matthewrichard.todd@LIGO.ORG - posted 09:43, Monday 02 June 2025 - last comment - 11:00, Monday 02 June 2025(84712)
RMs PSDs differences
M. Todd, C. Cahillane
Yesterday we were interested in some noise we were seeing around 6Hz in various ASC signals (mostly CHARD pitch). This motivated us to look at the RMs, so I took a PSD of each DOF for both RMs. We are not sure why there are such differences in all the dofs, and if there are unintended side-effects to this.
I'm specifically wondering why RM2 has larger peaks around 6.25 Hz in all dofs...
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This feature is the primary vertical resonance of the HTTS. The ISI HAM1's control system has still not yet been commissioned, so the decision to *unmute* the HTTS "because the ISI isolation performance should be much better than the Stack" will plague us until that's true. See "muting the HTTS blade springs" ECR E2200181, which confirms the 6.25 Hz resonance. See Integration Issue 33777 for historical notes, specifically Comment 2's record of IIET call discussion and agreement to *unmute*. I suspect the low-frequency performance will also improve once the ISI's controls are commissioned. Let's give Jim some time to figure out how to dance around the ~70 Hz feature that he's dealing with, see LHO:84638 (and last week's lock-acquisition problems do to ignoring it LHO:84640).