Virgo Logbook

Detector Characterisation (Spectral lines)

direnzo - 11:21 Tuesday 03 October 2023 (61873)

Wandering line between 970 and 1000 Hz

(This is an update of the entry that I wrote on Friday but that remained in the Draft)

This entry is a reminder for a wandering line, already identified by Federico Paoletti in #60093, and visible in Hrec and DARM data since we got to Low Noise 2 (April 2023). The line appears to oscillate, without any peculiar or repetitive pattern, between 970 and 1000 Hz. In the attachment, the spectrogram of this line over the last 5 days of Low Noise 3, as well as its tracking (red line).

In a follow-up entry, I will post a file with the time series corresponding to the frequencies of this wandering line and, possibly, the results of a brute force correlation analysis with the trend channels.

Images attached to this report

Comments to this report:

fiori, paoletti - 17:09 Friday 20 October 2023 (62242)

This line seems to follow the wandering pattern of the 6000 Hz line from the CEB UPS.... but flipped in frequency (!)

The attached figure compares 1 hour evolution of 6kHz line and that of the 980Hz line over the same period (it shows the SDB1 B1 PD1 Audio channel, but it is exacly the same in the Hrec channel).

Also noticeable in the attached figure, the hrec line is roughly centered at 980Hz, and its frequency span is roughly 1.5 larger than that of the 6000Hz line.

Note that the 6kHz sinus wave signal is generated by the CEB UPS and used for the IPS 50Hz reconstruction, its frequency thus follows the (natural) drift of the IPS 50Hz, see also https://logbook.virgo-gw.eu/virgo/?r=60968. The 6kHz noise line and several similar lines are sensed in all CEB IPS monitors and CEB magnetometers.

We have checked for possible aliasing (which might be a simple explanation for the flipping) from one hypothetical line at 19020 Hz in the SDB1 B1 PD1 Audio 100kHz channel, and it is not the case (and indeed it would be very unlikely).

Images attached to this comment

fiori - 17:13 Friday 20 October 2023 (62243)

... the bruco gives no coherence of hrec with aux channels at the line.

Paoletti, Fiori, Tringali - 9:50 Tuesday 24 October 2023 (62268)

Being a noise that travels through the mains, it lurks everywhere. This is also found, for example, in SSFS signals.

The 20 kHz sampled spectrogram of the IPS mains is clearly full of harmonics (as it must be), but also with some aliasing. Don't know the origin.

Images attached to this comment