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fabian.arellano - 12:49 Friday 06 September 2019 (10262) Print this report
Assesment of vibrations on oplev readout (from 2nd of September 2019).

With Yokozawa-san and Washimi-san.

In order to assess the origin of the features in residual motion measurement reported in entries 10209, 10210 and 10216,  on Monday 2nd of September we placed three accelerometers around the oplev. Namely, one at the oplev lower platform, another one at the upper platform and a third one close to the second one but on the large frame. We measured amplitude spectral densities with all the filters on and with some filters off (all in the SR area and half in the BS area).

The channel names and files used are the following:




  • SR3_ALIGNED_ASD_FFU-OFF_20190902.xml
  • SR3_ALIGNED_ASD_FFU-ON_20190902.xml
  • acc_oplev_upper_platform_FFU_ON.txt
  • acc_oplev_upper_platform_FFU_OFF.txt
  • index.txt

Channel names:

  • Lower platform: CH1 ACC : K1:PEM-SENSOR_RACK_SR3_BNC8_OUT
  • Upper platform: CH2 ACC : K1:PEM-SEOSOR_RACK_SR3_BNC9_OUT
  • On the large frame by the upper platform: K1:PEM-SEOSOR_RACK_SR3_BNC10_OUT

The following observations apply:

  • Below 7 Hz the redout of the microphone is larger with the fans off. Nevertheless, at frequencies higher than 60 Hz is smaller. Clearly there's something unusual and it shoud be checked.
  • In between 7 Hz and 60 Hz  the reduction in the microphone readout floor is small when turning the filters off. Some peaks are clearly smaller.
  • In the readout of the upper platform accelerometer and in the oplev for TM-L, TM-P and TM-Y some peaks are clearly smaller with the filters off, but the noise floor remains at the same level.
  • The coherence of the accelerometer at the upper platform and the oplev readout is shown. Above 10 Hz we have regions of high coherence.
  • The coherence between the same accelerometer and the IM-L, IM-P and IM-Y is shown in order to identify oplev injected noise. The coherence is relatively high at some frequencies, especially in IM-P from 16 to 18 Hz.

A strategy would be to filter the oplev signal with a low pass filter with a cuf-off frequency of about 9 Hz. In the files listed above there's still data to analyze.


Images attached to this report
Comments to this report:
tomotada.akutsu - 13:56 Friday 06 September 2019 (10379) Print this report

Are the spectra in Fig 1 from microphone? I guessed a microphone would not have sensitivity in such a low frequency region like below ~10Hz (well, it seems there are some measured signals down to 1Hz, though, in Fig 1 cool). So the noise changing might be just occasional phenomena, I guess.

fabian.arellano - 14:24 Friday 06 September 2019 (10380) Print this report

The first figure is the microphone data indeed.

  • It would be good to know what's the lowest frequency which such a device can measure. There's a lot of information in the PEM wiki but more time is required to search for that specific piece of information.
  • After turning the FFUs off, that section of the central room was clearly quieter to the human ear.
takaaki.yokozawa - 8:09 Saturday 07 September 2019 (10399) Print this report

First, please check the serial number of used PEM from

KAGRA wiki -> PEM subsystem page -> PEM sensor list

Then, you can find SR3 microphone is S1809038

This microphone range is about 20Hz, but I have microphone for lower frequency

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