40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log, Page 198 of 344  Not logged in ELOG logo
ID Date Authorup Type Category Subject
  11194   Thu Apr 2 04:11:20 2015 ericqUpdateLSCNot much locking, Xover measurement

A paltry two locks tonight, but not entirely useless. I had some issues keeping the PRMI locked, which some additional boosts helped with. But, my feeling was that our crossover process is not tuned well. 

At full lock, both sub-loops have high gain around the crossover region, so the usual DTT loop transfer function measurement produces a meausrement of Gdigital/G_aopath (or minus that. I.e. I'm not currently 100% which is the bad phase in this plot, though it intuitive looks like 0 ). Thus, we can directly look at the crossover frequency and the effect of the different filters there. (I've also been working on an up-to-date CARM loop model today, so this will help inform that). 

Below, the black traces are the crossover at the end of the script when using the 120:500 "helper," and purple is without it. As we turn up the AO path gain, the trace "falls" from above, which explains why we can see instabilities around the violin filter. 

Having the helper on definitely made the probability of surviving the first overall CARM gain ramp higher, but it's not currently intuitively clear to me why that is the case. Afterwards, we can turn the helper off, to keep the shallower crossover shape. This is what I've put in to the up script for now. I also added a few seconds delay for when the script wants to switch DARM to RF only; I found it was maybe speeding too fast through this point.

DTT xml attached

Attachment 1: CARMxOver_Apr3.png
CARMxOver_Apr3.png
Attachment 2: Apr2_Xover.xml.zip
  11195   Thu Apr 2 15:34:34 2015 ericqUpdateLSCNot much locking, Xover measurement

Here's the comparison of last night's crossover measurement to my loop model. Not stellar, but not totally off base. All of the digital filters are read directly from the foton filter file, and translated from their SOS coefficients, so they should be accurate. I may have tallied together the wrong arrangement of FMs, though. I will recheck. 

Although I don't have a measurement to compare it with yet (as I don't know where the crossover was, the filter statesolder, etc. for the older loop measurements), here's what my current CARM loop model looks like, just for kicks. Here, only the first CM board boost is on. If we turn on some super boosting, we can probably ease up on some of the digital boosts, lower the crossover frequency, and put some lowpass that suppress the violin filters' effect on the crossover and reduces digital sensing noise injection. 

Lastly, I'll just note that my current MIST model predicts that the CARM cavity pole should be at ~170Hz, and a peak arm transmission of 180 times single arm power. I saw powers of ~120 last night. 

Attachment 1: xOverModel.png
xOverModel.png
Attachment 2: loopModel.png
loopModel.png
  11196   Thu Apr 2 17:11:28 2015 ericqUpdateLSCNot much locking, Xover measurement

Whoops, I implemented the IOP downsampling filters wrong. Once I did that, it looked like just delay mismatch, so I added two more computation cycles for a total of four 16k cycles, which is maybe not so justified... Nevertheless, model and measurement now agree much better. Here are the corrected plots. 

 

Attachment 1: xOverModel.png
xOverModel.png
Attachment 2: loopModel.png
loopModel.png
  11206   Tue Apr 7 04:21:45 2015 ericqUpdateASCAngular Control during Locking

[J, Q]

Alignment is making it tough for locks to last more than 10 minutes. Many (but not all) locklosses correlate with some optic drifting away, and taking all of the light with it. The other locklosses are the quick ones that seem to pop up out of nowhere; we haven't made any headway on these. We wanted to get to a state where we could just let the interferometer sit for some minutes, to explore the data, but got caught up with alignment and PRMI things.

We're finding that both ITMs experience some DC force when entering full PRFPMI lock. I will calculate the torque expected from radiation pressure + offset beam spot, especially for ITMX, where we choose the spot position to be uncontrolled by ASS. 

I set up the QPD ASC servos to act in a common/differential way on the ETMs. The C1:ASC-XARM_[PIT/YAW] filter modules act on the common alignment, whereas the C1:ASC-YARM_[PIT/YAW] filter modules act on the differential alignment. This can soon be cleaned up with some model renaming to reduce confusion. 

Using DC oplev values as a guide, we are hand tuning ITM alignment once the AO path is engaged and we see the DC drift occurring. Then, we set the QPD servo offsets and engage them. 

In this manner, we were able to lock the interferometer at:

  • Arm transmission 150 x single arm power
  • POPDC indicated a recycling gain of ~5.5
  • ASDC/POPDC indicated a contrast of 99.8%
  • REFLDC indicated a visibility of 80%

We made the PRMI transition to 1f numerous times, but found that the sideband power fluctuations would get significantly worse after the transition. 

We found that the gains that were previously used were too small by a factor of a few. There is a DC change visible in REFL165 before and after the transition (Also POP55, aka REFL55, is not DQ'd angry). Really, it isn't certain that we've zero'd the offset in the CARM board either, so REFL55's zero crossing isn't necessarily more trustworthy that REFL165's. We can go back in the data and do some 2D histograming to see where in the error signal space the sideband power is maximized. 

Jenne reports:

  • The all RF transition succeeded 13/29 times. 
  • PRMI 1f transision succeeded 10/10 times. 
  11208   Wed Apr 8 13:26:47 2015 ericqUpdateLSCREFL55 signal back to its normal ADC inputs

As the POP55 demod board is actually demodulating the REFL55 signal, I have connected its outputs to the REFL55 ADC inputs. Now, we can go back to using the REFL55 input matrix elements, and the data will be recorded. 

I have changed the relevant lines in the locking script to reflect this change. 

  11210   Thu Apr 9 02:58:26 2015 ericqUpdateLSCAll 1F, all whitened

blarg. Chrome ate my elog. 

112607010 is the start of five minutes on all whitened 1F PDs. REFL55 has more low frequency noise than REFL165, I think we may need more CARM supression (i.e. we need to think about the required gain). This is also supported by the difference in shape of these two histograms, taken at the same time in 3f full lock. The CARM fluctuations seem to spread REFL55 out much more.  

I made some filters and scripts to do DC coupling of the ITM oplevs. This makes maintaining stable alignment in full lock much easier. 

I had a few 15+ minute locks on 3f, that only broke because I did something to break it.  

Here's one of the few "quick" locklosses I had. I think it really is CARM/AO action, since the IMC sees it right away, but I don't see anything ringing up; just a spontaneous freakout. 

Attachment 1: quickLockLoss.png
quickLockLoss.png
Attachment 2: 55_1.png
55_1.png
Attachment 3: 55_2.png
55_2.png
  11213   Fri Apr 10 12:09:19 2015 ericqUpdateLSCSome small progress, may have DAC problem?
Quote:

At the very end, the last 10 seconds or so, the POP110 power goes down, and sits at about half it's maximum value.  POP22 isn't quite as bad, in that it still touches the max, but the RIN is about 50%.  The carrier DC signals (TRX, TRY, POPDC) don't see this huge jump.  I don't think I was touching anything the last few tens of seconds.  I'm not sure yet how I can so significantly lose sideband power, without losing a similar amount of carrier power. 

I saw this same kind of behavior in my locklosses on Wednesday night; we should check out the 165 data, and see if the 3f PRCL error signal shows some drift away from zero.

