40m
QIL
Cryo_Lab
CTN
SUS_Lab
TCS_Lab
OMC_Lab
CRIME_Lab
FEA
ENG_Labs
OptContFac
Mariner
WBEEShop
|
40m Log |
Not logged in |
 |
|
Thu Jan 4 12:46:27 2018, gautam, Update, ALS, Fiber ALS assay 
|
Thu Jan 11 14:22:40 2018, gautam, Update, ALS, Fiber ALS assay
|
Thu Jan 11 20:51:20 2018, gautam, Update, ALS, Fiber ALS assay
|
Tue Jan 16 21:50:53 2018, gautam, Update, ALS, Fiber ALS assay
|
Thu Jan 18 00:35:00 2018, gautam, Update, ALS, Fiber ALS assay 
|
Fri Jan 19 11:34:21 2018, gautam, Update, ALS, Fiber ALS assay
|
Fri Jan 19 23:04:11 2018, gautam, Update, ALS, Fiber ALS assay
|
Wed Jan 24 00:33:31 2018, gautam, Update, ALS, Fiber ALS assay
|
Wed Jan 24 10:45:14 2018, gautam, Update, ALS, Fiber ALS assay
|
Thu Jan 25 23:59:14 2018, gautam, Update, ALS, Fiber ALS assay
|
Fri Jan 26 20:03:09 2018, gautam, Update, ALS, Fiber ALS assay
|
Wed Jan 31 15:45:22 2018, gautam, Update, ALS, Fiber ALS assay
|
Wed Jan 31 16:29:42 2018, gautam, Update, ALS, Modulation depths 
|
Wed Jan 31 16:33:53 2018, gautam, Update, ALS, ALS electronics at LSC rack
|
Wed Jan 31 22:32:11 2018, gautam, Update, ALS, ALS signal chain + power budget 
|
Thu Feb 1 01:24:56 2018, gautam, Update, ALS, D0902745 revamp underway
|
Fri Feb 2 00:26:34 2018, gautam, Update, ALS, D0902745 revamp underway
|
Fri Feb 2 13:16:55 2018, gautam, Update, ALS, ALS signals whitening switching 
|
Mon Feb 5 14:11:01 2018, gautam, Update, ALS, Huge harmonics in ALS channels 
|
Mon Feb 5 22:57:28 2018, gautam, Update, ALS, Huge harmonics in ALS channels
|
Tue Feb 6 11:13:26 2018, gautam, Update, ALS, Possible source of ground loop identified
|
Tue Feb 6 22:55:51 2018, gautam, Update, ALS, Possible source of ground loop identified
|
Thu Feb 8 00:33:20 2018, gautam, Update, ALS, D990694 characterization / THD measurement plan
|
Thu Feb 8 01:27:16 2018, Koji, Update, ALS, D990694 characterization / THD measurement plan
|
Fri Feb 9 13:37:44 2018, gautam, Update, ALS, THD measurement trial
|
Thu Feb 8 12:00:09 2018, gautam, Update, ALS, D990694 is NOT differential receiving
|
Thu Feb 8 13:13:14 2018, gautam, Update, ALS, D990694 pulled out  
|
Thu Feb 8 18:10:36 2018, gautam, Update, ALS, D990694 pulled out
|
Wed Feb 7 15:51:15 2018, gautam, Update, ALS, D0902745 revamp complete
|
Fri Feb 16 01:34:40 2018, gautam, Update, ALS, D0902745 in-situ testing 
|
Tue Feb 20 23:08:27 2018, gautam, Update, ALS, D0902745 in-situ testing
|
Thu Feb 22 00:09:11 2018, gautam, Update, ALS, D0902745 in-situ testing  
|
Sun Feb 25 00:03:12 2018, gautam, Update, ALS, Daughter board prototyping    
|
Mon Feb 26 20:55:56 2018, rana, Update, ALS, Daughter board prototyping
|
Tue Feb 27 21:10:45 2018, gautam, Update, ALS, Daughter board testing  
|
Wed Feb 28 19:13:25 2018, gautam, Update, ALS, ADC test for differential receiving in c1lsc
|
Fri Mar 2 01:45:06 2018, gautam, Update, ALS, new look ALS electronics
|
Mon Mar 5 17:27:34 2018, gautam, Update, ALS, new look ALS electronics - characterization
|
Thu Mar 8 00:40:25 2018, gautam, Update, ALS, new look ALS electronics - characterization
|
Thu Mar 8 19:38:37 2018, gautam, Update, ALS, digital unwhitening of daughter board
|
Thu Mar 8 23:50:27 2018, gautam, Update, ALS, First look at new ALS electronics
|
Fri Mar 9 01:07:01 2018, gautam, Update, ALS, First look at new ALS electronics
|
Mon Mar 12 22:08:31 2018, gautam, Update, ALS, Noisy POX
|
Mon Mar 12 23:57:31 2018, gautam, Update, ALS, Noisy POX 
|
Mon Mar 19 15:02:29 2018, gautam, Update, ALS, Noisy MC sensing
|
Thu Feb 1 15:31:12 2018, gautam, Update, ALS, ALS signal chain + power budget
|
Wed Feb 7 10:16:26 2018, gautam, Update, ALS, ALS signal chain + power budget
|
Thu Jan 25 13:18:41 2018, gautam, Update, ALS, Fiber ALS assay
|
|
Message ID: 13628
Entry time: Fri Feb 9 13:37:44 2018
In reply to: 13621
|
Author: |
gautam |
Type: |
Update |
Category: |
ALS |
Subject: |
THD measurement trial |
|
|
I quickly put together some code that calculates the THD from CDS data and generates a plot (see e.g. Attachment #1).
Algorithm is:
- Get data (for now, offile file, but can be readily adapted to download data live or from NDS).
- Compute power spectrum using scipy.signal.periodogram. I use a Kaiser window with beta=38 based on some cursory googling, and do 10 averages (i.e. nfft is total length / 10), and set the scaling to "spectrum" so as to directly get a power spectrum as opposed to a spectral density.
- Find fundamental (assumed highest peak) and N harmonics using scipy.signal.find_peaks_cwt. I downsample 16k data to 2k for speed. A 120second time series takes ~5 seconds.
- Compute THD as
where V_i denotes an rms voltage, or in the case of a power spectrum, just the y-axis value.
I conducted a trial on the Y arm ALS channel whitening board (while the X arm counterpart is still undergoing surgery). With the whitening gain set to 0dB, and a 1Vpp input signal (so nothing should be saturated), I measure a THD of ~0.08% according to the above formula. Seems rather high - the LT1125 datasheet tells us to expect <0.001% THD+N at ~100Hz for a closed loop gain of ~10. I can only assume that the digitization process somehow introduces more THD? Of course the FoM we care about is what happens to this number as we increase the gain.
Quote: |
I'm going to work on putting together some code that gives me a quick readback on the measured THD, and then do the test for real with different amplitude input signal and whitening gain settings.
|
|
|
|