Picking up where Arnaud left off nearly 2 weeks ago, alog 19208 post vent, I am looking at the health of the TMSX suspension. Basically, we reinvented what he stated - the TMSX LF and RT BOSEMs are less sensitive than they were "before". The TFs show a DC offset from the Model and the TFs taken a year ago. We're not sure why this is - Kiwamu suggests that a change in the stiffness of the suspension made during the June cable strain relieving likely would have caused the resonance peaks to shift as well as the DC offset... We don't think this DC shift is too serious - the loop gain in V and P need to be retuned.
I can drive the TMSX with PIT alignment bias and see the Left and Right (suspect) BOSEMs respond, so they are not "out of range" and are actuating.
I reran the TMSX TFS for PIT and VERT - Both look healthy to me, so whatever bad measurement was posted in the middle of the 19208 alog is still gone.
I agree with Betsy -- a change in stiffness would only affect the magnitude of the transfer function at low-frequencies. An overall scale factor discrepancy like what is shown here is typically a problem with an electronics gain being different (say, if a satellite pre-amp's circuits have much less gain than before), or an incorrect digital gain (say, if the EUL2OSEM / OSEM2EUL matrices were systematically incorrect). It might be that the diodes have a new, worse, open light current, and what is being used for digital compensation / normalization is now in correct. It would be difficult to believe / quite the coincidence that would a problem from *both* LF and RT at the same time. Recall that this is FRS Ticket #3246. ------ For reference, I also quote Keita who had replied on this over a small-email-list: "" Seems like TMSX RT and LF are bigger than before by maybe 5000 counts or so, which I didn't catch when we came out of chamber. We added small masses (strain relief parts) to TMS, so this makes sense qualitatively. These numbers were already big-ish before vent in a retrospect, and RT is now about 4000 counts away from the open value which is supposed to be -2*H1:SUS-TMSX_M1_OSEMINF_RT_OFFSET~26000 cts. No idea if 4000 counts is too small a margine there, nor if the BOSEM height is the cause of the poor measurement results. Anyway, my questions are, 1. Were the suspension bias sliders on or off during the measurement? If not, measure with nominal offset even though we don't know the right alignment for now. 2. Is the S/N of the PIT sensing considerably smaller than before? If it is, TMS should be noisier than before due to noisier PIT damping, which in principle compromise ASC performance for ITMs (DSOFT, CSOFT). Regardless of the answers, my gut feeling is that it's possible to run H1 without fixing the BOSEM height for O1 (unless TMSX is shaking too much due to this and the IFO wouldn't lock). ""
The PIT and VERT TFs that I ran this morning were with the bias sliders enabled.