Virgo Logbook

Interferometer_sensitivity_studies (General)

Paoletti, chiummo - 15:01 Tuesday 05 September 2017 (39382)

Tapping tests in DET Lab -- part 2

This morning we went back to the DET Lab to make some tapping tests with ITF down. Motivation for that was that we noticed during yesterday activity an unexplained sensitivity of the local controls of SDB2 to the tapping on the minilinks (see 39373 and attached pictures) and we wanted to exclude any possible although unlikely effect due to the ITF lock status.

What we did this morning was to repeat the tapping but trying to uncouple different stages. For instance we tried to walk the same way as we did yesterday, lean on the minilinks as yesterday, and so on.

The conclusion is that the only activity able to drive the LC of SDB2 crazy was the tapping on the middle part of the B1 link (see picture in previous entry, where it was referred to as N-3).

Below some details with GPS times:

Time: Sep05,17-11:06:27 -> GPS: 1188637603
Federico walks to approach the minilinks (no effect on LC)
Time: Sep05,17-11:07:52 -> GPS: 1188637688

Federico leans on the tubes, ready to tap (no effect)

Time: Sep05,17-11:10:24 -> GPS: 1188637840
tapping link N - 3 -> effect on LC
Time: Sep05,17-11:11:19 -> GPS: 1188637895

Time: Sep05,17-11:19:00 -> GPS: 1188638356
Federico just sits on the plataform and touches geophones after a while -> no effect on LC

Time: Sep05,17-11:20:00 -> GPS: 1188638416
Federico pushes on the south wall of SDB2 -> no effect on LC

Time: Sep05,17-11:21:02 -> GPS: 1188638478
Federico moves N -3 central part (where he used to hit) -> no effect on LC [O_o]

Time: Sep05,17-11:21:54 -> GPS: 1188638530
Federico knocks with backfinger on N-3, I hear clearly the tune of the tube vibrations -> LC go crazy

Time: Sep05,17-11:30:41 -> GPS: 1188639057
ENV_SDB2_ACC_Y moved from north side to south side of the SDB2 minitower (closer to N-3 minilink)

Time: Sep05,17-11:35:14 -> GPS: 1188639330
tapping on minilink north (N) -> no effect on LC
Time: Sep05,17-11:36:09 -> GPS: 1188639385

Time: Sep05,17-11:38:24 -> GPS: 1188639520
tapping on N -1 -> no effect on LC
Time: Sep05,17-11:39:30 -> GPS: 1188639586

Time: Sep05,17-11:41:08 -> GPS: 1188639684
N-2 (westmost part) -> no effect on LC, but 3-400 Hz structures on accelerometers
Time: Sep05,17-11:42:06 -> GPS: 1188639742

Time: Sep05,17-11:42:38 -> GPS: 1188639774
N-2 (eastmost part) -> no effect on LC, but 3-400 Hz structures on accelerometers
Time: Sep05,17-11:43:20 -> GPS: 1188639816

Time: Sep05,17-11:45:28 -> GPS: 1188639944
N -3 (westmost part) -> no effect on LC
Time: Sep05,17-11:46:08 -> GPS: 1188639984

Time: Sep05,17-11:47:15 -> GPS: 1188640051
SDB2 flange -> no effect on LC
Time: Sep05,17-11:48:01 -> GPS: 1188640097

Time: Sep05,17-11:49:18 -> GPS: 1188640174
N-3 eastmost part -> no effect on LC
Time: Sep05,17-11:50:10 -> GPS: 1188640226

Time: Sep05,17-11:52:03 -> GPS: 1188640339
N-3 center part -> huge effect on LC, stop immediately

Comments to this report:

Bertolini, Paoletti, chiummo - 13:06 Wednesday 06 September 2017 (39396)

So, with the help from Alessandro we went again to the DET Lab this morning to investigate more the relation between the tapping effects and the local controls of the SDB2.

This time in addition to the unlocked ITF, also the local controls of the SDB2 were left open so that we could have cleaner signals about the impact of tapping on them. We tapped on the usual culprit (N-3 minilink, aka B1 tube) and also on the top flange of the tower and close to the electric connection output (see attached picture). What we saw is basically that the LVDT signals have some frequencies excited most of all when the central part of the B1 minilink is hit - all the others spot being far less sensitive.

The reason for that is still under investigation.

