Q is writing the locking elog for the night, but just to reply to this thread: The IFO worked well tonight, so things are at least not broken.
Unfortunately, this kind of trend plot is not detailed enough to know if something has gone bad in a quantitative way. But at least we can tell that the suspension wire didn't break.
Alignment is making it tough for locks to last more than 10 minutes. Many (but not all) locklosses correlate with some optic drifting away, and taking all of the light with it. The other locklosses are the quick ones that seem to pop up out of nowhere; we haven't made any headway on these. We wanted to get to a state where we could just let the interferometer sit for some minutes, to explore the data, but got caught up with alignment and PRMI things.
We're finding that both ITMs experience some DC force when entering full PRFPMI lock. I will calculate the torque expected from radiation pressure + offset beam spot, especially for ITMX, where we choose the spot position to be uncontrolled by ASS.
I set up the QPD ASC servos to act in a common/differential way on the ETMs. The C1:ASC-XARM_[PIT/YAW] filter modules act on the common alignment, whereas the C1:ASC-YARM_[PIT/YAW] filter modules act on the differential alignment. This can soon be cleaned up with some model renaming to reduce confusion.
Using DC oplev values as a guide, we are hand tuning ITM alignment once the AO path is engaged and we see the DC drift occurring. Then, we set the QPD servo offsets and engage them.
In this manner, we were able to lock the interferometer at:
We made the PRMI transition to 1f numerous times, but found that the sideband power fluctuations would get significantly worse after the transition.
We found that the gains that were previously used were too small by a factor of a few. There is a DC change visible in REFL165 before and after the transition (Also POP55, aka REFL55, is not DQ'd ). Really, it isn't certain that we've zero'd the offset in the CARM board either, so REFL55's zero crossing isn't necessarily more trustworthy that REFL165's. We can go back in the data and do some 2D histograming to see where in the error signal space the sideband power is maximized.
It was only a mediocre locking night. I was foiled for a long time by 2 things, both of which are now taken care of in the scripts, so I don't waste so much time again.
Scripts are checked into the svn.
I used Q's handy-dandy 2D histogram plotter (..../scripts/general/dataHist, which I have taken the liberty of adding to the svn) to set the PRCL offset when I was locked on REFL165. Here is a version of the plot, when I had an offset of +10 in the PRCL filter bank. There was so much noise on the PRCL input that I quit bothering to try and put in an excitation or ramp the offset value. Note that I have since moved this offset to PRCL_A's offset instead, so taking this plot again should have PRCL_IN1 centered around zero.
I had trouble doing something similar for PRCL when I was locked on REFL55. At first, the offset was so poor that POP110 was only about half the value it was when locked on REFL165, and it had a huge amount of RIN. I tried just doing a z avg of the PRCL_B_IN1 (REFL55I) while locked on REFL165, and that said that REFL55I had an offset of +33.8 counts, so I tried an offset of -33.8 counts to get to zero. But, that was still terrible for POP110 power. As I increased the offset, eventually up to +30 counts, POP110 kept getting better and better. I lost lock at that point (while trying to get 10 sec of histogram data), so I'm not sure that +30 is the final value. I want to also get equivalent histograms with POP22 and POPDC (and maybe arm transmissions?) as the X-axis on these plots. There's no excitation, so all of these can be collected at once.
By babysitting the ITM alignment (looking at the rough DC values of the optical lever error siganls), and doing a little adjustment of the ASC differential offset, I was able to keep lock a few times for more than 2 or 3 minutes while all 1f. Not a whole lot longer than that though, even if I wasn't "poking" the interferometer other than maintaining alignment.
As the POP55 demod board is actually demodulating the REFL55 signal, I have connected its outputs to the REFL55 ADC inputs. Now, we can go back to using the REFL55 input matrix elements, and the data will be recorded.
I have changed the relevant lines in the locking script to reflect this change.
I was poking around with the PDFR hardware today.
I moved the Agilent which had its screen projected on the monitor. I have put it back...but please verify the settings before using it for tonight.
blarg. Chrome ate my elog.
112607010 is the start of five minutes on all whitened 1F PDs. REFL55 has more low frequency noise than REFL165, I think we may need more CARM supression (i.e. we need to think about the required gain). This is also supported by the difference in shape of these two histograms, taken at the same time in 3f full lock. The CARM fluctuations seem to spread REFL55 out much more.
