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then, I moved the accelerometer on top of the "X-hutch side" vessel, placed directly on the metal top case, inside the housing.
- the "no noise same range" image shows a standard situation during 10s when there no noise either on PZT or Accelerometer.
on can compare the noise level on the accelerometer with the previous post when it was outside on top of the housing.
its noise is much much lower... which means the housing is properly dumping the acoustic noise at this frequency around 20-30Hz.
so, we increase the accelerometer measurement sensitivity to better measure its noise.
- the "no noise new range" image shows a standard situation during 10s when there no noise either on PZT or Accelerometer but with a smaller range.
- the "noise 1,2,3" images show the situation when the PZT start to compensate large noise with good correlation with accelerometer placed on top of the optical vessel.
- the "noise 1,2,3 not clear" images show the situation when the PZT start to compensate large noise with correlation with accelerometer but the signal level is not the same as before.
this make me think the origin of the noise is maybe not coming from the inside of the optical vessel.
=> conclusion : we see for the first time a correlation between the PZT noise and some vibration/acoustic noise.
now, we have to investigate the precise origin of this noise (or the different sources).
| Ronic Chiche wrote: |
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this morning, I did some measurement with nobody interfering with the tests.
- the "no noise" image shows a standard situation during 10s when there is no noise either on PZT or Accelerometer.
most of the time, we are in this situation.
- the "slaping door" image shows the case where the large igloo door is opened and slaping when it closes.
the accelerometer and the PZT exhibit correlated noise when the door is slaping.
we can see a PZT "recovery" time longer than the perturbation.
but these events are rare and are not the source of the problematic perturbations.
- "noise 1,2,3" images show the typical situation when the PZT start to compensate large noise without any correlation with accelerometer placed on top of the housing.
=> conclusion, some external noise (to the housing) should not be the source of the perturbations on the PZT.
| Ronic Chiche wrote: |
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today I connected a copy of the laser PZT signal to the 2nd scope CH2 (with AC coupling to remove the DC offset) to be able to monitor synchronously the Accelerometer and laser PZT signals.
the accelerometer is still connected to the 2nd scope CH4 and placed on top of the housing.
I filtered both signals in the Labview Signal Express software with a low-pass filter at 30Hz to focus on low frequencies noise (~20Hz).
now, I need to wait to work with the bunker closed to compare with normal operation (if some people work in the same time in the bunker, obviously, we will get some correlation between the accelerometer and laser PZT signals.....)
| Ronic Chiche wrote: |
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I installed an accelerometer setup in the bunker.
presently, the accelerometer is placed on top of the housing and its signal is connected to the 2nd scope (33MHz and 500MHz RF beating) on channel 4.
the FPC is locked to ~90kW.
the accelerometer noise is filtered on the Labview Signal Express software in order to focus on the 20Hz noise.
one applied a RII elliptic 5th order low pass filter at 30Hz.
the 20Hz noise can be seen on the PZT which always compensate for CFP frequency drifts.
figure 1 : example of typical accelerometer filtered noise (yellow curve) when the PZT compensation (green curve) is quite (measurement on 4 seconds)
figure 2 : example of accelerometer filtered noise (yellow curve) when the PZT compensation (green curve) exhibits some 20Hz noise (measurement on 10 seconds)
conclusion : there is no clear evidence of a correlation between accoustic noise outside of the housing (measured by the accelerometer) and the 20Hz noise in the laser PZT compensation.
=> putting the 2 signals on 2 different scopes doesn't help because the slow acquisition done is not synchronous.
next try : use the same scope and put the accelerometer inside the housing, for example on top of one of the FPC vessel.
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