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ryousuke.sugimoto - 12:46 Monday 11 November 2024 (31574)

TF measurement between the geophone and OMC length error

[Yokozawa, Komori, Sugimoto]

We measured the transfer function and coherence between the geophone (K1:PEM-ACC_OMC_VACTABLEOMC_Y_OUT_DQ) and the OMC length error signal (K1:OMC-LSC_ERR_IN1_DQ). We used the speaker (K1PEM-EXCITATION_SR3_RACK_2_EXC) for the acoustic injection and the shaker (K1:PEM-EXCITATION_SR3_RACK_4_EXC) for the vibrational injection. Figures 1-6 show the measured transfer functions and spectra. The corresponding conditions for the eash figures are below. The injection’s effects were observed around 50-200 Hz, and coherence also seems to be the corresponding frequency.

Fig1,2:OMC dither amplitude 400, acrostic injection 10000 count (0-900 Hz white)
Fig3,4:OMC dither amplitude 400, shaker injection 1000 count (0-900 Hz white)
Fig5,6:OMC dither amplitude 400, shaker injection 1000 count (0-900 Hz white) with 50-200 Hz band path

Note: The geophone spectra increase broadly in the low-frequency region under injection conditions. We might have to check the geophone’s fixing method.

Images attached to this report

31574_1731296855_Fig1_20241111_OMCLSC_speker10000_dithe400.png

31574_1731296859_Fig2_20241111_OMCLSC_speaker10000_dithe400_coheence.png

31574_1731296865_Fig3_20241111_OMCLSC_shaker1000_dithe400.png

31574_1731296869_Fig4_20241111_OMCLSC_shaker1000_dithe400_coherence.png

31574_1731296874_Fig5_20241111_OMCLSC_shaker1000_dithe400_BP50-200.png

31574_1731296878_Fig6_20241111_OMCLSC_shaker1000_dithe400_BP50-200_coherence.png

Comments to this report:

takaaki.yokozawa - 13:35 Monday 11 November 2024 (31576)

I compared the spectrum of the OMC LSC ERR for each PEM injection.
Blue : Silent with 50 cnt dither amplitude
Green : Acoustic injection with 400 cnt dither amplitude
Brown : Shaker injection with 400 cnt dither amplitude
Red : Shaker injection 50-200 Hz with 400cnt dither amplitude.

Images attached to this comment

31576_1731300301_Screenshot from 2024-11-11 13-32-53.png

ryousuke.sugimoto - 23:28 Tuesday 12 November 2024 (31605)

I compared the transfer functions from the geophone to the OMC length error between those obtained using speaker injection and shaker injection.
Fig 1 shows the overall, and Fig 2 shows a zoomed view of 50–300 Hz, where coherence is observed (speaker: red, shaker: blue). While the results were mostly consistent, slight differences may provide insights into the noise path.

Images attached to this comment

ryousuke.sugimoto - 23:35 Tuesday 12 November 2024 (31607)

I also compared the measured geophone noise with the previous result obtained before the OMC stack was connected.
There were improvements in areas such as around 30-40 Hz and 75- 100 Hz. However, it also worsened in many regions.
Above about 280Hz, it was limited by the sensing noise.

Images attached to this comment