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ID Date Author Type Category Subjectdown
  16305   Wed Sep 1 14:16:21 2021 JordanUpdateVACEmpty N2 Tanks

The right N2 tank had a bad/loose valve and did not fully open. This morning the left tank was just about empty and the right tank showed 2000+ psi on the gauge. Once the changeover happened the copper line emptied but the valve to the N2 tank was not fully opened. I noticed the gauges were both reading zero at ~1pm just before the meeting. I swapped the left tank, but not in time. The vacuum interlocks tripped at 1:04 pm today when the N2 pressure to the vacuum valves fell below 65psi. After the meeting, Chub tightened the valve, fully opened it and refilled the lines. I will monitor the tank pressures today and make sure all is ok.

There used to be a mailer that was sent out when the sum pressure of the two tanks fell <600 psi, telling you to swap tanks. Does this no longer exist?

  15485   Wed Jul 15 19:23:44 2020 gautamUpdateGeneralEmergency light on in control room

The emergency lamps above the exit sign on the NW entrance to the control room are on. I tried opening and closing the door, but it remains on. Probably nothing to worry about, but noting here anyway.

  15486   Wed Jul 15 19:51:51 2020 KojiUpdateGeneralEmergency light on in control room

It happened before too. Doesn't it say it has occasional self-testing or something?

  15487   Wed Jul 15 20:58:40 2020 gautamUpdateGeneralEmergency light on in control room

True - it is now not on anymore.

Quote:

It happened before too. Doesn't it say it has occasional self-testing or something?

  7207   Thu Aug 16 18:59:18 2012 JenneUpdateSAFETYEmergency Exit door unlocked again

Koji just found the emergency exit door unlocked again.  NOT GOOD.

We have determined that if you use the emergency door to enter the lab, it leaves the door unlocked, unless you go back outside and deliberately lock it.  This means that someone has been using the emergency exit as a regular entrance. 

It's fine to leave by that door, but you should make a habit of entering through the regular door.  Using the back door as an entrance is a special case situation, when they have the main door blocked.

  2473   Mon Jan 4 17:21:30 2010 JenneConfigurationIOOElusive Mode Matching Solution found!

I think I have finally found a Mode Matching solution for our new Input Mode Matching Telescope!  And after looking at the layout diagram with Koji and Raffaele, it seems like all of the optics will fit into the chambers / onto the tables (not true as of last week). 

3. RoCMMT1 is -5m
   RoCMMT2 is 8m,
   with the MMTs 1.89m apart.
   This is a 1.6x telescope.
   MMT2 is 2.2641m from the PRM
   MMT1 is 2m from MC3.
   The Condition Number for this optical chain is 89219047.5781.

This layout is very similar to the one that Koji posted on the wiki yesterday:  Upgrade09/Optical Layout.  The difference is that I want to move MMT1 ~20cm closer to the MC13 table, so just on the other side of the main red beam that goes directly to PRM.  There is plenty of space there, so it should be all good.  The tricky bit is that the flat steering mirrors fit into things now while they are piezos, but they will be trickier to fit if we make them into Tip Tilts.  But I have full faith in Koji's amazing optical table layout skills, that he can make it happen. 

Unless there are major objections, I think this is the MMT that we're going to go with. (So speak now or forever hold your peace.)  The angle between tilt and translation isn't quite what we'd like it to be (at ~18deg), but it's not too terrible.  And we still have 99.5% overlap which is very important.

  2481   Wed Jan 6 03:44:41 2010 KojiConfigurationIOOElusive Mode Matching Solution found!

I am in the way to get a reasonable optical layout.
Please calculate the final results with the following conditions.

"Result" =
- mode overlapping with astigmatism
- alignment matrix (m/rad, rad/rad) for Pitch and Yaw
- alignment orthogonality
- sensitivity of the mode overlapping to the perturbations
  * histgram
  * individual scan of the optic positions

Optics chain: MC3 - SM1(flat) - MMT1(f=-5m) - MMT2(f=+8m) - SM2(flat) - PRM

Incident angles: SM1 24deg, MMT1 3deg, MMT2 1deg, SM2 44.5deg

Distances:
MC3 HR - SM1: 884mm
SM1 - MMT1: 1058.2mm
MMT1 - MMT2: 1890mm
MMT2 - SM2: 2007.9mm
SM2 - PRM HR: 495.6mm

It has ~200mm deviation from the solution. I can move only MMT1 for final optimization.
Give us the numbers if it can improve the performance.
Note that this move changes SM1-MMT1 and MMT1-MMT2 simultaneously.

Quote:

I think I have finally found a Mode Matching solution for our new Input Mode Matching Telescope!  And after looking at the layout diagram with Koji and Raffaele, it seems like all of the optics will fit into the chambers / onto the tables (not true as of last week). 

3. RoCMMT1 is -5m
   RoCMMT2 is 8m,
   with the MMTs 1.89m apart.
   This is a 1.6x telescope.
   MMT2 is 2.2641m from the PRM
   MMT1 is 2m from MC3.
   The Condition Number for this optical chain is 89219047.5781.

