J. Kissel, M. Evans

As the QUAD damping loops have evolved over the past few days, I've taken open loop gain TFs of the latest configuration that we believe to give us the most reduced motion thus fair (as measured by the TOP mass -- which may not be the right figure of merit). The first three attached are the results for the three degrees of freedom in question.

We can see that we have indeed significantly increased the amount of L damping, but P and Y have not changed that much, given the combination of adding boost filters at low frequency and decreasing gain.

The fourth attachment compares the components of each of the filters, just give a rough idea of the shape and frequency of the boost filters. 

I also add on as bonus information (pgs 4 and 5 of the fourth attachment) the filters used for the TMSY, designed by M. Evans. Granted, he's got a much more simple suspension to deal with so he can be more aggressive, but we could maybe learn a lesson or two from his design. Specifically, instead of the B. Shapiro tactic of fixing the elliptical filter at 50Hz and trying to gain damping gain by lowering the "turn-over" poles of the baseline AC-coupling filter (the FM1s), M. Evans fixes the poles and zeros of his baseline turn-over, then tailors his elliptic to push hard on the performance. The advantage there is that, if you don't care about noise, you always have a configuration (FM1 only) which is unconditionally stable with which you can turn the gain knob arbitrarily. This is not necessarily true for the B. Shapiro designs.

Back to the OLG TFs: The second attachment shows that we're probably squishing the Pitch just as much as before. As mentioned in my previous entry, this may mean we're locking the TOP mass to the Cage (in Pitch), and directly shorting the isolation of that stage. A quick fix to test this would be to lower the pitch gain by another factor of 3.

See if it helps!

Regarding the right figure of merit -- it seems like the UIM and below are showing little improvement. Perhaps, when one data mines the spectra for the times mentioned below, we should see how the UIM and PUM perform with respect to the TOP and the various configurations.

Note, that in the 4th page of the first 2 attachements I show the OLG TFs of not only L to L and P to P, but the cross degrees of freedom as well. These OLG TFs are a better way of comparing relative amplitudes, because they're in the same units. BUT the measurements were taken with the damping loops OFF, so the off-diagonal terms show the situation with no P damping -- which shows that the L to P cross-coupling is horrendous -- but it's not representative of the real situation.

The next measurement to do, would be to take the same measurement with damping loops CLOSED, and derive the open loop gains by measuring IN1/IN2 (another pioneering measurement). I'm out next week, so I may have to have someone do this one site .... or y'all can continue to play around, and see what you get. 

Best of luck!!