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ID Date Author Type Category Subject
  4272   Fri Feb 11 00:20:58 2011 SureshUpdateElectronicsREFL11: Photodiode requires replacement

 

This is with reference to Kevin and Jenne's elogs  # 3890, 4034 and 4048

While the electronics are working okay, there is no DC signal from the photodiode. 

Since the solderings and tracks on the PCB were fine I took a close look at the exposed front face of the photodiode.

REFL11_10Feb2011.jpg

As we can see, one of the thin wires on the top surface of the photodiode is broken.  We can see some wipe marks closer to the lower left edge..

Something seems to have brushed across the exposed face of the photodiode and dislodged the wire.

 

Question:

The new photodiode still has its protective can intact.   Do we need to remove the can and expose the photodiode before istallation?

 

  4271   Thu Feb 10 14:52:36 2011 AidanHowToComputersAdding filenames in MATLAB plots

The following code is incredibly useful when creating  MATLAB plots as it adds the filename of the script to the plot itself. I think it should be used for all MATLAB plots that go on the elog.

For example, I have no idea where the data/script is that was used to generate these plots.

 

orient landscape

xposn = 0.0;

yposn = -0.13; % you sometimes have to tweak this value depending on the page size and the number of subplots

text(xposn,yposn,[filename('fullpath'), '.m'], ...

     'Units', 'normalized', ...

     'Interpreter', 'none', ...

     'FontSize', 6)

print('-dpdf', [filename('fullpath'), '.pdf'])

  4270   Thu Feb 10 14:07:18 2011 josephbUpdateCDSUpdating dolphin drivers to eliminate timeouts when one dolphin card is shutdown

[Joe,Alex]

Alex came over and we installed the new Dolphin drivers so that the front ends using the Dolphin PCIe RFM network don't pause for a long time when one of the other nodes in the network go down.  Generally this pause would cause the code to time out and quit.  Now you can take c1lsc or c1sus down without having the other have problems.

We did note on reboot however, that the Dolphin_wait script sometimes (not always) seems to hang.  Since this is run at boot up, to ensure the dolphin card has had enough to allocate memory space for data to be written/read from by the IOP process, it means nothing else in the startup script gets run if it does happen.  In this case, running "pkill dolphin_wait" may be necessary.

Note that you may still have problems if you hit the power button to force a shutdown (i.e. holding it for 4 seconds for immediate power off), but as long as you do a "reboot" or "shutdown -r now" type command, it should come down gracefully. 

 

What was done:

Alex grabbed the code from his server, and put it /home/controls/DIS/ on fb.

He ran the following commands in that directory to build the code.

./configure  '--with-adapter=DX' '--prefix=/opt/DIS'

make

sudo make install

He proceeded to modify the /diskless/root/etc/rc.local to have the line:

insmod /lib/modules/2.6.34.1/kernel/drivers/dis/dis_kosf.ko

In that same file he commented out

cd /root

and

exec /bin/bash/

He then modified the run levels in /diskless/root/etc/inittab. Level 0, level 3, and level 6 were changed:

l0:0:wait/etc/rc.halt

l3:3:wait:etc/rc.level3

l6:6:wait:/etc/rc.reboot

Then he created the scripts he was refering to:

rc.level3 is just:

exec /bin/bash

rc.halt is:

/opt/DIS/sbin/dxtool prepare-shutdown 0
sleep 3
halt -p

rc.reboot is:

reboot

 

Basically rc.halt calls a special code which prepares the Dolphin RFM card to shutdown nicely.  This is why just hitting the power button for 4 seconds will cause problems for the rest of the dolphin network.

We then checked out of svn the latest dolphin.c in  /opt/rtcds/caltech/c1/core/advLigoRTS/src/fe

 

The Dolphin RFM cards have a new numbering scheme.  4 is reserved for special  broadcasts to everyone, so the Dolphin node IDs now start at 8.  So we needed to change the c1lsc and c1sus Dolphin node IDs.

To change them we went to /etc/dis/dishosts.conf on the fb machine, and changed the following lines:

 

HOSTNAME: c1sus
ADAPTER:  c1sus_a0 4 0 4
HOSTNAME: c1lsc
ADAPTER:  c1lsc_a0 8 0 4

to

HOSTNAME: c1sus
ADAPTER:  c1sus_a0 8 0 4
HOSTNAME: c1lsc
ADAPTER:  c1lsc_a0 12 0 4

The FE models for the c1lsc and c1sus machines were recompiled and then the computers were rebooted.  After having them come back up, we tested that there was no time out by shutting down c1lsc and watching c1sus. We then reveresed and shutdown c1sus while watching c1lsc.  No problems occured.  Currently they are up and communicating fine.

 

  4269   Thu Feb 10 11:16:31 2011 steveUpdatePEMsouth arm AC turned on

The air condition was off for the south arm. I  turned it on.

  4268   Thu Feb 10 05:06:35 2011 kiwamuUpdateGreen Lockingbeat noise : a little bit better, and 1Hz peak from amplitude noise coupling

 I repeated the same measurement as that Koji did before (see here) with the mixer-based frequency discriminator.

The frequency fluctuation of the beat note is now 50 kHz in rms integrated down to 0.1 Hz, which is a bit better than before.

However there still is the same undesired structure in the spectrum below 10 Hz.

 

 Screen_shot_2011-02-10_at_4.01.43.png

Fig.1 power spectra of the green beat note fluctuation in terms of frequency fluctuation.

   Red curves were taken when the IR was locked to the MC, and the green was locked to the X arm.

Blue curves were taken when both the IR and the green were locked to the X arm.

Black curve was also the one taken when the IR and the green were locked to the X arm, but showing the lower noise level.

I have no idea what exactly was going on when I took the black curve, but this noise level sometimes showed up.

The discrepancy may come from a kind of calibration error although I kept using the same calibration factor to convert the data from count to frequency.

Need more investigations.

 


 Additionally Koji and I took the coherence between the beat fluctuation and the transmitted lights of both the IR and the green.

It showed a strong coherence at 1 Hz, which is one of the dominant noise of the beat note.

This probably indicates that the 1 Hz peak is produced by a coupling from amplitude fluctuation.

Screen_shot_2011-02-10_at_4.52.13.png

 For monitoring the green transmitted light, I used the Jenne's PD (see here)

  4267   Thu Feb 10 00:23:25 2011 JenneUpdateGreen LockingGreen TRX DC PD installed on PSL

Using a stray beam that is generated as the transmitted green beam from the Xarm goes through the viewport to the PSL table, I installed a fast lens (because I was constrained for space) and a Thorlabs PDA36 photodiode on the PSL table.