I made some filters and scripts to do DC coupling of the ITM oplevs. This makes maintaining stable alignment in full lock much easier.
I had a few 15+ minute locks on 3f, that only broke because I did something to break it.
Here's one of the few "quick" locklosses I had. I think it really is CARM/AO action, since the IMC sees it right away, but I don't see anything ringing up; just a spontaneous freakout.
There was a period of short unexpected jackhammering this morning. I asked them to stop.
The good mood of GTRX was not changed.
Small steps tonight, but all in the forward direction.
On one of my better locks, I saw a kind of weird phenomenon with the PRMI sideband powers versus the carrier powers:
For the last 100 seconds of this plot, I'm all 1f. Alignment is being handled mostly by Q's DC coupled ITM oplevs, and the transmission QPD ASC loops, although I was trying to adjust the offsets in the ASC loops to improve transmission for a bit.
At the very end, the last 10 seconds or so, the POP110 power goes down, and sits at about half it's maximum value. POP22 isn't quite as bad, in that it still touches the max, but the RIN is about 50%. The carrier DC signals (TRX, TRY, POPDC) don't see this huge jump. I don't think I was touching anything the last few tens of seconds. I'm not sure yet how I can so significantly lose sideband power, without losing a similar amount of carrier power.
The ring-ups at about -70sec in the CARM and DARM outs are the bounce mode.
I tried looking at 2D histograms of different combinations of channels, for the time around -30 seconds where things looked pretty clean. It looks like the offsets that Q put in last night (+1 for MICH_B and -3 for PRCL_B) are still about right. The PRCL_IN1 and MICH_IN1 were centered around zero at the maximum power points. CARM and DARM had small offsets, which I put into the DARM_B and CARM_B filter banks (0.0066 for DARM_B, and 0.027 for CARM_B), although these are small enough that I don't know that they really do anything.
As a break from locking for a little while, I tried to see if I could get the TT3 and TT4 DAC channels to work for me. I had hoped it would be a quick and easy task, but I'm not seeing signal out. Since it wasn't working, I decided to go back to locking for the night, and look into the DAC in the daytime. I want to use one channel as the IN2 input of the CM board, and another as the external modulation input to the Marconi for transfer functions, so I need them to work.
As a side note on the input to the Marconi situation, it occurred to me that instead of laying a new cable, I can borrow the POP55 heliax. We don't have a POP55 diode right now, and the other end comes out across the hall from the Marconi, so it would be pretty easy to have a medium-length cable go from ITMX table to the Marconi. Objections to this?
I saw this same kind of behavior in my locklosses on Wednesday night; we should check out the 165 data, and see if the 3f PRCL error signal shows some drift away from zero.
Also, it's odd that CARM_IN1 and REFL11_I_ERR have different low frequency behavior in the plot you posted. I guess they have some difference in demodulation phase. REFL11_I's bump at -40sec coincides with the dip in arm power and a rise in REFLDC, but ASDC seems pretty smooth, so maybe it is a real CARM fluctuation.
I set the REFL11 analog demodulation angle (via cable length) about a year ago (ELOG 9850), with some assumption about PRCL having the same demod angle as CARM, but this was probably set with the arms misaligned. We should recheck this; maybe we're coupling some other junk into CARM.
I did a quick measurement get an idea of the ETM actuator calibration, relative to the ITMs. This will still hold if/when we revisit the ITM calibration via the Michelson.
For the test masses, I locked the arms individually using MC2 as the actuator, and took transfer functions from the SUS-[OPTIC]_LSC_EXC point to the PO[X/Y]_I_ERR error signals. There were two points with coherence less than 99% that I threw away. I then took the fraction at each point, and am using the standard deviation of those fractions as the reported random error, since the coherence was super high for all points, making the error of each point negligible relative to their spread.
With the data from ELOG 8242, this implies:
MC2 data was taken with the arms locked with the ETMs. The results are not so clean, the fractions don't line up; there is some trend with excitation frequency... The ratio is around the same as the ETMs, but I'm not going to quote any sort of precision, since I don't fully understand what's happening. Kind of a bummer, because it struck me that we could get an idea of the arm length mismatch by the difference in IMC frequency / arm FSR. I'll think about this some more...
