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Reports until 14:55, Wednesday 28 January 2015
H1 SUS (ISC)
brett.shapiro@LIGO.ORG - posted 14:55, Wednesday 28 January 2015 (16329)
You can now make damped triple and double Matlab models from the foton file

Like the quad model scripts (LHO 16126), I updated the generate_Triple_Model_Production.m and generate_Double_Model_Production.m functions so that you can specify a foton filter for the top mass damping loops.

The generate scripts is in

.../SusSVN/sus/trunk/Common/MatlabTools/TripleModel_Production

and

.../SusSVN/sus/trunk/Common/MatlabTools/TripleModel_Production

If youhaven't done so in the past week, you will also need to svn up

.../SusSVN/sus/trunk/Common/MatlabTools

since this is where the foton file reading functions are located (imported from the SeiSVN)

You can still specify the usual .mat struct file as before. The generate script looks for the .txt extension to determine if you are sending it a foton file.

 

Here is an example of how to make a model with damping filters read from foton:

hsts_model = generate_Triple_Model_Production(frequency_vector_for_plots, 'hstsopt_metal', [], 0, 1, '/opt/rtcds/lho/h1/chans/H1SUSMC1.txt')

IMPORTANT: The foton file does not know which filter modules are engaged. This information is coded into the function with a variable called medm_engaged_modules, which must be updated at the time of running the script. The script will output to the command line which modules are being used for each filter, and where to change in case you forget. For a variety of reasons I thought it more convenient from a user-point-of-view to have this coded into the function rather than as another input to the function, however this could be modified. This is the same in the quad script.

 

These functions have more instructions commented into their headers.

Just have the single sus scripts to go.

H1 AOS
keita.kawabe@LIGO.ORG - posted 13:35, Wednesday 28 January 2015 (16328)
green beam size on ITMs and baffle PDs

Summary:

Green straight shot beam size on ITMX is a factor of 0.87 of nominal (i.e. too small) while ITMY a factor of 1.2 too large.

The beam radius ratio is (X/Y)=0.72, which makes the ITMX baffle PD output current to be a factor of 2 larger than that of Y when you hit these PDs using a straight shot beam.

There used to be a factor of 2 to 2.5 unexplained difference between the photocurrent in ITMX and ITMY baffle diodes during initial green alignment, but the beam size explains a factor of 2, so the remaining factor is about 1.2 or so, which I don't care for now.

Background:

This is one of those health check type stuff. Baffle PDs could be used for scattering measurement but the health of some of those PDs were in question.

One of the suspicions came from the fact that, when looking at green straight shot beam during full initial alignment, PD current from X arm baffle is much larger than Y arm. A part of it comes from the laser power (there's about a factor of 2 or so difference) but the baffle PD current is a factor of 4 to 5-ish different, so there always was a factor of 2 to 2.5 unexplained.

Details:

I first used dither align script to point the TMS beam to PD1 and then PD4 of the ITM baffle. Since the horizontal distance between PD1 and PD4 is 11.3", the script allows us to calibrate TMS alignment slider.

Immediately after the script finished, I pointed the beam to PD4 center, move TMS in YAW in one direction by more than the beam radius,  and ran another script to move TMS in YAW, wait and measure PD4 current.

Attached is the YAW scan data (circles and crosses) as well as the fit to Gaussian profile assuming the same radius in PIT and YAW:

current = ofst+ A * 2/pi/w^2 * exp(-2*(X-X0)^2/w^2)

where w is the beam radius and A is an overall factor.

  beam radius [m] A [mA m^2] QPD_SUM
IX PD4 0.033 (0.038 nominal) 3.8E-7 46180
IY PD4 0.046 (0.038 nominal) 2.7E-7 26124
X/Y 0.715 1.4 1.77

The last column in the above table shows QPDA_SUM+QPDB_SUM. If everything makes sense, and if the beam was at the same height as the PD center during the scan, QPD_SUM ratio should agree with A ratio, but apparently it doesn't at 20%-ish level. This is good enough because the suspicion was that there was something grossly wrong about the baffle PDs.

