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ID Date Author Type Category Subjectdown
  12306   Fri Jul 15 17:44:37 2016 AakashSummaryGeneralAcromag Setup | SURF2016

Aidan has described the physical connections and initial setup here :  https://nodus.ligo.caltech.edu:30889/ATFWiki/doku.php?id=main:resources:computing:acromag#recovering_from_a_terminal_power_communication_outage  .

Since I used a Raspberry Pi(domenica.martian) for communicating to Acromag(acroey.martian) card, I had to recompile everything for linux-arm architecture. 

For EPICS installation, download the EPICS base from http://www.aps.anl.gov/epics/download/base/baseR3.14.12.3.tar.gz . Installing dependencies, build, install epics at /usr/local/epics. By downloading modbusApp source from https://llocds.ligo-la.caltech.edu/daq/software/source/epics-3.14.12.2_long-source.tar.gz  , build the modbusApp for linux-arm architecture in modules/modbus directory inside epics base.

Put all the files mentioned by Aidan and run a tmux session to grab channels.

Also, pyModbus can be used to read the channels. I'll put the physical connections schematic shortly.

  12360   Mon Aug 1 18:50:29 2016 AakashUpdateGeneralAcromag Setup | SURF2016

There were many unknown and unsolved problems with using modbusApp for linux-arm architecture. So I tried to install the necessary files to setup Acromag Busworks card 1221-000 on Zita(192.168.113.217), which is a linux-x86_64 machine on the martian network. After installing a few dependencies and seting up few symbolic links for some libraries, everything is successfully configured. Initially I was unable to run myiocconfig.cmd file(as mentioned by Aiden on ATF wiki page) due to a undefined macro error for envset. Later I found that this error might be due to THIS bug in epics base. So, I removed the first four lines of that given code and directly referenced the .db file's location and it worked.

Now, I am facing another issue while running this file but on different line. Random symbols are returned on the last second line of the file each time I run it. I have attached the screenshots of those errors. I tried changing the encoding of the file several times but still it is showing the same error.

 

Attachment 1: 1.png
1.png
Attachment 2: 2.png
2.png
Attachment 3: 3.png
3.png
Attachment 4: 5.png
5.png
Attachment 5: 6.png
6.png
Attachment 6: 7.png
7.png
Attachment 7: 8.png
8.png
  12366   Wed Aug 3 15:35:19 2016 AakashUpdateGeneralAcromag Setup | SURF2016

Lydia helped me to troubleshoot the Accromag connection problems which I was facing previously.  If power goes off/turned off manually, the ethernet cable has to be pulled out and put back again until only a non-blinking green light is observed. I was foolish enough that I did not use secure power connections. About the random symbol, a code block was not closed in the other supporting file which was being called in the main program. There are still some port errors and register errors, which I would work on later tonight.

  12368   Wed Aug 3 16:34:59 2016 LydiaUpdateGeneralAcromag Setup | SURF2016

Actually, if the power goes off and back on, the ethernet connection comes back online after about 5 seconds, or faster if it is disconnected and reconnected. The main issue was that the cable had partially slipped out (ie both power and network connections were loose); I suggest that the final setup should use ethernet cables that have a locking tab as this one does not. 

Quote:

Lydia helped me to troubleshoot the Accromag connection problems which I was facing previously.  If power goes off/turned off manually, the ethernet cable has to be pulled out and put back again until only a non-blinking green light is observed. I was foolish enough that I did not use secure power connections. About the random symbol, a code block was not closed in the other supporting file which was being called in the main program. There are still some port errors and register errors, which I would work on later tonight.

 

  12477   Wed Sep 7 18:00:47 2016 LydiaUpdateGeneralAcromag Progress

[Teng, Lydia]

We would like to establish a system for setting up ADC channels and integrating them into the existing EPICS framework, so that we can gradually switch over channels that are currently handled by the aging slow machines. Otherwise, we will be stuck when they eventually fail. As a preliminary test for this method, we are in the process of setting up an Acromag ADC to read the "Diagnostic" output of the PSL controller. This information will also be useful to monitor the health of the PSL. 

Today, we accomplished the following:

  • Configured the Acromag XT1221 for use on the martian netowrk. It is assigned the static IP 192.168.113.237, with hostname iocPSLmon. 
  • Connected the Acromag to a switch on the 1X6 cabinet, and set it up on a desk near the X arm door with a 24V DC power supply. 
  • Verified that the IP was reachable from a control room desktop. 
  • Modified the files from Aiden's wiki page (myiocconfig.cmd and IOCTEST.db) to reflect our setup. 
  • Attached input 0 to a DC voltage and retrieved the output over the network. 
    • Channel name: "C3:ACROMAG_INPUT0" 
    • Values are currently uncalibrated, the voltage is represented by a 16 bit signed integer
    • We changed the value of the DC input and verified that the channel output changed in the expected direction

The power supply has been turned off for the night. 

  12514   Thu Sep 22 20:18:27 2016 LydiaUpdateGeneralAcromag Progress

We moved the Acromag and its power supply to the X end, where we connected it to the diagnostic output of the NPRO controller. We renamed the channels to be descriptive of the pin outputs as described in the laser manual. We were able to recover readouts similar to those we found with a multimeter. 

We should figure out how to set up the channels on the front end machines: right now they are accessed through a tmux session running on pianosa. Once we are confident in the operation, we will make a box to contain the Acromag and wire connections and move the setup to connect to the PSL controller. 

  12554   Wed Oct 12 18:09:25 2016 LydiaUpdateGeneralAcromag Progress

[Lydia, Johannes]

Johannes acquired a crate to contain the Acromag setup and wiring, and installed a rail along the bottom panel so that the ADC units will be oriented vertically with the ehternet ports facing up. We briefly talkes about what the layout should be, and are thinking of using 2 rails, one for ADCs and one for DACs. We want to design a generic front panel to accept 25 pin D-Sub inputs and maybe also BNCs, which we can use for all the Acromag crates. 

I got the epics session for the acromag to run on c1iscex and was able to access the channel values using caget on donatella. However, I get the following warning: 

cas warning: Using dynamically assigned TCP port 48154,
cas warning: but now two or more servers share the same UDP port.
cas warning: Depending on your IP kernel this server may not be
cas warning: reachable with UDP unicast (a host's IP in EPICS_CA_ADDR_LIST)

 

It seems like there might be a way to assign a port for each unit, if this is a problem. 

