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ID Date Authordown Type Category Subject
  2459   Mon Dec 28 15:19:19 2009 AlbertoUpdateComputersBurtrestored to Dec 26 at 20:00

Since it wasn't sure whether all the front-ends had been restored after the bootfest, I burtrestored everything to Dec 26 at 20:00.

Always keep in mind that to burtrestore c1dcuepics, the snapshot file has to be modified by hand by moving the last quote up to the line before the last.

  2460   Mon Dec 28 15:34:14 2009 AlbertoUpdateABSLWorking on the AP table

I opened the auxiliary laser's shutter.

I'm currently working on the AP table.

  2461   Mon Dec 28 18:35:27 2009 AlbertoUpdateABSLWorking on the AP table

Quote:

I opened the auxiliary laser's shutter.

I'm currently working on the AP table.

 I finished working on the table.

I closed the AUX NPRO's shutter.

  2467   Wed Dec 30 10:58:48 2009 AlbertoUpdateGeneralAll watchdogs tripped this morning

This morning I found all the watchdogs had tripped during the night.

I restored them all.

I can't damp ITMX. I noticed that its driving matrix is all 1s and -1s as the the right values had been lost in some previous burtrestoring.

  2476   Tue Jan 5 09:18:38 2010 AlbertoOmnistructureElectronicsUniversal PDH Box Stored in the RF Cabinet

FYI: I stored the Universal PDH boxes in the RF cabiner in the Y arm.

  2479   Tue Jan 5 13:23:45 2010 AlbertoOmnistructureEnvironmentturning page

In the lab there are lots of old posters with outdated autocad drawings, or printouts with schematics of old electronics hanging on the walls.

Can we get rid of those and start giving the lab a fresh and modern look?

  2485   Fri Jan 8 10:03:04 2010 AlbertoOmnistructureLSCSPOB shutter was closed

This morning I found that there was no light on the SPOB PD. I went looking at the photodetector and I found that the shutter in front of it was closed.

I switched the shutter driver from n.c. to n.o. which had the effect of opening it.

I guess we inadvertently closed the shutter with Rana when last week we were tinkering with the ITMY  camera.

  2491   Sat Jan 9 09:47:03 2010 AlbertoUpdateLSCProblems trying to lock the arms

This morning I've been having problems in trying to lock the X arm.

The X arm's filter FM6 in the LSC screen starts blinking as it was halfloaded. Then the transmitted power drops from 1 to ~0.5 and eventually the arm loses lock.
To me it looked like a computer related issue. So I decide to reboot C1ISCEX by powercycling it.

That doesn't seem to have solved the problem. The X arm can get locked but TRX slowly moves between 0.2 and 1.

  2492   Sat Jan 9 11:07:30 2010 AlbertoUpdateLSCProblems trying to lock the arms

Quote:

This morning I've been having problems in trying to lock the X arm.

The X arm's filter FM6 in the LSC screen starts blinking as it was halfloaded. Then the transmitted power drops from 1 to ~0.5 and eventually the arm loses lock.
To me it looked like a computer related issue. So I decide to reboot C1ISCEX by powercycling it.

That doesn't seem to have solved the problem. The X arm can get locked but TRX slowly moves between 0.2 and 1.

The X arm is now locked with TRX stable at ~1.

I think earlier on today I was having problems with running the alignment scripts from op540. Now I'm controlling the IFO from Rosalba and I can easily and stably lock all degrees of freedom.

I needed the X arm to be locked to align the auxiliary beam of the AbsL experiment to the IFO. To further stabilize TRX I increased the loop gain from 1 to 1.5.

Now the auxiliary beam is well aligned to the IFO and the beat is going through the PRC. I'm finally ready to scan the recycling cavity.

I also changed the gain of the PRC loop from -0.1 to -0.5.