BTW we can do the same thing for IR beam, scanning MMT3, to assess the IR matching to the arms if we want to (or better yet, do the spiral scan to see both PIT and YAW).

Images attached to this report
H1 ISC
jim.warner@LIGO.ORG - posted 13:27, Wednesday 28 January 2015 - last comment - 13:39, Thursday 29 January 2015(16327)
Pop 18 trend showing window for last nights lock

Looks like lock was from about 9:14 UTC to 16:09 UTC. For posterity.

Images attached to this report
Comments related to this report
jeffrey.kissel@LIGO.ORG - 13:39, Thursday 29 January 2015 (16349)DetChar, ISC, SEI, SUS
Also for posterity:
- This is a DRMI lock stretch.
- IMC WFS DOF4 is OFF
- No corner station WFS engaged. 
- ISS second loop is *OFF*. 
- 10 [W] input reqested. 
- SEI was in the most recent nominal configuration -- 
    HPI Pump Servo ON, 
    Sensor Correction to ISI XY and HEPI Z, 
    (no ST0-1 Feed Forward yet), 
    Using 01_28 blends on the HAM ISIs, 
    "45 [mHz]" X&Y, LLO blends on BSC ISIs.

Great for offline, data-mining studies of
- Gain Problems with STS2B
- HAM3 0.6 [Hz] feature
- Coherence with HPI Pump Pressure.
- DAC major-carry transition glitches.
- Cavity performance with respect to SEI performance.
- Lock Loss statistics

Among other things...
H1 SEI (ISC, SEI)
evan.hall@LIGO.ORG - posted 13:22, Wednesday 28 January 2015 (16326)
M5.7 earthquake 40 km SW of Ferndale, CA

http://earthquake.usgs.gov/earthquakes/eventpage/nc72387946

Ground velocity exceeds 20 μm/s from 0.03 Hz to 0.1 Hz. IMC MC2 transmission is noticeably wobbly.

H1 CDS
patrick.thomas@LIGO.ORG - posted 11:47, Wednesday 28 January 2015 (16324)
Updated conlog channel list
Added 2 channels and removed 788.
H1 General
edmond.merilh@LIGO.ORG - posted 11:01, Wednesday 28 January 2015 (16320)
Morning Meeting Summary

Work Permit review.

SEI - continuing work on SDF system for BSC ISI. HEPI pump servo is ongoing tinvestigation. Maybe Jeff will run some TFs looking at 1Hz to 10Hz at some point today.

SUS - no big news. Thomas will ressurect the Drift Monitor this week sometime.

ISC/Commish - taking small steps in the positivedirection. Had a rather lengthy DRMI lock last night beginning ~01:30.

3IFO - no activities in LVEA. All activities across the street.

Facilities - Beam Tube cleaning is ongoing. Gutter work is don at LSB. Crew has moved to VPW.

CDS - variac installation at End station for Heater. Work in HAM6 area on Fast Shutter. R Abbott will be coming to work with this.

Gary will be moving ISS arrays and using the large airlock door in the LVEA

H1 CDS (DAQ)
david.barker@LIGO.ORG - posted 08:30, Wednesday 28 January 2015 (16322)
CDS model and DAQ restart report, Tuesday 27th January 2015

model restarts logged for Tue 27/Jan/2015
2015_01_27 01:43 h1fw0
2015_01_27 03:04 h1fw1

2015_01_27 08:57 h1iscex
2015_01_27 09:03 h1iscey
2015_01_27 09:18 h1isiham6

2015_01_27 16:32 h1fw1
2015_01_27 23:42 h1fw0

4 unexpected restarts. Light maintenance day, minor model changes for End ISCs and ISIHAM6 which did not require DAQ restart. Conlog frequently changing channels list attached.

