jeffrey.garcia@LIGO.ORG - posted 19:47, Tuesday 10 January 2012 - last comment - 08:33, Wednesday 11 January 2012(2003)
H2 ITMY M0 & R0 driven transfer functions
A. Effler, J. Garcia Measurements of driven transfer functions for the H2 ITMY M0 and R0 top masses were taken overnight for the suspension in the BSC8 chamber. The ISI was locked for this measurement and both M0 & R0 masses were left undamped. The attached plots are of the M0 top mass transfer functions. The R0 watchdog tripped during the final two DoFs and will be retaken tonight.
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Comments related to this report
This data looks great! I'd like to have more monolithic QUAD data against which to compare before officially accepting the dynamics of this suspension (read -- H2 SUS ETMY, which is coming soon!). Two points on model vs. measurement discrepancies: - The first pitch mode is lower (in frequency) than the model. I'll explore what this means regarding the parameters of the suspension (although we all know it's going to some break off that's ~1mm off from the model), but the real point of concern is control-ability. If the that pitch mode gets too close to the first longitudinal mode, then cross-coupling between L and P degrees of freedom makes control more difficult in that you cannot treat the DOFs as independent SISO loops. BUT for L and P, we'll have to do this anyways. - The DC magnitude of *all* degrees of freedom appears for be underestimated by a bit. This is indicative of imprecise calibration, not of anything physically flawed in the dynamics of the suspension. The calibration factor (60 [cts/m / cts/N]) was picked as a nice round number that scaled prior data to the model well. However, that prior data was taken on suspensions where the relative OSEM sensitivities we not well compensated -- at least not to the level of precision consistent with the level of discrepancy between model and measurement here. Nothing to worry about, and now that we have relative OSEM sensitivities better compensated, we should reassess this calibration factor (i.e scale it to the model with better precision).