Also, c1iscex doens't have tmux; what's the best way to run the modbusApp and then detach? Right now I just left an epics session running in an open terminal. 

Plans:

  • Deisgn crate connections and interior layout. Set up front panel to accept desired connections. 
  • Set up the crate with the Acromag XT1221 reading the diagnostic info from the X end NPRO in the X end rack.
  • Figure out how many of each type we need to replace c1auxex functionality, and order them.
  • Generate appropriate EPICS db files for acromag based on slow machine channels.
  • Add necessary units to X end Acromag crate and read in the same inputs as c1auxex. 
  • Set up everything else to look for c1auxex channels from Acromag instead. (Not sure about nuances of this step: should we name the channels something different at first? How to find everything that relies on c1auxex? Must be careful with SUS channel connections.)
  •  Determine number of units needed to replace all slow machines, and order thm. Likewise assemble as many crates as necessary with the right connections. 
  • Once we are confident that the replacement is complete and fully functional, disconnect c1auxex and repeat process for other slow machines. 
  12625   Fri Nov 18 00:25:08 2016 JohannesOmnistructure40m upgradingAcromag Chassis Development

I had Rich show me his approach to a chassis for the Acromag modules. The document tree for his design can be found on the DCC. Note that he's using the high densitymodel ES series, which is available as a bare board variant with pluggable screw terminals:

He can fit up to 4 of these in a 2U chassis and has outsourced the wiring from front panel Dsubs to the board connectors to an external company. At the 40m (and in West Bridge) we currently only have the rail mounted XT series

At first glance the specs are very similar. Both A/D and D/A flavors have 16-bit precision in both cases. The high density ES series with Rich's layout can achieve 128 A/D per 2U, 64 D/A per 2U, or 384 DIO per 2U. Into a 4U chassis of the type we have currently we can fit ~32 XT modules (assuming two rows), which results in very similar numbers, except for the DAC, of which we could fit more.

XT1221-000 (8 diff. channel 16-bit ADC)                          $495.00      $61.88/ch
XT1541-000 (8 channel 16-bit DAC and 4 discrete I/O )    $525.00      $65.63/ch
XT1120-000 (16 channel DIO)                                         $320.00     $20.00/ch

ES2162-0010 (32 diff. channel 16-bit ADC)                     $2050.00    $64.06/ch
ES2172-0010 (16 channel 16-bit DAC)                           $1400.00    $87.50/ch
ES2113-0010 (96 channel DIO)                                      $1100.00    $11.46/ch

It's cheaper to stick with the current XT models, but they need the bulkier 4U chassis. The good news is that actually all these models have 16 bit precision, which wasn't clear to me before. Lydia and I will work out what connectors we want on the boxes, and how many modules/channels we need where. Rich also got me in touch with Keith Thorne, who handles the analog I/O Acromag at LLO, and I will ask him for advice. From his documents on the DCC it seems that he is using yet another series: EN. The 968EN-4008 for example is a rail-mounted ADC with pluggable connections, but looses quite clearly in price per channel.

For a generic multipurpose DAQ interface box the ES series is the best approach in my opinion, because it offers a more compact design. We could for example fit 1 ADC, 2 DAC, 1 DIO in a 2U chassis for 32/32/96 channels. The combined price tag for this scenario would be ~$6k.

 

 

  12634   Tue Nov 22 13:55:32 2016 JohannesOmnistructure40m upgradingAcromag Chassis

Current Acromag chassis status:

I found out that Acromag offers DIN rail mounting kits for the open boards, so we can actually fit both XT series and ES/EN series in the same boxes, depending on the signal needs. The primary design driver will be the ES footprint, but if we find we don't need that many channels in some of the units, it's interchangable. For the wiring to the front panel - for which we will have a standard front panel express design, but may order modified ones for the custom needs of the 40m, I will contract the same company that Rich used for the wiring in his DIO box (Panel mount connectors terminating in loose wires/pre-routed plugs for Acromag units). We will either run a single DIN rail along the length of the chassis, or have two in parallel across.

Lydia and I took close looks at the breakout arrangements on the rack sides, and determined that because of the many cross-connects between non-DAQ ports it is not possible to redo and debug this in a reasonable amount of time without essentially shutting down the interferometer. So instead, we will connect the chassis directly to the slots that were previously leading to the slow machines. They come in two different flavors: The ADC modules have 64 pins, while the DIO and DAC ones have 50. There are a couple things we can do:

  • For ADC: Put favorite 64+ pin connector on front panel. I would advocate for the 68 pin VHDIC (SCSI-5). This standard ist widely used, has a sturdy connector, and usually off-the-shelf cables have twisted pair leads.
  • For DAC+DIO: Either use favorite 50 pin connector (there are 50-pin DSUB connectors, and also 50-pin IDC connectors with backshell), or also send the signals through VHDIC connectors, tolerating a few unused lanes. I would prefer the second option, after all it all goes to some 64 pin VME-crate backplane connector in the end, so if we ever get rid of the rack-side breakouts the wiring will much more uniform.
  • For good measure, we will add a few (16 maybe) BNC connectors to the front panel.
  • A standardized front panel could have a variety of different connectors by default: DSUBs, BNCs, etc., to be used when needed with some initial default wiring.
  • Note that THEORETICALLY we could even connect all backplane EUROCARD ports to the Acromag chassis and do the cross-connect wiring entirely inside, although that would make the inside extremely messy.

Based on Rich's design I will get started on a parts list and wiring diagrams to send out to the cable company.

Attachment 1: acroplan.pdf
acroplan.pdf
  12677   Wed Dec 14 19:16:57 2016 LydiaUpdateCDSAcromag Binary I/O testing

I looked into converting the QPD whitening switches for the X end to Acromag.

  • To test this out and be able to freely toggle filters without messing anything up, I added a temporary dummy cdsFiltCtrl module (ACROMAG_BIO_TEST) to the c1scx model.
  • The filters can be toggled from the automatically generated medm screen medm/c1scx/C1SCX_ACROMAG_BIO_TEST.adl
  • The control output of the dummy filter bank is sent to a channel named C1:SCX-ACROMAG_SWCTRL.
  • I was able to read in the appropriate bits from there and send them to the appropriate acromag channel using a calcout channel.
    • I couldn't get individual bo channels to work. This Acromag module is configured to write to 4 channels at a time, so I set that up with an analog output channel. The calcout channel shifts each relevant bit from C1:SCX-ACROMAG_SWCTRL to the right place for writing to the Acromag. 
  • I connected the Acromag XT1111 Binary I/O unit to a temporary power supply and verified that toggling the filters on and off changed the output appropriately. This is a sinking output model so the output pin is connected to the return if the switch is on. 