Non-image files attached to this report
H1 AOS
douglas.cook@LIGO.ORG - posted 08:16, Wednesday 28 January 2015 (16321)
ITMy OPLVR being scrubbed by copper pipes
I opened the gap between the bundle of copper pipes that were again rubbing on the ITMy optical lever TX pier causing the 10min-ish sawtooth signal. This is a temporary fix, but is more stable than the first time we saw this. It is in the planning to reroute the pipes and fix other similar issues with other oplvrs.
Keita ran a new scan verifying the fix.
H1 General
edmond.merilh@LIGO.ORG - posted 08:06, Wednesday 28 January 2015 (16318)
Observation Intent bit

The OIB was set to commissioning upon my arrival for shift at 08:00. DRMI was still locked. I'm going to try my hand at locking the arm(s) as no one is here working yet.

H1 SUS (DetChar, ISC, SEI)
rana.adhikari@LIGO.ORG - posted 01:19, Wednesday 28 January 2015 (16317)
RM maintenance

I touched up the RM suspension controls today. RM1 had been tripping its watchdog often during the engagement of the scripts which use the RMs to center the beams on the REFL WFS.

  1. Moved the RLP11 low pass filter into the damping filter banks. This is less aggressive than the 5 Hz Cheby low pass that was there and allows for more stable recovery from saturations. The damping gains were checked; seems reasonable.
  2. Turned on the LIMIT for the damping filter banks at 1000 counts. This is similar to what I did with the IM mirrors recently.
  3. With the DRMI aligned, I adjusted the alignment biases to center the beam on the REFL_A and REFL_B WFS.

Now, when the scripts turn these on the RMs do not trip and the beams are centered.

We have left the DRMI locked (on 1f), Guardian undisturbed starting around 1:13 AM for seismic performance evaluation.

H1 ISC
alexan.staley@LIGO.ORG - posted 00:54, Wednesday 28 January 2015 - last comment - 10:58, Wednesday 28 January 2015(16315)
CARM offset to ~100pm

Sheila, Evan, Rana, Eli, Kiwamu, Alexa

Today we were able to reduce the CARM offset from 800pm to 100pm. We made three major changes to acheive such an offset.

  1. We noticed that the sqrt(TRX+TRY) counts into the CM board was only about 100 pk-pk. We increased this to about 800pk-pk by reallocating some gain. We decreased the LSC-REFL_SERVO_IN1_GAIN from 0dB to -16dB, and increased the LSC-REFLBIAS_GAIN from 8 to 50.4.
  2. We added a z20:p40 to REFLBIAS in order to get more phase and push the UGF of TR CARM from 200 Hz to 150 Hz. This filter is only engaged after we have already turned off ALS COMM, at which point we do not need to compensate for the COMM PLL VCO.
  3.  We noticed that ASAIR_RF45_Q was rather noisy as we were reducing the CARM offset. We added an integrator FM2 (z2:p0) to ALS DIFF to reduce low frequency noise. This helped make TR CARM more stable.

Transition Process from 800 pm to 400pm

To start,

With some TR buildup (approximately 1ct on LSC-X/Y_TR_A_LF_OUT),

With CARM on sqrt(TRX+TRY),

Transition Process from 400pm to 100pm

With all the settings as above, we bring the CARM offset to -3.2 (or ~150pm). At this point we transitioned the in-air TR PDs to the IR TR QPD_Bs.  For reference, ASC-X/Y_TR_B_POW_NORM =1,1  and LSC-TR_X/Y_QPD_B_SUM_GAIN = 0.222, 0.175 respectively. Also, the QPD NSUM was about 400cts here. We continued to reduce the CARM offset to -4.5 cts (or ~80pm). At first,t the ASAIR_RF45_Q looked like a decent signal and responded well to a DIFF offset change. We turned on a servo for about 1.5min to ensure ASAIR was around zero (z servo -r LSC-ASAIR_A_RF45_Q_NORM_MON -g -11111 ALS-C_DIFF_PLL_CTRL_OFFSET).  We measured ASAIR_RF45_Q/DARM_IN1 = 3e7 (at this point DARM_IN1 is just ALS DIFF signal). Note: we added a -160dB FM10 filter in LSC-ASAIR_A_RF45. Then the PD_DOF_MATRIX for ASAIR_RF45_Q is 3.3. So far, we were able to transition from ALS DIFF to RF DARM 50% of the way, and then we broke the lock. We started to reconsider whether we were actually in the linear range for RF DARM. Maybe we should be using AS45Q/SQRT(TRX) at this point? This requires a model change; however, this is already impleneted in the l1lsc.mdl that is in the SVN, so we could just copy that.