Also, it's odd that CARM_IN1 and REFL11_I_ERR have different low frequency behavior in the plot you posted. I guess they have some difference in demodulation phase.  REFL11_I's bump at -40sec coincides with the dip in arm power and a rise in REFLDC, but ASDC seems pretty smooth, so maybe it is a real CARM fluctuation.

I set the REFL11 analog demodulation angle (via cable length) about a year ago (ELOG 9850), with some assumption about PRCL having the same demod angle as CARM, but this was probably set with the arms misaligned. We should recheck this; maybe we're coupling some other junk into CARM. 

  11214   Fri Apr 10 17:05:45 2015 ericqUpdateLSCRelative ETM calibration (Rough MC2 calibration)

I did a quick measurement get an idea of the ETM actuator calibration, relative to the ITMs. This will still hold if/when we revisit the ITM calibration via the Michelson. 

For the test masses, I locked the arms individually using MC2 as the actuator, and took transfer functions from the SUS-[OPTIC]_LSC_EXC point to the PO[X/Y]_I_ERR error signals. There were two points with coherence less than 99% that I threw away. I then took the fraction at each point, and am using the standard deviation of those fractions as the reported random error, since the coherence was super high for all points, making the error of each point negligible relative to their spread. 

This gives:

  • ETMX/ITMX: 2.765 +- 0.046
  • ETMY/ITMY: 2.857 +- 0.029

With the data from ELOG 8242, this implies:

  • ETMX: 13.00 +- 0.22 x 10 -9 / f2 m/counts
  • ETMY: 13.31 +- 0.15x 10 -9 / f2 m/counts

MC2 data was taken with the arms locked with the ETMs. The results are not so clean, the fractions don't line up; there is some trend with excitation frequency... The ratio is around the same as the ETMs, but I'm not going to quote any sort of precision, since I don't fully understand what's happening. Kind of a bummer, because it struck me that we could get an idea of the arm length mismatch by the difference in IMC frequency / arm FSR. I'll think about this some more...

Attachment 1: quickCal.png
quickCal.png
  11215   Fri Apr 10 18:39:39 2015 ericqUpdateLSCRelative ETM calibration (Rough MC2 calibration)

I didn't verify that the loop gain was low enough at the excitation frequencies. blush

I put a 1kHz ELP in both arm servos, and got cleaner data for both. The ETM numbers are pretty much consistent with the previously posted ones, and the MC2 data now is consistent across frequencies. However, the MC2 numbers derived from each arm are not consistent.

Now:

  • ETMX / ITMX: 2.831 +- 0.043
  • MC2 / ITMX: 3.260 +- 0.062
  • ETMY / ITMY: 2.916 +- 0.041
  • MC2 / ITMY: 3.014 +- 0.036

With the data from ELOG 8242, this implies:

  • ETMX: 13.31 +- 0.21 x 10-9 / f2 m/counts
  • ETMY: 13.59 +- 0.20 x 10-9 / f2 m/counts
  • MC2 in Xarm meters : 15.32 +- 0.30 x 10-9 / f2 m/counts
  • MC2 in Yarm meters : 14.04 +- 0.18 x 10-9 / f2 m/counts
This is, of course, pretty fishy. Each arm sees the same frequency fluctuation of the light coming out of the IMC, especially given that the MC2 to arm data was taken simultaneously for both arms. Now, one possible source of this kind of mismatch would be a mismatch of the arm lengths, but there is no way they differ by 10%, as they would have to in order to explain the above numbers. To me, it seems more likely that the ITM calibrations are off. 
Attachment 1: betterCal.png
betterCal.png
  11216   Mon Apr 13 19:34:02 2015 ericqUpdateIOOModulation Frequency Tuned to IMC Length

I've been fiddling with the mode cleaner and green beat box today, to try and get an absolute frequency calibration for MC2 motion. The AC measurements have all turned out weird, I get fractional power laws instead of the 1/f^2 that we expect from the MC2 pendulum. At DC, I get a rough number of 15 green kHz per MC2 count, but this translates to ~7e-10 m/count which is in contrast to the 6e-9 m/count from 2009. I will meditate on this a bit. 


In any case, while working at the IOO rack, I tuned the 11MHz modulation frequency, as was done in ELOGs 9324 and 10314, by minimizing one of the beats of the 11MHz and 29.5MHz sidebands. 

The new modulation frequency / current IMC FSR is 11.066209 +- 1 Hz, which is a only a few ppm change from the tuning from last July.

This implies a IMC round trip length of 27.090800m +- 2um.

Attached is a plot showing the beat of 55-29.5 going down as I changed the marconi frequency. 

 

Attachment 1: fMod_tuning.pdf
fMod_tuning.pdf
  11219   Wed Apr 15 02:26:41 2015 ericqUpdateLSCAttempted DRMI + ALS arms

I spent some time tonight trying to revive DRMI locking, with the arms held off on ALS. Not much news, I haven't been able to get more than a few short spurts of resonance, using 1F signals.

I did use SRY to measure the BS->SRCL coupling by exciting each mirror and looking at their relative coupling to AS55Q. I found that we should use a value of +0.28 +-0.01 in the MICH->SRM element.

  11220   Wed Apr 15 15:14:18 2015 ericqUpdateComputer Scripts / ProgramsCDSutils upgraded to v474

CDSutlils has been updated to the newest version, 474; there are some matrix interface methods that will make our locking scripts easier to read, modify, and maintain.

I've tested the ALS and CARM down scripts, and the LSC offsets script, and they all work fine. 

  11249   Sat Apr 25 18:50:47 2015 ericqUpdateVACPressure watch script broken

Ugh, this turns out to be because cron doesn't source the controls bashrc that defines where to find caget and all that jazz that many commands depend on. This is probably also why the AutoMX cron job isn't working either. 

Also, cron automatically emails everything from stderr to the email address that is configured for the user, which is why the n2 script blew up the foteee account and why the AutoMX script was blowing up my email yesterday. This can be avoided by doing something like this in the crontab:

0 8 * * * /bin/somecommand >> somefile.log 2>&1

(The >> part means that the standard output is appended to some log file, while the 2>&1 means send the standard error stream to the same place as stdout)

I made this change for the n2 script, so the foteee email account should be safe from this script. I haven't figured out the right way to set up cron to have all the right $PATH and other environment stuff, such as epics may need, so the script is still not working. 

  11265   Fri May 1 13:22:08 2015 ericqUpdateDAQPEM Slow channels added to saved frames

Rana asked me to include add slow outputs (OUT16) of the seismometer BLRMS channels to the frames. 

All of the PEM slow channels are already set up in c1/chans/daq/C1EDCU_PEM.ini, but up to this point, daqd had no knowledge of this file, since it wasn't included in c1/target/fb/master, which defines all the places to look for files describing channels to be written to disk. This file already includes lines for C1EDCU_LSC.ini and such, which from old elogs, looks like was set up by hand for subsystems we care about. 

Hence, since we now care about slow trends for the PEM subsystem, I have added a line to the daqd master file to tell it to save the PEM slow channels. This looks to have increased the size of the individual 16 second frame files from 57MB to 59MB, which isn't so bad.