The BNC cable runs along the edge of the PSL table, up the corner hole with the huge bundle of cables, and over to IOO_ADC_0. It's channel 3 on the simulink model, which means that it is plugged into connector #4.

With the green resonating TEM00, I have ~1.4V output from the photodiode, as seen on a voltmeter. This corresponds to ~1500 counts on the MEDM screen.

 

Note to self:  Switch to a ~1cm diode with a boatload of gain (either from the 40m or Bridge), and use transmission through a steering mirror of the actual beat note path, not the jittery viewport pickoff.  Want RIN noise level to be about 1e-5, only care about below ~100Hz so don't need broadband.

  4266   Wed Feb 9 23:48:12 2011 SureshConfigurationCamerasVideo Cable work: New Labels

[Larisa, Aidan,Steve,Suresh]

   Today was the first session for implementing the new video cabling plan laid out in the document " CCD_Cable_Upgrade_Plan_Jan11_2011.pdf"  by Joon Ho attached to his elog entry 4139.  We started to check and label all the existing cables according to the new naming scheme. 

So far we have labeled the following cables. Each has been checked by connecting it to a monitor near the Video Mux and a camera at the other end.

C1:IO VIDEO 8ETMYF

C1:IO-VIDEO 6 ITMYF

C1:IO-VIDEO 21 SRMF

C1:IO-VIDEO 25 OMCT

C1:IO-VIDEO 19 REFL

C1:IO-VIDEO 22 AS

C1:IO-VIDEO 18 IMCR

C1:IO-VIDEO 14 PMCT

C1:IO-VIDEO 12 RCT

C1:IO-VIDEO 9 ETMXF

C1:IO-VIDEO 1 MC2T

 

Next we need to continue and finish the labeling of existing cables.  We then choose a specific set of cables which need to be laid together and proceed to lay them after attaching suitable lables to them.

 

 

  4265   Wed Feb 9 15:26:22 2011 josephbUpdateCDSUpdated c1scx with lockin, c1gcv for green transmission pd

Updated the c1scx model to have two Lockin demodulators (C1:SUS-ETMX_LOCKIN1 and C1:SUS-ETMX_LOCKIN2).  There is a matrix C1:SUS-ETMX_INMUX which directs signals to the inputs of LOCKIN1 and LOCKIN2.  Currently only the GREEN_TRX signal is the only signal going in to this matrix, the other 3 are grounds.  The actual clocks themselves had to be at the top level (they don't work inside blocks) and thus named C1:SCX-ETMX_LOCKIN1_OSC and C1:SCX-ETMX_LOCKIN2_OSC.

 

There is a signal (IPC name is C1:GCV-SCX_GREEN_TRX) going from the c1gcv model to the c1scx model, which will contain the output from Jenne's green transmission PD which will eventually be placed. I've placed a filter bank on it in the c1gcv model as a monitor point, and it corresponds to C1:GCV-GREEN_TRX.

 

The suspension control screens were modified to have a screen for the Matrix feeding signals into the two lockin demodulators.  The green medm screen was also modified to have readbacks for the GREEN_TRX and GREEN_TRY channels.

 

So on the board, the top channel (labeled 1, corresponds to code ADC_0_0) is MCL.

Channel 2 (ADC_0_1) is assigned to frequency divided green signal.

Channel 3 (ADC_0_2) is assigned to the beat PD's DC output.

Channel 4 (ADC_0_3) is assigned to the green power transmission for the x-arm.

Channel 5 (ADC_0_4) is assigned to the green power transmission for the y-arm.

  4264   Wed Feb 9 10:25:46 2011 steveUpdateSAFETYAP table

I blocked the  AP table's south west 10" ID port since it is obsolete with the new layout.

Reminder: items on the enclosure self can fall down in an earthquake. I moved oscilloscope and heavy calorimeter head from the edge of the cliff.

Attachment 1: P1070395.JPG
P1070395.JPG
  4263   Tue Feb 8 16:44:43 2011 JenneUpdateComputersLIGO Grid Cluster client upgraded on Rossa

I did a yum-install of the latest ldg-client (to get onto the LIGO Clusters) on Rossa. 

I followed the instructions on the wiki page, and everything seemed to work nicely.

I think the new ldg client installs somewhere on the local computer, so if anyone wants cluster access on any other computer, they should follow the same directions.

  4262   Tue Feb 8 16:04:58 2011 josephbUpdateCDSHard coded decimation filters need to be fixed

[Joe, Rana]

Filter definitions for the decimation filters to epics readback channels (like _OUT16) can be found in the fm10Gen.c code (in /opt/rtcds/caltech/c1/core/advLigoRTS/src/include/drv).

At the moment, the code is broken for systems running at 32k, 64k as they look to be defaulting to the 16k filter.  I'd like to also figure out the notation and plot the actual filter used for the 16k.

Rana has suggested a 2nd order, 2db ripple low pass Cheby1 filter at 1 Hz.

 

  51 #if defined(SERVO16K) || defined(SERVOMIXED) || defined(SERVO32K) || defined(SERVO64K) || defined(SERVO128K) || defined(SERVO256K)
  52 static double sixteenKAvgCoeff[9] = {1.9084759e-12,
  53                                      -1.99708675982420, 0.99709029700517, 2.00000005830747, 1.00000000739582,
  54                                      -1.99878510620232, 0.99879373895648, 1.99999994169253, 0.99999999260419};
  55 #endif
  56
  57 #if defined(SERVO2K) || defined(SERVOMIXED) || defined(SERVO4K)
  58 static double twoKAvgCoeff[9] = {7.705446e-9,
  59                                  -1.97673337437048, 0.97695747524900,  2.00000006227141,  1.00000000659235,
  60                                  -1.98984125831661,  0.99039139954634,  1.99999993772859,  0.99999999340765};
  61 #endif
  62
  63 #ifdef SERVO16K
  64 #define avgCoeff sixteenKAvgCoeff
  65 #elif defined(SERVO32K) || defined(SERVO64K) || defined(SERVO128K) || defined(SERVO256K)
  66 #define avgCoeff sixteenKAvgCoeff
  67 #elif defined(SERVO2K)
  68 #define avgCoeff twoKAvgCoeff
  69 #elif defined(SERVO4K)
  70 #define avgCoeff twoKAvgCoeff
  71 #elif defined(SERVOMIXED)
  72 #define filterModule(a,b,c,d) filterModuleRate(a,b,c,d,16384)
  73 #elif defined(SERVO5HZ)
  74 #else
  75 #error need to define 2k or 16k or mixed
  76 #endif

  4261   Tue Feb 8 15:22:13 2011 kiwamuUpdateGreen Lockingnew electronics rack at X end

 Yesterday I moved the whole green electronics stuff, which had been sitting on the floor at the X end,  into a new electronics rack.

