jeffrey.kissel@LIGO.ORG - posted 11:30, Monday 04 August 2014 - last comment - 13:44, Tuesday 09 December 2014(13184)
H1 SUS ITMY Dorrs On TFs -- TOP looks good, lower stages discrepant with model by factor 2
J. Kissel, A. Pele Ran transfer functions over the weekend, to assess if the SUS is free after first contact removal and closing doors. While the top stages look great, this is the first time I've been exposed to a factor of two missing between model and measurement for the lower stages. While we don't expect the model to account for the dynamics of the reaction chain (which is why we see a whole bunch of "extra" features in the main-chain dynamics), we don't expect an overall gain mismatch. Arnaud informs me that this is true of every QUAD except one stage of one (including L1 SUS ITMY). No reason to pull doors off, but we should figure out where this discrepancy lies. And also , we should develop a model of the lower stage dynamics which include both chains.
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The reaction chain will displace about the same amount as the main chain for the lower stage measurements. Could this explain the factor of two gain relative to the model, since the OSEMs measure the difference between chains?
HA !
Plausible. Let's model it to find out!
I added a feature to .../SusSVN/sus/trunk/QUAD/Common/MatlabTools/QuadModel_Production/generate_QUAD_Model_Production.m to compile a quad model with both main and reaction dynamics to predict what the L1 (UIM) and L2 (PUM) OSEMs will measure. See the results in the attached pdf. The overall gain is still not 100%, but is definitely closer. Pitch has some obvious mismatch due to known extra stiffness on the reaction chain (from OSEM cables I think). The update to generate_QUAD_Model_Production.m has instructions commented into the header for using the new combined main/reaction model. I copy those instructions here. " You can compile multiple chains simultaneously, to predict what the UIM (L1) and PUM (L2) OSEMs will measure. To use this feature, sandwich the string '_with_' between the two build types you want to use, main chain 1st, reaction chain 2nd. For example, for a monolithic ITM use buildType = 'fiber_with_thincp' The combined model will only combine the outputs for the UIM (L1) and PUM (L2) L, P, and Y DOFs, to reflect the OSEM measurements. The inputs however will be shared for all the seismic inputs as well as the UIM and PUM L, P, and Y DOFs. The indices for inputs and outputs are unchanged. Caution: there is no error or warning for non-physical combinations. For example, 'fiber_with_fiber' will compile OK, but the results will be inconsistent with reality. "
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For future reference, attached are osems spectra from before the swap comparing top mass damping on / off
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