  11273   Tue May 5 10:40:05 2015 ericqHowToComputer Scripts / ProgramsHow to get a web page running on Nodus

How to get your own web page running on Nodus

  1. On any martian machine, put your stuff in /users/public_html/$MYPAGE/
  2. On Nodus, run: ln -s /users/public_html/$MYPAGE /export/home/
  3. Your site is now available at https://nodus.ligo.caltech.edu:30889/$MYPAGE/
  4. If you want to allow straight up directory listing to the entire internet, on Nodus run: sudoedit /etc/sites-available/nodus, and add the following lines towards the bottom:
<Directory /export/home/$MYPAGE>
    Options +Indexes
</Directory>
  11285   Tue May 12 08:51:08 2015 ericqUpdateCDSc1lsp and c1sup removed?
Quote:

was this change not elogged??

This is my sin.

Back in Febuary (around the 25th) I modified c1sus.mdl, removing the simulated plant connections we weren't using from c1lsp and c1sup. This was included in the model's svn log, but not elogged. blush

The models don't start with the rtcds restart shortcut, because I removed them from the c1lsc line in FB:/diskless/root/etc/rtsystab (or c1lsc:/etc/rtsystab). There is a commented out line in there that can be uncommented to restore them to the list of models c1lsc is allowed to run. 

However, I wouldn't suspect that the models not running should affect the suspension drift, since the connections from them to c1sus have been removed. If we still have trends from early February, we could look and see if the drift was happening before I made this change. 

  11297   Mon May 18 09:50:00 2015 ericqUpdateGeneralsome status
Quote:

Added this to the megatron crontab and commented out the op340m crontab line. IF this works for awhile we can retire our last Solaris machine.

For some reason, my email address is the one that megatron complains to when cron commands fail; since 11:15PM last night, I've been getting emails that the rampdown.py line is failing, with the super-helpful message: expr: syntax error

  11299   Mon May 18 14:22:05 2015 ericqUpdateComputer Scripts / Programsrsync frames to LDAS cluster
Quote:

Still seems to be running without causing FB issues.

I'm not so sure. I just was experiencing some severe network latency / EPICS channel freezes that was alleviated by killing the rsync job on nodus. It started a few minutes after ten past the hour, when the rysnc job started. 

Unrelated to this, for some odd reason, there is some weirdness going on with ssh'ing to martian machines from the control room computers. I.e. on pianosa, ssh nodus fails with a failure to resolve hostaname message, but ssh nodus.martian succeeds. 

  11301   Mon May 18 16:28:18 2015 ericqUpdateGeneralsome status
Quote:

4) Noticed that DAQD is restarting once per hour on the hour. Why?

It looks like daqd isn't being restarted, but in fact crashing every hour.

Going into the logs in target/fb/logs/old, it looks like at 10 seconds past the hour, every hour, daqd starts spitting out:

[Mon May 18 12:00:10 2015] main profiler warning: 1 empty blocks in the buffer                                     
[Mon May 18 12:00:11 2015] main profiler warning: 0 empty blocks in the buffer                                     
[Mon May 18 12:00:12 2015] main profiler warning: 0 empty blocks in the buffer                                     
[Mon May 18 12:00:13 2015] main profiler warning: 0 empty blocks in the buffer
...
***CRASH***

An ELOG search on this kind of phrase will get you a lot of talk about FB transfer problems. 

I noticed the framebuilder had 100% usage on its internal, non-RAID, non /frames/, HDD, which hosts the root filesystem (OS files, home directory, diskless boot files, etc), largely due to a ~110GB directory of frames from our first RF lock that had been copied over to the home directory. The HDD only has 135GB capacity. I thought that maybe this was somehow a bottleneck for files moving around, but after deleting the huge directory, daqd still died at 4PM. 

The offsite LDAS rsync happens at ten minutes past the hour, so is unlikely to be the culprit. I don't have any other clues at this point. 

  11302   Mon May 18 16:56:12 2015 ericqHowToCDSBypassing the CDSUTILS prefix issue
Quote:

export IFO=''

This makes things act weird:

controls@pianosa|MC 1> z avg 1 "C1:LSC-TRY_OUT"
IFO environment variable not specified.

  11307   Tue May 19 11:15:09 2015 ericqUpdateComputer Scripts / ProgramsChiara Backup Hiccup

Starting on the 14th (five days ago) the local chiara rsync backup of /cvs/cds to an external HDD has been failing:

caltech/c1/scripts/backup/rsync_chiara.backup.log:

2015-05-13 07:00:01,614 INFO       Updating backup image of /cvs/cds
2015-05-13 07:49:46,266 INFO       Backup rsync job ran successfully, transferred 6504 files.
2015-05-14 07:00:01,826 INFO       Updating backup image of /cvs/cds
2015-05-14 07:50:18,709 ERROR      Backup rysnc job failed with exit code 24!
2015-05-15 07:00:01,385 INFO       Updating backup image of /cvs/cds
2015-05-15 08:09:18,527 ERROR      Backup rysnc job failed with exit code 24!
...
 

Code 24 apparently means "Partial transfer due to vanished source files."

Manually running the backup command on chiara worked fine, returning a code of 0 (success), so we are backed up. For completeness, the command is controls@chiara: sudo rsync -av --delete --stats /home/cds/ /media/40mBackup

Are the summary page jobs moving files around at this time of day? If so, one of the two should be rescheduled to not conflict. 

  11308   Tue May 19 11:24:44 2015 ericqUpdateComputer Scripts / ProgramsNotification Scheme

Given some of the things we've facing lately, it occurs to me that we could be better served by having some sort of unified human-alerting scheme in place, for things like:

  • Local/offsite backup failures
  • Vaccumm system problems
  • HDD status for things like /frames/ and /cvs/cds/, whether the disks are full, or their SMART status indicates imminent mechanical failure

Currently, many of these things are just checked sporadically when it occurs to someone to do so, or when debugging random issues. Smoother IFO operation and peace of mind could be gained if we're confident that the relevant people are notified in a timely manner. 

Thoughts? Suggestions on other things to monitor, like maybe frontend/model crashes?

  11310   Tue May 19 14:51:44 2015 ericqUpdateModern ControlBrushing up on Wiener Filtering

As part of preparing for the SURF projects this summer, I grabbed ~50 minutes of MCL and STS_1 data from early this morning to do a little MISO wiener filtering. It was pretty straightforward to use the misofw.m code to achieve an offline subtraction factor of ~10 from 1-3Hz. This isn't the best ever, but doesn't compare so unfavorably to older work, especially given that I did no prefiltering, and didn't use all that long of a data stretch.

Code and plot (but not data) is attached. 

Attachment 1: mclData.png
mclData.png
Attachment 2: mclWiener.zip
  11311   Tue May 19 16:18:57 2015 ericqUpdateGeneralcrons fixed

I wrapped rampdown.py in rampdown.sh, which is just these lines:

#!/bin/bash
source /ligo/cdscfg/workstationrc.sh
/opt/rtcds/caltech/c1/scripts/SUS/rampdown.py > /dev/null 2>&1

This is now what megatron's cron runs. It appears to be working.

