ibrahim.abouelfettouh@LIGO.ORG - posted 15:51, Tuesday 27 August 2024 (79743)
BBSS Bounce and Roll Modes Measured
Ibrahim A, Jeff K
On 8/22, Jeff K and I ran some measurements of our assembled BBSS and determined the Bounce and Roll modes to be:
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Bounce: 19.835 Hz (model prediction: 19.56 Hz)
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BW: 0.01 (128s/avg)
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Averages: 50
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Excitation Waveform: Uniform Noise, 19-20 Hz
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Roll: 32.047 Hz (model prediction: 31.88 Hz)
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BW: 0.001 (1024s/avg)
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Averages: 50
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Excitation Waveform: Uniform Noise, 31-33 Hz
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Confirmation ASD (exponential avg) Excitation:
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BW: 0.02 (64s)
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Excitation Waveform: Sine
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Averages: 5
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I have linked this alog to the SWG Logbook in the case these results are needed for BRD development for the BBSS.
Screenshots of these peaks and the excitation spectra are attached and the Data can be found on the X1 (Test Stand) Network: at /ligo/svncommon/SusSVN/sus/trunk/BBSS/X1/BS/Common/Data/ under names:
Roll: 2024-08-22_1200_X1SUSBS_M1M2_Roll_V_0p001to40Hz.xml
Bounce: 2024-08-22_1200_X1SUSBS_M1M2_Bounce_V_0p01to40Hz.xml
Initial Measurement:
These values were found by taking a High BW Transfer Function using a noise injection into M1 Vertical in the 2Hz range in the neighborhood of the model values, reading at all BOSEMs in the M2 stage. (19-20Hz for Bounce and 31-33Hz for Roll). We then found the most coherent peak in that region to be our measured mode.
Mechanical Mode Confirmation:
After this, we ran an ASD and injected a sine wave at the found frequencies one-by-one, ringing up our modes for 5 averages before stopping the injection. We then watched the ASD and confirmed that given the number of averages it took to percieve a gradual ring-down at those frequencies (over 20 averages of for each at 0.02BW assuming a Q-Factor of ~1000, which is conservative), that the readout was indeed mechanical, and that these were indeed our Bounce and Roll modes.
Note: While the screenshots may say M3, this is simply because of our set-up being hooked up to the M3 stage electronically. These results were read from the M2 BOSEMs on the PUM of the BBSS. This cabling discrepancy has since been fixed.
Images attached to this report
