40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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New entries since:Wed Dec 31 16:00:00 1969
ID Date Authorup Type Category Subject
  6016   Sat Nov 26 07:22:20 2011 sureshUpdateComputers 

c1sus has been shutdown so that the optics dont bang around.  This is because the watch dogs are not working.

  6438   Thu Mar 22 17:41:15 2012 sureshUpdateCDSc1scx and c1scy not properly running

Quote:

It seems that neither c1scx nor c1scy is working properly as their ADC counts are showing digital-zeros.

Quote from #6434

The power was turned back on at 4pm It took some time for Suresh to restart the computers. We have damping but things are not perfect yet. Auto BURTH did not work well.

 When Steve and I restarted the c1iscex and c1iscey computers after the power shutdown, the models within them did not start-up automatically.  I had to start them manually from a terminal in the control room. 

I also tried rebooting the FB a couple of times.  Did not make any difference.

Manually starting the c1x05, c1scy and c1x01, c1scx models (with the Burt Restore button ON) did not resolve the issue of zeros in the epics screens.  though it did re-establish timing. 

  7950   Mon Jan 28 21:36:44 2013 tall guyFrogsGeneralsmall people on notice

If I catch anyone putting small booties into the large bootie bin, I will make said person eat small booties.

  3812   Thu Oct 28 19:10:26 2010 taraUpdateElectronicsTTFSS for 40m

I keep a set of new TTFSS for 40m in electronic cabinet along the North arm.

The set number is #6. It is working and has not been modified by me.

Other two sets,# 5 and #7, are kept at PSL lab.

  4512   Mon Apr 11 20:03:05 2011 taraUpdateElectronicsTTFSS for 40m

I brought TTFSS set #7 to 40m and kept it in the electronic cabinet.

note that Q4 transistor has not been replaced back to PZT2907A yet. It's still GE82.

Q3 is now pzt3904, not PZT2222A.

 

  6514   Tue Apr 10 11:08:29 2012 taraUpdatePSLcurved mirror behind AOM removed

We removed the curved mirror behind the AOM (ROC=0.3m) on PSL table. The mirror is now in PSL lab. See PSL:905 for more detail.

  7904   Wed Jan 16 10:57:37 2013 taraSummaryIOONoise budget for MC

I calculated thermal noise in mode cleaner (MC) mirrors and compared it with the measured MC noise. Thermal noise won't be a significant noise source for MC.

== Motivation==

 There is an idea of using MC and a refcav to measure coating thermal noise. One laser is frequency locked to MC, another laser is locked to an 8" refcav. Then the two transmitted beams are recombined so that we can readout the frequency noise. In this case, the transmitted beam from MC is a better reference (less frequency noise) than the beam from refcav. However, we need to make sure that we understand the noise sources, for example brownian noise, thermoelastic noise in both substrates and coatings, in MC more thoroughly.

==Calculation==

I used Rana's code for MC's technical noise sources from, svn. The same plot can be found in appendix C of his thesis. Then I added my calculation to the plot.  Jenne pointed me to 40m:2984 for the spot size and the cavity length. The spot radius on MC1 and MC3 is ~ 1.5mm, and ~3.4 mm@MC2, The round trip length is ~27m, thus the frequency fluctuation due to thermal noise is lower than that of refcav by 2-3 orders of magnitude. I calculated Brownian noise in coatings, Brownian noise in substrate, Thermoelastic noise in substrate. I assumed that the coatings are SiO2/Ta2O5, quarter stacks, coatings thickness for MC1/3 = 5um, for MC2 = 8um. The code can be found in the attachment.

mc_nb_TN.png

==result==

Total thermal noise on MC (Brownian + Thermoelastic on substrate and coatings of MC1-MC3) is plotted in dashed red. It is already below 10^-5 Hz/rtHz at ~20 Hz. This is sufficiently low compared to other noise sources. Beat signal from CTN measurement with 8" cavities is plotted in pink, the estimated coating brownian noise is plotted in a yellow strip. They are well above the measured MC noise between 100 Hz to a few kHz. Measuring coating thermal noise on 8" refcav seems plausible with this method. We can beat the two transmitted beams from IMC and refcav and readout the beat signal to extract the displacement noise of refcav. I'll discuss this with Koji if this is a good surf project.

 mc_nb_TN_2013_01_18.png

[the internal thermal noise in the original plotted is removed and replaced with the total thermal noise plot instead]

 note:I'm not sure about the current 40m MC configuration. The parameters used in this calculation are summarized in mcnoiseS2L1.m (in the svn page).