I didn't verify that the loop gain was low enough at the excitation frequencies.
I put a 1kHz ELP in both arm servos, and got cleaner data for both. The ETM numbers are pretty much consistent with the previously posted ones, and the MC2 data now is consistent across frequencies. However, the MC2 numbers derived from each arm are not consistent.
With the data from ELOG 8242, this implies:
I've been fiddling with the mode cleaner and green beat box today, to try and get an absolute frequency calibration for MC2 motion. The AC measurements have all turned out weird, I get fractional power laws instead of the 1/f^2 that we expect from the MC2 pendulum. At DC, I get a rough number of 15 green kHz per MC2 count, but this translates to ~7e-10 m/count which is in contrast to the 6e-9 m/count from 2009. I will meditate on this a bit.
In any case, while working at the IOO rack, I tuned the 11MHz modulation frequency, as was done in ELOGs 9324 and 10314, by minimizing one of the beats of the 11MHz and 29.5MHz sidebands.
The new modulation frequency / current IMC FSR is 11.066209 +- 1 Hz, which is a only a few ppm change from the tuning from last July.
This implies a IMC round trip length of 27.090800m +- 2um.
Attached is a plot showing the beat of 55-29.5 going down as I changed the marconi frequency.
It is here.
The 40m fenced area will start storing this large ~ 8000 lbs chamber on April 14. The asphalt will be cut, jack hammered the next 2-3 days in order to lay concrete.
Their schedule is from 8 to 5 starting tomorrow. We are asking them to work from 6 to 3pm
ETMX is about 12-15 ft away
I spent some time tonight trying to revive DRMI locking, with the arms held off on ALS. Not much news, I haven't been able to get more than a few short spurts of resonance, using 1F signals.
I did use SRY to measure the BS->SRCL coupling by exciting each mirror and looking at their relative coupling to AS55Q. I found that we should use a value of +0.28 +-0.01 in the MICH->SRM element.
CDSutlils has been updated to the newest version, 474; there are some matrix interface methods that will make our locking scripts easier to read, modify, and maintain.
I've tested the ALS and CARM down scripts, and the LSC offsets script, and they all work fine.
The SUS align/misalign scripts don't work after the new CDS utils upgrade.
I don't know if it's looking for the _SWSTAT channel to confirm that the offset has been turned on/off, or if it is trying to set that channel, to do the switching, but either way, the script is failing. Recall that our version of the RCG still has _SW1R and _SW2R, rather than the newer _SWSTAT for the filter banks.
ezca.ezca.EzcaConnectError: Could not connect to channel (timeout=2s): C1:SUS-PRM_OL_PIT_SWSTAT
Q, can you please (please, please, pretty please) undo this upgrade, and then hold off on any further changes to the system for a few weeks?
The DAC was fine. I realized tonight that the digital filter bank outputs were off, so I wasn't actually sending signals out. Oooops.
Q remotely reverted this change. Scripts seem to work again.
The IFO_overview of oplevs seems ok, The servos are working fine. The green arms are locked, but master and oplev_summary monitoring screens are not.
I'm proposing to Erick G. to postpone the oplev noise measurement.
Does anyone know where the Busby or Rai low noise pre-amp boxes are?
I think I need one in order to measure the noise of the Marconi. Right now, I am trying to measure the amplitude noise, but I'm not seeing anything on the SR785 above the analyzer's noise level.
The Rai box was in the Cryo lab, and the Busby box was in the TCS lab. Neither had been signed out. Lame. Anyhow, thanks to Evan and Zach's memories of having seen them recently, they have been returned to the 40m where they belong. (Also, I grabbed a spare Marconi while I was over there, for the phase noise measurement).
The laser below is dead. JDSU 1103P, SN P845655 lived for 3.5 years.
JDSU 1103P died after 4 years of service. It was replaced with new identical head of 2.9 mW output. The power supply was also changed.
The return spots of 0.04 mW 2.5 mm diameter on qpds are BS 3,700 counts and PRM 4,250 counts.
