As JessM reported in alog 12743, we were unable to turn on the X dof for the ETMY Stage1 Lvl2 Isolation. We traced this to a ring up at 739 hz. The peak was not evident until the gain for X was about 0.8 and peaked sharply at 0.9 (see dtt plots) and within a few seconds tripped the actuators at a gain of 1.

I added a 10dB notch at 739hz in FM3 and was able to turn on the level 2 completely. I have removed this notch from the filter file.

In this process I notice a peak pop up on the Y dof at 745hz but it doesn't erupt like the X's. When you look at the plant and filter design plots (attached,) it seems a lot of things could pop up if the plant were to change possibly by just a small amount.

I agree with JeffK that these loops should be looked at more closely especially by more experienced control loop types.