A little more ...

The farthest CARM offset we reached was -7 cts or ~60pm on sqrt(TRX+TRY) with the QPDs controlling CARM and ALS DIFF for DARM. Here we had 26 x single arm power, and REFL DC dropped from 80mW to ~75mW.

Comments related to this report
eleanor.king@LIGO.ORG - 01:00, Wednesday 28 January 2015 (16316)

Some lock loss times for today:

Lock losses while transitioning DARM from ALS-DIFF to AS_AIR_45_Q:

06:01:40 UTC (28jan)

06:33:34

07:53:45

stefan.ballmer@LIGO.ORG - 10:58, Wednesday 28 January 2015 (16323)
Almost there!
H1 SEI (DetChar)
jeffrey.kissel@LIGO.ORG - posted 21:09, Tuesday 27 January 2015 - last comment - 22:15, Tuesday 27 January 2015(16239)
Treatise on Corner Station HEPI Pump Servo Noise

J. Kissel, B. Lantz, H. Radkins

Hugh and I, with the remote advice from Brian, have been investigating the coupling between HEPI differential pressure noise and HEPI platform motion (see preliminary studies in LHO aLOGs 16231 and 16309). In summary, the coupling is smattered between every chambers DOFs, limiting the performance between 0.02 and 2 [Hz]. There's no pattern as to how this coupling occurs except that the coherence for a given DOF happens in a similar frequency band in all chambers. All chambers show differential pressure moderate coherence to HP, but we're still working on estimating the transfer functions between this "pringle" mode and any translations / rotations to assess this impact. Further, we still have set up any successful long stretches of IFO / WFS data for the DRMI, so this pressure noise' impact can't yet be assessed. However, for now, I continue under the assumption that *any* low frequency improvement, especially to RZ / YAW, will improve the relative angular fluctuations of the IFO and stabilize optical gains, etc.

Hugh has already revealed the punchline: this morning's pump-servo OFF data shows that the problem is entirely because is of noise on differential pressure sensor. I'll attach a comment with complete set of plots for proof in a bit.

Further discussion on the noise as it stands with the pump servo (i.e. ON), based on the attached plots, which include

is below. I post all of these discussion points for future reference and design considerations to show how nastily and diversely imposing sensor noise on the pump servo imposes the platform motion. But mostly, because I sorted through a TON of data and plots to make these conclusions, before we knew the source of the problem.

** For the HEPI L4C ASDs, I plot the *raw* sensor noise because (a) I'm trying to cram as much information on as few plots as possible, and (b) the scale factors for both the IPS and L4Cs are the same for each DOF, and are all between 0.3 and 1.1, so the estimation estimation is off by at most a factor of three. Mostly it's there just to guide the eye, as a primitive noise budget.

(1) Krishna (before coherence between all DOFs and chambers was fully flushed out), suspected that because we now run Z sensor correction is on HEPI, the extra drive force meant excess pressure noise coupling. However, compared to 23e3 [ct_{rms}] range, the Vertical RMS of 5 [ct_{rms}] is peanuts. Further discussion of DC / mean requested drive is below.

(2) Brian suspected that the passive filtering system, the accumulating bladders might not be operating at their nominal air pressure. However, pump 8's (out of 12 for the corner) bladder pressure was checked last week, and was within spec. There're still lots lots to check, but Hugh suspects they're also OK.