  2493   Sat Jan 9 15:02:01 2010 AlbertoUpdateABSLPRC scanning
I scanned the PRC in the frequency range of 30-60 MHz, untill the PLL lost lock. But everything is working fine.
The PRC remained lock for all time, with SPOB at ~1000.
I'm leaving the lab now, planning to come back tomorrow.
I turned the flipping mirrors down and closed the mechanical shutter of the auxiliary NPRO.
  2496   Sun Jan 10 16:05:51 2010 AlbertoOmnistructureEnvironmentLab Thermostats Temperature Lowered by 1 deg F

Rana noticed that recently the temperature inside the lab has been a little bit too high. That might be causing some 'unease' to the computers with the result of making them crash more often.

Today I lowered the temperature of the three thermostats that we have inside the lab by one degree:
Y arm thermostat: from 71 to 70 F
X arm thermostat: from 70 to 69 F
Aisle thermostat: from 72 to 71 F.

For the next hours I'll be paying attention to the temperature inside the lab to make sure that it doesn't go out of control and that the environment gets too cold.

  2500   Mon Jan 11 09:18:44 2010 AlbertoUpdateGeneralMeasurement running

I'm working on the AbsL experiment. A measurement which involved the PRC locked is running at the moment.

Please make sure of not interfering with the interferometer until it is done. Thank you.

  2501   Mon Jan 11 10:01:06 2010 AlbertoOmnistructureEnvironmentLab Thermostats Temperature Lowered by 1 deg F

Quote:

Rana noticed that recently the temperature inside the lab has been a little bit too high. That might be causing some 'unease' to the computers with the result of making them crash more often.

Today I lowered the temperature of the three thermostats that we have inside the lab by one degree:
Y arm thermostat: from 71 to 70 F
X arm thermostat: from 70 to 69 F
Aisle thermostat: from 72 to 71 F.

For the next hours I'll be paying attention to the temperature inside the lab to make sure that it doesn't go out of control and that the environment gets too cold.

 Today the lab is perceptibly cooler.

The temperature around the corner is 73 F.

  2502   Mon Jan 11 11:06:53 2010 AlbertoUpdateABSLMeasurement running

Quote:

I'm working on the AbsL experiment. A measurement which involved the PRC locked is running at the moment.

Please make sure of not interfering with the interferometer until it is done. Thank you.

 I'm done for the moement.

I realized that I need to take into account somehow the DC power from the photodiode. By now the measurement of the transmitted beat's power is affected by the total power circulating inside of the PRC and thus it depends on the cavity alignment.

I closed the laser shutter and turned down the flipping mirrors.

I'm planning to restart measuring by 2.30pm today. Till then the interferometer is available.

  2504   Mon Jan 11 16:59:14 2010 AlbertoUpdateABSLInterferometer Busy

I'm currently running a measurement on the PRC.

Please don't interfere with the IFO until it is done. Talk with Alberto if you've been intending to work inside the lab.

Thank you.

  2505   Mon Jan 11 19:36:13 2010 AlbertoUpdateABSLMeasurement running

Leaving for dinner. Back in ~1hr.

I left a measurement running. Please don't interfere with it till I'm back. Thanks.

  2508   Tue Jan 12 09:37:05 2010 AlbertoUpdateABSLIFO available

I finished measuring the AbsL for this morning. The IFO is again available.

Please don't mess up with the interferometer though. I'll be back in a couple of ours

  2512   Wed Jan 13 12:01:06 2010 AlbertoUpdateComputersc1dcuepics, c1lsc rebooted this morning
Since last night the alignemtn scripts couldn't work.
c1lsc wasn't working properly because attempts to lock the X arm would try to control ETMY and attempts of locking the Y arm, wouldn't actuate any optics.
Also, another sign of a malfunctioning c1lsc was that one of the LSC filter modules, FM6, couldn't get loaded properly. It looked like only half loaded on the LSC MEDM screen.
On the other hand, plotting the trend of the last month, c1lsc's CPU didn't look more loaded that usual.
 
