only DE fan off: 10:30 - 10:45 LT
both SR and DE off 10:53 - 11:17 LT
back on from 11:20 LT
We observe 100Hz line descreases: (Figure 1)
- by about factor 20 in SE_Cryo2 (seismometer on Cryo-trap, SR side) coincident to the switch off of SR fans. While fans of both turbo pumps
- by about a factor 4 in SE_Cryo_1 (Cryo-trap, DE side), Em_SETODE01 (DE viewport) and Em_SETODE01_tmp (DE tower), to which both SR and DE fans seem to contribute.
- we observe a consistent decrease of 100Hz line with one EM isolated seimometer (electrically isolated measuring sys, as used in Hunting of seismic 100Hz). This supports hypotheis that we are measuring real seism at 100Hz.
It has to be added that yesterday we verified that turbo pump cooling fans (measurements performed at NE) do vibrate at 100Hz (magnetosctriction effect).
Figures 2 and 3 show dark fringe noise: a small decrease of noise around 100Hz seems present, trend data measure a possible 10% noise drop between 100 and 105Hz which seems to persist during the switch off time, but it is too small to be significant.
However, not an evident bump was present since the beginning. A look to last week dark fringe spectrogram (Figure 4) shows that the usual halo fluctuation of 100Hz has disappeared or changed. Change seem to have occurred during commissioning time of last Thursday. This point should be better investigated.
Seismic noise reduces at some peaks around 45Hz, which are associated to cooling fans rotation: see Figure 5.
Figure 6 shows dark fringe noise around 45Hz: it seems a peak disappears when SR fans are switched off, however around 45Hz other peaks are present. Indeed we should proceed to a general switch off of all cooling fans of all turbo pumps, as originally proposed by Antonio.