It was replaced by JDSU P/N 22037130,( It has a new name for 1103P Uniphase ) sn P919639 of mfg date 12-2014
Beam shape at 5 m nicely round. Output power 2.8 mW of 633 nm
BS spot size on qpd ~1 mm & 60 micro W
PRM spot size on qpd ~1 mm & 50 micro W
+1 to both Evan and Zach for prompt info and +2 to you for getting more stuff than you started looking for. -2 karma to whomever had swiped them and hoarded without signing. You should put a 40m sticker on both of them. Make sure to check / use fresh batteries. The Busby box is BJT based and works on low impedance sources, the Rai box works on anything, but (I am guessing) has less CMRR.
Going back to Wiener filtering for a moment, I took a look at what the T-240 noise level looks like in terms of pitch motion on one of our SOS optics (eg. PRM).
The self-noise of the T-240 (PSD, in dB referenced to 1m^2/s^4/Hz) was taken by pulling numbers from the Users Guide. This is the ideal noise floor, if our installation was perfect. I'm not sure where Kissel got the numbers from, but on page 13 of G1200556 he shows higher "measured" noise values for a T-240, although his numbers are already transformed to m/rtHz.
To get the noise numbers to meters, I use: . The top of that fraction is (a) getting to magnitude from power-dB and (b) getting to asd units from psd units. The bottom of the fraction is getting rid of the extra 1/s^2.
Next I propagate this seismometer noise (in units of m/rtHz) to effective pendulum pitch motion, by propagating through the stacks and the transfer function for pos motion at the anchor point of the pendulum to pitch motion of the mirror (see eq 63 of T000134 for the calculation of this TF). This gives me radians/rtHz of mirror motion, caused by the ground motion:
I have not actually calibrated the POP QPD, so I will need to do that in order to compare this seismometer noise to my Wiener filter results.
Manasa and Steve,
Is this what you want? Dashed lines are dark.
BS and PRM oplevs are blocked for this measurement. I will restore to normal operation at 4pm today.
It doesn't work with the lens in there, but it seems pretty close. Please leave it as is and I'll play with it after 5 today.
To test what the inherent angular noise of the HeNe 1103P laser is, we're testing it on a table pointing into the BS OL QPD with only a few steering mirrors.
From the setup that I found today, I've removed the lens nearest to the laser (which was used for the BS and PRM) as well as the ND filter (what was this for?) and the lens placed just before the BS QPD.
With the ND filter removed, the quadrant signals are now ~15000 if we misalign it and ~9000 each with the beam centered.
In order to calibrate the OLPIT_IN1 and OLYAW_IN1 signals into mm of beam motion, I misaligned the mirror just before the QPD. The knobs on there actuate the 100 TPI screws and the knurling on the knob itself has 10 ridges, so that's 36 deg per bump.
PIT cal ~ 1.55 (knob deg / count) -->> 10 microns / count --->>> 10 urad / count
YAW cal ~ 1 (knob deg / count) -->> 6.5 microns / count --->>> 6.5 urad / count
Distance from the 45 deg turning mirror to the QPD silicon surface is 23 cm. Distance between knob tip and fixed pivot point is ~4 cm. 1 knob turn = 0.01" = 0.254 mm = 0.254/40 radians of mirror angle.
So 360 deg of knob gives 2*0.254/40 = 0.012 radians of beam angle = 0.012 * 230 mm ~2.3 mm of beam spot motion. Or 6.4 microns of translation / deg of knob.
The distance from the face of the laser to the QPD is 96 cm.
The punchline is that the laser shows a level of noise which has a similar shape to what's seen at LLO, but 10x lower.
The noise at 0.05 - 0.2 Hz is ~2-3x worse than the PR3 at LLO. Not sure if this is inherent to the HeNe or the wind in our setup.
BS & PRM oplev is restored. Note: the F -150 lens was removed right after the first turning mirror from the laser. This helped Rana to get small spot on the qpd.
It also means that the oplev paths are somewhat different now.
ETMX sus damping restored.
Just randomly found this old entry from 3 years ago. We should never have installed a GAP 2000 - they are an inferior type of InGaAs diode. We should add to our list replacing these with a 2 mm EG&G diode.
How many 2 mm EG&G InGaAs diodes do we have Steve? Can you please find a good clean diode case so that we can store them in the optics cabinet on the south arm?