Rebooting and restarting C1lsc wasn't enough and I also had to reboot c1dcuepics a couple of times beforse getting things back to work.
  2513   Wed Jan 13 12:03:00 2010 AlbertoUpdateABSLMeasurement now running. Please be careful

At the moment I'm running a measurement on the PRC and I'm planning to leave it going for the time we'll be at the 40m meeting.

Please be careful in the lab. Thank you.

  2519   Sun Jan 17 19:18:55 2010 AlbertoUpdateComputersBoot fest to restart the computer and c1iscey not responding.

Thi afternoon I found that the RFM network in trouble. The frontends sync counters had railed to 16384 counts and some of the computers were not responding. I went for a bootfest, but before I rebooted c1dcu epics. I did it twice. Eventually it worked and I could get the frontends back to green.

Although trying to burtrestore to snapshots taken at any time after last wednesday till today would make the RFM crash again. Weird.

Also, c1iscey seems in a coma and doesn't want to come back. Power cycling it didn't work. I don't know how to be more persuasive with it.

  2521   Mon Jan 18 18:34:01 2010 AlbertoUpdateABSLMeasurement in progress

I started a long measurement of the PRC's transmissivity. I'm leaving the lab and I'm going to be back at about 8 tonight. Please do not disturb the interferometer. it is important that the MC and the PRC stay locked all the time.

  2522   Mon Jan 18 20:58:40 2010 AlbertoUpdateABSLMeasurement in progress

Quote:

I started a long measurement of the PRC's transmissivity. I'm leaving the lab and I'm going to be back at about 8 tonight. Please do not disturb the interferometer. it is important that the MC and the PRC stay locked all the time.

 That measurement is finished. I'm now going to start another one that will take another hour or so. I'm leaving it running for the night. If you want to work on the IFO, it should be definitely done by 11pm.

  2531   Tue Jan 19 12:54:39 2010 AlbertoUpdateABSLMeasurement in progress

A measurement will be running for the next hour. Please be careful.

  2532   Tue Jan 19 16:21:18 2010 AlbertoUpdateABSLWatchdogs not working and then fixed

This afternoon the watchdogs stopped working: they didn't trip when the suspension positions crossed the threshold values.

I rebooted c1susaux (aka c1dscl1epics0 in the 1Y5 rack), which is the computer that runs the watchdog processes.

The reboot fixed the problem.

  2534   Wed Jan 20 20:11:56 2010 AlbertoUpdateABSLSome preliminary results from measuring PRC's transmissivity for an amplitude modulated beam
Here I'm posting a plot showing a set of measurements that I made in the past few days to determine the absolute length of the PRC cavity.
As in my other AbsL measurements, I inject an auxiliary laser beam into the cavity and look at the transmission. In the PRC case, the beam is injected through the dark port and I look at a pick-off of the REFL beam. The aux laser is phase locked to the PSL beam and I control the differential frequency between the two. The PSL and the aux beam interfere and beat at their differential frequency.
 
The attached plot shows the transmitted power as a function of the beat frequency.
 
Fitting the data with the model would let me determine the cavity length. 
By now I can estimate the length of the PRC at about 2.257m, but it's still a rather approximate value.
I can't provide accurate error bars yet. I need to optimize the measurements to get a more precise value.
 
I will go more through the details of the measurement technique and of the fitting function as soon as I have more definitive results.
 
The data points shown here were taken at different times and not always in optimal alignment condition of the PRC. 
To get a good fit of the data I should have fewer frequency segments, taken in a shorter period of time, and in which the power circulating inside of the cavity (ie SPOB) fluctuates as little as possible.
 
For what regards the time needed for a measurements, I already significantly sped up the measurements (i.e. optimizing the scanning and acquisition GPIB scripts, and fixing a couple of problems with the PDH box used in the PLL), and finally now I can scan several tens of MHz in few minutes.
About the frequency segments, so far they have been determined by two factors
1) Tthe frequency generator in the PLL: the Marconi works as a continuous wave generator only in limited ranges. Switching from one to another brakes the wave in a way that causes the PLL to lose lock.
2) Getting below 18 MHz a series of other beats appear on the PLL photodiode and make the PLL lose lock.
 