(3) I suspect the PID controller for the servo is likely not well-tuned for new differential pressure sensing, suggesting we need to remeasure plant (which could mean significant down time for the IFO). There's been some discussion offline in the SEI group as to how we should systematically characterize the pump servo plant, given there's no "fast" excitation point in the pump servo make a tranditional frequency-response transfer function difficult (see SEI aLOGs 684 and 686). For now, we suspect we can do a sufficient characterization with simple steps using the existing EPICs infrastructure. Characterization to-date (though very early on in aLIGO) was also made by step response (see E1100508), but the assumptions about the plant don't seem sound in retrospect, and were done when the pressure was still on an absolute "single ended" readback.

- Brian's "Allowable Pump Servo Noise" defined in T1100198, but contains a LOT of assumptions. One of which is that the open loop gain transfer function of the feed back loops is "100 at low frequency." As such, Brian suggests, if the HEPI feedback loops are gain limited, try adding some boost at these frequencies to suppress the noise. However, I argue, with Hugh's recent redesign of the controller (see LHO aLOG 15308, the relevant attachment re-attached here), RZ Loops for example have *plenty* of gain, upwards of 3000 - 4000 at 0.1 [Hz], typically asymptoting to a few million a DC. This is far more than Brian assumed, so I thing we're alright in the gain department. Regrettably, the differential pump pressure is an EPICs channel, so I can't get an ASD of the performance above ~8 [Hz], but I'll post more on that in the future comment.

- Differential Pressure Noise supposedly coupling increases with actuator force request, but I've not found this to be true empirically. Check out the table below. Colors of the text help indicate which requested DC offsets are small, and which are large (dark green is smallest, then light green, gold, orange, with bright red is largest, in bins of 50 [micro-whatevers] and anything higher than 200 [micro-whatevers] is marked as bright red). Cells shaded in gray show coherence between the differential pressure and the HEPI L4Cs.

There is no discernable pattern:

  X [um] Y [um] Z  [um] RX [urad] RY [urad] RZ [urad] HP ["um"] VP ["um"]
HAM2

24

-159

-142

27

160

-21

185

6

HAM3

3

109

-105

-24

-25

-124

131

93

HAM4

169

-124

-45

11

4

-78

141

-14

HAM5

47

-103

-17

97

-13

13

71

-19

HAM6

111

108

-283

1

115

1

320

-28

BS

3

39

-105

-162

-177

-20

-140

-58

ITMX

-118

13

127

32

-20

70

-1

11

ITMY

600

-63

-189

15

60

-16

-87

27


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Here're what patterns I was able to glean from the above table and attached plots:

- My best guess at this point is that it depends on the intricacy of how the piping is laid out between each chamber and the pumps. But it's only a guess, it's the only thing I know that significantly different between all chambers.

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

DTT templates for this data live here:

/ligo/svncommon/SeiSVN/seismic/HEPI/H1/Common/

2015-01-23_H1HPI_ActuatorDrive.xml

2015-01-23_H1HPI_PumpControllerNoise.xml

Non-image files attached to this report
Comments related to this report
jeffrey.kissel@LIGO.ORG - 22:15, Tuesday 27 January 2015 (16314)
J. Kissel, H. Radkins

Here's the proof -- checking every DOF and every corner station HEPI -- that all coherence disappears when the pump servo is turned off. I also attach a comparison of the open and closed loop ASD of the differential pressure against the goals and requirements defined in T1100198.

P.S. If you weren't excited about HEPI before now -- check this out. (Probably best to right-click and "save link as...")
Non-image files attached to this comment
H1 SUS
rana.adhikari@LIGO.ORG - posted 19:51, Tuesday 27 January 2015 - last comment - 12:31, Wednesday 28 January 2015(16313)
ETMX Bounce Mode ringup trend

The stopband filter we put in the ETMX OL servo yesterday seems to have done the job of preventing the ringups:

In the attached trend of the OLPIT 3-10 Hz BLRMS, you can see the ringup start around 6AM local time this Sunday, the 25th.

