1. MSC, focus on: WI ghost noise

2. 1 “Recent” history and effect July 11 July 22 Aug 1 Jul 28 Aug 1 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 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. - 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.

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 mantenance disappearence 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 Only one probe had been left for direct observation of one H-Accel saturation

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 a1 a2a3aV1aV2

12. 2 measurement before and after disturbance disappearence Reconstructed off-line accelerometers a1 a2a3aV1aV2

13. 3 saturation with unlock ! Reconstructed off-line accelerometers a1a2a3 aV1 aV2 Saturation appears only in few cases ! Note: a zoom analysis shows very fast deep 2e-4 s ! Visible only when very large ?