For the first problem, I'm thinking of using two Marconis and to mix their signals. I would keep one at 300MHz and I would scan the other from 300MHz to 500MHz. In fat, in that frequency range the Marconi has not discontinuity.
 
To try to avoid the other beats at low frequency, I'm not entirely sure about what to do yet. 
 
To be continued...
Attachment 1: 2010-01-19_PRCtransmissivityVsModel.png
2010-01-19_PRCtransmissivityVsModel.png
  2541   Fri Jan 22 02:54:06 2010 AlbertoUpdateABSLOvernight measurement

I'm leaving a measurement running overnight. It should be done in about one hour.

Tomorrow morning, If you need to use the interferometer, and you don't want to have the auxiliary beam going onto the dark port, you can turn down the flipping mirror and close the NPRO's mechanical shutter.

  2543   Fri Jan 22 14:40:49 2010 AlbertoUpdateABSLOvernight measurement

Quote:

I'm leaving a measurement running overnight. It should be done in about one hour.

Tomorrow morning, If you need to use the interferometer, and you don't want to have the auxiliary beam going onto the dark port, you can turn down the flipping mirror and close the NPRO's mechanical shutter.

 This is what I measured last night:

2010-01-21_PRCtransmissivityVsModel.png

 This is not a fit. It's just a comparison of the model with the data.

  2545   Mon Jan 25 16:30:37 2010 AlbertoUpdateABSL166 MHz sideband turned off

I turned off the modulation at 166MHZ becasue I don't need it if I'm only locking the PRC.

It was introducing extra amplitude modulations of the beam which interfered with the AbsL's PLL photodiode.

I'm going to turn it back on later on.

  2546   Mon Jan 25 16:46:33 2010 AlbertoUpdateABSL166 MHz sideband turned off

Quote:

I turned off the modulation at 166MHZ becasue I don't need it if I'm only locking the PRC.

It was introducing extra amplitude modulations of the beam which interfered with the AbsL's PLL photodiode.

I'm going to turn it back on later on.

 I turned back on the 166MHz modulation just a bit. I set the slider at 4.156.

When it was totally off the MZ seemd quite unhappy.

  2550   Wed Jan 27 11:02:30 2010 AlbertoUpdateABSLPRC Cavity Length
 I fitted the data from scanning the PRC by changing the beat frequency of the auxiliary laser beam with the PSL beam.
The data points that I've taken so far over the entire frequency range (0-300 MHz) are not continuous. For several reasons the PLL was unable to maintain lock for such a large range and I had to break it into smaller segments. The measurements to acquire them stretched over a too long period of time during which the status of the PRC changed.
 
Because of that, before I get a continuous set of data points (perhaps normalized by the circulating power inside of the cavity), I restricted the fit to a 55MHz range around 100MHz. I obtained the following numbers for the fit parameters:
Length PRC = 2.169 +/- 0.007 m
Schnupp Asymmetry: 0.471+/- 0.006 m
 
The fit is shown in the attached plot:
2010-01-21_PRCtransmissivityVsFit.png
When I fit over the entire set of data I get this:
 
2010-01-21_PRCtransmissivity_EntireFreqRange_VsFit.png
 
Length PRC = 2.224 +/- 0.005 m
Schnupp Asymmetry: 0.457+/- 0.005 m
 
The results are different. Evidently I have to improve the measurement. I'm working on it.
 
For posterity:
The function I used to fit the transmitted beat power vs. frequency is the following:
 
E_trans = - t_prm * r_itm * exp(1i*2*wb*l_prc/c) .* sin(wb*l_/c) ./ ( 1 + r_prm * r_itm * exp(1i*2*wb*l_prc/c) .* cos(wb*l_/c)
 
Where wb is the angular frequency of the beat, l_prc and l_ are the length of the PRC and the Schnupp asymmetry, respectively; r_itm, t_itm, r_prm, t_prm are reflectances and transmittances of PRM and ITM; c is the speed of light.
 
