Today we had an unlock, at 12:52:13 UTC, as SRCL oscillated at ~2.25 Hz (Figure) causing then the saturation of B1 and, eventually, the unlock.
During the afternoon shift we put online a new filter, SRCL_ctrl5c, which should address this problem by removing some unnecessary structures and gaining more at low frequency. This is intended to be used instead of SRCL_ctrl5b in LOW_NOISE_3.
We haven't tested it yet not to mix things up with the ongoing shift, but it will be tested soon.
the engagement went fine.
fig.1: time domain response comparison of older filter VS new filter.
fig.2: spectra comparison. As expected, the filter gains more at the region of 2 and 3 Hz. In that region, also the phase margin has been a little been improved. There is a predicted worsening in some LF region, but the overall accuracy has not been touched.
we leave this control on line by default. we will evaluate the response also in better weather conditions, with less wind and sea activity.
looking at the injection of yesterday we could fine tune the gain of the loop by increasing it of about a factor 1.2 in order to have the right UGF and the right gain at LF.