Around noon on Monday (1800 UTC), Evan and Alexa start damping the mode using the bandpass filter in the OL PIT servo. They stop around 2100 UTC when the mode is small. It then rings up for the next 7 hours until we turn the stopband filter on.

Then it rings down with a 1/e time of ~4 hours (which implies a bounce mode Q of ~440,000 if nothing else is driving it).

We should make sure to install these on all of the test mass OL servos.

Images attached to this report
Comments related to this report
rana.adhikari@LIGO.ORG - 12:31, Wednesday 28 January 2015 (16325)

Added the Bounce + Roll bandstop filter to all the ETM/ITM OLDAMP filter banks. In some cases, I have overwritten existing 'notch' filters there for this purpose. Its not a good idea to use 'notch' for these mechanical modes which drift in frequency.

I made the Roll bandstop wider since there's no phase hit from this higher frequency filter. The vertical lines in the plot show the expected bounce frequency (9.775 Hz) and the roll frequency (13.81 Hz) which has some small natural spread between the optics, but I figure this should catch them all, even when the VEA temperatures drift.

Non-image files attached to this comment
H1 General
edmond.merilh@LIGO.ORG - posted 15:59, Tuesday 27 January 2015 (16291)
Daily Ops Summary

06:30 Cris and Karen into LVEA- esit doors will be open

08:00 restarted digital camera images on FOM5

08:13 Rick, Darkham, Thomas and Nutsinee to EY for P-Cal work. Working close to STS.

08:14 :21, :22 Sensor correction is off @ EY to accomodate P-Cal work.

08:22 Sigg rebooting end station ISC

08:23 Gary moving ISS arrays from optics lab to H@ enclosure. Will be using exit doors from LVEA to accomodate. Sigg approves.

08:30 Cyrus installing new edge router for CDS. GC will be down for a few minutes.

08:34 Christina w/exterminator visiting all points to check mouse traps.

08:34 Hugh into CER

08:48 Cris and Karen to Mids

08:52 Jef to LVEA to get a LASER vibrometer.

09:00 Plumber on site for toilet maintanance.

09:02 Kyle called to infor about 2 Praxxair deliveries today.

09:08 Betsy out to W Bay

09:10 J Kissell ramping down SUS in HAM6 for ISI FE Model restart.

09:15 Restart HAM6 ISI FE Model. All sensor correction is turned off except for EX. No DAQ restaert required.

09:18 HAM6 restored and back online.

09:29 Karen leaving MY.

09:40 Praxxair called to announce arrival

09:44 Gary driving to EY to talk to Rick

10:08 Doug out to LVEA to move copper pipes under ITMY.

10:11 Rick et al back from the end station. Can't run excitations.

10:13 Jeff an TJ back from LVEA.HEPI pump ! needs electrial attention. Hugh will give more detail.

10:30 Jeff B back into LVEA by HAM2 vibrometer.

10:49 Betsy and Janine out of th LVEA.

11:15 Sudarshan to EX

12:00 Jef back out to LVEA HAM2

12:12 Jeff out of LVEA

12:15 Fil and co out of LVEA

12:30 Jim out to LVEA to get some parts

13:45 Kyle and Joe out tp EY mechanical room

14:20 Kyle ad Joe back from EY

15:20 Sudarshan out to EY

15:50 Sudarshan back from EY

H1 SEI
hugh.radkins@LIGO.ORG - posted 15:32, Tuesday 27 January 2015 (16309)
Quick Look at HEPI L4C Coherence with HEPI Pump Pressures: Servo On vs Servo Off

JeffK is going to produce a much more extensive result and possibly conclusions but the simple view is here.  I selected a few chambers to look at BS, ITMX and HAM5.  HAM5 is closest to the Pump Stations, HAM1 is certainly the farthest but it isn't unlocked.  HAM2 might be a better candidate but too late, I chose ITMX, the BS is where the pressure sensors are which derive the differential pressure channels.

