KAGRA Logbook

VIS (EY)

takafumi.ushiba - 13:55 Wednesday 22 May 2024 (29603)

ETMY F2 GAS signals got strange in this morning

After ETMY finalization work (klog29604), I noticed ETMY F2 GAS filter is very glitchy (fig1).
I checked F2 GAS LVDT spectra at several timing and confirmed the time when the problem happened.
Figure 2 shows the spectra of F2 GAS LVDT at 10:44 (blue) and 10:45, so LVDT signals got strange around 10:45.

Figure 3 shows the time series data of GAS signals around 10:45 JST.
Left and right cursors show 10:44 and 10:45 today, respectively.
Since the gurdian state is ISOLATED state, this time seems before our work (we requested SAFE state later, maybe around 10:50).
Also, RMS of GAS signals was reduced from 10:45, which is probably corresponding to the timing when I stopped the dry air injected to EYC.
I'm not so sure why stopping dry air caused glitcies on F2 GAS signals but anyway I have already asked Takahashi-san to check the situation.

Images attached to this report

29603_1716352899_Screenshot from 2024-05-22 13-38-07.png

29603_1716353167_Screenshot from 2024-05-22 13-37-19.png

29603_1716353172_Screenshot from 2024-05-22 13-37-07.png

Comments to this report:

ryutaro.takahashi - 8:50 Thursday 23 May 2024 (29618)

Previously, a strange peak of 70Hz was observed in the LVDT signal in IY. The peak disappeared by changing the modulation frequency from 10.0kHz to 10.3kHz. Anyway, we need to investigate at the site.

ryutaro.takahashi - 17:13 Thursday 23 May 2024 (29622)

I investigated the peaks that appeared in the F2 LVDT. The position of F2 was around 990um in free. There were not any strange peaks in the spectrum in the SAFE mode. The peaks appeared in the ISOLATED mode. I changed the setpoint for F2 from 1623um to 1423um. The peaks were still there. I offloaded F2 GAS with the FR to around 1600um. Then the peaks disappeared even in the ISOLATED mode.

I checked the resistance and inductance of the LVDT coils at the feedthrough flange. The resistance of the actuator coil (3-8pin) was very large.

	Befor O4a	This time
1-6	203.0Ω/38.8mH	227.6Ω/38.9mH
2-7	82.3Ω/9.6mH	88.7Ω/9.6mH
3-8	118Ω/70.1mH	251Ω/69.8mH
4-9	NC	NC

Images attached to this comment

ryutaro.takahashi - 19:46 Thursday 06 June 2024 (29780)

[Takahashi, Washimi]

We checked the resistance of the F2 LVDT coils at the feedthrough flange again. Though the resistance of the actuator coil (3-8pin) was large at 1kHz the last time, it was similar to the resistance before O4a in DC.

	Befor O4a	This time
1-6	203.0Ω	209.5Ω
2-7	82.3Ω	87.3Ω
3-8	118Ω	122.4Ω
4-9	NC	NC