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Paoletti, Fiori - 11:13 Wednesday 01 August 2018 (42269) Print this report
Electrical ground noise entering into the ITF

Since last Friday afternoon (July, the 27th) we have a temporary monitor of a noisy current flowing into the metallic mass of CEB

This monitor is simply a piezoelectric accelerometer (ENV_IB_ACC_X) that we have left on a soft pillow, so it does not read the acceleration from 20 Hz on (we tested it); we have then connected to ground (the metallic body of the INJ tower) the shield of its coaxial cable. The signal increase at 50Hz and in all its harmonics (ground loop), mainly on odd harmonics (e.g. 150Hz).

During a short and dirty lock (Friday afternoon 18:38 UTC + 480 seconds, see fig.1 and fig.2) we made the coherence between this electric noise monitor and other signals, and we found (see fig.3):

  • RFC is highly polluted all around mains signals (50Hz and all harmonics)
  • some SBE_EIB sensors ("geobench") also are dominated by this electrical noise
  • LSC_DARM is coherent around 150Hz and 350Hz
  • no coherence is visible in signals coming from the terminal buildings (e.g. LSC_B7_56MHz)

Waiting for a more robust and clean lock, it should be useful to repeat this type of measure more systematically, trying to disentangle as much as possible the path that this ground referred noise has to enter the ITF

We left the accelerometer ENV_IB_ACC_X as it is (the shield is grounded) until we need it for seismic analisys around the IB tower.

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Paoletti - 15:18 Wednesday 01 August 2018 (42276) Print this report

Other interesting signals, with high coherence with the electrical noise, are in this figure

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Paoletti - 11:37 Friday 03 August 2018 (42304) Print this report

For future reference and study only,  these are some plots comparing the old (June the 15th) and the new (this night) LSC_DARM spectrum, togheter with the actual coherence that LSC_DARM has with the electrical noise sensor ENV_IB_ACC_X

The first plot is the entire FFT from 50 to 500 Hz, while the following plots are interesting zooming around 150, 200 and 350Hz

To be repeated when sensitivity will be better.

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