R&D (FilterCavity)
EleonoraCapocasa - 18:33, Friday 17 May 2019 (1357)
DGS work progress: cabling and real time completed, BS loops engaged

What has been done:

1) The area around the work station of the new DGS has been cleaned and tidied up.

2) The cabling toward and from the new ADC and DAC has been realized.

3) The real time model has been completed to include all the suspensions (pic 1). It is mainly fine even if I could not implement some more sofisticated features (see dedicated entry #1359).

4) The damp on BS has been implemented. See TFs of pitch and yaw (pic2-3) and specra with open and closed loop (pic4-5).  They can be compraed with the "labview ones", measured in november 2016, reported in entry #337.

Some comments on BS CONTROL

1) TF are both one order of magnitude smaller wrt labview ones, this seems a bit strange to me. I would say It shouldn't depend on the digital system. But note that in KAGRA DGS there is a factor 2 btw ADC and DAC count calibration (entry #1315).

2) Pitch TF is less clean wrt labview one:  there is noise and lack of coherence in correspondece of the zero of the TF. Not that the maximum output of DAC is +/-5 V, while in labview was +/- 10 V. The max  white noise  amplitude I could send to avoid any saturation is 6500 count witch according to the count/ volt calibration corresponds to about 2 V.

3) Spectra levels look similar. A rough computation of the count -> rad calibration (using the information from entry #337 and  #1315) gives roughly 1.9e-7 rad/count.

4) There are more structures at high frequency then before. I don't think this corresponds to a real motion of the mirror but rather some oplev mount resonances. It is clearly visible in the time doman where it masks the low frequency motion. This excess of noise at high frequency wrt before showed up also in PR. The gain should be low enough not to feed this noise back to the mirror.

5) There is a high Q resonance at 10 Hz  which is effectively damped by the control.This was already observed in labview. Another line is present at 11.5 Hz both in pitch and yaw.  I don't think it is from the mirror and I fear the gain is not low enough at that frequency. To be investigated.

Images attached to this report
1357_20190517112412_medmpic.png 1357_20190517112425_bsyawtf.png 1357_20190517112430_bspichtf.png 1357_20190517112446_bsyawspe170519.png 1357_20190517112502_pitchspe160519.png