  2551   Thu Jan 28 09:14:51 2010 AlbertoConfigurationComputersc1iscey, c1iscex, c1lsc, c1asc rebooted

This morning the LSC scripts wheren't running properly. I had to reboot c1iscey, c1iscex, c1lsc, c1asc .

I burtrestored to Monday January 25 at 12:00. 

  2552   Thu Jan 28 09:17:32 2010 AlbertoUpdateLSC166 Modulation turned off

I temporarily turned off the 166 modulation.

  2553   Fri Jan 29 12:06:58 2010 AlbertoUpdateABSLMeasurement running today at lunch time

I just started a measuremtn that will be running for the next hour or so. Please be careful with the interferometer.

  2554   Fri Jan 29 13:14:49 2010 AlbertoUpdateABSLMeasurement running today at lunch time

Quote:

I just started a measuremtn that will be running for the next hour or so. Please be careful with the interferometer.

Done. IFO available

  2560   Tue Feb 2 15:30:03 2010 AlbertoFrogsTreasureWild Oats
FYI. Sitting on the top shelf of George I found an opened jar of raspberry jam and an opened jar of creamy peanut butter. Both are branded Wild Oats Market.
 
Wikipedia:
"Wild Oats Markets was an operator of natural foods stores and farmers markets in North America... Whole Foods officially completed their buyout of Wild Oats on August 27, 2007 [...]"
  2562   Tue Feb 2 18:15:47 2010 AlbertoUpdateelogElog restarted it

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

I just restarted it with the restarting script.

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

  2567   Wed Feb 3 10:46:12 2010 AlbertoUpdateelogelog restarted

 Again, this morning Zach told me that the elog had crashed while he was trying to post an entry.

I just restarted it.

  2576   Mon Feb 8 14:13:03 2010 AlbertoUpdateABSLPLL Characterization

Lately I've been trying to improve the PLL for the AbsL experiment so that it could handle larger frequency steps and thus speed up the cavity scan.

The maximum frequency step that the PLL could handle withouth losing lock is given by the DC gain of the PLL. This is the product of the mixer's gain factor K [rad/V ], of the laser's calibration C [Hz/V] and of the PLL filter DC gain F(0).

I measured these quantities: K=0.226 V/rad; C=8.3e6 Hz/V and F(0)=28.7dB=21.5. The max frequency step should be Delta_f_max = 6.4MHz.

Although in reality the PLL can't handle more than a 10 KHz step. There's probably some other effect that I'm not.

I'm attaching here plots of the PLL Open Loop Gain, of the PLL filter and of a spectra of the error point measured in different circumstances.

I don't have much time to explain here how I took all those measurements. After I fix the problem, I'm going to go go through those details in an elog entry.

Does anyone have any suggestion about what, in principle, might be limiting the frequency step?

I already made sure that both cables going to the mixer (the cable with the beat signal coming from the photodiode and the cable with the LO signal coming from the Marconi) had the same length. Although ideally, for phase locking, I would still need 90 degrees of phase shift between the mixing signals, over the entire frequency range for which I do the cavity scan. By now the 90 degrees are not guaranteed.

Also, I have a boost that adds another 20 dB at DC to the PLL's filter. Although it doesn't change anything. In fact, as said above calculating the frequency step, the PLL should be able to handle 100KHz steps, as I would want the PLL to do.

Attachment 1: 2010-02-08_Old_PDH_Box_Filter_TF_gain_knob_0_Boost_OFF.png
2010-02-08_Old_PDH_Box_Filter_TF_gain_knob_0_Boost_OFF.png
Attachment 2: 2010-02-08_PLL_OLG_gain_knob_0_Boost_OFF.png
2010-02-08_PLL_OLG_gain_knob_0_Boost_OFF.png
Attachment 3: 2010-02-08_PLL_Noise_Budget.png
2010-02-08_PLL_Noise_Budget.png
  2577   Mon Feb 8 14:56:17 2010 AlbertoUpdateABSLSuddenly a much better alignment of PRC

I just aligned PRM and locked PRC and I noticed that SPOB is much higehr than it used to be. It's now about 1800, vs 1200 than it used to be last week.

