-04-29_2330_H1SUSRM1_M1_WhiteNoise_L_0p01to50Hz.xml
2025-04-29_2330_H1SUSRM1_M1_WhiteNoise_P_0p01to50Hz.xml
2025-04-29_2330_H1SUSRM1_M1_WhiteNoise_Y_0p01to50Hz.xml
RM2 Transfer function templates:-
/ligo/svncommon/SusSVN/sus/trunk/HTTS/H1/RM2/SAGM1/Data
2025-04-29_2300_H1SUSRM2_M1_WhiteNoise_L_0p01to50Hz.xml
2025-04-29_2300_H1SUSRM2_M1_WhiteNoise_P_0p01to50Hz.xml
2025-04-29_2300_H1SUSRM2_M1_WhiteNoise_Y_0p01to50Hz.xml
Here's an ndscope of April 24th, the first day that we put RM1 and RM2 back in, to hopefully make stuff slightly less confusing.
After installation, we had checked the open light values for RM1 and updated the OFFSETs (green) before realizing that the ADC count signs on (almost) all the OSEMs had been flipped to positive, whereas previously they had been negative (a result of changing the In-Air to SatAmp cable for both RMs: 84027). We flipped them after realizing this, which then fixed the OSEMINF OUT values (cyan). Throughout this, we also had just left RM1's UL OSEM as it was since it was behaving strangely and was the only OSEM to still be reading in negative ADC counts. At the point of the pink cursor, troubleshooting was started for RM1 UL.
Some additions to this aLOG: - D2100049 is an in-vac quadrapus cable. So the swaps that he's talking about in the above aLOG are *seperate* from the in-air cable swap for RM1 and RM2 that's discussed in LHO:84027 - It's LHO:40853 (indeed, Mar 2018) where I identify that RM2 alone, out of all the remaining tip-tilts in the IFO has it's magnet polarities flipped. I had guessed this was true because the damping loops required a different sign that the other tip-tilts if I had the COILOUTF settings per T1200015 convention.