The plan from here:

  • Determine how to configure these outputs to be compatible with the QPD whitening board.
  • Modify the SUS PD whitening board to always use the analog filter and remove digital option in models.
  • Test DACs 
  • Verify that the QPD whitening gain switches aren't doing anything
  • Assemble new Acromag box for X end and connect to QPD whitening, SUS PD whitening and SOS driver boards
  7814   Wed Dec 12 11:49:05 2012 AyakaUpdateLSCAcoustic noise in POX and AS error signal

[Koji, Ayaka]

Last night, I injected acoustic noise at POX table and AS table with oplev controls on (LPF is on).

 

1. acoustic noise at the POX table

I set the microphones and speakers at the POX table and see the acoustic coupling.

POX_noise4.pdf

I could see slight change around 40 Hz. This can be caused by the oplev feedback loop because the speaker was on the same table as the ITMX oplev.

 

2. acoustic noise at the AS table

I controlled XARM with AS error signal and set the microphones and speaker on the AS table.

AScontXARM_acoustic.pdf

The resonance a 200 Hz seemed to be enhanced. But still we are not sure that it is caused by acoustic noise. Because this resonance is enhanced when the OL gain is high, and the gain adjustment was so critical that this resonance was easily enhanced even when the acoustic noise is not injected. And sometimes it has gone away.

  7707   Tue Nov 13 21:05:22 2012 AyakaUpdateWienerFilteringAcoustic noise cancellation with MC

 In order to perform acoustic noise cancellation with MCL signal, I am trying to find sweet spots for microphones.

I set microphones at various places around MC chambers, and see how coherent microphones and MC signals are.
I had checked the half part of MC.

  • data set #1
    place where I set the microphones (left), MCL signal (blue) and its error (green) (right top), and coherence between microphones (original: fine lines, error: thick lines) (right bottom).
    microphone_pos1.pdfpsd_coh1.png
  • data set #2
    microphone_pos2.pdfpsd_coh.png 
  •  data set #3
    microphone_pos3.pdfpsd_coh.png
  • data set #4
    microphone_pos4.pdfpsd_coh4.png

The acoustic noise around the MC2 chamber is most critical so far. I could subtract the signal and the sensitivity got 2 times better.
I will see the acoustic coupling from the other side of MC.

Attachment 4: psd_coh.png
psd_coh.png
  12442   Thu Aug 25 19:03:56 2016 PrafulUpdateElectronicsAcoustic Tab and Amp Suspension

My box has been suspended in the PSL using surgical tubing, and it has been connected to C1:PEM-MIC_1 (C17) with a BNC. I made a braided power cable as well but it turned out to be slightly too short... Once this is fixed, everything should be ready and we can see if it's working correctly. I also set up a new tab on the summary pages for this channel:

https://ldas-jobs.ligo.caltech.edu/~praful.vasireddy/1154941217-1154942117/pem/acoustic/

This data is back from when I had my solderless breadboard running near MC2. I'll add this tab to the real pages once the box is working (which could be a while since I'm gone for a month). Let me know if you see any issues with either the tab or the box/cables.

  12460   Thu Sep 1 15:28:01 2016 ranaUpdateElectronicsAcoustic Tab and Amp Suspension
  1. add photo of installation
  2. no more secret personal pages! put channels into the actual pages that we look at
  3. make it ASD instead of PSD, same as the other channels
  4. add specgram (whitened and not)
Quote:

My box has been suspended in the PSL using surgical tubing, and it has been connected to C1:PEM-MIC_1 (C17) with a BNC. I made a braided power cable as well but it turned out to be slightly too short... Once this is fixed, everything should be ready and we can see if it's working correctly. I also set up a new tab on the summary pages for this channel:

https://ldas-jobs.ligo.caltech.edu/~praful.vasireddy/1154941217-1154942117/pem/acoustic/

This data is back from when I had my solderless breadboard running near MC2. I'll add this tab to the real pages once the box is working (which could be a while since I'm gone for a month). Let me know if you see any issues with either the tab or the box/cables.

 

  12463   Thu Sep 1 17:25:02 2016 PrafulUpdateElectronicsAcoustic Tab and Amp Suspension

I'll add a picture of the installation when I get back to campus and finish hooking up the power cable. I haven't added this channel to the actual pages yet because there's not any data right now- the box is still unpowered because my braided power cable wasn't long enough. I just changed the format of the spectrum to ASD and added spectrograms. Here's how the tab looks now: https://ldas-jobs.ligo.caltech.edu/~praful.vasireddy/1155014117-1155015017/pem/acoustic/

Let me know if there's anything else to change.

Quote:
  1. add photo of installation
  2. no more secret personal pages! put channels into the actual pages that we look at
  3. make it ASD instead of PSD, same as the other channels
  4. add specgram (whitened and not)
Quote:

My box has been suspended in the PSL using surgical tubing, and it has been connected to C1:PEM-MIC_1 (C17) with a BNC. I made a braided power cable as well but it turned out to be slightly too short... Once this is fixed, everything should be ready and we can see if it's working correctly. I also set up a new tab on the summary pages for this channel:

https://ldas-jobs.ligo.caltech.edu/~praful.vasireddy/1154941217-1154942117/pem/acoustic/

This data is back from when I had my solderless breadboard running near MC2. I'll add this tab to the real pages once the box is working (which could be a while since I'm gone for a month). Let me know if you see any issues with either the tab or the box/cables.

 

 

  12614   Mon Nov 14 19:15:57 2016 JohannesUpdateGeneralAchievable armloss measurement accuracy

Looking back at elog 12528, the uncertainty in the armloss number from the individual quantities in the equation for \mathcal{L} can be written as:

\delta\mathcal{L}^2=\left(\frac{T_1(1-\frac{P_L}{P_M}-2T_1)}{4\gamma}\right)^2\left(\frac{\delta T_1}{T_1}\right)^2+T_2^2\left(\frac{\delta T_2}{T_2}\right)^2+\left(\frac{T_1(1-\frac{P_L}{P_M}-T_1)}{4\gamma}\right)^2\left(\frac{\delta\gamma}{\gamma}\right )^2+\left(\frac{T_1}{4\gamma}\right )^2\left[\left(\frac{\delta P_L}{P_L}\right )^2+\left(\frac{P_L}{P_M} \right )^2\left(\frac{\delta P_M}{P_M}\right )^2\right ]

Making some generous assumption about the individual uncertainties and filling in typical values we get in our measurements, results in the following uncertainty budget:

\delta\mathcal{L}^2\approx\left(12\,\mathrm{ppm}\right)^2\left(\frac{\delta T_1/T_1}{5\%}\right)^2+(0.7\,\mathrm{ppm})^2\left(\frac{\delta T_2/T_2}{5\%}\right)^2+\left(2\,\mathrm{ppm}\right)^2\left(\frac{\delta\gamma/\gamma}{1\%}\right )^2+\left(140\,\mathrm{ppm}\right )^2\left(\frac{\delta P/P}{2.5\%}\right )^2

In my recent round of measurements I had a 2.5% uncertainty in the ASDC reading, which completely dominates the armloss assessment.