This layout is very similar to the one that Koji posted on the wiki yesterday:  Upgrade09/Optical Layout.  The difference is that I want to move MMT1 ~20cm closer to the MC13 table, so just on the other side of the main red beam that goes directly to PRM.  There is plenty of space there, so it should be all good.  The tricky bit is that the flat steering mirrors fit into things now while they are piezos, but they will be trickier to fit if we make them into Tip Tilts.  But I have full faith in Koji's amazing optical table layout skills, that he can make it happen. 

Unless there are major objections, I think this is the MMT that we're going to go with. (So speak now or forever hold your peace.)  The angle between tilt and translation isn't quite what we'd like it to be (at ~18deg), but it's not too terrible.  And we still have 99.5% overlap which is very important.

 

  3461   Tue Aug 24 06:34:01 2010 AlastairUpdateGeneralElog...

...was down.  Have restarted it.

  2562   Tue Feb 2 18:15:47 2010 AlbertoUpdateelogElog restarted it

 Zach made me notice that the elog had crashed earlier on this afternoon. 

I just restarted it with the restarting script.

Instructions on how to run the last one are now in the wiki page. Look on the "How To" section, under "How to restart the elog".

  3994   Tue Nov 30 12:10:44 2010 josephbUpdateelogElog restarted again

The elog seemed to be down at around 12:05pm.  I waited a few minutes to see if the browser would connect, but it did not.

I used the existing script in /cvs/cds/caltech/elog/ (as opposed to Zach's new on in elog/elog-2.8.0/) which also seems to have worked fine.

  4168   Wed Jan 19 10:31:24 2011 josephbUpdateelogElog restarted again

Elog wasn't responding at around 10 am this morning.  I killed the elogd process, then used the restart script.

  2196   Fri Nov 6 18:02:22 2009 josephbUpdateComputersElog restarted

While I was writing up an elog entry, the elog died again, and I restarted it.  Not sure what caused it to die since no one was uploading to it at the time.

  11058   Mon Feb 23 15:04:10 2015 ZachUpdateGeneralElog restarted

The elog crashed while I was creating an entry to the Cryo log. I restarted it with the start-elog.csh script.

  2739   Wed Mar 31 10:34:02 2010 josephbUpdateelogElog not responding this morning

When I went to use the elog this morning, it wasn't responding.  I killed the process on nodus, and then restarted, per the 40m wiki instructions.

  3795   Wed Oct 27 11:52:45 2010 josephbUpdateelogElog needed to be restarted

I had to restart the elog on Nodus because it was no longer responding.

  1181   Fri Dec 5 20:40:38 2008 YoichiHowToComputersElog multi-keyword search
The current Elog search allows you to look for only one keyword in the text.
You cannot search for two keywords by simply separating them with a white space.
That is, a search term "abc def" matches a literal "abc def", not a text containing "abc" and "def".
This is extremely annoying. However, there are still some ways to search for multiple keywords.
The Elog search fields are treated as regular expressions.
In order to match a text containing "abc" and "def", you can use a search term "abc.*def".
A period (.) means "any character", and an asterisk (*) means "any number of repetition of the preceding character".
Therefore, ".*" matches "any number of any character" i.e. anything.
The search term "abc.*def" works fine when you know "abc" appears first in the text you are looking for.
If you don't know the order of appearance of the keywords, you have two choices: either to use,
"(abc.*def)|(def.*abc)"
or
"(abc|def).*(abc|def)"
The vertical bar (|) means "or". Parentheses are used for grouping.
The first example does exactly what you want. However, you have to list all the permutations of your keywords
separated by |. If you have more than two keywords, it can be a very very long search word.
(The length of the search word is O(n!), where n is the number of keywords).
In the second example, the length of the keyword is O(n). However, it can also match a text containing two "abc".
This means the search result may contain some garbages (entries containing only "abc").
I guess in most cases we can tolerate this.

To automatically construct a multiple keyword search term for the Elog, I wrote a bash script called elogkeywd
and it is installed in the control room machines.
You can type
elogkeywd keyword1 keyword2 keyword3
to generate a regular expression for searching a text containing "keyword1", "keyword2" and "keyword3".
The generated expression is of the second type shown above. You can then copy-and-paste the result to
the Elog search field.
The script takes any number of keywords. However, there seems to be a limit on the number of characters you can type
into the search field of the Elog. I found the practical limit is about 3 keywords.
  2187   Fri Nov 6 00:23:34 2009 AlbertoConfigurationComputersElog just rebooted

The elog just crashed and I rebooted it

  5556   Tue Sep 27 11:43:59 2011 JenneUpdateelogElog has been dying a lot lately...

WTF?

  3464   Tue Aug 24 14:29:18 2010 josephbUpdateelogElog down for 1 minute

I'm going to take the elog down for one minute and restart it under gdb (using a copy of gdb stolen from fb40m since I couldn't figure out how to install an old enough version on nodus from source).  The terminal with information is running on Rosalba under the "Phase Noise" panel, so please don't close it.  Ideally, the next time the elog crashes, I'll have some output indicating why or at least the line in the code.  I can then look at the raw source code or send the line back to the developer and see if he has any ideas.

