Rana, Alexa

Since we saw a lot of YAW motion from the BS last night, we decided to look at the L2Y coupling again. The  original filter FM1 installed in the drive align was created via alog9394.

We injected a sinusiodal excitation in BS-M2_LOCK_L and examined the M3 oplevs. First we excited at 0.01Hz, and measured peak-to-peaks via StripTool at several gains. Assuming a linear relationship, we then determined the best coupling gain to be 0.0025 (at 0.01Hz). Then we excited at 4.57Hz, and found the mag, phase at two gains. This allowed us to determine the coupling gain to be 0.002203 (at 4.57Hz). We then created a filter accordingly to match the respective gain couplings at low and high frequency. The filter is installed in FM2 (see first attached image). The gain in the filter bank should be set to -1 for either FM1 or FM2.  The second image shows both FM1 (blue) and FM2 (red).

For refernce FM2: zpk([0.694211+i*0.827328;0.694211-i*0.827328],[0.642788+i*0.766044;0.642788-i*0.766044],-0.0025,"n")