The rack now is placed under the cable rail close to the ETMX chamber.

DSC_2861_ss.png

  4260   Tue Feb 8 13:26:11 2011 AidanSummaryGreen LockingTemperature dependence of phase change of green on reflection

 I did a quick back of the envelope calculation of the expected green phase change on reflection from the aLIGO ITM.

The phase change per nm, K1 = delta phi/delta Lambda, around 532nm is ~1.5 degrees/nm (from the LMA data) [this number is approximately 100x smaller at 1064nm]

I assumed that very small changes in the thickness of the coating appear equivalent to shifting the spectra for reflection/transmission/phase-change-on-reflection up or down by delta lambda, where

delta Lambda/Lambda = delta h/h

where h is the total thickness of the coating and delta h is the change in the thickness of the coating.

Assume that delta h/h = alpha deltaT, where alpha is the coefficient of thermal expansion and delta T is the change in temperature. (approximately 1K)

Then delta phi = K1* Lambda * alpha * delta T = 1.5 degrees/nm * 532nm * 10^-5 K^-1 * 1.0 K =  8 * 10^-3 degrees.

Assume that 360 degree phase change corresponds to one FSR.

Therefore, the frequency shift due to temperature change in the coating = 8*10^-3/360 * FSR = 2.2 *10^-5 * FSR.

Therefore, the expected frequency shift per degree temperature change = 2.2*10^-5 * FSR [Hz/K]

  4259   Tue Feb 8 10:23:02 2011 AidanSummaryGreen LockingDigital Frequency Discriminator - reference

 

Here's the reference for the self-reference frequency detection idea. See Figure 2.

http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/mixers.pdf

  4258   Mon Feb 7 21:23:11 2011 ranaConfigurationPSLPSL FSS Temperature Sensor Interface box removed

I noticed that the RMTEMP channel was spiking myteriously when Kiwamu opened the PSL door. We found out that the LEMO connectors would intermittently short to the case and cause ~1 deg steps in the temeprature.

We have removed the case and examined it. Not only were the connections to the box intermittent, there was a cold solder joint inside on an unsecured flying add-on opamp. The whole thing is a giant hack.

PK was the last person to work on this box, but I'm sure that he wouldn't have left it in this state. Must be gremlins.

P2070555-1.JPG

The LEMO connectors on the front are the ones touching. The LT1021 is the badly soldered part.

  4257   Mon Feb 7 19:21:32 2011 Beard PapaMetaphysicsPhotosThe Adventures of Dr Stochino and Beard Papa

  4256   Mon Feb 7 10:37:28 2011 josephbUpdateComputersTemporarily removed cronjob for rsync.backup

The backup appears to have finished on nodus, and I've put the rsync job back in the crontab.

Quote:

I removed the rsync backup from nodus' crontab temporarily so as to not have multiple backup jobs running.  The job I started from yesterday was still running.  Hopefully the backup will finish by Monday.

The line I removed was:

0 5 * * * /opt/rtcds/caltech/c1/scripts/backup/rsync.backup

  4255   Sun Feb 6 02:29:28 2011 ranaUpdateElectronicsAnalog MFD: longer cable

I swapped over to a 3x longer cable (old 65 ft. Pasternak cable from ancient 40m days). The old one was 6m, the new one is 18.2 m. It was already coiled up so I put it into a tupperware box to shield it somewhat from the HVAC wind.

The noise went down nearly proportional to the length (after I recalibrated the DAQ channel for the ~3x higher phase->voltage gain). With this length, the peak-peak mixer range is 5.5 MHz, so still enough to go an FSR here.

mfd18.png

I give credit to the low frequency improvement entirely to Tupperware for their excellent containers. The current noise limit is most likely the SR560.

  4254   Sat Feb 5 23:03:04 2011 rana, kojiSummaryElectronicsAnalog Frequency Discriminator: splitter + mixer + long cable

This diagram shows the setup of the analog Mixer-Frequency Discriminator (MFD).

The idea is similar to the one of the Schnupp Asymmetry for our Michelson interferometers. The signal from the PD (or any signal source for which you want to know the frequency) is split into two legs; one leg is much longer than the other. The two legs are recombined at a mixer/demodulator. The demodulator output varies sinusoidally with the phase difference of two legs, the same as when we try to measure the phase noise of an oscillator, for example. This is the same concept as the digital frequency discriminator that Aidan and Joe put into the GFD FE system recently.

With a ~1m cable length asymmetry, we get 180 deg of phase shift for a ~100 MHz signal (recall that the speed of light in most of our cables is ~2 x 10^8 m/s). The mixer gives a linear output at 50 MHz (and 150 MHz, 250 MHz, etc.).

This single mixer based setup is fine for most everything we do. In order to get even more resolution, one can just use 2 mixers by splitting the signal with a 4-way instead of 2-way mixer. One setup can have a 0.5-1 m asymmetry to have a large range. The other can have a ~10-30m asymmetry to get a comb of linear readouts.

Typically, we will have some kind of weak signal at the photodiode and will use a 20 or 40 dB gain RF amp to get the signal into the mixer. In this case, the mixer output noise will be at the level of tens of nV/rHz. Any usual low noise audio amplifier (SR560 variety) will be enough to read out the signal.

Why the 50 Ohm terminator? If you look at the specs of the BLP-1.9 filter from Mini-Circuits (its the same for almost all of their LP filters) you see that there's ~90 dB of attenuation above ~30 MHz (where our signals 2*f product will show up). If we use an RF input signal of ~0 dBm, this means that we get a high frequency product of -95 dBm (~10 uVrms) which is OK. But the return loss is 0 dB above 5 MHz - this means that all of the high frequency content is reflected back into the mixer! The 50 Ohm terminator is there to absorb the RF signals coming out of the mixer so as to prevent them from going back into the mixer and mixing with the RF/LO signals. The 50 Ohm terminator does attenuate the DC/audio frequency signals we get out of the mixer by a factor of two, but that's OK since we are not limited by the mixer's thermal noise.


Noise Measurement:

To checkout the noise, we used a 6m RG-58 cable in one leg. We used the DS345 signal generator for the source. We adjusted the frequency to (~21 MHz) give a ~zero mean signal at the demod output. The 6m cable makes the demod output's peak-peak swing correspond to ~16 MHz. We then used an SR560, DC coupled, G=1000, low-noise, 2pole low pass at 1 kHz, to get the signal into the ADC.

 fsm.png

The attached plot shows the noise. We have caibrated the digital gain in the channel to make the output into units of Hz. The high frequency noise floor is ~0.3 Hz/rHz and the 1/f knee is at 10 Hz. This setup is already good enough for all of the green locking work at the 40m. In order to make this useful for the reference cavity work or the gyro, we will have to use a longer cable and a lower noise audio amplifier.

