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Local Control (BS)
majorana - 13:03 Tuesday 29 October 2019 (47448) Print this report
BS and SR roll (Tz)
BS: I updated the gain of Tz amplifier by readjusting the transimpedance.
- There is some ageing trend on the SLD source but I think we can cope with that, more importantly, I noticed that the driver of the SLD source providing SLD current monitor
used to display big fluctuations (15%) on the front panel. Apparently, the power monitored by the PSD sensor was not dramatically affected by that but I replaced the SLD driver. Let't see if the spectra improve (as initially they seem to).

Observation: SR logbook Task does not exist, it is time we added it ...
SR and PR Roll correction and accuracy spectra look very different, and that of SR is much worse concerning both accuracy and correction budgets (well known)

- In spite of different actuation cages, the two payloads are, in practice identical.
- The two roll control filters are identical but the gain applied at SR is 5.3 times larger

Not sure I have time to fully check the system during maintenance time, but there is a strong coherence with the transversal pendulum motion of the suspension that is transduced to the roll (also on transverse mirror motion I guess). Paolo has studied this issue of the SA transversal motion, which is well known.

The coherence shows up more pronounced as the gain is lowered (in the first plot the case of the same gain used for PR, 5.3 times lower, first plot set)
I might be wrong, but it seems to me we should give priority to the Z (S-N) of the suspension.

The mass distribution on the actuation cage certainly changes the recoil of the cage associated Tz control, we will remeasure the TF. as soon as possible to take into account a possible change of the control filter. I think we do it by tomorrow.
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