[Yokozawa, Michimura]
We did a tapping test around BS area with the PRFPMI locked with DC readout.
We found a excess noise around 70-100 Hz when tapping the duct between PR2 and BS.
We also found broadband excess noise around 100-400 Hz when tapping the duct between SR2 and SR3.
Tapping tool:
- Used box-end wrench M22/M24 with professional human hand.
Tapping timestamps:
Start_GPS_time Tapping_Point
1266530332 duct between PR2 and BS, PR2 side
1266530502 duct between PR2 and BS, BS side
1266530698 duct between BS and SR2, BS side
1266530857 duct between BS and SR2, SR2 side
1266531006 duct between SR2 and SR3, SR2 side
1266531140 duct between SR2 and SR3, SR3 side
1266531247 duct between SR3 and SRM, SR3 side
1266531424 Quiet
Each tapping lasted at least 60 seconds.
Result:
Attached shows DARM spectra when tapping different part of the vacuum ducts.
Tapping PR2-BS duct give excess noise around 70-100 Hz, many peaks are excited.
Tapping BS-SR2 duct give slight excess noise but not much.
Tapping SR2-SR3 duct give broadband exces noise around 100-400 Hz.
The DTT file lives in /kagra/Dropbox/Personal/yuta/Commissioning/202002/Hammering20200224.xml
Next:
PR2-BS area might be a cause of a bump around 70-100 Hz.
Let's install accelerometers here and subtract if possible.
Thank you for the interesting data; try to roll over the tubes with lossy material like rubber as was done for the air ducts at the end rooms??
About tapping the vacuum tubes, it sometimes might be different among the places where you hit and where fluctuated well, as the tubes also have their eigen-(spacial) modes and eigen frequency.
By the way, I'm slightly afraid that it might be nice to avoid using metal tools to tapping; I think the shook by the hitting metal against metal would be larger than your thought and it might be dangerous for the vauum structure, which is supporting atmosphric pressure somehow with keeping its balance so that it would not fly away; professional human (soft) hands are eventually the best.
Akutsu-san,
Thank you for your comment.
We use a rubber hammer to tap the chambers, not metal one.
> the tubes with lossy material like rubber as was done for the air ducts at the end rooms
Is it means an Aeroflex?
I remenber that we have stock of them around MCE.
miss entry
I do not know very well about VIS system, but somehow these duct vibration modes are not filtered well with current control loop.
My personal idea to reduce this noise sources.
1. attach a vibration detector(accelerometer, piezo electric or similar) to duct around BS(and possibly all TM mirrors)
2. design feedback control loop using these outputs to filtering these noise
Thanks for effort of commissioning team to make work IFO!