  3441   Thu Aug 19 09:52:51 2010 AlastairUpdateComputersElog down

 I restarted it using start-elog-nodus and this worked out fine - even though I did it from Pete's on my phone ;-)

  2302   Thu Nov 19 16:04:48 2009 AlbertoConfigurationelogElog debugging output - Down time programmed today to make changes

We want the elog process to run in verbose mode so that we can see what's going. The idea is to track the events that trigger the elog crashes.

Following an entry on the Elog Help Forum, I added this line to the elog starting script start-elog-nodus:

./elogd -p 8080 -c /cvs/cds/caltech/elog/elog-2.7.5/elogd.cfg -D -v > elogd.log 2>&1

which replaces the old one without the part with the -v argument.

The -v argument should make the verbose output to be written into a file called elogd.log in the same directory as the elog's on Nodus.

I haven't restarted the elog yet because someone might be using it. I'm planning to do it later on today.

So be aware that:

We'll be restarting the elog today at 6.00pm PT. During this time the elog might not be accessible for a few minutes.

  2303   Thu Nov 19 18:49:55 2009 AlbertoConfigurationelogElog debugging output - Down time programmed today to make changes

Quote:

We want the elog process to run in verbose mode so that we can see what's going. The idea is to track the events that trigger the elog crashes.

Following an entry on the Elog Help Forum, I added this line to the elog starting script start-elog-nodus:

./elogd -p 8080 -c /cvs/cds/caltech/elog/elog-2.7.5/elogd.cfg -D -v > elogd.log 2>&1

which replaces the old one without the part with the -v argument.

The -v argument should make the verbose output to be written into a file called elogd.log in the same directory as the elog's on Nodus.

I haven't restarted the elog yet because someone might be using it. I'm planning to do it later on today.

So be aware that:

We'll be restarting the elog today at 6.00pm PT. During this time the elog might not be accessible for a few minutes.

 I tried applying the changes but they didn't work. It seems that nodus doesn't like the command syntax.

I have to go through the problem...

The elog is up again.

  10323   Fri Aug 1 15:32:07 2014 ericqUpdateComputer Scripts / ProgramsElog and svn backups

Koji and Evan have both brought up a good point that we may not be backing up the svn and ELOG properly.

I have modified the rsync.backup script that nodus' cron runs every night that backs up /cvs/cds to what I presume are the tape backups at ldas-cit.ligo.caltech.edu.

Specifically, I added two rsync commands that grab the svn and elog directories from /export/home and copy them to their old locations in /cvs/cds/caltech. This way, the old locations are updated, and the tape backups stay current.

  5739   Tue Oct 25 21:23:17 2011 DmassBureaucracyelogElog Restarted

Elog went nonreponsive. SSH'ed into nodus to run restart script. Elog came back ~15 minutes later.

  3452   Fri Aug 20 20:36:05 2010 AlastairUpdateGeneralElog

 Elog was down, I restarted it.

  14405   Fri Jan 18 15:34:37 2019 gautamUpdateThermal CompensationElliptical reflector part number

Nobody documented this, but here is the part number with mechanical drawings of the elliptical reflector installed at EY: Optiforms E180. Heater is from Induceramics, but I can't find the exact part which matches the dimensions of the heater we have (diameter = 3.8mm, length = 30mm), perhaps it's a custom part?

The geometry dictates that if we want the heater to be at one focus and the ETM to be at the other, the separation has to be 7.1 inches. It certainly wasn't arranged this way before. It seems unrealistic to do this without clipping the main beam, I propose we leave sufficient clearane between the main beam and the reflector, and accept the reduced heating efficiency. 

Thanks to Steve for digging this up from his secret stash.

  1036   Wed Oct 8 22:23:43 2008 YoichiConfigurationElectronicsElectronics work bench cleanup
Yesterday, I cleaned up the electronics work bench. I figured that keeping the work bench
in order has larger effect on the work efficiency than buying expensive soldering stations.
Whoever works there should clean up the table after the work to the state shown on
the right side of the picture (at least).
If you leave the bench for a while (more than 30min) but intend to return later and
resume the work, please write your name and time on a piece of paper and put it on the bench.
Otherwise, your stuff can be taken away anytime.
  4584   Thu Apr 28 22:38:38 2011 AidanUpdateGreen LockingElectronics schematic for vertex beatbox

 With some assistance from Kiwamu and Koji, I've drawn up the electronics design for the Beat Box for the vertex green locking. The Omingraffle schematic is posted on the Green Locking Wiki page. It's also attached below. Some final touches are necessary before we can Altium this up.

 Attachment 1: Schematic of beatbox

Attachment 2: Front and back panel designs.

  4593   Sat Apr 30 05:14:33 2011 KojiUpdateGreen LockingElectronics schematic for vertex beatbox

- AC coupling for the comparator circuit of the green locking

In order to relieve the power consumption of the RF buffer, ac coupling circuits have been added.

The ac coupling before the buffer amp helps to relieve the power consumption in the chip.
But because of the distortion of the signal (and the limitation of the bandwidth), the output still has some DC (~0.6V).
Therefore, the output is also AC coupled.

Note that the BW pin of BUF634P should be directly connected to -15V in order to keep the bandwidth of the buffer.

The drawings are also uploaded on the green electronics wiki

  16992   Tue Jul 12 14:56:17 2022 TomislavSummaryElectronicsElectronics noise measurements

[Paco, Tomislav]

We measured the electronics noise of the demodulation board, whitening board, and ADC for WFSs, and OPLEV board and ADC for DC QPD in MC2 transmission. We were using SR785.

