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Sat Sep 19 23:59:22 2020, anchal, Summary, ALS, ALS noise budget update    
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Sun Sep 20 23:12:13 2020, rana, Summary, ALS, ALS noise budget update
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Tue Sep 22 00:14:43 2020, anchal, Summary, ALS, ALS noise budget update 
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Tue Sep 22 12:14:42 2020, rana, Summary, ALS, ALS noise budget update
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Wed Sep 23 11:13:49 2020, anchal, Summary, ALS, ALS noise budget update 
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Wed Oct 7 16:56:23 2020, anchal, Summary, ALS, ALS noise budget update - Updated AUX PDH Loop values 
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Thu Oct 8 11:59:52 2020, rana, Summary, ALS, ALS noise budget update - Updated AUX PDH Loop values
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Fri Oct 9 18:32:14 2020, anchal, Summary, ALS, ALS noise budget update - Updated AUX PDH Loop values
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Wed Oct 14 17:03:55 2020, anchal, Summary, ALS, ALS noise budget update - Added whitening filter for ADC
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Message ID: 15601
Entry time: Wed Sep 23 11:13:49 2020
In reply to: 15594
Reply to this: 15617
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Author: |
anchal |
Type: |
Summary |
Category: |
ALS |
Subject: |
ALS noise budget update |
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Yes, that loop was unstable. I started using the time domain response to check for the stability of loops now. I have been able to improve the filter slightly with more suppression below 20 Hz but still poor phase margin as before. This removes the lower frequency region bump due to seismic noise. The RMS noise improved only slightly with the bump near UGF still the main contributor to the noise.
For inclusion of real spectra, time delays and the anti-aliasing filters, I still need some more information.
Few questions:
- What anti-aliasing filters are used in ALS?
- Is the digital delay fixed to a constant upper limit or is it left to change as per filters? I have already used a 470 us delay (modeled with Pade 4th order approximation).
- I could not find a good place where channel names are listed with corresponding meaning. Where can I find them?
- Is there a channel which keeps record of lock status? In short, how do I find the in-lock times
Additional Info:
The code used to calculate the transfer functions and plot them is in the repo 40m/ALS/noiseBudget
Related Elog post with more details: 40m/15587 |
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# -----------------------------------------------------------------------------
# AUX
# -----------------------------------------------------------------------------
## Cavity Pole
C_AUX:
p: 1.8883e+04
k: 1.1865e+05
H_AUX:
z: 0
... 113 more lines ...
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