Alexa, Evan, Koji, Arnaud, Sheila, Rana
The good news is that ALS is quite stable tonight, staying locked for up to 2 hours.
- Earlier in the day we struggled for a while to recover alingment after maintence day. We had difficulty locking DRMI plus the arms, the DRMI ASC didn't work well, with the arms. We eventually turned off the ALS WFS, locked DRMI without the arms, used the ASC (MICH, SRC1, SRC2, and PRC2), and offloaded. Since then we have not had much problem with the DRMI alingment. It seems that actuating on the ITMs with the green WFS may be spoiling our DRMI alingment. For now the green ASC is off, with the inputs turned off, so that even when the Gaurdian thinks the WFS are on, they are not.
- We also have turned off the IMC ASC DOF4.
- DRMI lock acquisition has been slow tonight, sometimes taking about a half hour. We checked our open loop gains, which were all normal. We would like to spend some time speeding this up tomorow so we can make progress faster.
- We noticed that we were mostly adjusting the alingment of ETMX pitch in the positive direction after the arm transmission would drop, Arnaud noticed that the top mass moved by 10 um starting at 11 am this morning, the same time as a small temperature excursion.
- We have had two trips of ETMX tonight, which were ISI, Hepi and suspension trips (the first was at 5:15:26 UTC Jan 21st, the second at 7:30:15 UTC) Arnaud investigated the second one, and found that there was a large (200 um) impulse sent to HEPI from the tidal feedback right before the trip. The six hour trend of the signal sent to HEPI shows that the tidal system has sent some relatively large impulses to HEPI several times tonight (second screenshot).
We have been having trouble transitioning to 3F tonight. We can transition MICH and PRCL fine, but we have seen a lot of noise at 300 Hz when we try to transition SRCL to 3F. When we try to transition we see noise at 23.5Hz.
ALS lock loss times: (all Jan 21st UTC) 0:03:02, 0:34:26
ALS lock loss +HEPI, ISI and sus trips: 7:30:15, 5:15:26
Lockloss and bad misalingment of IMC due to DOF4: 6:35
DRMI + arms off resonance lock loss due to SRCL 3f transition at 01/21/14 08:06:00 UTC
Keita, Sheila, Daniel, Alexa
Here is a screen shot of what happened that caused HEPI and ISI trips on DIFF lockloss last night. First, the arms loose the green lock, at that time the DARM output becomes very large, the gaurdian ramps this down over ten seconds, durring which time the integrator in L1 is still integrating. The guardian eventually clears this integrator. Before the integrator was cleared, the arm cavity flashes, although the suspension was still swinging so this produced a momentary lock. The tidal comes on, with a large output because the integrator in L1 has not been cleared yet.
We have done 4 things to help prevent this in the future:
- added a limiter of 3x10^6 in the DARM filter bank
- added a limiter of 10 um in the LSC-X_TIDAL_ERR filter module (and Y)
- fixed a mistake in the guardian that meant only one of the boosts in L1_LOCK_L was being turned off on a lock loss.
- increased the speed of the ramping down of the DARM gain, so that the suspension history clearing will happen sooner.
The last thing that we need to do is add a delay to the logic for the tidal feedback, so that it does not engage prematurely on these momentary locks.