As can be seen from the plot, the ADC noise is below the measured noise. The noise of the SR560 with the input terminated is shown in grey - the measured noise of the MFD is very close to this. In order to improve the performance, the next step should be to use a longer cable. There's clearly going to be some trade-off between the temperature dependent effects which come with long cables (dphi/dT gets bigger) and trying to use a high gain ~1 nV/rHz amplfier at the mixer output.


Temperature Drift of the long cable:

Untitled.png

This 24-hour minute-trend shows the frequency wander as well as the room temperature. This is not proof of a temperature dependence, but if it is then we get ~3 kHz/deg for the sensitivity. If this is actually the cable and not the amplifier, then we'll have to hunt for a lower tempco cable and put it in a box to isolate it.

Attachment 1: mixer.pdf
mixer.pdf
  4253   Fri Feb 4 23:39:56 2011 rana, kojiUpdateLSCmixer based FD set up for noise test

We set up the mixer based FD to check out its noise performance.

It is being acquired as C1:GCV-XARM_FINE_OUT_DAQ.

We have calibrated it by driving the frequency of the RF signal generator and putting the value into the GAIN field. We got 100 kHz / 5450 counts; the _OUT_DAQ channel is now being recorded in units of Hz. The cable length has been adjusted so that the full mixer output can swing 16 MHz peak-peak before turning over.

Also, we did a lot of cable cleanup around the IO rack. Kiwamu and Suresh's setups were somewhat dismantled. The whole area was too messy and too hacky to be allowed to survive. Our "temporary" setups have a way of becoming permanent holding places for barrels, adapters, duct tape, etc.

  4252   Fri Feb 4 18:58:19 2011 ranaUpdateComputersTemporarily removed cronjob for rsync.backup

Quote:

I removed the rsync backup from nodus' crontab temporarily so as to not have multiple backup jobs running.  The job I started from yesterday was still running.  Hopefully the backup will finish by Monday.

The line I removed was:

0 5 * * * /opt/rtcds/caltech/c1/scripts/backup/rsync.backup

Actually, this is not true. Joe actually killed the currently running backup and set it to start tomorrow morning at 6AM. Its taking forever since its not an incremental backup but a new one due to the change in the setup.

  4251   Fri Feb 4 15:03:20 2011 josephbUpdateComputersModified cshrc.40m

Removed some lines from the PATH environment variable since they point to old codes which no longer work with the new frame builder and setup.

The change was:

#setenv PATH $LINUXPATH/bin:$GDSPATH/bin:$ROOTSYS/bin:$TDSPATH/bin:${SCRIPTPATH}:$PATH
setenv PATH $TDSPATH/bin:${SCRIPTPATH}:$PATH

  4250   Fri Feb 4 13:45:25 2011 josephbUpdateComputersTemporarily removed cronjob for rsync.backup
<p>I removed the rsync backup from nodus' crontab temporarily so as to not have multiple backup jobs running.&nbsp; The job I started from yesterday was still running.&nbsp; Hopefully the backup will finish by Monday.</p>
<p>The line I removed was:</p>
<p>0 5 * * * /opt/rtcds/caltech/c1/scripts/backup/rsync.backup</p>
<table align="left" width="786" cellspacing="1" cellpadding="1" border="2">
    <tbody>
        <tr>
            <td><span style="font-size: larger;">MC damp</span></td>
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            <td><span style="font-size: larger;">diaggui</span></td>
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            <td><span style="font-size: larger;">Frame builder</span></td>
            <td><span style="font-size: larger;">TDS</span></td>
            <td><span style="font-size: larger;">Cabling</span></td>
        </tr>
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</table>
  4249   Fri Feb 4 13:31:16 2011 josephbUpdateCDSFE start scripts moved to scripts/FE/ from scripts/

All start and kill scripts for the front end models have been moved into the FE directory under scripts:  /opt/rtcds/caltech/c1/scripts/FE/.  I modified the Makefile in /opt/rtcds/caltech/c1/core/advLigoRTS/ to update and place new scripts in that directory. 

This was done by using

sed -i 's[scripts/start$${system}[scripts/FE/start$${system}[g' Makefile

sed -i 's[scripts/kill$${system}[scripts/FE/kill$${system}[g' Makefile

  4248   Fri Feb 4 11:10:27 2011 SureshUpdateGreen LockingVCO PLL Frequency noise

This measurement pertains to the BL2002 VCO PLL unit.

 

Our goal is to measure the frequency fluctuations introduced by the VCO. 

 

First the VCO calibration was checked.  It is -1.75 MHz per volt.  The calibration data is below:

VCO_calibration.png

 

 

 

Next we measured the Transfer function between points A and B  in the diagram below using the Stanford Research System's SR785.  This measurement was done with loop opened just after the 1.9MHz LPF and with the loop closed.

VCO_PLL_Servo.png

 

The TF[open] / TF [closed ] gave the total gain in the loop.  As shown below:

VCO_Transfer_Functions.png

Green curve is the Transfer Function with the loop open and the red with that of the loop closed.

Gain Shown below is the quotient TF[open]/TF[closed]

 

VCO_Gain.png

 

 c) As can be seen from the graph above the loop gain is >>1 over 0.1 to 300Hz.  And hence the frequency noise of the VCO is just the product of the voltage noise and the VCO calibration factor over this range,

d) the noise power at the point B was measured and multiplied by the VCO calibration  factor to yield dF(rms)/rtHz:

VCO_PLL_Freq_Noise.png

The green line with dots are the data

The blue line is the rms frequency fluctuation.

This corresponds to a arm length fluctuation of about 20pm.

 

 

  4247   Thu Feb 3 17:25:03 2011 josephbUpdateComputersrsync script was not really backing up /cvs/cds

So today, after an "rm" error while working with the autoburt.pl script and burt restores in general, I asked Dan Kozak how to actually look at the backup data.  He said there's no way to actually look at it at the moment.  You can reverse the rsync command or ask him to grab the data/file if you know what you want.  However, in the course of this, we realized there was no /cvs/cds data backup.

Turns out, the rsync command line in the script had a "-n" option.  This means do a dry run.  Everything *but* the actual final copying.

I have removed the -n from the script and started it on nodus, so we're backing up as of 5:22pm today.

I'm thinking we should have a better way of viewing the backup data, so I may ask Dan and Stewart about a better setup where we can login and actually look at the backed up files.

