Low frequency sensors Guralp CMG40T

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Low frequency sensorsGuralp CMG-40T

• Sensors on the floor side by side
• Two Sensors are not synchronised by the DAQ
  system.
• Synch is done using DAQ time on file
• Looking forward for a better synchronization

Coherence versus date
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Low frequency sensors(2)
No Synched
Synched
Coherence versus nb of points for FFT
If the time difference is small then cohere
from MatLab is able to find the correlation
provided we compute it in a time interval greater
than the time difference
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PSD and RMS
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Guralp resolution
Integrated difference
Not great
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Stabilized table versus ground
Correlation between 2 sensors One on ground the
second on stabilized table
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Resolution

• Use 2 sensors on ground side by side to compute
  coherence and deduce resolution
• Integrated difference Compute PSD and
  integrated RMS from relative velocities v1 and v2
• Corrected difference 2(1-Coherence)Sqrt(PSD1PSD2
  )

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GSV-320 versus VE-13
1 nm
1 nm

• VE-13 sensors less sensible than GSV-320

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TMC stabilized table
CERN result reproduced (S.Redaellis thesis )
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SP400

• Electrochemical motion sensor
• Special electrolytic solution
• Four platinum mesh electrodes ( 2 anodes and 2
  cathodes )
• An external acceleration creates a differential
  pressure across the channel and forces the liquid
  to move with velocity V. Ions move to the
  electrodes .

• 0.1 to 50 Hz
• Non magnetic
• 10KV/(m/s)

2 sensors from Andrei Seyri _at_ SLAC
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Correlation function (SP400)