The most recent numbers are 57 ppm for the YARM and 21 ppm for the XARM, but both with an uncertainty of near 150 ppm, so while these numbers fit well with Gautam's estimate of the average armloss via PRG, it's not really a confirmation.

I set the whitening gain in ASDC to 24 dB and ran LSC offsets, and now I'm getting a relative uncertainty in measured reflected power of .22%, which would be sufficient for ~25ppm accuracy according to the above formula. I'm going to start a series of measurements tonight when I leave, should be done in ~2 hours (10 pm) the latest.

If anybody wants to do some night work: I misaligned ITMY by a lot to get its reflection off ASDC. Approximate values are saved as a restore point. Also the whitening gain on ASDC will have to be rolled back (was at 0dB) and LSC offsets adjusted.

  12618   Tue Nov 15 20:35:19 2016 JohannesUpdateGeneralAchievable armloss measurement accuracy

I had a mistake in my script that reported the wrong error after averaging several datapoints, and because I hadn't looked at the individual numbers I didn't catch it so far. Thanks to Gautam it is no more.

The updated numbers are (with fresh, more trustworthy data):

XARM: 21 +/ 35 ppm
YARM: 69 +/- 45 ppm

This looks much better. I'm planning to take more data with the AS110 PD rather than AS55 when I get the chance, increase the averaging time, and also sigma filter the datapoints. That should get us to a good spot and cut down the uncertainty even further.

  12624   Thu Nov 17 21:54:11 2016 JohannesUpdateGeneralAchievable armloss measurement accuracy

I don't like AS110 or AS55. Neither of them are designed for DC and so the DC readout chain is hokey. How about use an actual transimpedance PD with a 100-1000 Ohm resistor and a 3 mm diode? This would eliminate the alignment sensitivity and the drifts due to electronics and room lights.

This looks much better. I'm planning to take more data with the AS110 PD rather than AS55 when I get the chance, increase the averaging time, and also sigma filter the datapoints. That should get us to a good spot and cut down the uncertainty even further.

 

  8580   Wed May 15 17:17:05 2013 JamieSummaryCDSAccounting of ADC/DAC channel availability

We need ADC and DAC channels for a couple of things:

  • POP QPD: 3x ADC
  • ALS PZTs: 3x 2x 2x DAC (three pairs of PZTs, at ends and vertex, each with two channels for pitch and yaw)
  • Fibox: 1x DAC

What's being used:

  • c1iscex/c1iscey:
    • DAC_0:   7/16 = 9 free
    • ADC_0: 17/32 = 15 free
  • c1sus:
    • DAC: ?
    • ADC: ?
  • c1ioo
    • DAC_0:   0/16 = 16 free ?? This one is weird. DAC in IO chassis, half it's channels connected to cross connect (going ???), but no model links to it
    • ADC_0: 23/32 = 9 free
    • ADC_1:  8/32 = 24 free
  • c1lsc
    • DAC_0: 16/26 = 0 free
    • ADC_0: 32/32 = 0 free

What this means:

  • We definitely have enough DACs for the ALS PZTs.  The free channels are also in the right places: at the end stations and in the c1ioo FE, which is close to the PSL and hosts the c1als controller.
  • We appear to have enough ADCs for the QPD in c1ioo.
  • We don't have any available DAC outputs in c1lsc for the Fibox.  If we can move the Fibox to the IOO racks (1X1, 1X2) then we could send LSC channels to c1ioo and use c1ioo's extra DAC channels.

Of course we'll have to investigate the AA/AI situation as well.  I'll try to asses that in a follow up post.

PS: this helps to identify used ADC channels in models:

grep adc_ sus/c1/models/c1scx.mdl | grep Name | awk '{print $2}' | sort | uniq

 

  8583   Wed May 15 19:32:04 2013 ranaSummaryCDSAccounting of ADC/DAC channel availability
  1. What are we using 16 DAC channels for in the LSC?
  2. What are the functions of those IOO DAC channels which go to cross-connects? If they're not properly sending, then we may have malfunctioning MC or MCWFS.
  3. Can we just use the SLOW DAC (4116) for the ALS PZTs? We used this for a long time for the input steering and it was OK (but not perfect).
  8585   Wed May 15 22:47:11 2013 JamieSummaryCDSAccounting of ADC/DAC channel availability

Quote:
  1. What are we using 16 DAC channels for in the LSC?

For the new input and output tip-tilts.  Two input, two output, each requires four channels.

Quote:
  1. What are the functions of those IOO DAC channels which go to cross-connects? If they're not properly sending, then we may have malfunctioning MC or MCWFS.

I have no idea.  I don't know what the hardware is, or is supposed to be, connected to.  DAC for WFS??  Was there at some point supposed to be fast output channels in the PSL?

Quote:
  1. Can we just use the SLOW DAC (4116) for the ALS PZTs? We used this for a long time for the input steering and it was OK (but not perfect).

 Probably. I'm not as familiar with that system.  I don't know what the availability of hardware channels is there.  I'll investigate tomorrow.

  9429   Wed Nov 27 16:29:21 2013 JenneUpdateCDSAccidentally turned off SUS IO chassis

[Jenne, Koji]

I was trying to lock the Yarm, and saw that I was not getting signals to go between the LSC and SCY models.  I had digital zeros for TRY, and when I overrode the trigger and tried to force signal to ETMY, I had digital zeros at the SUS-ETMY_LSC input. The corresponding filter bank in the rfm model was receiving signals, so the Dolphin connection between LSC and SUS was okay, it was just the RFM connection going to the end station that wasn't succeeding. 

