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VIS (SR2)
fabian.arellano - 15:24 Wednesday 16 March 2022 (20095) Print this report
Health check via transfer functions.

With Takahashi-san.

Summary: in order to assess the health of the supension, we measured transfer functions (with the automeasurement system) and compared them with old measurements from July 2019. The tower and IM are healthy.

The differences between the new and the old measurements were negligible in the tower and IM. The behaviour of that section of the suspension seems stable at least from July 2019 until now. I suggest to use today's measurements as references (except IM-Y). The DoF IM-Y was measured again because an additional peak appeared at  578 mHz (Fig. 1). In a later measurement the peak disapeared (Fig. 2). Likely, this peak was just residual motion from the previous measurement in IM-T, which has a resonance at  the same frequency (Fig. 3).

Some details are the following:

  • State of the suspension: TWR_FLOAT.
  • Directory: /kagra/Dropbox/Measurements/VIS/PLANT/SR2/2022/03/
  • Identification number of the sets of measurements:
    • Tower: 202203160955
    • IM: 202203161101
  • The measurements files we compared with are in the directory: /kagra/Dropbox/Subsystems/VIS/TypeBData/SR2/TF/Measurements/20190725/
  • Additional measurements are in /kagra/Dropbox/Subsystems/VIS/TypeBData/SR2/TF/Measurements/20220316/

The DC amplitudes of the various degrees of freedom are, in units of dB:

  • IP-L LVDT: -13.0
  • IP-T LVDT: -12.9
  • IP-Y LVDT: -36.3
  • F0 GAS: -36.9
  • F1 GAS: -22.7
  • BF GAS:  -27.0
  • IM-L: -57.0
  • IM-T: -56.9
  • IM-V:  -46.1
  • IM-R:  -6.4
  • IM-P: -4.3
  • IM-Y: -3.4

An additional entry will be written for the mirror transfer functions.

Images attached to this report
Comments to this report:
fabian.arellano - 17:23 Wednesday 16 March 2022 (20101) Print this report

With Takahashi-san.

Summary: we measured transfer function for the mirror stage. They suggest the system is healthy.

Screenshots of the transfer functions are attached. All of them show a different DC gain with respect to the reference used, which is a few years old. The difference lilkely comes because we recalibrated the QPDs during the recent remedyng campaign. Otherwise they are similar enough.

The IM-L measurement (FIg. 1) requires further explanation because it gives the impression the slopes after the resonace are slightly different. In reality, the reference measurement is very noisy at those frequencies (the coherence is very low) and it's difficult to say what the slope is. Nevertehless, I did calculate the slope for the new measurement (in red) and it's close to what we expect, which is a f^-2 behaviour.

The DC amplitude, in units of dB, are:

  • TM-L: -52.2
  • TM-P: -33.5
  • TM-Y: -37.8

Please, note we need to use these values with caution becuase the coherence is not good at very low frequencies.

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