In addition, tomorrow I'm planning to add cron jobs which will put changes to files in the /chans and /scripts directories into the SVN on a daily basis, since the backup procedure doesn't really provide a history for those, just a 1 day back backup.

  4246   Thu Feb 3 16:45:28 2011 josephbUpdateCDSGeneral CDS updates

Updated the FILTER.adl file to have the yellow button moved up, and replaced the symbol in the upper right with a white A with black background.  I made a backup of the filter file called FILTER_BAK.adl.  These are located in /opt/rtcds/caltech/c1/core/advLigoRTS/src/epics/util.

I also modified the Makefile in /opt/rtcds/caltech/c1/core/advLigoRTS/ to make the startc1SYS scripts it makes take in an argument.  If you type in:

sudo startc1SYS 1

it automatically writes 1 to the BURT RESTORE channel so you don't have to open the GDS_TP screen and by hand put a 1 in the box before the model times out.

The scripts also points to the correct burtwb and burtrb files so it should stop complaining about not finding them when running the scripts, and actually puts a time stamped burt snapshot in the /tmp directory when the kill or start scripts are run.  The Makefile was also backed up to Makefile_bak.

 

  4245   Thu Feb 3 16:08:06 2011 AidanUpdateComputer Scripts / ProgramsRCG VCO frequency error

Joe and I were looking at the RCG VCO algorithm to determine if we could adapt it to run at a faster rate (you can currently change its frequency at 1Hz). I noticed that the algorithm that is used to calculated the values of sine and cosine at time T1  is a truncated Taylor series which uses the values of sine and cosine calculated at time T1 - Delta t . I was concerned that there would be an accumulating phase error so I tested the algorithm in MATLAB and compared it to a proper calculation of sine and cosine. It turns out that at a given 'requested' frequency there is a constantly accumulating phase error - which means that the 'actual' frequency of the RCG VCO is incorrect. So I have plotted the frequency error vs requested VCO frequency. It gets pretty bad!

 Here's the code I used:

dt = 1/16384;

diffList = [];
% set the frequencies

flist = 1:5:8192;
for f = flist;
   
    % get the 'accurate' values of sine and cosine
    tmax = 0.05;
    time1 = dt:dt:tmax;
    sineT = sin(2.0*pi*f*time1);
    cosineT = cos(2.0*pi*f*time1);
   
    % determine the phase change per cycle
    dphi = f*dt*2*pi;
    cosT1 = 1:numel(time1);
    sinT1 = 0*(1:numel(time1));
   
    % use the RCG VCO algorithm to determine the values of sine and cosine
    for ii = 1:numel(time1) - 1;                 
        cosNew = cosT1(ii)*(1 - 0.5*dphi^2) ...
                      - (dphi)*sinT1(ii);
        sinNew = sinT1(ii)*(1 - 0.5*dphi^2) ...
                      + (dphi)*cosT1(ii);
                 
       
        cosT1(ii+1) = [ cosNew];
        sinT1(ii+1) = [ sinNew];
       
    end
    % extract the phase from the VCO values of sine and cosine
    phaseT = unwrap(angle(cosineT + i* sineT));
    phaseT1 = unwrap(angle((cosT1 + i*sinT1)));
   
    % determine the phase error for 1 cycle
    diff = phaseT1 - phaseT;
    % determine the frequency error
    slope = (diff(2) - diff(1))/(dt);
   
    diffList = [diffList, slope];
    disp(f)
    pause(0.001)
end

% plot the results

close all
figure
orient landscape
loglog(flist, abs(diffList/(2.0*pi)))
xlabel('Requested VCO Frequency (Hz)')
ylabel('Frequency error (Hz)')
grid on

print('-dpdf', '/users/abrooks/VCO_error.pdf')

Attachment 1: VCO_error.pdf
VCO_error.pdf
  4244   Thu Feb 3 11:13:52 2011 KojiUpdateElectronicsPOY Shot Noise and Dark Spectrum

I wonder why POY11 has the dark noise level of 90nV/rtHz that is 5 times larger than that of POX (18nV/rtHz)
even though the Q are the same (~15) and the transimpedance is better (3.9k instead of 2k).

What cause this high noise level?
What is the expected dark noise level?

Quote:

[Koji and Kevin]

I measured the shot noise of POY and fit the data to determine the RF transimpedance at 11 MHz and the dark current. The transimpedance is (3.860 +- 0.006) kΩ. I realize that there are not many data points past the dark current but I did not want to take any further data because the light bulb was getting pretty bright. If this is a problem, I can try to redo the measurement using a lens to try to focus more of the light from the bulb onto the photodiode.

I also measured the spectrum and recorded a time series of the RF signal with the light to the photodiode blocked. These measurements do not show any large oscillations like the ones found for POX.

The plots of the measurements are on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY.

 

  4243   Thu Feb 3 04:43:58 2011 SureshUpdateElectronicsAdded two new DAQ channels

[Suresh, Joe]

We added the following two new DAQ channels into the c1:GCV model.  The daq:analog input channels are on card ADC0 and correspond to channels 3 and 4 on the card.

c1:GCV-EXT_REF_OUT_DAQ   Sampling rate=2kHz  acquiring a 1Hz sine wave from the SRS Function Generator DS345.  This is using the Rb 10MHz signal as an external frequency reference.

c1:GCV-PLL_OUT_DAQ    Sa.rate=2kHz acquiring the demodulated signal from the PLL servo.

This work is connected to the study of VCO PLL loop noise at frequencies below 0.1Hz.    We are trying to measure phase noise in the VCO PLL servo at low frequencies as this noise would result in arm length fluctuations in the green-locking scheme.

 

 

 

  4242   Thu Feb 3 01:46:54 2011 KevinUpdateElectronicsPOY Shot Noise and Dark Spectrum

[Koji and Kevin]

I measured the shot noise of POY and fit the data to determine the RF transimpedance at 11 MHz and the dark current. The transimpedance is (3.860 +- 0.006) kΩ. I realize that there are not many data points past the dark current but I did not want to take any further data because the light bulb was getting pretty bright. If this is a problem, I can try to redo the measurement using a lens to try to focus more of the light from the bulb onto the photodiode.

I also measured the spectrum and recorded a time series of the RF signal with the light to the photodiode blocked. These measurements do not show any large oscillations like the ones found for POX.

The plots of the measurements are on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY.

  4241   Wed Feb 2 15:07:20 2011 josephbUpdateCDSactivateDAQ.py now includes PEM channels

[Joe, Jenne]

We modified the activateDAQ.py script to handle the C1PEM.ini file (defining the PEM channels being recorded by the frame builder) in addition to all the optics channels.  Jenne will be modifying it further so as to rename more channels.

