Alexa, Sheila, Kiwamu
we were able to lock ALS diff somewhat stably tonight, with a ugf around 5.5 Hz.
- by comparing our settings with those in alog 11877 Alexa found that we were missing a high pass in the L3 lock filters for ETMX. We copied this, as well as FM6 and FM 7 (part of our plant inversion) to ETMY.
- L1 LOCK_L filters of ETMY were changed to match the ETMX filters.
- we were then able to lock with the 2 boosts on, and a gain of 0.4 in the input matrix. This was stable, and stayed locked, but it seems as though we must not have had much phase margin with such a low ugf (1Hz) and both boosts on.
- With the DARM offset set to 0.0195 we locked the 01 and 00 mode of the IR to the Y-arm.
- We eventually rung up the bounce and roll modes of both quad, making locking difficult for some time.
- We added an L2P filter for ETMY L1 drive align (FM 8 z0.5, p10), that has the same gain at high and low frequencies as the previous filters (FM1 + FM2) but without the high Q resonances in between. This filter seemed to help ... ??
- Kiwmau changed the coild driver state request for L1 from 2 to 1 for both ETMs, so that the low pass filters are off. This allowed us to set the input matrix gain of DARM to 1 and brought the UGF up to 5.5Hz for DARM (for this scenario the two boosts of DARM were off).
(free-swinging and in-loop spectra)
After playing with some gain settings and enabling LSC filters, I became able to robustly close the loop with a UGF of 10-ish Hz. I ended up with a L3_LOCK_GAIN of 1 for both ETMX and ETMY. In order to avoid DAC saturation I intentionally decreased the input element to 0.8. This seemed to help reducing DAC saturation events. I edited ALS_DIFF guardian accordingly. The attached below is ALS DIFF spectra of tonight:
(Red): in-loop spectrum, calibrated in um. (Blue): (almost) free-swing spectrum, calibrated in um. The blue curve was measured by conrolling ALS DIFF with an extremely low UGF. The in-loop RMS was about 600 pm which is almost the same as what we had in the HIFO-XY time (see for example, alog 11878). However, we are having 0.5-ish Hz feature in the in-loop spectrum which maybe due to some kind of angular coupling. I have not investigated this yet. Anyway, we are essentially back to the HIFO-XY performance.
(Out-of-loop measurements)
I was able to let the Y arm be on top of a resonance. A DARM offset that I found good was -0.0651.
Short term stability:
Please look at the red-ish and cyan curves which are IR_TRX and TRY respectively when the arms were held by ALS comm and diff.
Long term stability:
Things drifted on a time scale of 5-10 min. Also I noticed that the IR alignment in Y arm was not optimum. It should be roughly twice higher than it have been. Also, ETMY L2P was obviously worse than ETMX. Maybe the green alignment in the Y arm was simply not good ?
This lock strech can be found between 22:50 and 23:12 in PDT.