I also added the workstationrc line to the n2 and chiara HDD checking scripts that run on nodus, which should resolve the issue from ELOG 11249

  11318   Wed May 20 11:41:59 2015 ericqUpdateGeneralsome status

West cyclinder is empty, east is at 2000 psi; regulated N2 pressure is 64psi. I'll replace the west one after the meeting.

  11319   Fri May 22 11:59:54 2015 ericqUpdateSUSDampRestore script problem

PRM watchdog tripped, but the damprestore.py script wouldn't run. 

It turns out the script tries to import some ezca stuff from /users/yuta (angry), which had been moved to /users/OLD/yuta (crying). 

I've moved the yuta directory back to /users/ until I fix the damprestore script. 

  11321   Fri May 22 18:09:58 2015 ericqUpdateComputer Scripts / ProgramsifoCoupling

I've started working on a general routine to measure noise couplings in our interferometers. Often this is done with swept sine measurements, but this misses the nonlinear part of the coupling, especially if the linear part is alreay reduced through some compensation or feedforward scheme. Rana suggested using a series of narrow band-limited noise injections. 

The structure I'm working on is a python script that uses the AWG interface written by Chris W. to create the excitations. Afterwards, I calculate a series of PSD estimates from the data (i.e. a spectrogram), and apply a two-sample, unequal variance, t-test to test for statisically significant increases in the noise spectra to try and evaluate the nonlinear contriubutions to the noise. I've started a git repository at github.com/e-q/ifoCoupling with the code. 

So far, I've tested one such injection of noise coupling from the ETMX oplev error point to the single arm length error signal. It's completely missing the user interface and structure to do a general series of measurements, but this is just organizational; I'm trying to get the math/science down first. 

Here's a result from today:

Median, instead of the usual mean, PSDs are used throughout, to reject outliers/glitches.

The linear part of the coupling can be estimated using the coherence / spectrum height in the excitation band, but I'm not sure what the best what to present/paramerize the nonlinear parts of each individaul excitation band's result is.

Also, I anticipate being able to write an excitation auto-leveling routine, gradually increasing the exctiation level until the excited spectrum is some amount  noisier than the baseline spectrum, up to some maximum amount configurable by the user. 

The excitation shaping could probably be improved, too. It's currently and elliptic + butterworth bandpass for a sharp edge and rolloff. 

I'm open to any thoughts and/or suggestions anyone may have!

Attachment 1: ETMX_PIT_L_coupling.png
ETMX_PIT_L_coupling.png
  11322   Sat May 23 22:43:10 2015 ericqUpdateGeneralifo recovery log

Running train-of-thought elog:


East N2 cylinder found empty, replaced. West is >2kpsi


Removed Yuta-specific code from damprestore. A grep for 'yuta' in the python files within /scripts/ shows some other occurances, but nothing that is really in use at this time. New feature of damprestore.py: remembers oplev status.


Ran LSCoffsets. 

WFS offsets relieved (all <20).

Adjusted FSS offset to minimize MC_FAST_MON

ASS ran (but the arm alignment has been astoundingly stable lately. I haven't touched it all this week)

ITMX is the only optic that got a correction over 20 counts. 

BS and *TM oplev spots look well centered, except for ITMX. 

I undid the gain reduction rana introduced because X ASS seemed to be really slow. It is currently fine in its older state. What's going on here?


Some network latency stuff is going on, even freezing up terminals when trying to write text files. This may (or may not) be correlated with the summary page rysnc jobs on nodus. It occurs to me that we have a DAQ ethernet network seperate from the martian network, but the frame transfers need to go through the martian network, since nodus is the only way out to the outside world. If we had a machine/gateway directly from the DAQ network to the caltech network, the martian network wouldn't get bogged down when frames are being uploaded


GTRY = 0.55, ok. Aligned GTRX to 0.52, also ok

Y beatnote was found easily. Have spent >30 minutes looking for X green beatnote. Typical FSS slow and X temperature ranges don't seem to be giving much. Will check the beat alignment with a scope, but if the beat is too high to begin with, it may not work...


I suspect a problem with the X Green BBPD

I could see the IR beatnote between the PSL and AUX X lasers at the input to the frequency counter. (I believe it is a real beatnote because it reacted as expected to the end temperature moving, and stabilizing the end laser to the arm). However, when placing the IR beatnote at a frequency which should've made the green beatnote visible on an analyzer and/or scope, no beatnote was found. I played with the beat alignment to no avail; the DC output of the BBPD behaved as expected, but I never saw anything in the RF output or on the control room analyzer. sad I also checked the beatnote signal chain by hooking up a 1mV 26MHz signal into the cable that hooks up to the RF out of the BBPD; the signal showed up clearly on the control room analyzer. 

I'm not sure what may have happened. ELOG 9996 may be related. 

I'm calling it a night. 

  11326   Wed May 27 02:53:57 2015 ericqUpdateGeneralifo recovery log

Given my suspicion of fault with the X Green BBPD, Koji generously provided me with another one that he had confirmed to be working. 

However, I turns out I was mistaken. With the existing BBPD, I did indeed witness a beat in the RF output, but it is somehow something like 20dBm smaller than it should be. This is why I missed it the other night. Here's a video of a RF output on a scope, wherein the beat is only barely visible because I've set the trigger level very low. I could not make the beatnote any larger through any alignment motions; I had gotten to this point by doing near/far field overlap on the PSL table. 

I'm not sure what could have caused this. Mode mismatch? By eye, the beam spots looked about the same in the near and far fields, and we haven't had to touch the mode matching in quite some time... I've given up on trying to solve this for tonight. 


Just for kicks, I hooked up the fiber PD IR beatnotes as inputs to the ALS DFD. The X beat is too small to even really see above the control room analyzer's noise floor, but the Y beat looked big enough. With the arms locked on IR, the phase tracker output RMS was a few kHz, so not even worth thinking about any further. Not so surprising. 

Finally, I put back / hooked up everything in its nominal state. 

  11327   Wed May 27 15:20:54 2015 ericqUpdateComputer Scripts / ProgramsChiara Backup Hiccup

The local chiara backups are still failing due to vanished source files. I've emailed Max about the summary page jobs, since I think they're running remotely. 

  11328   Wed May 27 17:14:08 2015 ericqUpdateLSCX Aux Laser crystal temperature changed

Rana suspects that the lack of X beatnote is related to the PSL laser temperature change (ELOG 11294). 

I used the information on the wiki and old elogs (wiki-40mELOG 6732), to deduce that the new end laser temperatures should be:

  • X end-> 38.98 C
  • Y end-> 35.80 C

I went out to the X end and found the laser crystal temperature set to 40.87, which is not what the measurements I linked to suggest would be the ideal temperature for the previous NPRO laser temperature of 30.89, which would be 37.02. I could not find any elog describing the choice of this setpoint.  

I've changed the X end laser crystal temperature to the value above. I've hooked up the X IR and green beatnotes to go the control room analzyer, and have been looking for the beatnote as I adjust the digital temperature offset, but haven't found it yet...

If this proves totally fruitless, we can just put the lasers back to their original temperatures, since it's unclear if it helped the PC drive noise levels. 

  11333   Thu May 28 17:12:32 2015 ericqUpdateIOOFSS SLOW not engaged: is this intentional?

Yes, I had turned it off while looking for the PSL/X AUX beat, and forgot to turn it back on.