Koji restarted the c1scy model, and then went inside the IFO room, and found that the SUS IO chassis power was offWe must have accidentally turned it off while we were in there earlier.  Koji turned on the power, and also restarted the rfm model, and we now have real signals going back and forth. 

Yarm is locked, ASS worked nicely, etc, etc, so things seem normal again (with the Yarm....ETMX stuff is still out of order).

  830   Tue Aug 12 21:38:19 2008 JohnUpdateLSCAccidental higher order mode resonances in the arms
Recently we had been having some trouble locking the full IFO in the spring configuration (SRC on +166).
It was thought that an accidental higher order mode resonance in the arms may have been causing problems.

I previously calculated the locations of the resonances using rough arm cavity parameters(Elog #690). Thanks to Koji
and Alberto I have been able to update this work with measured arm length and g factors for the y arm (Elog #801,#802).
I have also included the splitting of the modes caused by the astigmatic ETM. Code is attached.

I don't see any evidence of +166MHz resonances in the y arm.


In the attached plot different colours denote different frequencies +33, -33, +166, -166 & CR.
The numbers above each line are the mn of TEMmn.
Solid black line is the carrier resonance.
Attachment 1: HOMresonances.png
HOMresonances.png
Attachment 2: HOMarms2.m
%Check for accidental resonances of HOM in the arms (maybe due to
%sidebands). At the moment there is only data for the y arm.

clear all
close all
clc


%Stuff one might change often
modeorder = 0:5;          % Look for TEMmn modes where m,n run over modeorder
... 157 more lines ...
  5289   Tue Aug 23 16:23:33 2011 JenneUpdateVACAccess connector in place

[Steve, Bob, Jamie, Kiwamu, Valera, Jenne]

The access connector is now in place, in preparation for pump-down.  Tomorrow (hopefully) we will do all the other doors.

 

  1692   Tue Jun 23 23:14:36 2009 ClaraConfigurationPEMAccelerometers relocated

Both accelerometers have been moved in an attempt to optimize their positions. The MC1 accelerometer was moved from one green bar to the other (I don't know what to call them) at the base of the MC1 and MC3 chambers. That area is pretty tight, as there is an optical table right there, and I did my best to be careful, but if you suspect something has been knocked loose, you might check in that area. The MC2 accelerometer was moved from the horizontal bar down to the metal table on which the MC2 chamber rests.

  2078   Fri Oct 9 17:41:04 2009 JenneUpdatePEMAccelerometers relocated

[Sanjit, Jenne]

The set of 6 accelerometers which were semi-randomly placed underneath the MC2 tank are now back into 2 separate sets of 3 - one set at MC2 and one set at MC1.  The channel names once again reflect reality, i.e. MC1_Y is actually under the MC1 tank, and aligned with the y direction.  Also, the Guralp under MC1 was moved a little bit to the left, because Sanjit wanted to put the accelerometers where the seismometer had been. 

  2079   Sun Oct 11 04:12:44 2009 ranaUpdatePEMAccelerometers relocated

Some of these channels are not like the others.

Attachment 1: Untitled.png
Untitled.png
  11389   Wed Jul 1 16:16:46 2015 IgnacioUpdateGeneralAccelerometers reinstalled for future huddle test

Today, I installed the Wilcoxon accelerometers in the table near the end of the mode cleaner. I only set three of them up instead of all six. They were set up just as Rana suggeted we should have them properly set up, i.e. cables being tighten up, and a box on top to prevent any airflow introducing any disturbances. We are planning on running the huddle test on these guys once the upgrade? to the interferometer is done.

The cables were tightly clamped to the table as shown below, I used a thick piece of shock absorbing rubber to do this.

 A small piece of thin rubber was used to hold each of the accelerometers tightly to the table in order not to damage them.

We had to borrow Megan's and Kate's piece of black foam in order to seal one of the sides properly, as the cable had to come out through somewhere. We didn't want to mess with drilling any holes into the box! 

There was a small crack even after using the foam. I sealed it up with duck tape.

The box isn't perfect, so there were multiple cracks along the bottom and top of it that could potentially allow for air to flow to the inside. Eric suggested that we should be super careful this time and do it right, so every crack was sealed up with ducktape.

 

Finally, we needed something heavy to be placed on top of the box to hold everything well. We used Rana's baby to accomplish this goal.

Just kidding! Rana's baby is too delicate for our purposes. A layman box of heavy cables was used instead. 

 

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

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

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

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

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

Some remarks:

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

Attachment 1: IMCcoherence_Jun172015.xml.zip
Attachment 2: IMCcoherence.png
IMCcoherence.png
  172   Wed Dec 5 23:19:03 2007 AndreyConfigurationPEMAccelerometers are turned on

All accelerometers have been turned on, as Alan asked during Wednesday meeting.

Typical power spectra and coherence plots are attached below.

"East" in the name means that the previous location of accelerometrs was to the east from "Beamsplitter" (the location for "east" accelerometers was not changed, actually, it is still near ITMX), while "west" means that previously accelerometers were to the west from the BS, but now their new location is near the ETMX.

I will change the names of the channels tomorrow (Thursday) when someone (Tobin?) will show to me how to do it.

P.S. (addition made on Dec. 19th, 2007, by Andrey) I intended to change the names of accelerometers the next day, Thursday Dec. 06,
but I did not do it that day (did not understand how to do it), then I fell ill, and eventually
I changed the names of accelerometers on December 19th, see entry to ELOG #204)
Attachment 1: Power_Sp_and_Coh_XY-EAST.pdf
Power_Sp_and_Coh_XY-EAST.pdf
Attachment 2: Coherence-ZX_East.pdf
Coherence-ZX_East.pdf
Attachment 3: Coherence-ZY_East.pdf
Coherence-ZY_East.pdf
Attachment 4: Power_Sp_WEST.pdf
Power_Sp_WEST.pdf
Attachment 5: Coherence-ZX_West.pdf
Coherence-ZX_West.pdf
Attachment 6: Coherence-XY_West.pdf
Coherence-XY_West.pdf
Attachment 7: Coherence-YZ_West.pdf
Coherence-YZ_West.pdf
  151   Fri Nov 30 20:17:26 2007 AndreyConfigurationPEMAccelerometers and alum.plates for them
All 6 accelerometers which were located near the ITMX are turned off and disconnected from the power cords.
Actually these accelerometers are now in the office area on the electronics bench (to the left from Steve Vass' place).