Below some field notes with the GPS times:

Time: Sep06,17-09:48:12 -> GPS: 1188719308
approaching
tapping on N-3 center
lots of structures on LVDTs (30-60Hz)

peaks already there grow when tapping on specific spots
Time: Sep06,17-09:49:57 -> GPS: 1188719413

Time: Sep06,17-09:51:36 -> GPS: 1188719512
again tapping onto N-3 center, but with the hardest hammer tip
same effect (see second picture: pic1.png)
Time: Sep06,17-09:52:37 -> GPS: 1188719573

Time: Sep06,17-09:56:09 -> GPS: 1188719785
tapping on sdb2 flange close to N-3
smaller effect
Time: Sep06,17-09:56:41 -> GPS: 1188719817

Time: Sep06,17-09:57:50 -> GPS: 1188719886
tapping on the top of the chamber east side before EDB
small effect
Time: Sep06,17-09:58:36 -> GPS: 1188719932

Time: Sep06,17-10:00:37 -> GPS: 1188720053
tapping bottom flange
same effect as top part
Time: Sep06,17-10:01:22 -> GPS: 1188720098

Time: Sep06,17-10:01:40 -> GPS: 1188720116
electric output flange east
a bit larger than before?
Time: Sep06,17-10:02:47 -> GPS: 1188720183

Time: Sep06,17-10:11:11 -> GPS: 1188720687
N-3 tapping to see better what is on ACC_Y
Time: Sep06,17-10:12:33 -> GPS: 1188720769

Images attached to this comment

bertolini - 14:59 Wednesday 06 September 2017 (39397)

The tapping test has shown that structures around 30,42,44,52 Hz normally already present in the spectrum of all top stage LVDT and geophones are largely enhanced when the B1 mini-link is excited. The displacement recorded by the LVDTs was up to few micrometers RMS which is huge but
it doesn't explain why the suspension control unlocks.
Instead, a check of the raw signals from the 3 geophones used for the IP control clearly shows that all of them clip during the tapping. This
indeed will cause the suspension control to unlock. The plot shows the geophone raw signal in normal conditions vs during the tapping.
All three geophones were clipping, GEO_H0 at 52Hz, GEO_H1 at 44Hz, GEO_H2 at 52Hz. The reason why the geophones are so sensitive to these modes is that, since these are tilt modes, they couple unfiltered to the IP platform.

Images attached to this comment

Paoletti, Fiori, Pasqualetti - 16:15 Friday 22 September 2017 (39547)

Today, after the damping of the N-3 link tube done by Vac team (it will be reported in another dedicated entry), we repeated tapping tests while interferometere was locked.

We did not have the same problems reported in entry 39373 (SDB2 out of control and interferometer unlocked due to SDB2 IP Geophones saturation), so the work done on the link is an improvement.

We report the GPS time (UTC) of the tapping tests, with some brief comments.

- please have a look at linked entry for figures and explanation of links location

(note: we move the little temporary accelerometer ENV_SDB2_LINK_ACC over every “tapped” link)

tapping over “N” Link

Time: Sep22,17-12:35:33 -> GPS: 1190118949

Time: Sep22,17-12:36:36 -> GPS: 1190119012

We see a peak around 90Hz in the accelerometer, and (maybe) also in Hrec.

Also, some structures at 240Hz in Hrec

tapping over N -1

Time: Sep22,17-12:39:56 -> GPS: 1190119212

Time: Sep22,17-12:40:56 -> GPS: 1190119272

Low frequency (<30Hz) noise in Hrec

tapping over N-2

Time: Sep22,17-12:44:09 -> GPS: 1190119465

Time: Sep22,17-12:45:33 -> GPS: 1190119549

We see structures between 60 and 70Hz in Hrec

tapping over N-3

Time: Sep22,17-12:48:39 -> GPS: 1190119735

Time: Sep22,17-12:50:21 -> GPS: 1190119837

No visible structures in Hrec, moreover the SDB2 is now stable (interferometer does not unlock as before)

accelerometer ENV_SDB2_LINK_ACC is left over this last link (N-3) for the time being

fiori - 15:53 Monday 02 October 2017 (39641)

Just double checked the last tappings on SDB2 mini-links, after pipes damping. Indeed seems 410Hz, 440Hz and 255Hz did not excite during the tappings: see attached plots.

Images attached to this comment