Betsy, Jeff Garcia, Brett

After cabling the ITMy reaction chain its 3rd vertical mode went too high in frequency with respect to its metal incarnation and with respect to the model. The model told us that this mode is largely motion between just the top mass and UIM (using the ModalDecomp2.m Matlab function which is on the SVN). So Betsy increased the amount of slack in the cables between these two stages. Jeff then remeasured transfer functions at the top mass.

See the attached pdf. Page 3 shows the change in the vertical TFs. Blue is the before, red is the after.

The result is that the 3rd vertical mode snapped nearly all the way back to its proper place. Before adjusting the cables the 3rd mode was at 3.94 Hz. Now it is at 3.63 Hz. On August 10th when the ITMy was still metal, this mode was 3.58 Hz. The new reaction chain model (to be posted to the SVN shortly) also predicts 3.58 Hz. On page 5 you can see the < 2 Hz pitch mode also dropped in frequency, which is good news.

Score one for using the model's mode shapes!

ModalDecomp2.m can be found on the SVN at 
https://redoubt.ligo-wa.caltech.edu/svn/sus/trunk/Common/MatlabTools/