I made today 4 new aluminum mounting plates for the accelerometers (I drilled holes and made threads in them). On Monday I will buy short screws and install accelerometers on these new mounting plates. These mounting plates will be screwed directly into the metallic frame which is firmly cemented to the ground. Before yesterday accelerometers were mounted on top of blue stack towers, not on the ground directly, so we hope that new measurements of the ground noise will be more realistic.

The 4 mounting plates are on the same desk -> on the electronics bench (to the left from Steve Vass' place). Please do not displace them.

Attached is a drawing of the aluminum mountain plate.
Attachment 1: Scheme_Aluminum_Piece-inches.pdf
Scheme_Aluminum_Piece-inches.pdf
  853   Tue Aug 19 14:25:38 2008 SharonUpdatePEMAccelerometer's calibration - update
Goal - Make sure the accelerometers are calibrated among themselves (have the same power spectrum when they are all together reading the same movements).

What I did - took the accelerometers off their usual X Y Z setting and set the 3 MC2's and 3 MC1's next to each other covered by a box.
Then I brought MC2 X to MC1 X and placed them in a box so I have a referance between the 2 groups.

Result - Seems MC1 accelerometers are much alike and have the same power spectrum when placed together for all frequencies. MC2 accelerometers seem to do the same until approximately 30 Hz. (decided not to correct for that since we don't really care about the accelerometers in such high frequencies).

When comparing the 2 X's, they also seemed to be almost perfectly correlated. I chose the gain by dividing the two and finding the mean of that in the range of 2 to 30 Hz. After correcting for all the accelerometers, I matched the gains of each group to its X accelerometer.

You can see the plots, taking into consideration that the groups were never together (pretty messy getting the cables all around).

Here are the numbers, when the MC2 and MC1 gains are calculated by comparing them to their X direction.

gain MC1 X_over_MC2 X=

1.0870


gain_MC2_Y =

0.9944


gain_MC2_Z =

0.9479


gain_MC1_Y =

1.0394


gain_MC1_Z =

0.9149
Attachment 1: acccalibafter.png
acccalibafter.png
Attachment 2: acccalibbefore.png
acccalibbefore.png
  882   Mon Aug 25 17:45:34 2008 rana, josephb, robHowToPEMAccelerometer range
Joe shows us by jumping up ~15" in the control rom that the accelerometers are set with not enough gain.

Since this is taken around 5:30 in the evening, so we can take the nearby time series to represent what a
high noise level is. I recommend we up the gain using the ICS-110B .ini file.
Attachment 1: Screenshot-4.png
Screenshot-4.png
  7262   Thu Aug 23 21:53:18 2012 YaakovUpdatePEMAccelerometer location

The MC1 accelerometer cube (3 accelerometers arranged in x,y,z) is under the PSL table, as I found it at the beginning of the summer.

The MC2 accelerometer cube is on the table where I worked on the STACIS, right when you walk into the lab from the main entrance. Their cables are dangling near the end of the mode cleaner, so the accelerometers are ready to be placed there if wanted.

All accelerometers are also plugged into their ADC channels.

  3355   Wed Aug 4 01:44:56 2010 KojiConfigurationPEMAccelerometer located on and below the PSL table

[Jenne and Koji] 

In order to characterize the seismic vibration of the PSL table, we put the accelerometers on and below the PSL table.

On the PSL: MC2 Accelerometers (X, Y, Z) - being connected to CH1-3 of the preamps
East side of the PSL table. X, Y, and Z is directed to North, East, and Up.

On the ground: MC1 Accelerometers (X, Y, Z) - being connected to CH4-6 of the preamps
Beneath the West side of the PSL table. X, Y, and Z is co-aligned to the MC2 ACC.

I found that the C1:PEM-ACC_MC1_Z has large noise in the low freq (~1Hz) region. I tracked down the noise source
and found the noise is still present in the down stream even when the CH17 (C1:PEM-ACC_MC1_Z) of the ADC IF BNC
(@1Y7) was terminated.

I consulted with Jenne and decided to connect this channel to CH14, which is vacant and has name
C1:PEM-AUDIO_MIC2 (16k).
(for the details of the channel configurations, see /cvs/cds/caltech/chans/daq/C1ADCU_PEM.ini)

I first tried magnetometer channels to steal, but they didn't seem reacting (and the connected to the wrong channels).
I am feeling that we should once entirely check the I/F box.

Note that there looks the difference of the gain by x10 between C1:PEM-ACC_MC* channels and C1:PEM-AUDIO_MIC2.

[From Jenne:  The gain difference is because the C1:PEM-ACC_MC* channels have gain=10 in the .ini file, while C1:PEM-AUDIO_MIC2 uses the default gain=1. ]

Attachment 1: IMG_2675.jpg
IMG_2675.jpg
Attachment 2: IMG_2678.jpg
IMG_2678.jpg
Attachment 3: IMG_2682.jpg
IMG_2682.jpg
  3395   Tue Aug 10 22:40:55 2010 KojiSummaryPEMAccelerometer located on and below the PSL table

Result of the accelerometer measurement

Introduction

We wanted to characterize the PSL table before the work before its lifting up.
We put a set of three-axis Wilcoxon accelerometers on the ground and another set on the PSL table through the weekend.

Result

- The data at 9th Aug 00:00(UTC) is used. This was Sunday 5PM in the local time.
- The freq resolution was 0.01Hz. The # of avg was 50.

- The accelerometer signals were calibrated by the value 1.2e-7 V/(m/s^2). We use this absolute value of the spectrum for the comparison purpose.

- The accelerometers were aligned to North(X), East(Y), and Up(Z). There was the coherence observed from 2~20Hz.
  The transfer functions are valid only this frequency region although we still can set the lower bound of them.

- The transfer functions in the horizontal directions show huge peaks at around 20Hz. The Q of the peaks are ~30 to ~100.
  The vertical transfer function shows somewhat lower peak at around 50Hz with Q of ~10.

Some thoughts

- The low resonant freq and the high Q of the horizontal mode comes from the heaviness of the table.

- We are going to raise the table. This will usually mean that we get the lower resonant freq. This is not nice.

- So, the decision to use 6 tripods rather than 4 was right.
- The steel tripods are expected to give both more rigidity and more damping than the chep-looking hollow Newport legs.
- Concrete grouting of the tripods will also lower the effective height and will benefit for us.