I looked at all DOFs (not VP) and we see/saw lots of coherence with HP RZ and Z on most chambers.  HP & RZ being the largest.  I show HP, RZ and the oplev YAW and Pitch of the optic on the platform in the attached plot.  The top group is the BS, the middle traces are HAM5 and SR3, and, the bottom group is the ITMX.

Pretty much nothing seen on the Oplevs but the coherence on the RZ and HP loops when the HEPI Servo is on is pretty clear compared to when the drive to the Pump Stations is fixed ignoring the pressure signals.

More Details:  Switched the Servo to Manual state at 1510utc this morning and made one output tweak at 1514.  The Sensor corrections to the BSCs were turned off at 1549--this may come into the spectra toward the ends of these 10 average 1mHz BW measurements.  The current traces are with the servo off and are started at 1515utc.

The servo was turned back on at 1716utc.  The reference traces (dashed) in the plots where started at this time.

My current conclusion from this is the noisy pressure channels is injecting this noise into the drive signal and it is getting to the platform.  We will tune the controller to help deal with this but the noisy signals must be addressed.

Images attached to this report
H1 ISC (DetChar, ISC)
evan.hall@LIGO.ORG - posted 00:40, Tuesday 27 January 2015 - last comment - 16:59, Tuesday 27 January 2015(16281)
More work on handing off to sqrt(TRX+TRY)

Alexa, Elli, Sheila, Rana, Evan

Today we worked some more to make the sqrt(TRX+TRY) handoff more robust.

Now we can pretty reliably complete the transition by hand. We are working on implementing the transition in the guardian.

We have tried to reduce the CARM offset while locked on sqrt(TRX+TRY), but we cannot seem to get beyond 2 or 3 times the single-arm power without blowing the lock. The next step is to go through the CARM reduction sequence more carefully and characterize the OLTF of the CARM loop in this state.

Gain redistribution

As discussed in LHO#16252 et seq., we suspect that the common-mode board has gain-dependent offsets. If this is true, it explains why the interferometer can be knocked out of lock while ramping down or turning off ALS COMM.

To boost the CARM loop's immunity to these offsets, we redistributed gains as follows:

Even with these changes, success is not guaranteed. The gain steps can be heard very clearly when listening to LSC-CARM_IN1, and turning off ALS COMM on the summing board will blow the lock about half the time. We can get better results by using the gain slider on the common-mode board, but we can still hear the gain steps.

Modified handoff procedure

A lockloss plot is attached for an unexplained lock loss during the CARM offset reduction after handing off to sqrt(TRX+TRY). Other lock loss times, all 2015-01-27 UTC: 03:56:53, 04:05:25, 05:36:16, 06:40:59, 07:56:02, 08:37:20. The last four are during CARM offset reduction after the handoff is complete.

For a sqrt(TRX+TRY) offset of −1.5 ct, the gain we need for REFL_DC_BIAS is 50 ct/ct. Our OLTF looks good here. However, when we reach an offset of −2, we seem to lose lock, even though there is no obvious nastiness in the CARM spectrum.

Mystery

Today, locking DRMI without arms was pretty painless. In contrast, DRMI+arms lock acquisition was very, very slow for most of the morning and afternoon. After about 5pm local, it became painless as well. This may have been correlated with our changing the trigger settings to be twice as high with arms (compared to no arms), since the POP18 buildup is twice as high. But we haven't investigated this systematically.

Images attached to this report
Comments related to this report
eleanor.king@LIGO.ORG - 11:20, Tuesday 27 January 2015 (16294)

Last night Sheila requested DRMI_LOCKED on the ISC_LOCK guardian when she left for the night at 1am to che k if this configuration is stable. 

DRMI with green in the arms and IR held off resonance stayed locked overnight, and the power slowly degraded untill 4.30am when the lock dropped.  Cuardian relocked DRMI untill 6am when DRMI lock dropped and did not recover.  This shows that this configuration is fairly stable.

