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MSC, focus on: WI ghost noise

This article explores the recent history and effects of Wi ghost noise, a disturbance that has been present since 2006. It analyzes the patterns and potential causes of the noise, highlighting its impact on accelerometers and sensors. The article also discusses tests conducted during maintenance and possible solutions to mitigate the noise. (500 characters)

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MSC, focus on: WI ghost noise

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  1. MSC, focus on: WI ghost noise

  2. 1 “Recent” history and effect July 22 Aug 1 Aug 1 July 11 Jul 28 The disturbance, with us since Dec 17 2006, had disappeared before VSR1 appeared again on July 11th. Warning on July 22nd, unlock on Jul 28th Note: we could not cope with it without quad compensation

  3. 2 unlock list • Jul 28 15:16 • Aug 1 23:41 spike on accel., saturation, noise disappearence • Aug 3 16:48 no spike on accel., noise slowly re-appeared • Aug 3 23:58 spike on accel., saturation • Aug 4 12:15 spike to be checked • Aug 5 19:47 no visible spike * • Aug 5 21:08 no visible spike * • Aug 6 00:27 no visible spike * • Aug 6 01:00 (to be checked) * * In some cases we see noise increase of accelerometers but no saturation is visible. The disturbance produces an effect in the range 40-200 mHz, similar to that due to the wind through accelerometers. The indicator we use (WI_F0_tyLVDT) is in principle d.o.f. most uncoupled from the seism.

  4. 2 tests during mantenance on August 1st - I Only “light” tests during VSR1, as reccommended by Electronics crew • Hypotheses: • - Mechanical offset on LVDTs => spurious torque exerted by DC control • of the suspension => anomalous position of the IP => seismic noise • more coupled to the top stage. • tests of opening and closing the ID • tests of download • new card with for direct probe of F0 sensors used during the mantenance

  5. 2 tests during mantenance on August 1st - II Basic problem: the rest position after the first three ID opening significantly changes. Difficult to imagine a featured compensation of the IP position at each opening of ID. Note: the relation with The disturbance is not clear. Tomorrow, if the noise is present, new IP positioning tests

  6. 2 tests during mantenance on August 1st - III • H accelerometers • comparison with NI • two noise bumps

  7. 2 disappearence Aug 1st 23:41 UTC - I disappearence mantenance Meanwhile setting back to adjusting mode, no action on the suspension !

  8. 2 disappearence Aug 1st 23:41 UTC - II • Note: at the first glance we notice that during locking/unlocking periods, tyLvdt is very noisy, differently with respect to NI. • There should be no reason: • investigated the logic and card checked, apparently it is unexplained • deeper investigation shows that also accelerometer signals during these periods are more noisy: a physical disturbance ? Sensors ? Electronics ? • a spike appeared just before the miracle at 23.41 of Aug 1st

  9. 2 disappearence Aug 1st 23:41 UTC - III saturation Only one probe had been left for direct observation of one H-Accel

  10. 2 disappearence Aug 1st 23:41 UTC - IV Zoom: A very fast event At the limit of the detectable frequency BW

  11. 2 measurement before and after disturbance disappearence Reconstructed off-line accelerometers a2 a3 aV1 aV2 a1

  12. 2 measurement before and after disturbance disappearence Reconstructed off-line accelerometers a2 a3 aV1 aV2 a1

  13. 3 saturation with unlock ! Reconstructed off-line accelerometers a1 a2 a3 aV1 aV2 Saturation appears only in few cases ! Note: a zoom analysis shows very fast deep 2e-4 s ! Visible only when very large ?

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