We replaced the dead photodiode on MC REFL PD with a new one (GAP 2000). We measured the frequency response of the PD and tuned the resonant frequency using inductor L5 (in the circuit diagram) to be 29.575MHz - over an average of 10 measurements.
RFpds box is moved from RF cabinet E4 to clean cabinet S15
Inventory updated at https://wiki-40m.ligo.caltech.edu/RF_Pd_Inventory
Large Area InGaAs PIN Photodiode -- C30642GH 6 pieces in stock
Large Area InGaAs PIN Photodiode with a 2,0 mm active diameter chip in TO-5 package with flat glass window
Large area InGaAs PIN photodiode with useful diameter of 2,0 mm in a T0-5 package with a flat glass window. The C30642GH provides high quantum efficiency from 800nm to 1700nm. It features high responsivity, high shunt resistance, low dark current, low capacitance for fast response time and uniformity within 2% across the detector active area.
Few 1/4 -20 socket cap head screw with washers were tested for optimum torque.
QJR 117E Snap On torque wrench was used. I found that 40 lb in was enough.
These numbers will varie with washers, material it's going into and so on!
The standard among high-strength fasteners, these screws are stronger than Grade 8 steel screws. They have a minimum tensile strength of 170,000 psi. and a minimum Rockwell hardness of C37. Length is measured from under the head.
Inch screws have a Class 3A thread fit. They meet ASTM A574.
Black Oxide—Screws have been heat-treated for hardness, which results in a dark surface color.
Rana is next to calibrate his feelings and declare the right number.
Than Koji....and so on
Once we a number, than I buy more torque wrenches to fit it.
Q: please update this Wiki page with the go-back procedure:
I ran the "off" script for the Xarm ASS, followed by the "on" script, and now the Xarm ASS doesn't work. Usually we just run the freeze/unfreeze, but I ran the off/on scripts one time.
Koji, if you have some time tomorrow, can you please look at it? I am sorry to ask, but it would be very helpful if I could keep working on other things while the ASS is taken care of.
Steve, can you please find a cable that goes from the LSC rack to the IOO rack (1Y2 to 1X2), or lay a new one? It must be one single long cable, without barrels sticking it together. This will help me actuate on the Marconi using the LSC rack's DAC.
I made a script that checks the N2 pressure, which will send an email to myself, Jenne, Rana, Koji, and Steve, should the pressure fall below 60psi.
The script checking the N2 pressure is not working. I signed into the foteee account to look at some of the picasa photos, and there are thousands of emails (one every 10 minutes for the past month!) with error messages. Q, can you please make it stop (having errors)?
The error looks like it's mad about a "caget" command. I don't have time to investigate further though.
For 1/4-20 bolts made of 18-8 Stainless Steel, the recommended torque varies from 65-100 inch-pounds, depending upon the application, the lubrication, how loose the bolt is, if there's a washer, etc.
For our case, where we are going into a tapped, ferromagnetic stainless table, its less clear, but it will certainly by in the 60-80 range. This is close to the 5-6 foot-lbs that I recommended on Wednesday.
I've ordered 3 torque wrenches with 1/4" drive so that we can have one at each end and one in the toolbox near MC2. We'll indicate the recommended torque on there so that we can tighten everything appropriately.
Recently, Steve replaced the HeNe which was sourcing the BS & PRM OL. After replacement, no one checked the beam sizes and we've been living with a mostly broken BS OL. The beam spot on the QPD was so tiny that we were seeing the 'beam is nearly the size of the segment gap' effect.
Today I removed 2 of the lenses which were in the beam path: one removed from the common PRM/BS path, and one removed from the PRM path. The beams on both the BS & PRM got bigger. The BS beam is bigger by a factor of 7. I've increased the loop gains by a factor of 6 and now the UGFs are ~6 Hz. The loop gains were much too high with the small beam spots that Steve had left there. I would prefer for the beams to be ~1.5-2x smaller than they are now, but its not terrible.
Many of the mounts on the table are low quality and not constructed stably. One of the PRM turning mirror mounts twisted all the way around when I tried to align it. This table needs some help this summer.
In the future: never try locking after an OL laser change. Always redo the telescope and alignment and check the servo shape before the OL job is done.