I will post an elog with more detail this evening, but I found a temperature which restored the X green beatnote at its nominal amplitude (-30dBm) with no mode hops within +-1 IR beat GHz, and offloaded the slow offset slider to the X-end laser crystal dial. I will look for the Y beatnote after dinner. 

Currently the control room analyzer is hooked up to recieve the Y IR and green beats; no X signals. 

  11335   Fri May 29 02:05:08 2015 ericqUpdateLSCEnd Laser temperatures set

Both green beatnotes have been found with nominal amplitudes. (X: -30dBm Y: -20dBm), at temperatures which don't seem to be prone to mode hopping. 

X = 42.64, Y ~40.15

Both arms can lock on ALS, but as Koji mentioned in ELOG 11334, the ALS noise seems anomalously high. 


Details

The temperatures I posted in the previous log ended up not being so useful. To find the right end laser temperatures, I looked at the IR beatnotes on the control room analyzer out to 1GHz, and swept around the SLOW_SERVO2_OFFSET channels to change the laser temperature. During this time, the end green shutters were closed, the PSL shutter was closed, the FSS slow servo was off, and the FSS_SLOWDC was set to 0.0. (The green PSL shutter had to be open, because the IR beat fiber is coupled after it.)

For each arm, I found three temperatures where an IR beat could be observed; as Koji mentioned on Wednesday, we should use the middle mode. For each of the arms, scanning around from the middle to move the beat by +-1GHz did not cause a mode hop - the beat stayed visible on the scope. Once I found a real IR beat for the X arm, I took at look at the RF output of the X BBPD, and found my alignment from the other night was actually pretty good; I made a minor touch up to maximize the green beat. 

For the AUX X innolight, I was able to find the actual temperature of the laser crystal when at the correct point, remove the digital offset, and return to the same temperature with the controller front panel dial. This temperature is 42.64 degrees Celcius. There is no diode temperature control on the unit, as far as I could tell, but the maximum green transmitted power through the X arm is about the same as it's ever been, around GTRX=0.5. 

My motivation for doing this was that I always have problems remembering the historical typical values for the digital temperature offset. It seems much cleaner to me to set things up such that a beat is visible "at the origin" (i.e. FSS_SLOWDC=0 and SLOW_SERVO2_OFFSET=0) I suppose that this will also depend on what mode of the PMC we're locked to. During my time working today, its been locked near the middle of its range, currently sitting at 145V. 

However, for the AUX Y lightwave, I was a little perplexed to find that moving the the laser crystal setpoint around does not apear to change the real laser temperature at all. Thus I could not offload the digital offset in the same way. Aditionally, the lightwave controller does not have the same temperature measuring accuracy as the innolight, even with the back panel voltage readout that is hooked up to the multimeter that lives under the optical table. The best I can tell is around 40.1-40.2 degrees C. Y_SLOW_SERVO2_OFFSET of -10690 counts gives a beat <100MHz at FSS_SLOWDC=0. This is actually very close to the previous operating point, so the same mode seems to still work. 

The arms now easily lock on ALS, albeit with higher noise. With arms locked on ALS, POX and POY show >1kHz rms noise. frown 


I gave the PRFPMI locking script a few tries, but it's having problems keeping the PRMI locked. The ALS is a few times noisier than usual, and I haven't revisited the validity of the PRC angular feedforward, so I'm not so surprised. 

  11336   Fri May 29 11:28:42 2015 ericqUpdateComputer Scripts / ProgramsChiara Backup Hiccup

I've changed the chiara local backup script to read a folder exclusion file, and excluded /users/public_html/detcharsummary, and things are working again. 

This was neccesary because the summary pages are being updated every half hour, which is faster than the time it takes for the backup script to run, so the file index that it builds at the start becomes invalid later on in the process. 


Thinking about chiara's disk, it strikes me that when we went from the linux1 RAID to a single HDD on chiara, we may have tightened a bottleneck on our NFS latency, i.e. we are limited to that single hard drive's IO rates. This of course isn't the culprit for the more recent dramatic slowdowns, but in addition to fixing whatever has happened more recently, we may want to consider some kind of setup with higher IO capability for the NFS filesystem. 

  11340   Mon Jun 1 10:26:53 2015 ericqUpdateCDSRCG Upgrade Imminent

We are planning on upgrading the 40 CDS system to the latest version of the LIGO RCG software, in three weeks when Jamie is back in town. 

Jamie and I spoke last week, to hash out a general plan for upgrade and preperations I can make in the meantime. 


Preparation of our models for the upgrade includes;

  • Check if any of the default RCG parts (filter modules, etc.) have substantially different default behavior / ports
  • Cleaning up unterminated/hanging connections in the diagrams (Jamie tells me RCG is more strict about this now)
  • Going through all of the build logs for our models to find what custom blocks are being pulled in from the userapps svn
  • Confirm all of our running blocks and models are committed to svn 
  • In a new, isolated, folder, checkout the latest version of the userapps repo
  • See what blocks have changed, and what model changes might be neccesary. 

Once we think we know what needs to be changed in our models, we can check out the latest version of the RCG source, without linking it as the active version, and create a new build directory, without touching the old one, and create new copies of the 40m models with the neccesary modifications. This way, we can work on getting all of the 40m models compiled, without touching any of the live, running, systems

Once our models are compiling successfully, we can work on building daqd, nds, mxstream, etc. 


Additionally, we want to have some set of tests and diagnostics, to make sure we have not introduced unwanted behavior. 

To this end I will create some test models and DTT templates, where a series of measurements can be run, like

  • OLTF/delay measurement of a single all-digital loop within one model
  • OLTF/delay measurements of a few all-digital loops split across two models, using IPC communcation, RFM, dolphin
  • Hook up DAC -> resistor/amplifier/??? -> ADC, to check things like DAC output, ADC noise levels, IOP delays.

I'll run these test before touching anything, and make sure I understand all of the results, so that an apples-to-apples comparison can be made after the upgrade is complete. 


Updates will be posted as I hash things out. I'm sure we have not yet thought of everything to think about and test, so ideas and feedback are very welcome. 

  11345   Wed Jun 3 17:04:08 2015 ericqUpdatePEMWilcoxon Accelerometer Huddle Test

I've set up the Wilcoxon accelerometers on the SP table for a huddle test, to estimate their noise levels. 

They're clamped down to the table along the same axis, and their housings are in good contact, in hopes to make them as correlated as possible. 

Steve helped me move the DAQ cables from under the BS/PRM oplev table, to dropping from the cable tray above the POX table, so I could get them plugged in at the SP table. This also helps reduce the rats nest by the access connector, and is a fine location for when the accelerometers are attached at MC1 & MC2. 

A quick glance at DTT shows coherence of >0.9 from about 2-100Hz for all six. A three-corner-hat deal will provide an easy estimate of the noise floor of each one. If we feel like being fancy / accounting for possible gain differences, we could try some MISO wiener action, but that is probably overkill. 

