stuart.aston@LIGO.ORG - posted 11:37, Friday 22 June 2012 - last comment - 07:20, Monday 25 June 2012(3229)
PR2 (HSTS) Phase 1b testing M1-M1 transfer funtions plus M1, M2 and M3 power spectra
[Stuart A, Betsy B, Deepak K, Andres R, G2] After taking an initial set of M1-M1 transfer functions earlier in the week on PR2 (HSTS), it was observed by Jeff B that somehow a magnet had become detached from the M2 mass (see LHO aLog entry 3157). Thanks to the efforts of the assembly team, this magnet was rapidly re-attached and left to cure for a period of 24 hrs. PR2 was re-suspended yesterday, and a small pitch offset corrected. AOSEMs were then adjusted to their final operating positions and aligned. The canopy/cover was fitted over PR2. Following this re-work, it was prudent to take another M1-M1 transfer function with damping loops OFF for all degrees of freedom, which can be found below (see 2012-06-21_1700_X1SUSPR2_M1_ALL_TFs.pdf). Damping loops were then turned ON and a further complete set of M1-M1 transfer functions taken overnight. All the transfer functions obtained have now been plotted against all other HSTS suspensions previously measured on both LLO and LHO test-stands (see allhstss_2012-06-22_AllHSTS_ALL_ZOOMED_TFs.pdf). n.b. Yellow trace = X1 PR2 M1 (2012−06−21_1700) with damping loops OFF Purple trace = X1 PR2 M1 (2012−06−21_2120) with damping loops ON The transfers functions obtained again demonstrate good agreement with the model and the spread of all HSTS measurements obtained thus far. Power spectra have been taken with damping loops both ON and OFF for each stage (012-06-22_0800_X1SUSPR2_M*_ALL_Spectra.pdf). Power spectra plots, with both damping ON and OFF have been produced, which compare LHO PR2 and LHO MC2 measurements (allhstss_2012-06-22_ALL_Spectra_Don.pdf and allhstss_2012-06-22_ALL_Spectra_Doff.pdf). In addition, power spectra for specific degrees of freedom (L, P and Y) can be more conveniently compared across multiple stages (M1, M2 and M3) of the same suspension in the final plots found below (allhstss_2012-06-22_X1SUSPR2_M1M2M3_Spectra_ALL_Don.pdf). A BURT snapshot has been taken of the current functioning environment "20120622_x1sushxts27_PR2.snap", which has been stored in the following directory:- opt/rtcds3/tst/x1/cds_user_apps/trunk/sus/x1/burtfiles. This BURT snapshot directory has also been tidied to remove old or incomplete snapshots. All of the above data, plots, scripts, and snapshots have been committed to the SUS svn as of this entry. This should now provide sufficient measurements to complete Phase 1b testing of the PR2 suspension and allow it to progress to Phase 2 (chamber-side) testing.
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Comments related to this report
The M3 stage watchdog was observed to be perpetually tripping and could not be reset. This is due to watchdogs being triggered for the OPELV_RMS and OPLEV_SUM, which are not visible/settable in the medm screens. To rectify this I have manually set the following:- caput X1:SUS-HXTS_M3_WD_OPLEV_RMS_MAX 5 caput X1:SUS-HXTS_M3_WD_OPLEV_SUM_MIN -10 For now, this prevents the watchdog from tripping.
These results look excellent. The only thing that concerns me (where the level of concern (from 1 = "it's awesome. no worries" to 10 = "OMG take it apart and rebuild it") is a 5.5) is the cross-coupling I see in the individual comparison with the model, i.e. in 2012-06-21_1700_X1SUSPR2_M1_ALL_TFs.pdf. In there, I see cross-coupling between degrees of freedom which we don't normally expect to be there: 1st Yaw Mode (@ 1.09 Hz) into T and L 2nd Yaw Mode (@ 2.04 Hz) into T and L 2nd Roll/Pitch Mode (@ 1.51 Hz) into Y 2nd Vert or 3rd Long Mode (@ 2.80 Hz) into Y I'm not terribly concerned, because -- as usual -- the cross coupling is reduced to barely visible with damping loops ON. But, it's something to watch out for with this guy as he progresses through the testing (i.e. we'll look with more scrutiny after the optic is swapped). To refresh one's memory -- the reason why we care: (1) When the model doesn't match measurements, we can't trust the model to accurately predict other transfer functions which we can't normally measure (2) If the transfer functions (which are representative of the "plant" upon which we design control loops) are *different* between suspensions by some (as-yet-to-be-quantified) significant amount, then it will make copying and pasting control systems more difficult and time consuming to design. I think with this suspension, and all others, we're doing fine in both these departments -- but again, we won't really know until we start locking some cavities and really try to push the SUS's to their limit.