 

  3163   Wed Jul 7 00:15:29 2010 tara,RanaSummaryPSLpower spectral density from RefCav transmitted beam

I measured the RC transmitted light signals here at the 40m. I made all connections through the PSL patch panel.

Other than two steering mirrors in front of the periscope, and the steering mirror for the RFPD which were used to steer

the beam into the cavity and the RFPD respectively, no optics are adjusted.

We re-aligned the beam into the cavity (the DC level increased from 2 V to 3.83V) (Fig2) (We could not recover the power back to what it was 90 days ago)

and the reflected beam to the center of the RFPD.

 

I measured the spectral density of the signal of the transmitted beam behind RefCav in both time and frequency domain.

This will be compared with the result from PSL lab later, so I can see how stable the signal should be.

I did not convert Vrms/rtHz to Hz/rtHz because I only look at the relative intensity of the transmitted beam which will be compared to the setup at PSL lab. 

 

 

 We care about this power fluctuation because we plan to measure

 photo refractive noise on the cavity's mirros

(this is the noise caused by dn/dT in the coatings and the substrate,

the absorption from fluctuating power on the coating/mirror changes

the temperature which eventually changes the effective length of the cavity as seen by the laser.)

      

      The plan is to modulate the power of the beam going into the cavity,

the absorption from ac part will induce frequency noise which we want to see.

Since the transmitted power of the cavity is proportional to the power inside the cavity.

 Fluctuations  from other factors, for example, gain setting,  will limit our measurement. 

That's why we are concerned about the stability of the transmitted beam and made this measurement.


 

  3210   Tue Jul 13 21:04:49 2010 tara,ranaSummaryPSLTransfer function of FSS servo

 I measured FSS's open loop transfer function.

For FSS servo schematic, see D040105-B.  

4395A's source out is connected to Test point 2 on the patch panel.

Test Point 2 is enabled by FSS medm screen.

"A" channel is connected to In1, on the patch panel.

"R" channel is connected to In2, on the patch panel.

the plot shows signal from A/R.

Note that the magnitude has not been corrected for the impedance match yet.

So the real UGF will be different from the plot.

 

-------------------------

4395A setup

-------------------------

network analyzer mode

frequency span 1k - 10MHz

Intermediate frequency bandwidth 100Hz

Attenuator: 0 for both channels

Source out power: -30 dBm

sweep log frequency

------------------------------

medm screen setup

-----------------------------

TP2: enabled

Common gain -4.8 dB

Fast Gain 16 dB

  3570   Mon Sep 13 22:51:07 2010 tara,valeraConfigurationPSLbeam scan for RCAV

On Friday, Valera and I calculated the modematching for reference cavity from AOM.

We scan the beam profile where the spot should be.

The first beam waist in the AOM is 103 um, the lens (f= 183 mm, I'm not sure if I have the focal length right) is 280 mm away.

The data is attached. The first column is marking on the rail in inches,

the second column is distance from the lens, the third and fourth column are

vertical and horizontal spot radius in micron. Note that the beam is very elliptic because of the AOM.

