ross.kennedy@LIGO.ORG - posted 20:16, Monday 11 July 2016 - last comment - 21:19, Monday 11 July 2016(28333)
PI damping filters
During the lock today I had to change some of the damping filter settings as different modes rang up. Similarly to what Nutsinee was seeing on Saturday the 18040Hz and the 15009Hz ETMY modes were the ones causing the most trouble. From the strip tool you can see where I have changed the damping filter settings.
The current phase and gain states for these filters are:
- ETMY_PI_OMC_DAMP_MODE1_DAMP (15009Hz): gain=-500 phase=0deg
- ETMY_PI_DAMP_MODE4_DAMP (18040Hz): gain=3000 phase=0deg
Also when I was trying to damp the 18040Hz mode earlier there was a difference in thet rends of the OMC and QPD rms monitors. From the OMC rms it seemed theat the damping was effective but it's clear from the QPD rms that the mode was still ringing up and broke lock.
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The lock after this had several PI ringing up and again the damping filter settings needed changed.
The purple line here refers to the 14980Hz ITMY mode which needed to change phase 3 times in order to damp it. At the start of the lock it was set at -60 degrees. After the first increase it was changed to 0 degrees and it went down. After 5 minutes it started ringing up again and so I changed the phase to 60 degrees. This damped it for ~13 minutes and then rang up again so I changed the phase to 30 degrees which damped it again. The yellow line and the red line refer to the QPD and OMC rms for the 18040Hz ETMY mode respectively. After seeing the difference between the rms of the OMC and QPD signal earlier it becomes more apparent that at larger mode amplitude the QPD signal becomes more reliable. After this mode became unstable I changed the phase to -30 degrees which damped the mode. This mode is currently being damped using the QPD signal. The dark green is the 15009Hz mode which rings up a bit more slowly than the rest. I changed the phase from 0 degrees to 60 degrees which damped it. The light blue line is the 15520Hz ITMX mode. I had iwave tracking on this one but I had to change to just a bandpass filter after the rms started clipping. I changed the phase from -30 degrees to 30 degrees which damped the mode.
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