Images attached to this comment
rana.adhikari@LIGO.ORG - 01:58, Tuesday 27 January 2015 (16282)ISC, SUS

After changing our ALS gain rampdown to be in the CM board rather than ahead of it, we never broke lock due to the rampdown. However, we only tried it in this new way twice.

The lock loss plot attached above was typical of our current lock loss mystery. After moving to a new CARM offset, the CARM error signal seems stable (no peaking in the spectrum) and the loop shape looks good. The lock breaks without any characteristic sound - just a sudden lock loss. Investigation of the 5 LSC error and control signals shows no instability in the 100 ms before lock loss. The lock loss happens several seconds after the CARM offset is done ramping. Since the signal from the Thorlabs Transmon PDs is only 2000-3000 counts, we think that they are not saturating.

No guess yet about what is happening. Any speculations on lock loss causes is welcome.


We struggled with the ETMX bounce mode all of today. It seems to have started ringing up around 3 AM last night (according to the ETMX OL 3-10 Hz BLRMS trend). We spent a couple of hours damping it around noon today, but then it slowly started growing again today. We've now installed a 60 dB stopband filter centered at 9.77 Hz in the OL loops to see if this will stop the ringups. We have also installed a resonant gain filter for 9.77 Hz in the CARM loop to reduce the arm power fluctuations during the offset reduction.

To better monitor the bounce mode, we set up the ETMX OL lockin screens to demod the OLPIT signal at 9.67 Hz. So now one can trend the 0.1 Hz beat note in the lowpassed output of this to see what the Bounce mode peak height is at all times. Probably should make a dedicated BLRMS for each suspension with an OL to monitor its bounce mode height.

lisa.barsotti@LIGO.ORG - 08:47, Tuesday 27 January 2015 (16287)ISC
I am taking a look at the lock losses Evan listed in this entry. 

All the correction signals seem good except the BS one. 

This is, for example, lock loss 4_05 UTC, with different zoom of the correction signals during CARM offset reduction. 

Probably a campaign of loop measurements for the vertex DOFs can help. 
Images attached to this comment
lisa.barsotti@LIGO.ORG - 10:20, Tuesday 27 January 2015 (16293)ISC
More lock loss science.

As far as I can tell, 5:36 and 6:40 are similar to the previous lock loss 4:05, while in 7:55 looks like CARM is indeed the culprit..
kiwamu.izumi@LIGO.ORG - 11:49, Tuesday 27 January 2015 (16300)

(BS oplev seems OK)

Given the prior lock loss science by Lisa, I speculated that the BS oplev loops were doing something bad such as glitches. (Note that the people did not use the ASC loops last night so that the oplev damping loops on BS had been engaged all the time). Looking into the last five lock losses that Evan posted, I am concluding that the oplev damping loops were not glitching or disturbing the MICH loop. The attached are 60 seconds full time series of various BS oplev-related channels for the five lock losses. The 4:05 event is the only one which clearly showed DAC saturation and the rest of them did not saturate the BS DAC before the lock loss. The oplev sum sometimes shows a fast transient, but it happens right after each lock was lost -- indicating that the transient was caused by the motion on the oplev QPD as the BS was kicked and it is NOT initiating the lock loss.

(TRX seems always lower than TRY)

I don't know if this is related to the cause of the lock losses, but I found that TRX have been consistently lower than TRY by roughly 10 % regardless of how big the CARM offset was. It is unclear if this discrepancy is from an unintentional offset in the ALS diff operating point or some kind of calibration error in TRs. In any case, we should fix it in order to reduce DARM coupling in the TR_CARM signal path.

Images attached to this comment
peter.fritschel@LIGO.ORG - 14:37, Tuesday 27 January 2015 (16308)

What is the CARM offset and offset reduction in physical units? (pm or Hz of the arm cavitites)

alexan.staley@LIGO.ORG - 16:08, Tuesday 27 January 2015 (16311)

Peter, we can use Kiwamu's plot to convert this offset into physical units (alog 15389). An offset of -0.5cts gives about 800 pm. We were able to bring the carm offset to about 300 pm stabily.

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