Regarding the demodulation board, we did 2 series of measurements. For the first series of measurements, we were blocking WFS (attachment 1) and measuring noise at the output of the demod board (attachment 2a). This measurement includes dark noise of the WFS, electronics noise of demod board, and phase noise from LO. For the second series of the measurements, we were unplugging input to the demod board (attachment 2b & 2c is how they looked like before unplugging) (the mistake we made here is not putting 50-ohm terminator) and again measuring at the output of the demod board. This measurement doesn't include the dark noise of the WFS. We were measuring it for all 8 segments (I1, I2, I3, I4, Q1, Q2, Q3, Q4). The dark noise contribution is negligible with respect to demod board noise. In attachments 3 & 4 please find plots that include detection and demodulation contributions for both WFSs.

For whitening board electronics noise measurement, we were terminating the inputs (attachment 5) and measuring the outputs (attachment 6). Electronics noise of the whitening board is in the attachments 7 & 8.

For ADC electronics noise we terminated ADC input and measured noise using diaggui (attachments 9 & 10). Please find these spectra for WFS1, WFS2, and MC TRANS in attachments 11, 12 & 13.

For MC2 TRANS we measured OPLEV board noise. We did two sets of measurements, as for demod board of WFSs (with and without QPD dark noise) (attachments 14, 15 & 16). In the case of OPLEV board noise without dark noise, we were terminating the OPLEV input. Please find the electronics noise of OPLEV's segment 1 (including dark noise which is again much smaller with respect to the OPLEV's electronics noise) in attachment 17.

For the transfer functions, demod board has flat tf, whitening board tf please find in attachment 18, ADC tf is flat and it is (2**16 - 1)/20 [cts/V], and dewhitening tf please find in attachment 19. Also please find the ASD of the spectral analyzer noise (attachment_20).

Measurements for WFS1 demod and whitening were done on 5th of July between 15h and 18h local time. Measurements for WFS2 demod and whitening were done on 6th of July between 15h and 17h local time. All the rest were done on July 7th between 14h and 19h. In attachment 21 also find the comparison between electronics noise for WFSs and cds error signal (taken on the 28th of June between 17h and 18h). Sorry for bad quality of some pictures.

  16998   Wed Jul 13 13:26:44 2022 ranaSummaryElectronicsElectronics noise measurements

as I said to you yesterday, I don't think image 2a shows the output of the demod board. The output of the demod board is actually the output connector ON the demod board. What you are showing in 2a, is the signal that goes from the whitening board to the ADC I believe. I may be msitaken, so please check with Tega for the signal chain.

  16958   Tue Jun 28 18:19:09 2022 TomislavUpdateElectronicsElectronics noise

I measured electronics noise of WFSs and QPD (of the WFS/QPD, whitening, ADC...) by closing PSL and measuring the error signal. It was needed to put the offset in C1:IOO-MC_TRANS_SUMFILT_OFFSET to 14000 cts (without offset the sum of quadrants would give zero, and 14000 cts is the value when the cavity is locked). For WFS that are RF, if there is intensity noise at low frequencies, it is not affecting the measurement.

In the attachment please find the power spectrum of the error signal when the PSL shutter is on and off.

  16963   Wed Jun 29 18:53:38 2022 ranaUpdateElectronicsElectronics noise

this is just the CDS error signal, but is not the electronics noise. You have to go into the lab and measure the noise at several points. It can't be done from the control room. You must measure before and afte the whitening.

Quote:

I measured electronics noise of WFSs and QPD (of the WFS/QPD, whitening, ADC...) by closing PSL and measuring the error signal. It was needed to put the offset in C1:IOO-MC_TRANS_SUMFILT_OFFSET to 14000 cts (without offset the sum of quadrants would give zero, and 14000 cts is the value when the cavity is locked). For WFS that are RF, if there is intensity noise at low frequencies, it is not affecting the measurement.

In the attachment please find the power spectrum of the error signal when the PSL shutter is on and off.

 

  15980   Wed Mar 31 00:40:32 2021 KojiUpdateElectronicsElectronics Packaging for assembly work

I've worked on packing the components for the following chassis
- 5 16bit AI chassis
- 4 18bit AI chassis
- 7 16bit AA chassis
- 8 HAM-A coil driver chassis
They are "almost" ready for shipment. Almost means some small parts are missing. We can ship the boxes to the company while we wait for these small parts.

  • DB9 Female Ribbon Receptacle AFL09B-ND Qty100 (We have 10) -> Received 90 on Apr 1st
  • DB9 Male Ribbon Receptacle CMM09-G Qty100 (We have 10) -> Received 88 on Apr 1st
  • 4-40 Pan Flat Head Screw (round head, Phillips) 1/2" long Qty 50 -> Found 4-40 3/8" Qty50 @WB EE on Apr 1st (Digikey H782-ND)
  • Keystone Chassis Handle 9106 36-9106-ND Qty 50 -> Received 110 on Apr 1st
  • Keystone Chassis Ferrule 9121 NKL PL 36-9121-ND Qty 100 -> Received 55 on Apr 1st
  • Chassis Screws 4-40 3/16" Qty 1100 -> Received 1100 on Apr 1st
  • Chassis Ear Screws 6-32 1/2" 91099A220 Qty 150 -> Received 400 of 3/8" on Apr 1st
  • Chassis Handle Screws 6-32 1/4" 91099A205 Qty 100 -> included in the above
  • Powerboard mounting screw 4-40 Pan Flat Head Screw (round head, Phillips) 1/4" long Qty 125 -> Received 100 on Apr 1st

And some more additional items to fill the emptying stock.