  14105   Thu Jul 26 01:52:01 2018 terraUpdateThermal Compensationheater work update

Just a quick update: over the past few days we've taken (at least) 5 scans around each peak [carrier - HOM3] at 9.4V/0.8A, 4 scans around [carrier - HOM5] at 12V/0.9A hot state with the reflector setup. We also have (at least) 5 scans of carrier - HOM5 in cold state. I attach a rough overview of the peak magnitude shifts in the first attachment. Analysis ongoing. All data stored in annalisa/postVent/{date}

Initial shifts just based on rought peak placement in the meantime:

            [9.4V/0.8A]   [12V/0.9A]

HOM1    10 kHz         20 kHz

HOM2    18 kHz         28 kHz

HOM3     30 kHz        40 kHz

HOM4     N/A             26 kHz

HOM5     N/A             35 kHz

I also attach the heating thermal transient from today (12V/0.9A) as seen by the opLevs. We see a shorter time constant for pitch, longer for yaw, preceeded by a dip in yaw. Similar behavior yesterday for slightly less heating, though less pronounced pre-dip. The heater is offcentered on the optic horizontally; likely this is part of the induced yaw. The spikey stuff i removed is from people walking around inside during the transient.

I've left the heater and LSC off for the night. Heater off at 2:07 am local time.

Please don't touch the oplevs; we're taking a cool down measurement.

  14110   Sat Jul 28 00:45:11 2018 terra, sandrineSummaryThermal CompensationHeater measurements overview

[Sandrine, Koji, Terra]

Summary: We completed multiple scans at different heating powers for the reflector set up, observing unique HOM peak shifts of tens of kHz. We also observed HOM5 shifts with the cylinder set up. Initial Lorentzian fittings of the magnitude give tens of Hz resolution. I summarize the main week's work below. 

Set-up

Heater set-up is described in several previous elogs, but attachments #1 and #2 show the full heater set-up and wiring/pinouts in and out of vacuum, since we're all intimately aware of how confusing in-vacuum pinouts can be. We are not using the Sorenson power supply (as described in 14071); we just have the BKPrecision power supply 1735 sitting next to the ETMY rack and are manually going out to turn on/off. 

We've continued to use the scan setup described in elog 14086, which is run using /users/annalisa/postVent/AGfast.py. Step by step notes for setting up the scan, running the scans, and processing the scans are attached in notes.txt.

Inducing/witnessing HOMs

The aux input beam was already clipped and on wednesday (after Trans was centered, 14093) we also clipped the output aux beam with razor blade (angled vertically and horizontally, elog 14103) before PDA255; we clipped ~1/3 of the output beam. Attachment #3 shows before and after clipping output, where orange 'cold' == unclipped, black 'mean' == clipped (all in cold state). Up to HOM5 is visible. 

Measurements

Below is a summary of the available scan data. We also have cold (0A) scans CAR-HOM5 and full FSR scans for most configurations. 

Elliptic Reflector
current[A] voltage[V] power[W] scans
0.4 2 0.8 CAR-HOM3(x1)
0.5 3.4 1.7 CAR-HOM3(x1)
0.6 5 3.0 CAR-HOM3(x1)
0.8 9.4(9.7) 7.5(7.8) CAR-HOM5(>x5)
0.9 12 10.8 CAR-HOM5(x4)
1.09 17 18.5 CAR-HOM3

 

 

 

 

 

 

 

Cylinder + Lenses
current[A] voltage[V] power[W] scans
0.9 15 13.5 CAR-HOM5(odds x4)

We tried the cylinder set-up again tonight for the first time since inital try and can see shifts of HOM5 - see attachment #5; we haven't looked in detail yet, but it looks like odd modes are more effected, suggesting the ring heat pattern is off centered from the beam axis. 

Scan data is saved in the following format: users/annalisa/postVent/scandata/{reflector,cylinder}/{parsed,unparsed}/{CAR,HOM1,HOM2,HOM3,HOM4,HOM5}{_datetime}{_parsed,_unparsed}.{txt,pdf}

Minimum heating

On 7/26 we increased the power to the elliptical reflector heater in steps to find the minimum heater power required to see frequency shifts with our measurement setup. Lowest we can resolve is a shift in HOM3 with 1.7W (0.5A/3.4V). According to Annalisa's measurements in elog 14050, this would be something like 30-60 mW radiated power hitting the test mass. We only looked at CAR - HOM3 for this investigation; data for scans at 0.4A, 0.5A, 0.6A is available as indicated above.

Lorentizian Fitting

The Lorentzian fitting was done using the equation a + b / sqrt(1+((x-c)/d*2), where a = constant background, b = peak height above background, c = peak frequency, d = full width at half max. 

