Virgo Logbook

Reports 1-1 of 1

Interferometer_sensitivity_studies (General)

swinkels - 20:41 Wednesday 18 February 2009 (22111)

Coherence with magnetometers

I had a look at the coherences between all the magnetometers and B1 during the AC OFF test (240 seconds of good data starting at 918576234). There is some broad-band coherence with the magnetometers of the central building between 20 and 30 Hz of about 15%, which agrees pretty well with the noise projection of the previous entry. The other buildings do not seem to contribute, see fig 1.

There is another interesting feature just below 3100 Hz, also coming from the central building, see fig 2. Fig 3 shows that this is a line that moves around a little bit. At this high frequency, it is probably not a direct magnetic coupling to the magnets on the mirrors, but something that enters via the electronics.

Images attached to this report

Comments to this report:

paoletti - 21:29 Wednesday 18 February 2009 (22112)

This ~3kHz moving line recall an old analysis, made during E1 run (2002), where we discovered a signal like this one that was due to a beat between the double of the sampling ADC frequency (40kHz) and the frequency of one VME (crate 39) switching power supply.
The first one was very stable, but the second one was moving around 36400Hz with temperature and load, creating a beat of about 3600Hz.