 

Attachment 1: PEM_100809.pdf
PEM_100809.pdf
  930   Thu Sep 4 18:02:34 2008 rana, josephbConfigurationPEMAccelerometer gains increased by 10
We increased the Accelerometer gains by 10 by modifying the C1ADCU_PEM.ini file.
[C1:PEM-ACC_MC1_X]
chnnum=15014
gain = 10

etc.
The plot shows the before and after for one channel. The ADC noise floor is ~10^-2 counts/rHz in this plot so now
we can do much better noise subtraction.
Attachment 1: acc.png
acc.png
  673   Tue Jul 15 11:47:56 2008 JenneDAQPEMAccelerometer channels in ASS Adapt MEDM screen
Jenne, Sharon

We have traced which accelerometers correspond to which channels in the C1ASS_TOP MEDM screen.

Accelerometer Channel
------------- --------------------------
MC1-X C1:ASS-TOP_PEM_2_ADAPT_IN1
MC1-Y C1:ASS-TOP_PEM_3_ADAPT_IN1
MC1-Z C1:ASS-TOP_PEM_4_ADAPT_IN1
MC2-X C1:ASS-TOP_PEM_5_ADAPT_IN1
MC2-Y C1:ASS-TOP_PEM_6_ADAPT_IN1
MC2-Z C1:ASS-TOP_PEM_7_ADAPT_IN1

SEISMOMETER C1:ASS-TOP_PEM_1_ADAPT_IN1
  368   Tue Mar 11 23:14:01 2008 ranaConfigurationPEMAccelerometer and Seismometer movements
Steve and Matt moved the accelerometers and seismometers today.
The accelerometers are now placed around the MC and the seismometer is in-between MC1 & MC2.

We have changed the names of the acc channels to reflect whether they are close to MC1/MC3
or MC2. We tested the accelerometer to channel name mapping by switching gains at the wilcoxon
breakout box and also by tapping. It seems now that the previous setup near the ITMX/ETMX had
some few channels mislabeled which would have given some confusing results.

Alex, Jay, and Rolf came over today and installed, then de-installed some of the hardware for
sending the PEM channels over to the C1ASS machine where the adaptive filter front end will go.
Everything should be back to the way it was...hopefully, the guys will modify the ADCU PEM
code to send the signals to the new FE over the reflective memory net and then send them to the
MCL inputs of the suspensions. So the first incarnation should use the accelerometers and seismometer
to drive MC1 and/or MC3.
Attachment 1: Acc.pdf
Acc.pdf
  369   Wed Mar 12 00:36:52 2008 ranaConfigurationPEMAccelerometer and Seismometer movements
I used the MISO FIR Wiener matlab code to see how well we might do in principle.

The attached 3 page PDF file shows the MC_L control signal (force on MC2) and the residual
after subtracting off the accelerometer and seismometer using a 32 Hz sample rate and
512 taps (page 1), 1024 taps (page 2), and 2048 taps (page 3). As Matt smarmily points out,
there's not a lot to win by going beyond 512; maybe a factor of sqrt(2) for a factor of 4
tap number.
Attachment 1: finished.pdf
finished.pdf finished.pdf finished.pdf
  370   Wed Mar 12 00:40:35 2008 ranaConfigurationPEMAccelerometer and Seismometer movements
Same as above but with 2048 taps and a 128 Hz sample rate. Does much better at the 16 Hz bounce mode.
Attachment 1: mc2048-128.pdf
mc2048-128.pdf
  371   Wed Mar 12 00:47:26 2008 ranaConfigurationPEMAccelerometer and Seismometer movements
And this is a cool snapshot showing how this operation used 16 cores on menkar !
Attachment 1: Screenshot.png
Screenshot.png
  283   Mon Jan 28 19:35:55 2008 ranaSummaryPEMAccelerometer and Seismometer Coherences
The attached PDF shows that there is some strange behavior at low frequencies.

From the plot it looks like to me that the Wilcoxon accelerometers (which are supposed to have good response down to 0.05 Hz) are not displaying real seismic motion below 0.3 Hz. Because the coherence length for seismic waves at those frequencies should be 100's of meters we should expect that the accelerometers would have good coherence (>0.8) down there. Instead, my guess is that its all air currents, temperature, or electronics noise. These sensors are not reliable indicators for the microseism.

The Ranger seismometer, however, seems to work fine down to just below the microseism. The Ranger is mounted down around the X end and pointing in the z-direction. The coherence I plotted between it and EX_Z is larger than any other acc/seis pair (as expected).

JM and I discussed what could be done; if we get a SURF student who's into building stuff we can ask them to make a styrofoam hut for the Wilcoxons to see if that helps anything. JM also asked what the point of all this is.

IF we want to do good Adaptive Noise subtraction then we need sensors which can sense the motion which disturbs the mirrors and they need to sense it with a good SNR to get a good subtraction ratio. If the styrofoam thing doesn't work, we should probably look into getting a Guralp 3-axis seismometer for the corner area and just move the accelerometers down to the ends. The sites have Guralp CMG-40T units (~ 8k$). I think we should check out the CMG-3T or the CMG-3ESP.

Does anyone know someone in the Geo depts that we can borrow one from?
Attachment 1: Acc.pdf
Acc.pdf
  330   Fri Feb 22 02:51:20 2008 AndreyUpdatePEMAccelerometer ITMX seems to be broken

As people probably know,

I am trying (for a long time) to create a computational program that calculates the evolution of accelerometer time-domain data through stacks and pendulum transfer functions to test masses, and calculate the RMS of differential arm lenght spectrum.

I noticed on Tuesday that time-domain signals from the two accelerometers (one is near ETMX, the other one is near ITMX) seem to have different amplitudes of fluctuations around the mean value. I suspected that this is the main reason why I cannot get the awaited result of minimum of RMS for equal values of Q-factors for ETMX and ITMX suspensions (because we subtract two very different numbers, so we cannot get anything close to zero). I took amplitude spectra of the accelerometer data (dttfft2), and they look very differently for ETMX and ITMX accelerometers. I believe that spectrum of ETMX accelerometer represents seismic noise, but accelerometer ITMX seems to provide us with irrelevant and wrong data. No peaks, just almost monotoneous decreasing curve, and 10 times smaller amplitude. Therefore, ITMX seems to be broken.

I will try tomorrow to clap my hands, shout, yell, near the broken accelerometer to confirm that the accelerometer is broken (more precisely, that either accelerometer itself is broken,
or cable connections, or DAQ channel, but something is wrong). Now it is very late, and I am going home.

