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Environmental Monitoring (Environmental Monitoring)
fiori, paoletti - 11:43 Friday 02 November 2018 (43392) Print this report
Acoustic injections CEB October 24 (sound tracks)

On October 24 (27 Mpc, 17W) we performed new acoustic injections in CEB (Figure 1). In place of the usual white noise, we injected some sound tracks (you can listen to them in the attached .wav) which proved as well effective.

These injections look definitively better that those performed on October 5 (17Mpc, 25W) since the sensitivity was very bad at that time, one reason being the SDB1 picomotors which were forgotten on after the Sept intervention in SDB1.

Figure 2 (spectrogram) and Figure 3 (ffts) show excited peaks. Essentially all of existing peaks between 300 and 500 Hz got excited during the injection (it is possible that the injection triggered some misalignment which increased the coupling of some peaks).

It makes sense to compare this injection with that of August 24 (22Mpc, 25W), we did right before SDB1 intervention, because ITF alignment conditions were good at both times (sensitivity stable) and also at both time SDB1 motors were OFF as well (R.Gouaty switched them off on July 25: 42211).

Here a list, with some notes that relate the peaks evidenced during this acoustic injection with those present on August 24, Hz:

  • 343  also on Aug 24
  • 386  NEW since Aug 24
  • 392  also in Aug (slightly moved)
  • 401  also in Aug (Turbo pump line, coherent with ACC DT)
  • 418  also in Aug (small cohe <=0.06 with ACC DT)
  • 436  NEW  (jumping line) we had in O2 as well (small cohe <=0.06 with ACC DT) (could it be related to the uncoated aluminium OMC covers??)
  • 464  NEW  (some cooling fan) cohe with ACC DT and EDB mic (it moved, in August it was around 458)... something inside DET?
  • 476  NEW  (small cohe <=0.06 with ACC DT)
  • 524  also in Aug

Figure 4 and Figure 5 show a projection of CEB microphone onto Hrec, most of existing peaks are matched.

Figure 6 shows the measured TF (CEB mic to Hrec) compared with that measured on Aug 24 before Sept. SDB1 intervention: they are very similar except for the higher measured coherence at the NEW peaks (386, 436, 476).

Also attached are the measured TF files, and the log file of the injections.


 

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fiori - 13:10 Friday 02 November 2018 (43394) Print this report

The attached plot compares DARM in two clean and stable periods of October 24 (27MpC 17W) and August 24 (22 Mpc, 25W). Also shown is the accelerometer on DT tower East flange and its coherence with DARM.

We can see that most of the structures in DARM (listed in the above elog) have some (although small) coherence with this accelerometer, and this points to some residual light scattered from SDB1 off the DT tower walls.

The second plot zooms into the 450-500Hz  region that is where the coherence is more evident. In this region most of the peaks can be associated to an external source: some are related to BS-SR turbo (456 Hz comb at least), the 358 -> 364Hz is most likely a drifting fan (to be found). There is also a 412Hz, to be found.

One note: we can assume this comparison representative of the effect of thechanges that occurred before and after the Sept 11-13 intervention on SDB1 and scattered light related action. Seems there is no large improvement (unfortunately) but also no significant worsening. One thing that definitively seem appeared after that intervention is the jumping peak.

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