  • 18AWG wires (we have orange/blue/black 1000ft, I'm sending ~1000ft black/green/white)
  • Already consumed 80% of 100ft 9pin ribbon cable (=only 20ft left in the stock)
  15986   Thu Apr 1 18:16:28 2021 KojiUpdateElectronicsElectronics Packaging for assembly work

All small components are packed in the boxes. They are ready to ship.

 

  15697   Wed Dec 2 23:07:19 2020 gautamUpdateASCElectrical LO signal for AS WFS

I'm thinking of making some modifications to the RF distribution box in 1X2, so as to have an extra 55 MHz pickoff. Koji already proposed some improvements to the layout in 2015. I've marked up his "Possible Improvement" page of the document in Attachment #1, with my proposed modifications. I believe it will be possible to get 15-16 dBm of signal into a 4 way RF splitter in the quad demod chassis. With the insertion loss of the splitter, we can have 9-10 dBm of LO reaching each demod board, which will then be boosted to +20 dBm by the Teledyne on board. The PE4140 mixer claims to require only -7 dBm of LO signal. So we have quite a bit of headroom here - as long as we limit the RF signal to 0dBm (=0.5 Vpp from the LMH6431 opamp at 55 MHz, we shouldn't be having a much larger signal anyways), we should be just fine with 15 dBm of LO power (which is what we will have after the division into the I and Q paths, and nominal insertion losses in the transmission path). These numbers may be slight overestimates given the possible degradation of the RF amps over the last 10 years, but shouldn't be a show-stopper.

Do the RF electronics experts agree with my assessment? If so, I will start working on these mods tomorrow. Technically, the splitter can be added outside the box, but it may be neater if we package it inside the box. 

  15700   Thu Dec 3 11:02:35 2020 ranaUpdateElectronicsElectrical LO signal for AS WFS

looks good to me.

The thing I usually look for is how much the downstream system (mixers, etc) can perturb the main oscillator. i.e. we don't want mixer in one chain to reflect back and disturb the EOM chain. But since our demods have amplifiers on the LO side we're pretty immune to that.

  15702   Thu Dec 3 13:55:52 2020 KojiUpdateASCElectrical LO signal for AS WFS

I got a bit confused by your description.

The demod board claims that the nominal power at each LO port is 10dBm. So we want to give at least 16dBm to the (external?) 4way power splitter, but we only have 15dBm. As you said, the actual LO power reaching the FET mixier (PE4140) is the level of ~20dBm. But you said the requirement for the mixer is -7dBm. So are you proposing to reduce the LO level (slightly) than the LIGO recommendation because the minimum for PE4140 is -7dBm?
If that's the message, then I can say "yes". We supply 8~9dBm to the LO ports instead of 10dBm. I suppose the mixers don't care about this level of reduction.

Looking at my original post [40m ELOG 11817], the necessary modification is much larger than you have indicated in your post (as yours is the modification of my modification plan.)
If you do your modification you have to deal with the components rearrangement in the chassis. I think you can still accomplish it as you are going to remove an amplifier and gain the space from it.

The main RF line still has 5dBm Attn. How about to insert another 3dB power splitter there and create a spare 55MHz port for the future use?

Before doing any modification you should check how much the distributed powers are at the ports.
Also your modification will change the relative phase between 11MHz and 55MHz.
Can you characterize how much phase difference you have between them, maybe using the modulation of the main marconi? And you might want to adjust it to keep the previous value (or any new value) after the modification by adding a cable inside?

 

  15704   Thu Dec 3 20:38:46 2020 gautamUpdateASCElectrical LO signal for AS WFS

I removed the Frequency Generation box from the 1X2 rack. For the time being, the PSL shutter is closed, since none of the cavities can be locked without the RF modulation source anyways.

Prior to removal, I did the following:

  1. Measured powers at each port on the front panel 
    • Gigatronix power meter was used, which has a maximum power rating of 20dBm, so for the EOM drive outputs which we operate closer to 25-27 dBm, I used a 20 dBm coupler to make the measurement.
    • Attachment #1 summarizes my findings - there doesn't seem to be anything majorly wrong, except that for the 11 MHz EOM drive channel, the "7" setting on the variable attenuator doesn't seem to work. 
    • We can probably get a replacement from MiniCircuits, but since we operate at 0dBm variable attenuation nominally, maybe we don't need to futz around with this.
  2. Measured the relative phasing between the 11 MHz and 55 MHz signals using an oscilloscope.
    • I measured the relative phase for the EOM drive channels, and also the demod channels.
    • The scope can accept a maximum of 5V RMS signal with 50ohm input impedance. So once again, I couldn't make a direct measurement at the nominal setting for the EOM drive channel. Instead, I used the variable attenuator to set the signal amplitude to ~2V RMS. 
    • I will upload the time-domain plots later. But we now have a record of the relative phasing that we can try and reproduce after making modifications. FWIW, my measured phase difference of 139 degrees is reasonably consistent with Koji's inferred from the modulation spectrum.