See attached figures: time-scale is 10^(-1), 10^0, 10^1, 10^2 Hz.
Attachment 1: Accelerom-EYMX-Feb22.jpg
Accelerom-EYMX-Feb22.jpg
Attachment 2: Accelerom-ITMX-Feb22.jpg
Accelerom-ITMX-Feb22.jpg
  2859   Wed Apr 28 16:15:02 2010 KevinUpdatePSLAccelerometer Calibration

Koji, Steve, and Kevin looked into calibrating the Wilcoxon accelerometers. Once calibrated, the accelerometers will be used to monitor the motion of the PSL table.

We want to use the shaker to shake each accelerometer and monitor the motion with an OSEM. We will make a plate to attach an accelerometer to the shaker. A flag will also be mounted on this plate.The OSEM will be mounted on the table next to the shaker and positioned so that the flag can block the LED light as the plate moves up and down. We will then measure the motion of the accelerometer as it is shaken from the OSEM signal. The OSEM signal will be calibrated by keeping the plate and the flag still and moving the OSEM down along the flag a known distance with a micrometer.

  11460   Wed Jul 29 17:51:56 2015 IgnacioUpdatePEMAccelerators moved back to MC1 and MC2

We are done taking accelerator huddle test data. So I moved back all six accelerometers and cables to MC1 and MC2. I also relabel each of the accelerometers properly since the labels on them were confusing.

QED

 

Attachment 1: FullSizeRender.jpg
FullSizeRender.jpg
Attachment 2: FullSizeRender_2.jpg
FullSizeRender_2.jpg
  2889   Thu May 6 18:25:20 2010 JenneUpdatePEMAcc power supply turned on

The accelerometer power supply / preamp board has been OFF because of exciting new accelerometer measurements.  It's now on, so watch out and make sure to turn it back off before plugging / unplugging accelerometers.

  5100   Wed Aug 3 01:30:04 2011 JenneUpdateLSCAbsolute length of Xarm and Yarm measured

So far, this is just preliminary, because I haven't done full error analysis to determine the error on my measurements.  That will hopefully be done by tomorrow afternoon (so before we start taking off doors).

I find that the length of the Xarm is:  37.5918 meters.

I find that the length of the Yarm is:   37.5425 meters.

I used the mass-kicking technique, as summarized by Kiwamu, and fully described by Alberto.  More words / description to follow with the full error analysis.

  1115   Wed Nov 5 12:41:36 2008 AlbertoUpdateLSCAbsolute Length and g-factor measurements conclusions
Absolute Length and g-Factor Measurement for the 40m Arm Cavities, Summary of Results

MOTIVATION OF THE EXPERIMENT
Lately locking the interferometer in the so called spring configuration (SRC on +166 MHz sideband) has been difficult and a possible resonance of an higher order mode of the +166 MHz sideband in the arms was
hypothesized as the cause. We wanted to know the frequencies of the HOMs of the sidebands and see where they are, relatively to the carrier resonance.

THE EXPERIMENTAL TECHNIQUE IN BRIEF
A second laser beam from an NPRO is injected into the interferometer through the AS port. The beam is mode matched to the arm cavities so that it can resonate inside of these. The secondary beam interferes with
the PSL beam and the incident intensity on one end mirror, excluding by now any higher mode, is I(t)=I1+I2+(interference terms)*exp[-i*(f1-f2)*t]. The last term comes from the beat between the two fields at the
relative frequency of the two lasers. For beating frequencies multiple of the FSR of the cavity, the beat gets transmitted and appears at the trans PD.
Whereas the PSL has a constant frequency, the NPRO frequency fluctuates, so that the relative phase between the two is not constant. To prevent that, a PLL servo locks the phase of the NPRO to that of the PSL.
The result is a beat frequency at the steady and tunable value set by the local oscillator of the PLL.

Length Measurement
One arm at a time, the cavity is locked to the TEM00 mode of the main laser. The beat frequency is then scanned for a few cavity FSRs and the transmitted power is measured. A linear fit of the resonant frequencies gives
us the FSR of the cavity.

g-factor Measurement
For non-planar Fabry-Perot cavities, the HOMs of the laser are not degenerate and resonate in the cavity at frequencies different from the correspondent fundamental mode. The shift in frequency is measured by the
Transverse Mode Spacing (TMS) and it is a function of the g-factors of the cavity:

TMS=FSR*acos[sqrt(g1*g2)]/pi

with g1=1-L/R1, where L is the cavity absolute length and R1 the radius of curvature of the input mirror, and similarly for g2 for the end mirror.
We measured the TMS by means of the beat between an HOM of the main laser and the TEM00 of the secondary beam. To do that we locked the cavity to either TEM01/10 and looked at the transmitted power for frequencies
of the beat around the TMS expected from the design parameters of the cavity.
Since the phase of the intensity of the beat between TEM01/10 and TEM00 has only DC components if measured across a symmetric portion of the spot, it is necessary to brake the symmetry of the incident beam on the
PD by chopping it just before it hits the sensor.
We approximated g1=1 for the ITMs. The effect of an astigmatic ETM is to brake the degeneracy of the TEM10 and TEM01 modes and split their resonant frequencies. By measuring that shift, we can evaluate the radius
of curvature of the mirror for the axis of the two transverse modes.

EXPERIMENTAL RESULTS
X Arm
FSR     =  (3897627 +/- 5 )   Hz
L       = (38.45833  +/- 0.00005) m
g2x     =   0.31197  +/- 0.00004
g2y     =   0.32283  +/- 0.00004
R-ETM_x = (55.8957   +/- 0.0045) m
R-ETM_y = (56.7937   +/- 0.0038) m

Y Arm
FSR     = ( 3879252 +/- 30 )  Hz
L       = (38.6462   +/- 0.0003) m
g2x     =   0.31188  +/- 0.00004
g2y     =   0.32601  +/- 0.00004
R-ETM_x = (56.1620   +/- 0.0013) m
R-ETM_y = (57.3395   +/- 0.0011) m


CONCLUSIONS
The attached graphs,one for the X arm and the other for the Y arm, plot the distributions of the first HOMs of the sidebands near the carrier resonance in the arm cavities. As it appears, the resonances of
the +166 sideband are far enough for not resonating in the arm cavities if the arms are locked to the carrier.
We have to look for something else to explain the locking problem of the interferometer in the spring configuration.
Attachment 1: 2008-11-04_file_02-05.png
2008-11-04_file_02-05.png
Attachment 2: HOM_resonances_Xarm.png
HOM_resonances_Xarm.png
Attachment 3: HOM_resonances_Yarm.png
HOM_resonances_Yarm.png
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