  4240   Wed Feb 2 12:55:34 2011 KojiSummaryGreen LockingFreq fluctuation measured by the freq divider and Rana's analog PFD

I found that some flakiness of the beat signals comes from the RF components for the beat detection.
They are touching the racks in an indefinite way. If we move the components the output of the analog PFD
goes crazy.

Once Kiwamu is back I will ask him to clean up all of the green setting in an appropriate way.

 

  4239   Wed Feb 2 10:44:26 2011 KojiSummaryGreen LockingFreq fluctuation measured by the freq divider and Rana's analog PFD

The freq fluctuation of the beat note has been measured with the following condition

  • The IR beam only locked to the MC. The green beam locked to the arm
  • Both of the IR and green locked to the x-arm

Calibration
- The output of the freq divider is already calibrated to have the unit of MHz.

- The transfer function between the analog PFD channel and the digital PFD output was measured to be -23dB = 0.7.
  The gain of the XARM-FINE channel was changed to 0.7 such that the output is calibrated in MHz.

Results

- I have not checked the analog noise level of the analog PFD path. We may need more whitening gain (by icreasing the gain of SR560).

- The analog PFD is always better than the digital PFD above 20Hz.

- Both the digital and analog PFD showed good agreement below 20Hz.
  Note the measurement was not simultaneous.

- When the arm is locked with the ETMX being actuated , the fluctuation of the arm length must be stabilized by a huge factor
(~10^5 according to Kiwamu's entry) However, we only could see the stabilization factor of 30.

As this residual is the difference of the freq noise felt by the IR and the green,
this is a real issue to be tackled.

- The RMS fluctuations of the arm with and without the IR beam being locked are 2MHz and 0.1MHz,
which correcponds to the arm length motion of 250nm and 13nm, respectively.
Ed: I had to use 532nm in stead of 1064nm. The correct numbers are 130nm and 7nm.

- Without the IR locked, The typical peak-to-peak fluctuation of the beat freq was 10MHz.

Attachment 1: 110201_green_freq_fluctuation.pdf
110201_green_freq_fluctuation.pdf
  4238   Wed Feb 2 09:56:55 2011 KojiSummaryGreen LockingInstalled the freq divider and Rana's PFD

- The freq divider and Rana's PFD were hooked up to the ADCs. (Attachment 1)
(I leave the analog PFD not explained in this entry.)
For this purpose, the VCO feedback signal has been disconnected and the beat signal was moved from the VCO loop to the analog PFD.

The output level of the splitter was +12dBm and was too high for the freq divider.
So, I had to stupidly add an attenuator of 10dB before the box.

- Gain of the digital PFD LPF

The LPF of the digital PFD had the gain of -4096 to let the output signal indicate the direct frequency reading.

The gain has been changed to -67.108864
such that the output shows the direct reading of the beat freq in the unit of MHz

-4096*2^14/10^6 = -67.108864

 

- Attachment 2 shows the acquired beat note through the freq divider.
The blue is the beat note between "green locked" and "IR locked only to MC" (i.e. MC vs XARM)
The red is the beat note with the both beam locked to the arm

The freq divider is a bit flaky in some freq region as the divided output sometimes shows freq jumps or the captured at a freq.
I still don't know why it happens. We have to check why this happens.

Attachment 1: freq_divider_installation.pdf
freq_divider_installation.pdf
Attachment 2: 110201_freq_divider_output.pdf
110201_freq_divider_output.pdf
  4237   Wed Feb 2 03:27:20 2011 KojiSummaryGreen Locking85MHz Freq divider

The freq divider was built and installed in the beat detection path.

Attachment 1: Circuit diagram

  • Input stage:  Wideband RF amp with DC block at the input and the output. The gain is 10dB typ.
  • 2nd stage: Ultra fast comparator AD9696. Note: AD9696 is an obsolete IC and there are only a few extra at Wilson house.
    The output is TTL/CMOS compatible.
  • 3rd stage: 14bit binary ripple counter (fmax~100MHz.)

Note: I have added 7805/7905 regulators to the circuit as I could not find -5V supply on the 1X1/2 racks.

Attachment 2: Packaging

  • The box is german made Eurocard size box from Techno-Isel Linear Motion http://www.techno-isel.com/lmc/Products/EnclosureProfiles11055.htm
    The box is excellent but I didn't like the fixing bolts as they are self-tapping type. I tapped the thread and used #6-32 screws.
     
  • The prototyping board is BPS's (BusBoard Prototype System http://www.busboard.us/)  SP3UT. The card size is 160mm x 100mm.
    The other side is a ground plane and the small holes on the board are through holes to the ground plane.
    This particular card was not easy to use.
     
  • The input is SMA. Unfortunately, it is not isolated. The output is an isolated BNC.
     
  • The supply voltage of +/-15V is given by the 3pin D-connector. The supply voltages have been obtained from the cross connect of 1X1.

Attachment 3: Input specification

  • The input frequency is 10MHz~85MHz. At lower frequency chattering of the comparator against the multiple zero crossing of the (relatively) slow sinusoidal waves.
  • The input amplitude. There are no apparent degradation of the freq jitter when the input power was larger than -30dBm.

 

Attachment 1: freq_divider.pdf
freq_divider.pdf
Attachment 2: IMG_3816.JPG
IMG_3816.JPG
Attachment 3: IMG_3818.JPG
IMG_3818.JPG
  4236   Tue Feb 1 17:34:21 2011 JenneUpdateSUSETMX and PRM watchdogs tripped

I sat down in the control room to find that ETMX and PRM's watchdogs had been tripped.  I don't know how long they've been crazy, but there was a big something that showed up in the seismometers around 16:30UTC, or ~11:30 this morning.  I don't find any significant earthquakes on the USGS site for that time though, so it might be more local, i.e. work next door or trucks or whatever.

I take back the suggestion that it was that seismic event.  Clearly the PRM and the ETMX were kicked at different times, neither of which is the same as the seismic action. Mystery.  You can see they have been ringing down for a while though, which is neat. 

Attachment 1: Seis_1Feb2011.png
Seis_1Feb2011.png
Attachment 2: Seis_SUS_1Feb2011.png
Seis_SUS_1Feb2011.png
  4235   Tue Feb 1 15:09:41 2011 KojiOmnistructureGeneralProjector - fixed

The projector in the controls room has been fixed the orange blinking of the status LED.

What we needed was to push "Volume -" and "Menu" for 5 sec.
This resets the timer of the lamp. When the timer reaches 2500 hours, it automatically start sabotaging.

