I succeeded in green-locking the X arm by feeding back the beat signal to ETMX.
Here are some quick reports. Some more details will be posted tomorrow.
The below shows a time series data of the PLL feedback signal when the servo was acquiring the lock.
At t = -2 sec. I started feeding back the signal to ETMX with the gain 50 times smaller than its nominal.
Then at t = 0 sec.I switched on a low frequency boost (pole 0.1Hz and zero 1Hz) to make it more robust.
At t = 3 sec. I increased the gain to the nominal.
Finally the UGF became ~ 60 Hz according to my open loop measurement by diaggui.
However I couldn't make the UGF higher than 60Hz because the more gain caused a instability for some reasons.
Here is a diagram for the green locking.
I used the same VCO box as we setup on the last Friday (see #4189).