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hirotaka.yuzurihara - 16:48 Tuesday 06 July 2021 (17404) Print this report
Investigation of PMC correlation with microphones when FFU turned off

[Kenta, YamaT, Yuzu]

This is a coutinuous work from this log.

Yesterday Kenta kindly took a time for PMC unlocking on 05 July 15:41:30 ~ 15:46:30 JST. I compared the spectrum of microphone in PSL room between several situations, such as PMC lock / unlock and  FFU on / off.

I attached the figure of result.

  • When we compare the spectrum between FFU off and FFU on (while other conditions remain the same), the amplitude of microphones were decreased significantly (see blue and green curves or see red and black curves) From this observation, the microphone spectrum is limited by FFU sound.
  • We doubted that the locked PMC is making the sound by shaking PZT and it makes the correlation between the microphone and PMC PZT signal. We can test this hypothesis by this result.
  • When we compare the spectrum between PMC lock and PMC unlock (while FFU is turned off), we can't see the significant difference on spectrum. (especially see black and green curves) This indicate that the PMC itself didn't make a sound enough to be received microphone in PSL room.
  • To make clear the origin of sound or correlation, we need more investigation.
  • Figure2 shows the coherence between mic1 and PMC PZT in several situation. When PMC is unlocked (locked), we obtain the low (high) coherence. 
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