Isn't anyone related to that? If so, may I please know how he/she did it?

  2579   Mon Feb 8 15:41:51 2010 AlbertoUpdateABSLSuddenly a much better alignment of PRC

Quote:

Quote:

I just aligned PRM and locked PRC and I noticed that SPOB is much higehr than it used to be. It's now about 1800, vs 1200 than it used to be last week.

Isn't anyone related to that? If so, may I please know how he/she did it?

 oops, my bad.  I cranked the 33MHz modulation depth and forgot to put it back.  The slider should go back to around 3. 

 I was actually hoping that the alignment got better.

  2581   Tue Feb 9 09:07:06 2010 AlbertoUpdateABSLPLL Characterization

Quote:

Lately I've been trying to improve the PLL for the AbsL experiment so that it could handle larger frequency steps and thus speed up the cavity scan.

The maximum frequency step that the PLL could handle withouth losing lock is given by the DC gain of the PLL. This is the product of the mixer's gain factor K [rad/V ], of the laser's calibration C [Hz/V] and of the PLL filter DC gain F(0).

I measured these quantities: K=0.226 V/rad; C=8.3e6 Hz/V and F(0)=28.7dB=21.5. The max frequency step should be Delta_f_max = 6.4MHz.

Although in reality the PLL can't handle more than a 10 KHz step. There's probably some other effect that I'm not.

I'm attaching here plots of the PLL Open Loop Gain, of the PLL filter and of a spectra of the error point measured in different circumstances.

I don't have much time to explain here how I took all those measurements. After I fix the problem, I'm going to go go through those details in an elog entry.

Does anyone have any suggestion about what, in principle, might be limiting the frequency step?

I already made sure that both cables going to the mixer (the cable with the beat signal coming from the photodiode and the cable with the LO signal coming from the Marconi) had the same length. Although ideally, for phase locking, I would still need 90 degrees of phase shift between the mixing signals, over the entire frequency range for which I do the cavity scan. By now the 90 degrees are not guaranteed.

Also, I have a boost that adds another 20 dB at DC to the PLL's filter. Although it doesn't change anything. In fact, as said above calculating the frequency step, the PLL should be able to handle 100KHz steps, as I would want the PLL to do.

I might have found the problem with the PLL that was preventing me from scanning the frequencies by 100KHz steps. A dumb flimsy soldering in the circuit was making the PLL unstable.

After I fixed that problem and also after writing a cleverer data acquisition script in Python,  I was able to scan continuosly the range 10-200MHz in about 20min (versus the almost 1.5-2 hrs that I could do previously). I'm attaching the results to this entry.

The 'smears' on the right side of the resonance at ~33MHz, are due to the PSL's sideband. I think I know how to fix that.

As you can see, the problem is that the model for the cavity transmission still does not match very well the data. As a result, the error on the cavity length is too big (~> 10 cm - I'd like to have 1mm).

Anyway, that was only my first attempt of scanning. I'm going to repeat the measurement today too and see if I can come out better. If not, than I have to rethink the model I've been using to fit.

Attachment 1: 2010-02-08_PRCtransmissivity_EntireFreqRange_VsFit.png
2010-02-08_PRCtransmissivity_EntireFreqRange_VsFit.png
  2582   Tue Feb 9 10:10:58 2010 AlbertoUpdateABSLback to analog

I want to try to do the measurement with the network analyzer used as local oscillator, instead of the Marconis that I'm using now. Tha could give me better noise rejection. It would also give me information about the phase.

Also I wouldn't dislike abandoning the GPIB interfaces to acquire data.