The fitting is still being edited and optimized. We will crop the data to zoom in around the peak more.

The Lorentzian fit of the magnitude shows ~10Hz of resolution. (See attachment 6 for the carrier at 8A and attachment 7 for HOM 1 at 9A)

We're working on fitting the full complex data.

 

 

  340   Sun Feb 24 10:51:58 2008 tfFrogsEnvironment40m in phdcomics?
  28   Mon Oct 29 23:25:42 2007 tobinSoftware InstallationCDSframes mounted
I mounted the frames directory on mafalda and linux3. It's intentionally not listed in the /etc/fstab so that an fb crash won't prevent the controls machines from booting. The command to mount the frames directory is:

mount fb40m:/frames/frames /frames
  31   Tue Oct 30 16:55:40 2007 tobinRoutine Drag-wiping perfected
Steve, Tobin

Steve procured an assortment of syringes from the bio storeroom and we practiced drag-wiping the SOS in the flow bench. Using a 50 microliter Hamilton syringe to deliver 16 microliters of methanol seems perfect for drag-wiping the small optics. Drag-wiping in the downward direction seems to work very well, since we can squirt the optic directly in the center, and the (half) piece of kodak lens tissue fits easily between the bottom two earthquake stops.
  32   Tue Oct 30 19:32:13 2007 tobinProblem FixedComputersconlogger restarted
I noticed that the conlogger wasn't running. It looks like it hasn't been running since October 11th. I modified the restart_conlogger script to insist that it run on op340m instead of op440m, and then ran it on op340m.
  33   Tue Oct 30 20:15:24 2007 tobinOtherEnvironmentearthquake
Rana, Tobin

Largish (M5.6) earthquake in San Francisco sent our optics swinging.
  39   Wed Oct 31 15:02:59 2007 tobinRoutineIOOMode Cleaner Mode Tracking
I processed the heterodyned mode cleaner data yesterday, tracking the three 28 kHz modes corresponding to MC1, MC2, and MC3. Unfortuntately the effect of our MC power chopping is totally swamped by ambient temperature changes. Attached are two plots, one with the tracked mode frequencies, and the other containing dataviewer trends with the MC transmitted power and the room temperature. Additionally, the matlab scripts are attached in a zip file.
  45   Thu Nov 1 11:45:30 2007 tobinConfigurationIOOMode cleaner drag-wiping
Andrey, Bob, David, John Miller, Rana, Rob, Steve, Tobin

Yesterday we vented the vacuum enclosure and opened up the chamber containing MC1 & MC3 by removing the access connector between that chamber and the OMC chamber. Rana marked MC1's location with dogs and then slid the suspension horizontally to the table edge for easy drag-wiping access. The optic was thoroughly hosed-down with the dionizer, in part in an effort to remove dust from the cage and the top of the optic. Drag-wiping commenced with Rob squirting (using the 50 microliter syringe) and Tobin dragging (using half-sheets of Kodak lens tissue). We drag-wiped the optic many (~10) times, concentrating on the center but also chasing around various particles and a smudge on the periphery. There remains one tiny speck at about the 7:30 position, outside of the resonant spot area, that we could not dislodge with three wipes.

Today we drag-wiped MC3. First we slid MC1 back and then slid MC3 out to the edge of the table. We disconnected the OSEM cables in the process for accessibility, and MC1 is perched at an angle, resting on a dog. We did not blow MC3 with the deonizer, not wanting to blow particles from MC3 to the already-cleaned MC1. We drag-wiped MC3 only three times, all downward drags through the optic center, with Steve squirting and Tobin dragging. Some particles are still visible around the periphery, and there appears to be a small fiber lodged near the optic center on the reverse face.

Andrey and Steve have opened up MC2 in preparation for drag-wiping that optic after lunch.
  71   Tue Nov 6 16:48:54 2007 tobinConfigurationComputersscopes on the net
I configured our two 100 MHz Tektronix 3014B scopes with IP addresses: 131.215.113.24 (scope0) and 113.215.113.25 (scope1). Let the scripting commence!