Also, I reduced the height of the RG3.3 in the OL loops from 30 to 18 dB. The BS OL loops were conditionally stable before and thats a no-no. It makes it oscillate if it saturates.
Upgraded python on megatron. Added lines to the crontab to run autoMX.py. Edited crontab to have a PYTHONPATH so that it can run .py stuff.
But autoMX.py is still not working from inside of cron, just from command line.
I spent a day to fix the XARM ASS, but no real result. If the input of the 6th DOF servo is turned off, the other error signals are happy
to be squished to around their zeros. So this gives us some sort of alignment control. But obviously a particular combination of the
misalignment is left uncontrolled.
This 6th DOF uses BS to minimize the dither in ITMX yaw. I tired to use the other actuators but failed to have linear coupling between
the actuator and the sensor.
During the investigation, I compared TRX/TRY power spectra. TRX had a bump at 30Hz. Further investigation revealed that the POX/POY
had a big bump in the error signals. The POX/POY error signals between 10-100Hz were coherent. This means that this is coming from
the frequency noise stabilized with the MC. (Is this frequency noise level reasonable?)
The mysterious discovery was that the bump in the transmission exist only in TRX. How did the residual frequency noise cause
the intensity noise of the transmission? One way is the PDH offset.
Anyway, Rana pointed out that IMC WFS QPDs had large spot offsets. Rana went to the AS table and fixed the WFS spot centering.
This actually removed the bump in TRX although we still don't know the mechanism of this coupling.
The bump at 30Hz was removed. However, the ASS issue still remains.
Ugh, this turns out to be because cron doesn't source the controls bashrc that defines where to find caget and all that jazz that many commands depend on. This is probably also why the AutoMX cron job isn't working either.
Also, cron automatically emails everything from stderr to the email address that is configured for the user, which is why the n2 script blew up the foteee account and why the AutoMX script was blowing up my email yesterday. This can be avoided by doing something like this in the crontab:
0 8 * * * /bin/somecommand >> somefile.log 2>&1
(The >> part means that the standard output is appended to some log file, while the 2>&1 means send the standard error stream to the same place as stdout)
I made this change for the n2 script, so the foteee email account should be safe from this script. I haven't figured out the right way to set up cron to have all the right $PATH and other environment stuff, such as epics may need, so the script is still not working.
Since python from crontab seemed intractable, I replaced autoMX.py with a soft link that points at autoMX.sh.
This is a simple BASH script that looks at the LSC FB stat (C1:DAQ-DC0_C1LSC_STATUS), and runs the restart mxstream script if its non-zero.
So far its run 5 times successfully. I guess this is good enough for now. Later on, someone ought to make it loop over other FE, but this ought to catch 99% of the FB issues.
Today I tried some things, but basically, lowering the input gain by 10 made the thing stable. In the attached screenshotstrip, you can see what happens with the gain at 1. After a few cycles of oscillation, I turned the gain back to 0.1.
There still is an uncontrolled DoF, but I that's just the way it is since we only have one mirror (the BS) to steer into the x arm once the yarm pointing is fixed.
Along the way, I also changed the phase for POX, just in case that was an issue. I changed it from +86 to +101 deg. The attached spectra shows how that lowered the POX_Q noise.
I also changed the frequencies for ETM_P/Y dither from ~14/18 Hz to 11.31/14.13 Hz. This seemed to make no difference, but since the TR and PO signals were quieter there I left it like that.
This is probably OK for now and we can tune up the matrix by measuring some sensing matrix stuff again later.
I have unplugged POXDC and POYDC from their whitening inputs. They have labels on them which whitening channel they belong to (POY=5, POX=6) on the DCPD whitening board.
TT3_LR's DAC output is Tee-ed, going to the POYDC input and also to an SR560 near the Marconi.
TT4_LR's DAC output is Tee-ed, going to the POXDC input and also to the CM board's ExcB input.
Thank you both.
I have updated the .snap file, so that it'll use these parameters, as Rana left them. Also, so that the "unfreeze" script works without changes (since it wants to make the overall gain 1), I have changed the Xarm input matrix elements from 1 to 0.1, for all of them. This should be equivalent to the overall gain being 0.1.