Attachment 1: AccHuddle.jpg
AccHuddle.jpg
  11346   Fri Jun 5 11:59:59 2015 ericqBureaucracyGeneralMaintenance Tasks, IFO upgrades

At wednesday's meeting, Rana, Koji, Steve, and I started making a list of maintenence tasks that should be done/checked on a regular basis. The actual scheduling of these has not yet been considered. They include:

  • N2 Tank pressure / cylinder replacement
  • Headlamp, walkie talkie battery recharge
  • Workstation software updates
  • Coffee bean and filters
  • Multimeter battery levels
  • Sorensen DC power supply voltage settings and current draws
  • UPS' status (Vacuum, NFS host, workstations)
  • SR560s, battery powered scopes plugged in
  • Rack Fuses intact
  • Take pictures of electronics racks, optical tables
  • Replace PSL HEPA filter

Next, we brainstormed work that can be done to improve the interferometer performance, and what order/precedence they should take. 

In the end, it was decided that the plan for the next few weeks was to focus on improving the ALS noise levels, and, more importantly, seeking to make the performance more consistent. We need to know what is limiting us, and what we extent we can expect to improve things. To this end, I am working on reviving a ALS noise budget; using the noise budget from the green locking paper to inform a simulinkNB kind of thing.

Here are all of the items we listed during this brainstorming session.

Some near-term/priority tasks are:

  • Installing the accelerometers near MC1 and 2
  • Installing green steering PZT mirrors at the Y end table, commission dither alignment
  • Improving the X end green mode matching
  • ALS noise budgeting
  • Upgrade the realtime system to RCG v2.9

More down the line, other things we thought about were:

  • Cleanup of bench power supplies (FSS box has one, where else?)
  • Fixing the ETMX suspension issues 
  • Upgrade SOS suspension code to the appropriate aLIGO block
  • Upgrade to the green PDH electronics
  • Understanding / tuning the FSS servo laser PZT vs. PC crossover
  • Undestanding / tuning the 11MHz vs 55MHz modulation phase
  • Replacing the slow vxworks machines with the Acromag setup Aiden has set up for the CTN lab
  • QPD upgrade
  • New/better green beatbox
  • Finalize the manifestation of the IR beat control (Freq counter vs. fast DFD)
  • Explore the idea of using an analog output of the ALS beatbox as fast input to the CM board
  • Replace triple resonant EOM driving circuit with double resonant one
  • X end table layout/enclosure upgrade
  11347   Mon Jun 8 15:51:31 2015 ericqUpdateCDSRCG Diagnostics

I've started making some model changes for RCG diagnostic tests. 

I put some blocks down in C1TST and C1RFM to test the delays of all-digital loops and one loop with a direct DAC->ADC (which currently uses a janky 1-pin lemo -> BNC -> 2-pin lemo situation (which will be improved)). 

Here's what C1TST looks like now. 

I've taken TFs of all three loops. The all digital loops are flat on the order of microdBs. 

The delay in loop A (single loop, one model) is consistent with one 16k cycle, plus or minus 0.25 nsec. 

The delay in loop C (single loop, two models connected via RFM) is consistent with two 16k cycles, plus or minus 0.5 nsec. 

I haven't yet grabbed the whitening and AA/AI shapes for loopB, to calibrate the real delay. 

All of these files currently live in /users/ericq/2015-06-CDSdiag, but I'll make somewhere outside of the user directory to collect all of these tests soon. 

Attachment 1: newTST.png
newTST.png
  11350   Wed Jun 10 02:50:39 2015 ericqUpdatePEMWilcoxon Accelerometer Huddle Test

Here are some results for the 3-corner hat subtraction for the six accelerometers, from ~1 hour of data that didn't look to have any sharp features/glitches from human activity in the lab. 

I used the python uncertainties package to try and get an estimate of the uncertainty in the subtracted noise floor, by taking into account every possible possible combination of 3 sensors and the fluctuations in the spectrograms of the subtracted signals. I've attached the python code if anyone is interested in the implementation. 

I pulled out the accelerometer data sheets to read their slightly varying V/g calibration (which differs on the order of a few percent from unit to unit). This improved the subtraction factor from ~20 to over 100 at some frequencies. I've edited the filter modules such that the OUT_DQ channels are already calibrated into m/s^2.

Attachment 1: hats2Acc.png
hats2Acc.png
Attachment 2: 3hatcode.zip
  11351   Wed Jun 10 03:19:58 2015 ericqUpdateLSCAUX PDH error measured in CDS

Looking over the old noise budget in the green locking paper, it seems the main technical noise sources were the AUX PDH error and DFD noise. I'm working on quantifying the current state of these noises. 

Rather than lugging out the analyzers every time I wanted to make a measurement of the AUX PDH error signals, I set out to make the existing digitized channels (ALS-[X/Y]_ERR_MON) usable for easier, and continuous, monitoring. Sadly, up until now the signals were poorly conditioned, and drowning in ADC noise. (When locked, the Y error signal was only +-10 counts!)

Of course, given the bandwidth of the green servos (10kHz), this won't tell us the full story of the what the green PDH lock is doing, but does indicate how much residual frequency noise exists in the ALS control band. 

I'm currently using SR560s at G=20 at each end to amplify the ERR MON outputs of the uPDH boards before sending them to the ADCs; now that I've found a gain that works, I'll modify the error point monitor buffer opamps inside the uPDH boards themselves during the daytime. 

The AUX Y error signal was going into an AA board with some funky filtering going on that I didn't want to mess with. Instead, I've moved the signal to the pentek generic board whose first four channels are used for the oplev segments, and the second quartet are unused, save for the TST channel I hooked up yesterday. 

On the pentek board, I changed the 4th order 800Hz lowpass to a 4th order 8kHz lowpass on the last three channels through some resistor swapping. (At first it was just the last two, but I found I was getting weird signals in the 32nd channel; and if I recall correctly from my cymac work, the 32 ADC channel is used for some timing signal or something...). I also turned off the 1:10 whitening filters on the last four channels via PCB jumper. 

I then unhooked the PZT drive and let the PDH error signals swing around, to calibrate the ADC counts into HZ. Now, the ALS-[X/Y]_ERR_MON_OUT_DQ are calibrated in green Hz! Here are the spectra.

As we've seen in the past (ELOG 10464), the X green is limited by the dark noise of the PD from 10-100Hz. This isn't so great. The RMS noise from 300Hz downwards (which is maybe the band where the ALS control would inject noise into the mirror motion) is about Y:10Hz X:40Hz.

During this time, the test masses were not under any longnitudinal control, so I'm not sure why there is such a difference in the height of the suspension resonance peaks, unless there's some differene in the low frequency PDH TFs that I've forgotten about. 

Now, with these references, we can easily check if the PDH loops change qualitatively over longer time periods.

I'll be including the effect of these noises in the upcoming revised ALS noise budget.

Attachment 1: AUXspectra.png
AUXspectra.png
  11355   Fri Jun 12 17:09:58 2015 ericqUpdateLSCBeatbox needs whitening gain

Short entry just to preview a new development; more detail about this investigation will soon follow. 

The beatbox I and Q signals are too small at the ADC! I was able to reduce the RMS out of loop ALS sensitivity (arm locked on POX) by 300Hz with G=10 SR560s between the beatbox output and the ADC whitening chassis input. Increasing the beat note amplitude via RF amplifier had no positive effect. 