  2604   Tue Feb 16 09:51:22 2010 AlbertoUpdateGreen Lockingtake some optics away from the ETM end table

Quote:

In the last two days Steve and I took some optics away from the both ETM end table.

This is because we need an enough space to set up the green locking stuff into the end table, and also need to know how much space is available.

Optics we took away are : Alberto's RF stuff, fiber stuff and some optics obviously not in used.

The picture taken after the removing is attached. Attachment1:ETMX, Attachment2:ETMY

And the pictures taken before the removing are on the wiki, so you can check how they are changed.

http://lhocds.ligo-wa.caltech.edu:8000/40m/Optical_Tables

The PD Kiwamu removed from the Y table was TRY, which we still need.

My bad if he took that. By mistake I told him that was the one I installed on the table for the length measurement and we didn't need it anymore.

I'm going to ask Kiwamu if he can kindly put it back.

  2605   Tue Feb 16 10:01:16 2010 AlbertoConfigurationLSCArms and PRC not locking

Since last Friday either the arms or the PRC can't lock.

The montors show the beam flashing on the end mirrors, but the cavity can't get locked. The error signal looks fine. I suspect a computer problem.

Also PRC can't lock. SPOB is suspiciously stuck at about -95. Although that's not a fixed number, but covering the by hand the SPOB PD on the ITMY table doesn't change the number. I check the DC output of the photodetector and it is actually seen the beam.

Suspecting computer problems started after last Thursday's IP switch, I rebooted the frame builder, c1dcuepics, c1daqctrl and all the front ends. I then burtrestored to February 1st at 1:00 am.

Before I burtrestored c1iscepics, SPOB had gone back to more typical numbers around 0, as it usually read when PRC wasn't locked.

But burtrestoring c1iscepics, return it to the -95 of earlier.

Burterestoring to other times or dates didn't solve the problems.

  2608   Tue Feb 16 15:25:00 2010 AlbertoConfigurationLSCArms and PRC not locking

 

 shock.jpg

  2640   Thu Feb 25 15:49:05 2010 AlbertoAoGCDSNew IO Chassis for the new CDS
Yesterday Kiwamu and I went to Downs to take all the available parts of the IO chassis that Gary and I had put together over there.
 
We've got only 3 of the 5 that we need for the Upgrade. The other 2 are currently being used for some other purpose in Downs labs.
 
I'm not sure about what each chassis has supposed to contain. They all also look different from each other.
Anyway, it looks like there should be a sort of motherboard and an IO Chassis Interface Board (DCC# D0902029) in each of them. The IO Chassis Interface Board is just a board with a bunch of PCI slots.
 
This is what the 3 chassis that we've got yesterday have:
Chassis 1
- 1 very big "motherboard"
- power supply
Chassis 2
- small motherboard
- IO Interface Board (DCC# D0902029)
- power supply
Chassis n.3
- "Dolpjin" motherboard
- IO Interface Board
- power supply
 
Apparently 2 of these 3 chassis are still missing their IO interface boards,
 
Also all chassis are still missing all the connections to powering, fans, LEDs, power and reset buttons. It's not clear how these connections should be. Gary didn't know it either.
  2653   Wed Mar 3 18:32:25 2010 AlbertoUpdate40m Upgrading11 MHz RFPD elctronics
** Please add LISO file w/ component values.
 
I designed the circuit for one of the 11 MHz photodiodes that we're going to install in the 40m Upgrade.

This is a simple representation of the schematic:

          gnd
#          |
#          Cw2
#          |
#          n23
#          |
#          Lw2
#          |
#           n22
#          |
#          Rw2                
#                 |                   |\            
#           n2- - - C2 - n3 -  - -  - |  \          
#            |    |      |   |        |4106>-- n5 - Rs -- no
# iinput    Rd   L1     L2 R24    n6- |  /     |           |
#      nin - |    |      |   |    |   |/       |         Rload    
#           Cd   n7     R22 gnd   |            |           |          
#            |    |      |        | - - - R8 - -          gnd              
#           gnd  R1     gnd      R7 
#                 |               |
#         gnd               gnd
#                 
#
#

I chose the values of the components in a realistic way, that is using part available from Coilcraft or Digikey.