After last week's work on the BS/PRM oplev table, I think the PRM oplev got centered while the PRM was misaligned. With the PRM aligned, the oplev spot was not on the QPD. It has been centered.
I'm sad. And frustrated.
The PRCL angular feed forward is not working, and without it I am having a very difficult time keeping the PRMI locked while the arms are at high power (either buzzing, or the one time I got stable high power partway through the transition). Obviously if the PRMI unlocks once CARM and DARM are mostly relying on the REFL signals, I lose the whole IFO.
Q and I had been noticing over the last few weeks that the angular feed forward wasn't seeming quite as awesome as it did when I first implemented it. We speculated that this was likely because we had started DC coupling the ITM optical levers, which changes the way seismic motion is propagated to cavity axis motion (since the ITMs are reacting differently).
Anyhow, today it does not work at all. It just pushes the PRM until the PRMI loses lock. I am worried that, even though Rana re-tuned the BS and PRM oplev servos to be very similar to how they used to be, there is enough of a difference (especially when compounded with the DC coupled ITMs) that the feed forward transfer functions just aren't valid anymore.
Since this prevents whole IFO locking, I spent some time trying to get it back under control, although it's still not working.
I remeasured the actuator transfer function of how moving PRM affects the sideband spot at the QPD, in the PRMI-only situation. I didn't make a comparison plot for the yaw degree of freedom, but you can see that the pitch transfer function is pretty different below ~20Hz, which is the whole region that we care about. In the plot below, black is from January (PRMI-only, no DC-coupled ITMs) and blue is from today (PRMI-only, with DC-coupled ITMs, and somewhat different BS/PRM oplev setup):
I calculated new Wiener filters, and tried to put them in, but sometimes (and I don't understand what the pattern is yet) I get "error" in the Alternate box, rather than the zpk version of my sos filter. It seems to go away if you use fewer and fewer poles for fitting the Wiener filters, but then the fit is so poor that you're not going to get any subtraction (according to the residual estimation plot that uses the fitted filters rather than the ideal Wiener filters). The pitch filters could only handle 6 poles, although the yaw filters were fine with 20.
The feed forward just keeps pushing the PRM away though. I flipped the signs on the Wiener filters, I tried recalculating without the actuator pre-filtering, I don't know why it's failing. But, I'm not able to lock the interferometer. Which sucks, because I was hoping to finally get most of my noise coupling measurements done today.
Yesterday morning was dusty. I wonder why?
The PRM sus damping was restored this morning.
Yesterday afternoon at 4 the dust count peaked 70,000 counts
Manasa's alergy was bad at the X-end yesterday. What is going on?
There was no wind and CES neighbors did not do anything.
Air cond filters checked by Chris. The 400 days plot show 3 bad peaks at 1-20, 2-5 & 2-19
Based on Jenne's chiara disk usage monitoring script, I made a script that checks the N2 pressure, which will send an email to myself, Jenne, Rana, Koji, and Steve, should the pressure fall below 60psi. I also updated the chiara disk checking script to work on the new Nodus setup. I tested the two, only emailing myself, and they appear to work as expected.
The scripts are committed to the svn. Nodus' crontab now includes these two scripts, as well as the crontab backup script. (It occurs to me that the crontab backup script could be a little smarter, only backing it up if a change is made, but the archive is only a few MB, so it's probably not so important...)
This watch script gives little time to replace N2 cylinder. When the regulated supply drops below 60 psi the cylinder pressure is 60 psi too.
It is more of a statement that V1 is closed and act accordingly. It's only practical if you are in the lab.
Rana pointed it out correctly that we need this message 24 hrs before it happens. This requires monitoring of total supplies , not the regulated one.
So we need pressure transducers on each nitrogen cylinder, before the regulator. The sum of the two N2 cylinder when they are full 4000 - 4500 psi
The first email should be send out at 1000 psi as sum of the two cylinders. This means that you have 1 day to replace nitrogen cylinder.
Most of the time the daily consumption is 750 +-50 psi
However sometimes this variation goes up ~750 +-150 psi
We want to have a VAC page in the summaries, so Steve - please put a list of important channel names for the vacuum system into the elog so that we can start monitoring for trouble.
Also, anyone that has any ideas can feel free to just add a comment to the summary pages DisQus comment section with the 40m shared account or make your own account.