There is still a reasonable gap between this and the beatbox's noise levels, as measured with a marconi. There may be additional headroom for whitening gain; the SR560 maximum output range is smaller than the ADC input range. 

The high frequency noise has >0.5 coherence with the PDH error signal above a kHz or so, but not much below that. 

We should probably either modify the output whitening of the beatbox, or introduce some (variable?) whitening gain in a seperate circuit. 

Attachment 1: beatGain.png
beatGain.png
  11356   Sat Jun 13 18:37:46 2015 ericqUpdateLSCBeatbox needs whitening gain

Here are the promised details!

I was worried about the lack of whitening gain, as I saw that the DC phase tracker Q output (which is the magnitude of the signal in the beatbox's I-Q plane) was no more than 200 ADC counts for X (~120mV), and 800 for Y (~500mV). I.e. this is the largest DC value that either the I or Q ADC channels can see, and the RMS fluctuations are on the order of mV, meaning we're wasting our entire ADC rangeno

However, I also had doubts about this since, even in the nominal state, the ASD of the ADC signals before dewhitening was higher than the expected ADC noise level. However, because of the non-linearity of the conversion of the BEAT_I and Q signals into the phase tracker output, evaluating the contribution of the beatbox output and ADC input voltage noises takes a few more steps. 

So, I hooked up a Marconi as the signal source for the beatbox's X channel , with no modulation (presumably the phase noise of the Marconi output is significantly lower than the sensitivity of the beatbox). For all of these measurements, the beat frequency was kept around 50MHz, with an amplitude of -30dBm on the control room analyzer, which is a typical X ALS operating point. 

At this point, the beatbox output noise was below the ADC noise (as measured by an SR785). Nevertheless, I found that the beat spectrum driven by the Marconi lined up to be very close to the ALS beat spectrum across a wide band, explaining much of the noise. 

At this point, I inserted SR560s in between the beatbox I and Q outputs, and the AA chassis leading to the ADC. A gain of 10 reduced the resultant phase tracker noise by that same factor at nearly all frequencies. A further increase in gain did not lead to the noise changing appreciably, probably because the real beatbox noise was now contributing, as is suggested by some common peaks in the direct beatbox output phase tracker spectra.

Going back to the real green beat signal with the SR560s still at G=10, I obtained the result shown in ELOG 11355. I will soon repeat this process with the Y ALS. 

As I mentioned in the previous ELOG, we may be further helped by more whitening gain than can be provided by the SR560s (and we obviously need a robust long term circuit for this gain). If it then turns out we are limited by beatbox noise to a degree we are not happy with, we could perhaps look into reintroducing some RF gain into the X beat. As Koji mentions in ELOG 8855, the beatbox operates best at an RF input of around -4dBm.

Attachment 1: ADCdiagnosis.png
ADCdiagnosis.png
  11357   Sat Jun 13 23:52:14 2015 ericqUpdateLSCBeatbox needs whitening gain

Nice find!

We ought to use our noise model of the ALS signal chain to determine what the right gains are, rather than hunt and peck. More likely we'll start from the right gains.​

Once the gains and/or whitening filters make sense, maybe we'll see some effect from fixing the green PDH loops.

  11358   Mon Jun 15 11:54:44 2015 ericqUpdateCDSParts not in SVN

I ran the following command to find which models/parts are not under version control, or have modifications not commited:

grep "mdl" $(cat models.txt) | awk '{print $NF}' | sort | uniq | xargs svn status

models.txt includes lines like "/opt/rtcds/caltech/c1/rtbuild/c1ass.log" for each running model. These are the build logs that detail every file being sourced. 

The resultant list is:

?       /opt/rtcds/userapps/release/cds/common/models/BLRMS_HIGHFREQ.mdl
C       /opt/rtcds/userapps/release/cds/common/models/rtdemod.mdl
M       /opt/rtcds/userapps/release/cds/common/models/SCHMITTTRIGGER.mdl
?       /opt/rtcds/userapps/release/isc/c1/models/blrms.mdl
?       /opt/rtcds/userapps/release/isc/c1/models/IQLOCK.mdl
?       /opt/rtcds/userapps/release/isc/c1/models/PHASEROT.mdl
?       /opt/rtcds/userapps/release/sus/c1/models/QPD_WHITE_CTRL_MUX.mdl

I will commit the uncommited c1 parts, and think about what to do about the rtdemod and SCHMITTRIGGER parts. 

Once I check out the latest revision of the userapps repo (in a seperate location), I will do something similar to look for models that have changed since the svn revision that is checked out in our running system. 

  11359   Mon Jun 15 16:55:39 2015 ericqUpdatePEMAccelerometers installed

The accelerometers have been installed at MC1 and MC2. MC2 data is live, I haven't yet run the cables from the MC1 set to the preamp yet, though. 

Attachment 1: MC2.jpg
MC2.jpg
Attachment 2: MC1.jpg
MC1.jpg
Attachment 3: mc2accspectra.png
mc2accspectra.png
  11362   Wed Jun 17 15:31:50 2015 ericqUpdatePEMAccelerometers fully installed

MC1 accelerometer has been plugged in. The modecleaner locking has been intermittent today, but I looked at a 15 minute lock in DTT, looking at the STS1 seismometer and both accelerometer triplets. Plot and DTT xml attached.

For the sake of not cluttering up everything with legends, the coherence plots are organized by direction (x, y, z), and include the coherence of each of the three sensors (sts, acc1, acc2) with the IMC control signal and the IMC transmitted RIN. 

Some remarks:

  • The 1 Hz pendulum motion is about equal amounts of X and Y, which makes sense, as MC1 and 3 are at an angle
  • The ~3 Hz stack motion seems to be entirely in the X direction. Why?
  • The bounce/roll bands are strongly coherent with Z motion at MC2. 
  • The STS does not appear to have any low frequency advantage over the accelerometers, in terms of coherence, contrary to what I would expect even without a thermal enclosure. 
  • The control signal and RIN RMSs are clearly dominated by noise in the 1-3Hz band, where we have reasonable coherence. Good prospects for noise subtraction...

Attachment 1: IMCcoherence_Jun172015.xml.zip
Attachment 2: IMCcoherence.png
IMCcoherence.png
  11364   Fri Jun 19 01:55:35 2015 ericqUpdateGreen LockingBeatBox Assay: not looking good
Quote:

But, it has no whitening. Can we do the whitening part externally? Perhaps we can run the RF signals from the output of the beat RF Amps over to the LSC rack and then put the outputs into the LSC Whitening board and acquire the signals in the LSC ?

I like this idea; it gives us more control over the whitening, and saves the IPC delay. We could use the currently vacant AS165 and POP55 channels. 

We'd only have to move the phase trackers to c1lsc, which means 12 more FMs total. This is really the only part of the c1als model our current system uses, the rest is from before the ALS->LSC integration. 

  11365   Fri Jun 19 03:00:56 2015 ericqUpdateCDSLibrary Model Parts examined

All simulink diagrams being used at the 40m are now under version control. I have compiled, installed, and restarted all current models to make sure that the files are all in a working state, which they seem to be. I have checked the latest version of the userapps svn repository to /opt/rtcds/userapps2.9, to compare the files therein with our current state. 

