Virgo Logbook

Environmental Monitoring (Environmental Monitoring)

Paoletti, Fiori, Tringali, Pinto - 16:05 Friday 22 September 2023 (61751)

48Hz WE F7 crossbar resonance high again

As of mid-August, the 48.1 Hz that we label as "WE crossbar" became more excited. This occurred on Monday, August 14, within an unlock between 11:00 and 14:30 UTC. No particular action is reported in the logbook.

Today at 10:23 UTC we went to WEB and unplugged the mains cables from the motor crates, because we know that in the past there has been an unexpected coupling with some noise flowing through them.
The cables have been temporarily tagged (they are usually connected to a "smart power strip"), so that they can be reconnected in the right location.

We will test whether the 48 Hz noise is reduced at the next lock, after which we will make a final decision for the right system configuration.

It may be worth repeating the same action at NEB as well.

Images attached to this report

Comments to this report:

Paoletti, Tringali - 16:53 Friday 22 September 2023 (61752)

Indeed it worked! The bump at 48.1 Hz has completely disappeared.

(the sidebands around the 50 Hz mains line are not related to this action, but developed overnight during the last lock.)

Images attached to this comment

fiori - 14:57 Monday 02 October 2023 (61861)

Just a further look to the effect of unplugging the WE F7 stepper motor crate. Note that the crate was already OFF, the action was unplugging it from the mains.

Figure 1 is a VIM spectrogram across the time of the action.

Figures 2 and 3 quantify better the reduction in the Hrec spectrum before (purple, no 50Hz FF) and after (blue) the unplug of the crate. The orage plot is the O3 hrec.

The unplugging reduced the noise between about 40 Hz and 55 Hz (Figure 2) and also a peak at about 70Hz (another F7 corssbar mode) disappeared (Figure 3). There was no effective coherence with UPS,IPS and magnetic channels (Figure 2 and 3 show just the UPS_CURR_R channel, but also the other have been checked).

The frequency of the reduced noise is similar to that observed when the same action (unplugging) was done in O3. Instead this time the amplitude of the affecting noise was signlificantly larger.

Images attached to this comment