There appears to be a Matlab Instrument Control Toolbox driver for this scope.
  72   Tue Nov 6 18:18:15 2007 tobinConfigurationComputersI broke (and fixed) conlogger
It turns out that not only restart_conlogger, but also conlogger itself checks to see that it is running on the right machine. I had changed the restart_conlogger script to run on op340, but it would actually silently fail (because we cleverly redirect conlogger's output to /dev/null). Anyway, it's fixed now: I edited the conlogger source code where the hostname is hardcoded (blech!) and recompiled.

On another note, Andrey fixed the "su" command on op440m. It turns out that the GNU version, in /usr/local/bin, doesn't work, and was masking the (working) sun version in /bin. Andrey renamed the offending version as "su.backup".
  73   Tue Nov 6 23:45:38 2007 tobinConfigurationComputerstektronix scripts!
I cooked up a little script to fetch the data from the networked Tektronix scope. Example usage:

linux2:scripts>tektronix/tek-dump scope0 ch1 foo.csv

"scope0" is the hostname of the scope, "ch1" is the channel you want to dump, and "foo.csv" is the file you want to dump it to. The script is written in Python since Python's libhttp gave me less trouble than Perl's HTTP::Lite.
  80   Wed Nov 7 14:05:59 2007 tobinConfigurationIOOMC ringdown
Modeling the mode cleaner as a simple cavity with all losses lumped together, we expect the cavity power to be
attenuated by a factor (1-L) after each interval (2l/c)=1/fsr. Therefore we can get the cavity loss L
(including power lost through transmission) from the ringdown time constant tau as:

L = 1 - exp[ - 1/(tau * fsr) ]

From this we have to subtract the 2000 ppm transmission for each of MC1 and MC3, and divide by three to spread
the losses across the three optics.

I get 168 39 ppm loss per optic based on a very simple exponential fit to the tails (t>0) of four of Andrey's data files.

By comparison, I get 154 37 ppm from Rana's data files from before the vent.
  84   Thu Nov 8 15:57:53 2007 tobinConfigurationPSLshelf removed
I removed the sheet metal shelf from the PSL enclosure, for easier access to the ISS.

ISS investigations ongoing.
  85   Thu Nov 8 18:44:01 2007 tobinConfigurationPSLISS
Tobin, Rob

With the Sense PD blocked, I adjusted the offset trim of the fourth stage in the ISS servo until the current shunt signal was zeroed. After this adjustment, we are able to crank the ISS gain all the way up to 30 dB without CS saturations (provided the HEPA is turned down to a very quiet level), getting about 35kHZ UGF at that gain setting. However, the current shunt mean value was still enormous.

Examining the current shunt signal on a fast scope, we saw an enormous (>2Vpp) 3.6 MHz sawtooth signal. Going up the chain of op-amps, we found that U1, as measured at the "Filter Out" testpoint, is oscillating wildly at 12 MHz (680 mVpp).
  100   Wed Nov 14 12:33:35 2007 tobinAoGEnvironmentconstruction
The construction crews are running a jack-hammer right outside of the control room.
  101   Wed Nov 14 12:47:19 2007 tobinUpdatePSLISS
John, Tobin

With John's notch filter installed and the increased light on the ISS sensing diode, we were able to get a UGF of about 60 kHz with the gain slider set to about 20 dB. This morning we met with Stefan to learn his ISS-fu.

His recommendations for the ISS include:
  • Replace the cables from the board to the front panel connectors if this hasn't already been done.
  • Replace the input opamps with 4131's. Be sure to test both positive and negative input signals.
  • Check that all the compensation capacitors are in place and are 68 pF
  • Make sure all the feedback loops have high frequency rolloff
  • The ISS board reads the PDs differentially; make sure the PD sends differentially.
  • Add a big (ie 10uF tantalum) capacitor to the PD to suppress power supply noise
  • Add bigger power supply bypass caps to the ISS
I just took sensing noise spectra (from the PD DC bnc ports) and then took the photodiodes off the table to check that they have the negative end of the differential line connected to ground. (I placed black metal beam blocks on the table in place of the ISS PD's. Also, from the ISS schematic, it looks like it sends a differential output to the PD DC bnc ports, but we have been plugging them directly into the SR785 (grounding the shield). We should make a little BNC-doodle that separates the signal+shield to go into the A and B inputs on the spectrum analyzer.) Opening up one of the photodiodes, it appears that the negative line of the differential output is not connected. Will continue later this afternoon.
  103   Wed Nov 14 17:50:00 2007 tobinUpdatePSLISS
Here's the current wiring between the ISS and its PDs:

pin cable PD ISS
1 blue +5 +5
2 red +15 +15
3 white -15 -15
4 brown OUT IN PD +
5,6,7,8 no connection no connection GND
9 black GND IN PD -


The schematics for the ISS and the PDs are linked from our wiki.

We'll connect the ISS GND to the PD GND.
  106   Thu Nov 15 18:06:06 2007 tobinUpdateComputersalex: linux1 root file system hard disk's dying
I just noticed that Alex made an entry in the old ilog yesterday, saying: "Looks like linux1 root filesystem hard drive is about to die. The system log is full of drive seek errors. We should get a replacement IDE drive as soon as possible or else the unthinkable could happen. 40 Gb IDE hard drive will be sufficient."
  109   Thu Nov 15 18:37:06 2007 tobinUpdateComputerspossible replacement for linux1's disk
It looks like the existing disk in linux1 is a Seagate ST380013A (this can be found either via the smartctl utility or by looking at the file /proc/ide/hda/model). It appears that you can still buy this disk from amazon, though I think just about any ATA disk would work. I'll ask Steve to buy one for us.
  110   Fri Nov 16 11:27:18 2007 tobinUpdateComputersscript fix
I added a tidbit of code to "LIGOio.pm" that fixes a problem with ezcastep on Linux. Scripts such as "trianglewave" will now work on Linux.
# On Linux, "ezcastep" will interpret negative steps as command line arguments,
# because the GNU library interprets anything starting with a dash as a flag.
# There are two ways around this.  One is to set the environment variable
# POSIXLY_CORRECT and the other is to inject "--" as a command line argument
# before any dashed arguments you don't want interpreted as a flag.  The former
# is easiest to use here:

if (`uname` =~ m/Linux/) {
    # Add an environment variable for child processes
    $ENV{'POSIXLY_CORRECT'} = 1;
}
  111   Fri Nov 16 14:11:26 2007 tobinUpdateComputersop140
Alan called to say that Phil Ehrens will be coming by to take op140 off our hands.
  112   Fri Nov 16 14:31:43 2007 tobinUpdateComputersop140 disks
Phil Ehrens stopped by and took op140's disks.
  117   Tue Nov 20 11:10:07 2007 tobinUpdateComputersepics access from matlab
I installed "labca", which allows direct access to EPICS channels from within Matlab. It comes with both Linux and Solaris binaries (and source) but I've only tried it on linux.

To set it up, run these shell commands:
pushd /cvs/cds/caltech/users/tf/build/labca_2_1/bin/linux-x86
setenv PATH ${PATH}:`pwd`
cd /cvs/cds/caltech/users/tf/build/labca_2_1/lib/linux-x86
setenv LD_LIBRARY_PATH ${LD_LIBRARY_PATH}:`pwd`
popd
Then start matlab, and within matlab type:
addpath /cvs/cds/caltech/users/tf/build/labca_2_1/bin/linux-x86/labca
help labca
foo = lcaGet('C1:PSL-FSS_RCTRANSPD')
It seems like reasonably well-written software, and is being actively maintained right now. If we like it, I can build a more recent version, install it in a more permanent location, etc.
  118   Tue Nov 20 13:06:57 2007 tobinConfigurationComputerslinux1 has new disk
Alex put the new hard disk into linux1 along with a fresh install of linux (CentOS). The old disk was too damaged to copy.