Surprisingly, only two files in the userapps svn have been changed since they were checked out here, and only one of these is a real change of any kind. 

LSC_TRIGGER.mdl was edited at some point simply to align some drawn lines; no functionality was changed. 

SCHMITTTRIGGER.mdl was edited to change the "INVERT" epics channel from an arbitrary EPICS input, to binary (true/false) input. This does not change the connectivity diagram, and in fact, I don't think we use this option in any of our scripts, nor is it exposed on our medm screens. 

Thus, I think that the only place for block changes can bite us is changes in the fundamental blocks in CDS_PARTS that are used in our custom 40m library parts. 

For posterity, these are the files used in compiling all of our running models. (Path base: /opt/rtcds/userapps/release)

/isc/common/models/CALIBRATION.mdl
/isc/common/models/FILTBANK_TRIGGER.mdl
/isc/common/models/LSC_TRIGGER.mdl
/isc/common/models/QPD.mdl
/cds/common/models/FILTBANK_MASK.mdl
/cds/common/models/lockin.mdl
/cds/common/models/rtbitget.mdl
/cds/common/models/rtdemod.mdl
/cds/common/models/SCHMITTTRIGGER.mdl
/cds/common/models/SQRT_SWITCH.mdl
/cds/c1/models/c1rfm.mdl
/cds/c1/models/c1tst.mdl
/cds/c1/models/c1x01.mdl
/cds/c1/models/c1x02.mdl
/cds/c1/models/c1x03.mdl
/cds/c1/models/c1x04.mdl
/cds/c1/models/c1x05.mdl
/isc/c1/models/ALS_END.mdl
/isc/c1/models/BLRMS_40M.mdl
/isc/c1/models/BLRMS_HIGHFREQ.mdl
/isc/c1/models/blrms.mdl
/isc/c1/models/c1als.mdl
/isc/c1/models/c1ass.mdl
/isc/c1/models/c1asx.mdl
/isc/c1/models/c1cal.mdl
/isc/c1/models/c1ioo.mdl
/isc/c1/models/c1lsc.mdl
/isc/c1/models/c1oaf.mdl
/isc/c1/models/c1pem.mdl
/isc/c1/models/IQLOCK.mdl
/isc/c1/models/IQ_TO_MAGPHASE.mdl
/isc/c1/models/PHASEROT.mdl
/isc/c1/models/RF_PD_WITH_WHITENING_TRIGGERING.mdl
/isc/c1/models/SENSMAT_LOCKINS.mdl
/isc/c1/models/TT_CONTROL.mdl
/isc/c1/models/UGF_SERVO_40m.mdl
/sus/c1/models/c1mcs.mdl
/sus/c1/models/c1scx.mdl
/sus/c1/models/c1scy.mdl
/sus/c1/models/c1sus.mdl
/sus/c1/models/lib/sus_single_control.mdl
/sus/c1/models/QPD_WHITE_CTRL_MUX.mdl
  11368   Mon Jun 22 12:57:09 2015 ericqSummaryLSCX/Y green beat mode overlap measurement redone

I took measurements at the green beat setup on the PSL table, and found that our power / mode overlap situation is still consistent with what Koji and Manasa measured last September [ELOG 10492]. I also measured the powers at the BBPDs with the Ophir power meter.

Both mode overlaps are around 50%, which is fine. 

The beatnote amplitudes at the BBPD outputs at a frequency of about 50MHz are -20.0 and -27.5 dBm for the X and Y beats, respectively. This is consistent with the measured optical power levels and a PD response of ~0.25 A/W at 532nm. The main reason for the disparity is that there is much more X green light than Y green light on the table (factor of ~20), and the greater amount of green PSL light on the Y BBPD (factor of ~3) does not quite make up for it. 

One way to punch up the Y beat a little might be to adjust the pickoff optics. Of 25uW of Y arm transmitted green light incident on the polarizing beamsplitter that seperates the X and Y beams, only 13uW makes it to the Y BBPD, but this would only win us a couple dBms at most. 

In any case, with the beat setup as it exists, it looks like we should design the next beatbox iteration to accept RF inputs of around -20 to -30 dBm. 


In the style of the referenced ELOG, here are today's numbers. 

            XARM   YARM 
o BBPD DC output (mV)
 V_DARK:   +  1.0  + 2.2
 V_PSL:    +  7.1  +21.3
 V_ARM:    +165.0  + 8.2


o BBPD DC photocurrent (uA)
I_DC = V_DC / R_DC ... R_DC: DC transimpedance (2kOhm)

 I_PSL:       3.6   10.7
 I_ARM:      82.5    4.1


o Expected beat note amplitude
I_beat_full = I1 + I2 + 2 sqrt(e I1 I2) cos(w t) ... e: mode overwrap (in power)

I_beat_RF = 2 sqrt(e I1 I2)

V_RF = 2 R sqrt(e I1 I2) ... R: RF transimpedance (2kOhm)

P_RF = V_RF^2/2/50 [Watt]
     = 10 log10(V_RF^2/2/50*1000) [dBm]

     = 10 log10(e I1 I2) + 82.0412 [dBm]
     = 10 log10(e) +10 log10(I1 I2) + 82.0412 [dBm]

for e=1, the expected RF power at the PDs [dBm]
 P_RF:      -13.2  -21.5


o Measured beat note power (no alignment done)     
 P_RF:      -20.0  -27.5  [dBm] (53.0MHz and 46.5MHz) 
    e:       45.7   50.1  [%]                         

 

  11371   Mon Jun 22 20:59:19 2015 ericqUpdateLSCDFD Delay length

I've been thinking a bit about what the ideal cable length / delay time for the upgraded ALS beatbox should be. Here are some thoughts, but no conclusions yet. 

If you're not running your beatbox mixer in compression, there are two competing effects when you change the cable length. At first, more delay gives better sensitivity, but this does not go on to infinity, because cable attenuation eventually kills your signal. It turns out that the ideal length can be derived to be whatever length gives you 20/ln(10) = -8.7dB of attenuation. Frank found this out in PSL ELOG 825, and I found an HP document that derives this (and other useful DFD math) to the wiki, here.

In PSL ELOG 826, Frank calculated this ideal length for a 160MHz carrier in various kinds of cables. 

However, this is not the end of the story. In the case of the DFD, we actually benefit from operating the mixer in compression, as makes our sensitivity less sensitive to flucuations in the beat amplitude. In this situation, the HP doc states "For maximum sensitivity, more delay can be added until the signal level out of the delay line is 8.7dB below the phase detector (mixer) compression point." I'm not sure I really understand the logic behind this statement, though. 

Lastly, Koji mentioned the fact that the splitter in the demod board does not split at exactly 90 degrees, making the trajectory in the IQ plane an ellipse. This means that if the beat signal is moving around the ellipse a lot, or even wrapping around it, we can suffer from some nonlinear signal conversion. Also, if the raw DFD sensitivity is very high, the free swinging mirrors will cause the signal to swing around faster than the phase tracker can keep up. This should be easy to avoid, however; I doubt we will use so much cable that the beat would move by so much. 

I intend to take all of this into account when picking a cable length! Jessica is going to help us make a nice box for them, too. 

ELOG V3.1.3-