We've got the spare lamp. It is in the top drawer of the computer cabinet on which the label makers are.

  4234   Mon Jan 31 18:25:25 2011 AidanUpdateGreen LockingDFD - results from the new filters (and running with AWG)

Quote:

This is a plot showing the old filters and the new ones we added this morning.

The new ones have a Cheby for AC coupling below 10 Hz and then a 500 Hz LP after the mixer. The LP frequency has been increased so that we can use this signal in a feedback loop to the ETM with a ~100 Hz UGF.

Joe injected a 234.567 etc. Hz sine wave into the excitation channel in the DFD INPUT filter. The spectrum of the output of the LP filter with the new filter is shown below with the RMS calculated from 300Hz down to 1mHz - see first attachment. The RMS is equal to about 2.5Hz. (Incidentally, the RMS is very much higher (slightly less than 400Hz - see second attachment) if you calculate it from 7kHz down to 1mHz). 

Attachment 1: DFD-bandwidth_noise_CLP500_to_300Hz.pdf
DFD-bandwidth_noise_CLP500_to_300Hz.pdf
Attachment 2: DFD-bandwidth_noise_CLP500_to_7000kHz.pdf
DFD-bandwidth_noise_CLP500_to_7000kHz.pdf
  4233   Mon Jan 31 16:12:11 2011 steveUpdateVACVertex crane upgrade shorth coming

 The upgrade is almost finished. I found that the passive latch lock  is not closing down all the way. It has about a 3/8" gap.    See Atm. 1 & 2

The service man was here this morning and agreed to fix it.  They will be back next week. The latch needs an other spring to push it into full lock. 

We tested all possible sequences of operation of the new upgrade. It performed to specification.

 

 

Quote:

 

Attachment 1: P1070364.JPG
P1070364.JPG
Attachment 2: P1070358.JPG
P1070358.JPG
  4232   Mon Jan 31 12:40:38 2011 rana, joeUpdateGreen LockingDFD - medm screen

This is a plot showing the old filters and the new ones we added this morning.

The new ones have a Cheby for AC coupling below 10 Hz and then a 500 Hz LP after the mixer. The LP frequency has been increased so that we can use this signal in a feedback loop to the ETM with a ~100 Hz UGF.

Attachment 1: a.pdf
a.pdf
  4231   Mon Jan 31 10:31:30 2011 josephbUpdateWienerFilteringImprovement in H1 Wiener FF prediction by using weights and taps

Rossa is a rather beefy machine. It effectively has 8 Intel i7 Cores (2.67 Ghz each) and 12 Gigs of ram.  Megatron only has 8 Gigs of ram and just 8 Opterons (1 GHz each).  Rosalba has 4 Quad Core2  (2.4 GHz) with only 4 Gigs of ram. 

MC damp dataviewer diaggui AWG c1ioo c1sus c1iscex RFM The Dolphins Sim.Plant Frame builder TDS
                       
  4230   Mon Jan 31 07:41:23 2011 AidanUpdateGreen LockingDFD - medm screen

I added an MEDM screen for the DFD to the GREEN screen. It is displayed in the attached screen shot.

This screen is located in: /cvs/cds/rtcds/caltech/c1/medm/c1gfd/C1GFD_DFD.adl

Attachment 1: Screenshot-3.png
Screenshot-3.png
  4229   Mon Jan 31 07:03:59 2011 AidanSummaryGreen LockingDFD - noise spectra

Quote:

I've had a go at trying to estimate the frequency noise of the digital frequency discriminator (DFD). I input a 234.5Hz (0.5Vpp) signal from a 30MHz function generator into the ADC. The LP output of the DFD measured 234.5Hz. However, this signal is clearly modulated by roughly +/- 0.2Hz at harmonics of 234.5Hz (as you can see in the top plot in the dataviewer screenshot below). So the frequency noise can be estimated as rms of approximately 0.2Hz.

This is supported by taking the spectra of the LP output and looking at the RMS. Most of the power in the RMS frequency noise (above the minimum frequency) comes from the harmonics of the input signal and the RMS is approximately 0.2Hz.

I believe this stems from the rather basic LP filter (three or four poles around 10Hz?) that is used in the LP filter to remove the higher frequency components that exist after the mixing stage. (The currently loaded LPF filter is not the same as the saved one in Foton - and that one won't load at the moment, so I'm forced to remember the shape of the current filter).

 The attached screen capture from data viewer shows the LP_OUT hovering around 234.5Hz.

 Here is the spectrum of the input into the DFD (a 234.5Hz sine wave, 0.5 Vpp) and the spectrum and RMS of the LP output. The linewidth of the input signal is clearly much less than 0.1Hz, where as the RMS noise (above 2mHz) is approximately 0.2Hz and the main contributions are clearly the harmonics of the 234.5Hz signal.

Attachment 1: DFD-bandwidth_noise.pdf
DFD-bandwidth_noise.pdf
  4228   Sun Jan 30 19:26:03 2011 KojiSummaryGreen LockingPrototype freq divider

A prototype freq divider has been made which works up to ~40MHz.

74HC4060 (14bit binary ripple counter) divides the freq of the input signal, which is comverted by the comparator LT1016
into the rectangular signal. The division rate is 2^14.

Attachment1: Circuit diagram

Attachment2:
Photo, the prototype bread board

Attachment3:
Photo, the spectrum of the freq divided output. The 40MHz input has been divided into 2.4k.
There are the 3rd and 5th harmonics seen. The peak was pretty sharp but the phase noise was not evaluated yet.


The circuit was made on the prototype bread board which is apparently unsuitable for RF purposes.
Indeed, it was surprising to see its working up to 40MHz...

In order to increase the maximum freq of the system we need the following considerations

  • RF PCB board
  • Input RF buffer (or amplifier) with a 50Ohm input impedance.
  • Faster comparator. LT1016 has the response time of 10ns, which is not enough fast.
  • Faster counter. Faster chip 74HC4020 has already been ordered.
Attachment 1: freq_divider.pdf
freq_divider.pdf
Attachment 2: IMG_3813.jpg
IMG_3813.jpg
Attachment 3: IMG_3814.jpg
IMG_3814.jpg
  4227   Sun Jan 30 17:15:09 2011 AidanSummaryGreen LockingDigital Frequency discriminator - frequency noise

I've had a go at trying to estimate the frequency noise of the digital frequency discriminator (DFD). I input a 234.5Hz (0.5Vpp) signal from a 30MHz function generator into the ADC. The LP output of the DFD measured 234.5Hz. However, this signal is clearly modulated by roughly +/- 0.2Hz at harmonics of 234.5Hz (as you can see in the top plot in the dataviewer screenshot below). So the frequency noise can be estimated as rms of approximately 0.2Hz.