Alex speculates that the old disk failed due to overheating and that linux1 could use an extra fan to prevent this in the future.
  127   Tue Nov 27 20:47:00 2007 tobinUpdatePSLFSS
Rana, Tobin

We looked at the RF PD signal to the FSS (siphoning off a signal via a minicircuits directional coupler) and also took an open loop transfer function of the FSS. In the transfer function we saw the step at 100 kHz (mentioned by Rob) as well as some peculiar behavior at high frequency. The high frequency behavior (with a coupling of ~ -20 dB) turns out to be bogus, as it is still present even with the beam blocked. Rearranging the cabling had no effect; the cause is apparently inside the FSS. The step at 100 kHz turns out to be a saturation effect, as it moved as we lowered the signal amplitude, disappearing as we approached -60 dBm. (Above the step, the measurement data is valid; below, bogus.)

Transfer functions will be attached to this entry.

Some things to check tomorrow: the RF signal to the PC, RF AM generation by the PC, LO drive level into the FSS, RF reflection from the PC, efficiency of FSS optical path, quality of RF cabling.
  136   Wed Nov 28 19:44:18 2007 tobinUpdatePSLHEPA
I found the HEPA turned off completely. I turned it on.
  137   Wed Nov 28 21:51:52 2007 tobinConfigurationPSLISS
I replaced the front-end differential receivers for the ISS's "inner-loop" sensor and monitor diode inputs with lower-noise THS4131's (formerly THS4151's). I verified operation by taking the transfer function from the "PD+" and "PD-" inputs (separately) to the testpoint following the differential receiver; the surgery appears successful.

I measured the dark spectra at the ISS's DC PD BNC ports and found a noise floor of ~ 16 nV/rtHz, compared with a floor of ~ 22 nV/rtHz last week. This seems to add up, assuming the DC PD port has 0dB gain: the 4131 has a rated noise of 1.3 nV/rtHz and the 4151 a noise floor of 7.6 nV/rtHz, a difference of 6 nV/rtHz. The other change made in that time was to add a larger power supply bypass capacitor in the PD.

There are two of the old 4151 chips still on the ISS board on the two "outer-loop" channels that we don't use. If I dig up any more 5131's I will replace these too for completeness.

There is currently no light on the ISS diodes; I'm not sure where it's intended to come from.
  140   Thu Nov 29 14:29:22 2007 tobinConfigurationComputerslinux1 httpd/conlogger fixed
I think I fixed the conlogger web interface on linux1.

Steps necessary to do this:
0. Run "/etc/init.d/httpd start" to start up httpd right now
1. Run "/usr/sbin/ntsysv" and configure httpd to be started automatically in the future
2. Copy /cvs/cds/caltech/conlogger/bin/conlog_web.pl to /var/www/cgi-bin and chown to controls
8. Hack the conlog_web.pl to (0) use /usr/bin/perl (1) not use Apache::Util, and (2) function with the newer version of CGI.pm
9. Enjoy!

The following steps are optional, and may be inserted between steps 2 and 8:
3. Try to install Apache::Util (via "perl -MCPAN -e shell" followed by "Install Apache::Util")
4. Notice that the installation dies because there is no C compiler installed
5. Bang head in disgust and abomination over a Linux distribution shipping without a C compiler installed by default
6. "yum install gcc"
7. Annoyed by further dependencies, go to step 8
  158   Mon Dec 3 16:24:47 2007 tobinHowToComputersGNU screen
GNU screen is a utility that can be quite handy for managing long-running psuedo-interactive terminal programs on remote machines. In particular, I think it might be useful in developing and testing "Matlab DMT" tools on Mafalda.
  159   Mon Dec 3 17:55:39 2007 tobinHowToComputer Scripts / Programslinemon
Matlab's Signal Processing toolbox has a set of algorithms for identifying sinusoids in data. Some of them (e.g., rootmusic) take the number of sinusoids to find as an argument and return the "most probable N frequencies." These could be useful in line monitoring.
  162   Mon Dec 3 22:20:09 2007 tobinConfigurationPSLISS
I replaced the painfully short 1' cables on the ISS photodiodes with luxurious five foot cables, made by chopping a ten foot Amphenol cable (P/N:CS-DSPMDB09MM-010) in half and using each half for one of the diodes. All of the ISS GND connections are wired to the PD GND, as is the PD- differential signal. The diodes are installed on the PSL table, but I have not tested them beyond looking at the DC values as I blocked/unblocked the beam.
  163   Tue Dec 4 23:16:35 2007 tobinUpdatePSLISS
I was confused to find that I could increase the ISS gain slider all the way from 15dB to 30dB without seeing much of any increase in gain in the measured open-loop transfer function. While making these swept-sine measurements, the saturation indicator almost never tripped, indicating it was seemingly happy. But then I noticed an odd thing: if I disable the test ("analog excitation") input, the saturation indicator trips immediately. I hooked up a scope to the current shunt test point (TP12). With the test input enabled, the loop closed, and the analog excitation port connected to the SR785, I see a a 5 Vpkpk, 2.55 MHz triangle wave there. It is there even if I set the SR785 excitation amplitude to zero, but it disappears if I disconnect the cable from the SR785.

