Noise Analysis Tools
at Virgo
Gabriele Vajente
ILIAS WG1 meeting - Frascati 21.03.06
Summary
Tools for monitoring non-stationary noises
Project for an automatic noise budget tool
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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Part 1
Non-Stationary Noise Monitor
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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Non Stationary Noise Monitor
Purpose
Monitor time evolution of noise level in dark
fringe
Find correlation with ITF status (alignment,
environmental conditions, etc.)
Two parts
Running online: NonStatMoni
Running offline periodically:
NonStatMoniOffline
Compute band-limited RMS
Identify lines
Trends
Correlation with ITF status
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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NonStatMoni – Band-limited RMS
Band-limited RMS
Compute short
spectra (1, 5, 10 s)
every 1 s
Output RMS in
bands in the main
data stream
Fully configurable
(channel,
spectrum length,
etc.)
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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NonStatMoni – Lines identification 1
Main data stream
Lines identification
Separate lines from
“background”
Band-limited RMS of
background
Frequency, height, SNR
of main lines (SNR
threshold)
Running only during
“locked” periods
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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NonStatMoni – Lines identification 2
In main data
stream
Number of
lines found
Background
band-limited
RMS
Frequency,
height, SNR
for each line
found
full RMS
full RMS
bkg RMS
bkg RMS
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
1.11 kHz
3.88 kHz
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NonStatMoniOffline - Summary
Run periodically,
analyze all locks
of last period
Output as web
pages
Summary of
monitored
channels
Links to locked
periods details
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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NonStatMoniOffline – Lock details 1
Run periodically,
analyze all locks
of last period
Output as web
pages
Plot of RMS
time evolution
Spectrum of
RMS evolution
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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NonStatMoniOffline – Lock details 2
Run periodically,
analyze all locks
of last period
Output as web
pages
Time plot
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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NonStatMoniOffline – Lock details 3
Run periodically,
analyze all locks
of last period
Output as web
pages
Spectrum plot
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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NonStatMoniOffline – Lock details 4
Run periodically,
analyze all locks
of last period
Output as web
pages
Coherence table
and plots
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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Examples of applications
Enviromental monitoring (seismometers
and microphones)
Airplanes
Monitor bandlimited RMS for
seismic sensors
in all buildings.
One can recover
direction and
speed
F. Fidecaro
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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Correlation with alignment and freq noise
PR yaw
BS yaw
NE pitch
Freq. noise
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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Modes ring-down
3884 Hz
Line height [Hz/rHz]
t = 106 ± 7 s
Q = 1.29 x 106
RMS between 100 and 200 Hz [Hz/rHz]
During lock acquisition mirror and violin modes are
strongly excited
Extimation of Q factor
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
167 Hz
t = 550 ± 20 s
Q = 2.89 x 105
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Part 2
Automatic Noise Budget Project
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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Automatic Noise Budget
Purpose
To measure precise projection of technical
noises into dark fringe (or other channels)
Why
To precisely identify the contribution of the
most important noise sources
To track the evolution of noise couplings
To gain data to model noise couplings
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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Method
1.
2.
Measure transfer function
from error/correction signal
to dark fringe with noise
injection
Project the normal noise
using the measured TF
SINGLE CAVITY
Dark fringe
NOISE
Interferometer
Control loop
NOISE
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
SINGLE CAVITY
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TF measurement methods
Full measurement
By injecting (white) noise
into each channel
separately
Slow (at least 60s per
channel)
Precise measurements of
TFs
Might cause saturation
problems or unlocks
Need to “shape” the noise
Fast measurement
Measure once the TFs with
full method
Use calibration lines to
correct their overall gain
Fast (can inject lots of lines
simultaneously)
Might be not very precise
Can easily track time
evolution
Lines measurement
Inject several (10) lines for each d.o.f. at different frequencies
Need to know the approximate shape of the TF
Faster than full, more accurate than fast
Less saturation problems
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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Technical noise sources
Control noises
Longitudinal (DARM, MICH, PRCL)
Angular (PR, BS, NI, NE, WI, WE tx & ty)
Input beam noises
Frequency noise
Laser power noise
Input beam jitter (translation & tilt)
IMC controls (angular and longitudinal)
Modelled noises
Shot noise (need only power measurements)
Dark noise
DAC noise
Phase noise
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
3 dof
12 dof
1 dof
1 dof
4 dof
3 dof
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Outcomes of the tool
Noise budgets
Transfer functions
Using permanent calibration lines
Track time evolution of noise couplings and
ITF performances
Better identify non-stationarity sources
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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Conclusions
Non-stationary Monitor
Developed and tested, already running online
Monitor dark fringe and 25 environmental
channels
Automatic generate summary web pages
Automatic Noise Budget
Clear project
Already tested some noise injection in single
cavity configuration
ILIAS WG1 meeting, Frascati 21.03.06 – Gabriele Vajente
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