One thing I noticed was that we're using very stiff coax cabling (RG405) inside this box? Do we need to stick with this option? Or can we use the more flexible RG316? I guess RG405 is lower loss, so it's better. I can't actually find any measurement of the shielding performance in my quick google searching but I think the claim on the call yesterday was that RG405 with its solder soaked braids offer superior shielding.

Before doing any modification you should check how much the distributed powers are at the ports.
Also your modification will change the relative phase between 11MHz and 55MHz.
Can you characterize how much phase difference you have between them, maybe using the modulation of the main marconi? And you might want to adjust it to keep the previous value (or any new value) after the modification by adding a cable inside?

  15705   Thu Dec 3 21:14:38 2020 KojiUpdateASCElectrical LO signal for AS WFS

Let's use RG405 for better shielding. It is not too stiff. The bending  (just once) does not break the cable.

Are you going to full replacement of the 55MHz system? Or just remove the 7dBm and then implement the proposed modification for the 55MHz line?

  15706   Thu Dec 3 21:44:49 2020 gautamUpdateASCElectrical LO signal for AS WFS

I'm open to either approach. If the full replacement requires a lot of machining, maybe I will stick to just the 55 MHz line. But if only a couple of new holes are required, it might be advantageous to do the revamp while we have the box out? What do you think?

BTW, now that I look more closely at the RF chain, I have several questions:

  1. The 1 dB compression power of the ZHL-2 amplifiers is ~29 dBm, and we are driving it at that level. Is this okay? I thought we always want to be several dBm away from the 1dBm compression point?
  2. Why do we have an attenuator between the Marconi input and the first ZHL-2 amplifier? Can't we just set the Marconi to output 8 or 9 dBm?
  3. The Wenzel frequency multiplier is rated to have 13dBm input and 20 dBm output. We operate it with 12 dBm input and 19 dBm output. Why throw away 1 dBm?

I guess it is feasible to have +17 dBm of 55 MHz signal to plug into the Quad Demod chassis - e.g. drive the 55 MHz input with 20 dBm, pick off 3dBm to the front panel for ASC. Then we can even have several "spare" 55 MHz outputs and still satisfy the 9 dBm input that the ZHL-2 in the 55 MHz chain wants (though again, isn't this dangerously close to the 1dB compression point?). The design doc claims to have done some Optickle modeling, so I guess there isn't really any issue? 

Quote:

Are you going to full replacement of the 55MHz system? Or just remove the 7dBm and then implement the proposed modification for the 55MHz line?

  15707   Fri Dec 4 03:02:40 2020 KojiUpdateASCElectrical LO signal for AS WFS

1. That's true. But we are already in that regime with the Var attn at 0dB, aren't we? We can reduce the input to the amp by 1-2dBm sacrificing the EOM out by that amount (we can compensate this for the demo out by removing the 1dB attn).

2. Not 100% sure but one possible explanation is that we wanted to keep the Marconi output large (or as large as possible) to keep the SNR between the signal and the noise of the driver in Marconi. The attenuator is less noisy compared to the driver noise.

3. My guess is that theoretically we were supposed to have 13dBm input and 20dBm output in design. However, the actual input was as such.  We can restore it to the 13dBm input.

  3207   Tue Jul 13 14:59:04 2010 GopalUpdateOptic StacksEigenfrequency Analysis of Single Stack Complete

Via reconfiguration of Viton parameters (previously posted), I managed to debug the COMSOL run time errors and null pointer exceptions. Listed are the resultant eigenfrequencies obtained through structural analysis testing. For all tests, the bottom of the Viton springs are constrained from motion, and all other parts are free to oscillate. Notice that color variations signify displacement from the equilibrium position. Also note that different initial conditions produce different eigenmodes:

No initial displacement:

Eigenmode_Stack_4.png


0.01 m x-displacement:

Eigenmode_Stack_4_xdisp.png


0.01 m y-displacement:

Eigenmode_Stack_4_ydisp.png


 0.01 m z-displacement:

 Eigenmode_Stack_4_zdisp.png


Clearly, the plate has its first harmonic between 210-215 Hz, which is much greater than seismic noises (which never exceed the 10-Hz range). This suggests a highly attenuating transfer function. Since the remaining three plates have been designed to resonate similarly, it is likely that the entire stack system will also function very well.

Next steps:

1) Extend the eigenfrequency analysis to obtain a transfer function for the single-plate system

2) Expand the CAD model to include all four stack layers, and perhaps a base

 

  3199   Mon Jul 12 18:37:10 2010 GopalUpdateOptic StacksEigenfrequency Analysis of Simple Objects

Eigenfrequency analysis has been successfully completed in COMSOL on both a tutorial camshaft, as well as a homemade metal bar.

Upon increasing in complexity to the busbar, I once again began getting into run time errors and increased lag. It seems that this is due to undefined eigenvalues when solving the linear matrices. I tried many boundary values as well as initial conditions in case this was the issue, but it was not. There seems to be some sort of an internal inconsistency. This is no longer a matter of tweaking parameters.