I found oscillations at TP20, TP30, TP36, TP41, and TP42. Many of these are in the (unused) "outer loop" circuitry and currently lack compensation capacitors.
  166   Wed Dec 5 16:57:36 2007 tobinHowToComputer Scripts / ProgramsSR785 data converter on linux
I was pleased to find that the SR785 Data Viewer (including the command line conversion utility) installs and works in linux using WINE (on my laptop at least). There are some quirks, of course, but I was able to extract my data.
  167   Wed Dec 5 17:49:57 2007 tobinUpdatePSLISS
Attached is a plot of the ISS RIN with a variety of gain settings.

Unfortunately the dark noise is huge now--a result of the new cables & wiring?
  169   Wed Dec 5 18:22:03 2007 tobinUpdatePSLISS dark noise
Attached is a plot of the dark noise spectrum of the ISS photodiodes (1) before fooling with them, (2) after replacing the 4151's with 4131's (improvement!), and (3) after replacing the cables and changing the wiring (disaster!).
  171   Wed Dec 5 20:32:51 2007 tobinUpdatePSLISS dark noise
The ISS dark noise is not coming from the PD heads; the spectrum is essentially unchanged when the PD is unplugged from the ISS. Did the input opamps both get semi-fried in the same way? (They worked so well when they were first installed.) What else changed? I'm baffled. Frown
  177   Thu Dec 6 19:30:43 2007 tobinUpdatePSLISS dark noise - 60 Hz!
A higher resolution spectrum [attached] shows that nearly all of the excess dark noise on the ISS is in 60 Hz harmonics (with some 256 Hz harmonics too--are these from the DAQ?).

With the loop closed and the slider at 5dB, the laser light coming out has a noise floor of 10^-7 RIN or better from 40 Hz to 8 kHz.

Now to figure out why all this 60 Hz is getting in... (I tried turning off all the lights and the HEPA, and moving the SR785 further away, none of which did anything.)
  181   Fri Dec 7 18:28:30 2007 tobinUpdateComputer Scripts / Programscompiled matlab hoses itself
Andrey pointed out to me that some matlab functions in the Signal Processing Toolbox were dying with errors. Looking into the .m file (identified using the "which" command), I was surprised to see binary garbage rather than glistening, clear Matlab prose. Then I noticed the directory in which it was finding the .m file:
>> which decimate
/cvs/cds/caltech/apps/mDV/extra/linetrack_c_mcr/toolbox/signal/signal/decimate.m
See that "linetrack_c_mcr" directory? This is what is generated when a "compiled" (grumble) Matlab program is run--it decompresses itself into a subdirectory containing weird semi-compiled binary .m files. Unfortunately this is somehow getting incorporated into the matlab path. (I assume there is something in mDV that says "put all subdirectories into the path.")

I hate the Matlab compiler.
  182   Fri Dec 7 18:31:30 2007 tobinUpdateComputer Scripts / Programscompiled matlab hoses itself
Addendnum. The reason the linemon_mcr command was in the path was because of the user issuing the command "addpath(genpath(pwd))" where genpath(D) "returns a path string starting in D, plus, recursively, all the subdirectories of D."

The Matlab compiler is still bad, however.
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