This is supported by taking the spectra of the LP output and looking at the RMS. Most of the power in the RMS frequency noise (above the minimum frequency) comes from the harmonics of the input signal and the RMS is approximately 0.2Hz.

I believe this stems from the rather basic LP filter (three or four poles around 10Hz?) that is used in the LP filter to remove the higher frequency components that exist after the mixing stage. (The currently loaded LPF filter is not the same as the saved one in Foton - and that one won't load at the moment, so I'm forced to remember the shape of the current filter).

 The attached screen capture from data viewer shows the LP_OUT hovering around 234.5Hz.

Attachment 1: _Untitled_(modified).png
_Untitled_(modified).png
  4226   Sat Jan 29 03:13:44 2011 ranaUpdateWienerFilteringImprovement in H1 Wiener FF prediction by using weights and taps

(Jenne, Rana)

Tonight we noticed that there were significant improvements to be had in the predicted DARM Wiener filtering FF performance by using weighting filters and more taps in the FIR filter.

The plots below tell the story:

The first one shows the improvement in the residual (black & blue) by applying a weighting filter. The weight filter tilts the spectrum up at HF and applies and all real pole BP from 10-20 Hz.

The second plot shows the improvement gotten by using 3000 instead of 2000 taps for the Wiener filter. With the larger number of taps we not only get the big improvement at LF, but also some beefy reduction in the higher frequency stack modes and the LOS roll mode.

I'm not sure why we haven't run across this before; the weighting filter was arrived at today by just iterating by hand on the placement of poles and zeros until the trace looked nice.

Jenne is going to run this new filter on the S5-month that we have been using for stationarity testing.

* Some notes:

** this Wiener stuff is faster, by far, on rossa than either megatron or rosalba or my laptop. More than a factor of 3.

*** there is a bug with Macports/Matlab - if you get fftw3 with Macports, it sets itself as the right version to use. This confuses matlab in some cases.

     if you get the error about libfftw3.dylib, whe trying fft in matlab after installing macports, then you can fix it by setting the Matlab lib/ path with the fftw libraries to be ahead of /opt/local/lib in the LD_LIBRARY_PATH in your .cshrc.

Attachment 1: darmweight.png
darmweight.png
Attachment 2: darm3000.png
darm3000.png
  4225   Sat Jan 29 00:31:05 2011 SureshUpdateGeneralVertex crane upgrade completed

The Vertex crane is smarter and safer now.  This upgrade ensures that the two sections of I-beam (8ft, 4ft) remain firmly latched to form a straight member till the latch is released.

In specific, it ensures that problems such as this one do not occur in the future.

 

The new safety features are:

When the I-beam sections are latched together, a pneumatic piston ensures that the latch is secure. 

If the latch is not engaged the trolley does not move outward beyond the end of the 8-foot section of the I beam.

If the trolley is out on the 4-foot section of the beam then we cannot disengage the latch.

 

How does it work?

 

 Vertex_Crane-2.png Vertex_Crane-4.png

 

The state of the Limit Switch 1 changes when the trolly goes past it.    The Limit Switch 2 gets pressed when the two sections are latched together.

The pneumatic piston raises or lowers the latch.  The Pneumatic Latch Switch operates a pneumatic valve controlling the state of the piston.

 

 

Vertex_Crane-3.png P1280545.JPG

The new controller now has Pneumatic Latch Switch in addition to the usual Start, Stop, Up, Down, In and Out buttons. 

Each of the Up, Down, In and Out buttons have two operational states:  Half pressed (low speed) and Full pressed (High Speed).  Their functions remain the same as before.

 

The new Pneumatic Switch:

When this switch is 'Engaged' and the 4 ft section is swung in-line with the 8 ft section, the two sections get latched together.

To unlatch them we have to throw the switch into the 'Disengage' state.  This makes the piston push the latch open and a spring rotates the 4 ft section about its pivot.

Limit Switch 2 is not pressed (I-beams not aligned straight) ==> Limit Switch 1 will prevent the trolley from out going beyond the 8 ft section.

While Limit Switch 2 is pressed we cannot disengage the latch.

 

Note: 

   The pneumatic piston requires 80psi of pressure to operate.  However we have only 40psi in the lab and the piston seems to operate quite well at this pressure as well.  I believe a request has been made to get an 80psi line laid just for this application.

 

Attachment 1: Vertex_Crane-2.png
Vertex_Crane-2.png
Attachment 2: Vertex_Crane-4.png
Vertex_Crane-4.png
  4224   Fri Jan 28 18:19:21 2011 JenneUpdateIOOWFS2 has some kind of oil on it

Mystery solved!

I removed WFS2 from the AP table (after placing markers so I can put it back in ~the same place) so that I could take some reflectivity as a function of angle measurements for aLIGO WFS design stuff.

I was dismayed to discover, upon glancing at the diode itself, that half of the diode is covered with some kind of oil!!!.  The oil is mostly confined to quadrants 3 and 4, which explains the confusion with their quantum efficiency measurements, as well as why the readback values on the MEDM WFS Head screen for WFS2 don't really make sense. 

The WFS QPD has a piece of glass protecting the diode itself, and the oil seems to be on top of the glass, so I'm going to use some lens tissue and clean it off.

Pre-cleaning photos are on Picasa.

Update:  I tried scrubbing the glass with a Q-tip soaked with Iso, and then one soaked in methanol.  Both of these failed to make any improvement.  I am suspicious that perhaps whatever it is, is underneath the glass, but I don't know.  Rana suggested replacing the diode, if we have spares / when we order some spares.

Oily_WFS2.jpg

Quote:

Problem with 2 quadrants of WFS2?

While doing all of this, I noticed that quadrants 3 and 4 of WFS2 seem to be different than all the rest.  You can see this on the MEDM screens in that all 6 other quadrants, when there is no light, read about -0.2, whereas the 2 funny quadrants read positive values.  This might be okay, because they both respond to light, in some kind of proportion to the amount of light on them.  I ended up getting QE of ~72% for both of these quadrants, which doesn't make a whole lot of sense since the spec for green is 70%, and silicon is supposed to be less good for infrared than green.  Anyhow, we'll have to meditate on this.  We should also see if we have a trend, to check how long they have been funny.

 

  4223   Fri Jan 28 15:50:44 2011 JenneConfigurationPSLThe PSL has a name!

Back in the days when we were talking about getting a new 2W PSL, I was given naming rights by Rana for this new laser. 

Today, the 40m PSL was given its new name: Edwin.

Here he is, with his shiny new label:

EdwinTheLaser.jpg

ELOG V3.1.3-