Next steps:

1) Try using the same techniques on the actual mirror stacks to see if we get lucky.

2) In the likely case that this doesn't happen, continue the debugging process. If necessary, a good deal of time may need to be spent learning the COMSOL lower-level jargon.

  3246   Mon Jul 19 16:11:17 2010 GopalUpdateOptic StacksEigenfrequency Analysis of Full Stack

Expanding on the single-layer model, I added the second, third, and fourth layers to the stack in COMSOL. Eigenfrequency analysis run times increased exponentially as the model multiplied in complexity. The following images document the some of the important eigenfrequencies:


First Eigenmode: y-translational, 3.34 Hz:

Eigenfrequency_1_4Stacks.png


Second Eigenmode: x-translational, 3.39 Hz:

Eigenfrequency_2_4Stacks.png


Third Eigenmode: z-rotational, 3.88 Hz:

 Eigenfrequency_3_4Stacks.png


Sixth Eigenmode: z-translational, 8.55 Hz:

Eigenfrequency_6_4Stacks.png


As expected, the eigenfrequencies are generally lower, but still in the same range, as the single-layer model, because of greater mass but constant weight-per-spring distribution.

Next Steps:

1) Extend a single stack to the full stack system, which consists of three stacks like this. Perform similar eigenmode analysis.

2) Analyze the mirror suspension system and incorporate a similar pendulum on the top plate.

3) Make transfer function measurements between seismic and mirror motions.

  10630   Wed Oct 22 02:35:45 2014 JenneUpdateLSCEfforts at hopping PRMI to REFL165

[EricQ, Jenne]

The first half of our evening was spent working on CARM and DARM in PRFPMI, and then we moved on to the PRMI part.

I moved the DARM ALSdiff -> TransDiff transition to be after the CARM ALScomm -> SqrtInvTrans transition in the carm_cm_up script.  After I did that, I succeeded every time (at least  10?  We did it many times) to get both CARM and DARM off of the ALS signals. 

We tried for a little while looking at transitioning to REFL11 normalized by the sum of the transmissions, but we kept losing lock.  We also several times lost lock at arm powers of a few, when we thought we weren't touching the IFO for any transitions.  Looking at the lockloss time series did not show any obvious oscillations in any of the _IN1 or _OUT channels for the length degrees of freedom, so we don't know why we lost lock, but it doesn't seem to be loop oscillations caused by changing optical gain.  Also, one time, I tried engaging Rana's "Lead 350" filter in FM7 of the CARM filter bank when we were on sqrtInvTrans for CARM, and the arm powers were around a few, but that caused the transmission signals to start to oscillate, and after one or two seconds we lost lock.  We haven't tried the phase lead filter again, nor have we tried the Boost2 that is in FM8. 

We increased the REFL11 analog gain from 0dB to 12dB, and then reset the dark offsets, but still weren't able to move CARM to normalized REFL11. Also, I changed the POP22 demod phase from 159 degrees to 139 degrees. This seems to be where the signal is maximized in the I-phase, while the arms are held off resonance, and also partway up the resonance peak. 

We then decided that we should go back to the PRMI situation before trying to reduce the CARM offset further.  We can robustly and quickly lock the PRMI on REFL33 while the arms are held off resonance with ALS.  So, we have been trying to acquire on  REFL33 I&Q, and then look at switching to REFL 165 I&Q.  It seems pretty easy to get PRCL over to REFL165 I (while leaving MICH on REFL33 I).  For REFL33, both matrix elements are +1.  For PRCL on REFL165, the matrix element is -0.08.  We have not successfully gotten MICH over to REFL 165 ever this evening. 

We went back and set the REFL165 I&Q offsets so that the outputs after the demod phase were both fluctuating around 0.  I don't know if they were around +/-100 because our dark offsets were bad or what, but we thought this would help.  We were still able to get PRCL transitioned no problem, but even after remeasuring the MICH REFL33 vs. REFL165 relative gains, we still can't transition MICH.  It seems like it's failing when the REFL33Q matrix element finally gets zeroed out, so we're not really getting enough signal in REFL165Q, or something like that, and throughout the rest of the transition we were depending entirely on REFL33Q. 

So. Plan:

  • Get PRMI on REFL165 while arms are held off resonance. 
    • May require PRCL-MICH FF decoupling, by combining error signals?
    • May require looking back at simulations to see what we expect the relative gains and signs to be.
  • Look at CARM loop stability in simulation for REFLDC, REFL11, and normalized REFL11.  Is there a stable loop path from about 100pm down to 0pm on normalized REFL11?
  5906   Wed Nov 16 10:08:17 2011 SureshUpdateIOOEffect of turning on the MC2_TRANS_PIT and YAW loops in ASC

I turned on the two remaining loops in the ASC system to see if we can lock.   I put in some ones into the WFS_OUTPUT matrix

WFS_OUTMATRIX.png

and locked the MC2_TRANS_PIT and MC2_TRANS_YAW loops.

