However, the vertical coils are above 4 V and the horizontal coils only at 0.7 V. Therefore, this error can only be reset by moving the counter masses on the bench; the vertical back-left and front right coils are at +4.2 and -4.2 V; so the bench has a a tilt both in Tx and Tz. I think the counter masses need to be moved and then the low-noise loop activated.
I asked the operator to contact the LAPP group.
The issue of oscillation at SNEB is not due to the 4V on 2 of the vertical coils, we can have up to 10 V on these coils.
Other benches works fine with a similar voltage send to the vertical coils.
We worked on the issue with Alessandro at the end of the morning and we managed to reduced the oscillation of the bench in X, see plot attached .
A detailled entry will be posted later by Alessandro.
Romain checked the SNEB_LC controls carefully and concluded that the large TZ displacement was caused by the large X displacement of the MultiSAS (triggered by the large microseismic activity of this morning). It also appeared that the bench was moving substantially more than the ground pointing to some ongoing issue with the top stage controls. Lowering the control gain did not help, so that we decided to disable the inertial control of SBE along X and use only the LVDTs to damp the chain modes and compensate for drifts. After this action we observed a huge reduction of the X motion (Plot1: showing the RMS motion of the bench is compared to RMS motion of the ground for which we took the corresponding SAT F0 LVDT signal.) that was beneficial also, as expected, for reducing the bench angular motion in TZ (Plot3).
In order to further improve the X control we engaged the tracking wrt NE SAT by using the VPM button, but we could not observe any improvement. Therefore we checked the tracking section of the SBE config file and it turned out that the tracking action is still tied to the trigger logic used in O3 based on the arm cavity power. We disabled then the trigger such that now the tracking can be really engaged on the VPM (manually). The effect of the tracking along X can be seen in Plot 2: the error signal (SNEB_F0_x) shrinks significantly and no excess motion of the bench wrt to ground is longer visible. Further work on the SBE controls is needed to improve the performance, especially in Z.