Using LISO I simulated the Tranfer Function and the noise of the circuit.

I'm attaching the results.

I'll post the 55MHz rfpd later.

Attachment 1: rfpd11_v2_TF.pdf
rfpd11_v2_TF.pdf
Attachment 2: rfpd11_v2_Noise.pdf
rfpd11_v2_Noise.pdf
  2655   Thu Mar 4 08:43:35 2010 AlbertoUpdate40m Upgrading11 MHz RFPD elctronics

Quote:
** Please add LISO file w/ component values.

oops, forgotten the third attachment...

here it is

Attachment 1: rfpd11_v2.fil
# Resonant RF diode front end
#
#		  gnd
#		  |
#		  Cw2
#		  |
#		  n23
#		  |
#		  Lw2
#		  |
... 60 more lines ...
  2656   Thu Mar 4 19:53:56 2010 AlbertoUpdate40m Upgrading11MHz PD designed adjusted for diode's resistance; 55 MHz RFPD designed
After reading this study done at LIGO MIT in 1998 I understood why it is difficult to define an effective impedance for a photodiode.

I read a few datasheets of the C30642GH photodiode that we're going to use for the 11 and 55 MHz. Considering the  values listed for the resistance and the capacitance in what they define "typical conditions" (that is, specific values of bias voltage and DC photocurrent) I fixed Rd=25Ohms and Cd=175pF.

Then I picked the tunable components in the circuit so that we could adjust for the variability of those parameters.

Finally with LISO I simulated transfer functions and noise curves for both the 11 and the 55MHz photodiodes.

I'm attaching the results and the LISO source files.

 

Attachment 1: rfpd55_Noise.pdf
rfpd55_Noise.pdf
Attachment 2: rfpd55_TF.pdf
rfpd55_TF.pdf
Attachment 3: rfpd11_v2_TF.pdf
rfpd11_v2_TF.pdf
Attachment 4: rfpd11_v2_Noise.pdf
rfpd11_v2_Noise.pdf
Attachment 5: rfpd11_v2.fil
Attachment 6: rfpd55.fil
  2680   Thu Mar 18 12:27:56 2010 AlbertoUpdateABSLPLL reconstructed

Quote:

Last night (Mar 17) I checked the PLL setup as Mott had some difficulty to get a clean lock of the PLL setting.

  • I firstly found that the NPRO beam is not going through the Faraday isolator well. This was fixed by aligning the steering mirrors before the Faraday.
     
  • The signal from the RF PD was send to the RF spectrum analyzer through a power splitter. This is a waist of the signal. It was replaced to a directional coupler.
  • Tee-ing the PZT feedback to the oscilloscope was producing the noise in the laser frequency. I put the oscilloscope to the 600Ohm output of the SR560, while connectiong the PZT output to the 50Ohm output.
  • In addition, 6dB+6dB attenuators have been added to the PZT feedback signal.

Now the beating signal is much cleaner and behave straight forward. I will add some numbers such as the PD DC output, RF levels, SR560 settings...

Now I am feeling that we definitely need the development of really clean PLL system as we use PLL everywhere! (i.e. wideband PD, nice electronics, summing amplifiers, stop poking SR560, customize/specialize PDH box, ...etc)

I also had noticed the progressive change of the aux NPRO alignment to the Farady.

I strongly agree about the need of a good and robust PLL.

By modifying the old PDH box (version 2008) eventually I was able to get a PLL robust enough for my purposes. At some point that wasn't good enough for me either.

I then decided to redisign it from scratch. I'm going to work on it. Also because of my other commitments, I'd need a few days/1 week for that. But I'd still like to take care of it. Is it more urgent than that?

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