The effect of doing so is visible in the error signals.  The black loops are with all ASC loops off, Blue traces are with the WFS1 and 2 loops locked and Red traces are with all loops locked.  I took the red traces to a lower frequency to see if the suppression of the error signals at low frequencies is disturbed by the switching on of the MC2_TRANS loops.  They seem to be working fine without adding any perturbation above the UGF.

WFS_servo_err_20111115.png

I measured the  Transfer Function coefs (at 10Hz using the WFS Lockins)  with MC2_TRANS loops locked in this rudimentary fashion

  WFS1P WFS2P MC2TP WFS1Y WFS2Y MC2TY
MC1P -23.8541 15.2501 -24.3470 -3.3166 -2.0473 -0.1202
MC2P 29.7402 54.7689 29.5102  -0.2922 -17.4226 0.0310
MC3P 34.3612 10.7279 33.9650 6.6582 -4.0892 0.2333
MC1Y 0.9510 -6.3929 0.8722 -98.2414 -82.9129 -4.2802
MC2Y 12.0673 6.1708 11.9502 237.1172 20.7970 14.6480
MC3Y -0.8498 2.8712 -1.4195 -20.6031 111.2531 -1.5234

 

The green and blue bits are the only relevant parts since we ignore the off diagonal parts.  And most of these off diagonal coefs are indeed quite small (<5% of the max).  I have marked the not-so-small ones in yellow.

I then calculated the output matrix elements in two different ways.

a) Using a null vector in the place of MC_DoF --> MC2_TRANS transfer coefs.  The output matrix we get is

 

  WFS1P WFS2P Null Vector
MC1P -1.0000 0.8271  -0.8880
MC2P 0.0962 1.0000  0.4431
MC3P 0.9306 -0.2913  -1.0000

 

  WFS1Y WFS2Y Null Vector
MC1Y -0.2340 -0.5840 1.0000
MC2Y 1.000o -0.1551  0.4714
MC3Y -0.3613 1.0000 0.6571

 

b) Without using the null vector.  i.e. using the MC_DoF --> MC2_TRANS transfer coefs and inverting the full matrix.  The output matrix we get is

 

   WFS1P WFS2P  MC2TP
 MC1P  0.1471  -0.8880  0.8655
 MC2P  1.0000  0.4431  -0.4369
 MC3P  -0.7634  -1.0000  1.0000

 

  WFS1Y WFS2Y MC2TP
MC1Y 0.1401 1.0000 -1.0000
MC2Y 0.1449 0.4714 -0.3627
MC3Y 1.0000 0.6571 -0.6775

 

I plan to try out these two output matrices and measure the OL TFs of the MC2_TRANS and see if we can include these into ASC in a useful fashion.

  12316   Wed Jul 20 14:03:01 2016 ericqUpdateSUSEffect of thicker ruby standoffs

The new ETMX ruby guide rods are slightly thicker than the old aluminum ones; specifically 1.27mm vs 1.0mm.

Since we did not change the guide rod location in response to this fact, the vertical position of the suspension point changes, which in turn changes the dynamics of the suspension. Specifically, since the standoff is placed below the guide rod, the suspension point is lowered, which makes the pitch mode softer. I crunched a few numbers and have determined that this effect should not be a problem.

Given the wiki's value of the ETMX pitch resonance frequency of 0.829 Hz, I predict a the new pitch resonance frequency of 0.800 Hz.

(wiki link: https://wiki-40m.ligo.caltech.edu/Suspensions/Mechanical_Resonances)


A useful document about the dynamics of our suspension can be found at T000134

From this document, one will find that the effect of changing the suspension point height over the optic center of mass,`b`, on the pitch resonance frequency (while keeping all other dimensions equal) to be:

\frac{\omega'_\theta}{\omega_\theta} \approx \sqrt{\frac{b'}{b}}

The top of the standoff is fixed by the guide rod, so let's say that b' is given by the position of the center of the Ruby standoff. This is then smaller than the previous b by the differences in the radii of the standoffs:

b' = b - \frac{\oslash_{\textrm{ruby}}-\oslash_{\textrm{Al}}}{2}

The nominal value of b is 0.985mm. Thus, the pitch resonance frequency is changed by factor of 0.965, i.e. 3.5% smaller. Then, taking the wiki value of 0.829 Hz results in 0.800Hz, a 30mHz decrease.

  1512   Thu Apr 23 18:09:11 2009 YoichiUpdateEnvironmentEffect of cryopump
The attached is the trend plot of the MC1 accelerometer for 3 days.
It is evident that the seismic level increased by a factor of two on Wednesday morning (when Steve started the cryopump).
  9537   Wed Jan 8 13:01:48 2014 GabrieleSummaryLSCEffect of PRC length mismatch on error signals

I ran a simulation of a double cavity with a PRC length mismatched w.r.t. the modulation frequency. I summarized the results in the attached PDF. I think it would be important to have a cross check of the results.

In brief:

A mismatch between PRC length and modulation frequency do have an effect on error signals

Multiple zeros appear in REFL_3f/PRCL that can be removed by careful tuning of the demodulation phase (however, the shape of the signal makes difficult to understand which phase is good…)

No visible effect on REFL_1f/CARM

But a large PRCL signal appears in REFL_1f_I, which is used to control CARM. This is not good.

A mismatch of the order of 0.5 cm has a small effect.

 

 

 

 

 

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