Displaying reports 65281-65300 of 83192.Go to page Start 3261 3262 3263 3264 3265 3266 3267 3268 3269 End
Reports until 17:54, Tuesday 12 May 2015
H1 TCS
eleanor.king@LIGO.ORG - posted 17:54, Tuesday 12 May 2015 (18392)
TCS maintenance morning

Nutsinee, Elli

Both CO2 lasers tripped, about 10 minutes from each other, the H1:TCS-ITMX_CO2_INTRLK_RTD_OR_IR_ALRM had tripped, due to Filberto's working near Ham4 (the temperature sensor which will eventually be attached to the viewport is currently on the electronics rack next to the CO2 laser tables and is sensitive to people working near it.  CO2 X power on the IMTX has been returned to 0.22W. 

HWS X was working.  Then we touched the picomotors on the periscope mirrors and lost the alignment due to hysteresis. Dang.  HWSY SLED is aligned to irisis, green beam still clipping somewhere.

We have decided to leave EY HWS plugged into its separate power supply for the time being.

H1 SEI
hugh.radkins@LIGO.ORG - posted 16:41, Tuesday 12 May 2015 (18390)
LHO SEI STS2-B Study Update

Geez yes, another update.  See 18354 for past summary.

Something bad for sure for HAM2 (STS2-B) Seismometer but intermittent between very bad and poor.  See screenshot on above reference for when it is running very bad.

I moved the HAM2 instrument back over close (6') to the ITMY sensor.  And I completely swapped the cables.  That is, the HAM2 instrument is entirely on the ITMY sensor chain. and vice versa for the ITMY instrument except that there is a temp cable running from the satellite box to the interface chassis.  See attached.

I've zoomed into the coherence.  Again the Y axis is the worst, X is a little better and Z is actually very good.  Notice how the coherence between ITMY and HAM2 goes up to much higher frequency now indicating no channel wiring errors.  Also notice how the traces associated with ITMY (HAM2, red & blue) don't get to solid 1 coherence like the green trace between ITMY instrument and HAM5.  So while suttle, clearly even when only performing poorly, this sensor could be better.  The problem could be just at the sensor/cable connection but playing with that will be painful for someone, likely me.  I think it should be addressed at the shop.

Images attached to this report
H1 CDS
james.batch@LIGO.ORG - posted 16:40, Tuesday 12 May 2015 (18384)
Cesium Frequency Standard, Time Distribution System Calibration is Complete
WP #5195 

Dave Barker, Jim Batch

The 4310B Cesium Frequency Standard has been synchronized to the 1PPS output of the Symmetricom NTP server in the MSR. The 1PPS leading edge from the 4310B is now leading the 1PPS leading edge from the NTP server by 60 to 64nS, within the +/- 100nS specification of the 4310B.

The 4310B was then used to synchronize the Timing Solutions Time Distribution System (TDS).  The 10MHz output of the 4310B is connected to the 10MHz input of the TDS flywheel, the 1PPS output of the 4310B was connected to channel 1 input of an oscilloscope, and the 1PPS out of the TDS was connected to channel 2 of the oscilloscope.  The slew of the TDS was adjusted to provide 0 offset between the 4310B and the TDS 1PPS.

A second (older) 4310 was then synchronized to the 1PPS output of the Symmetricom NTP server in the MSR using the same procedure as the 4310B.  This 4310 is in a short equipment rack with a UPS and has been powered for over 1 month.  This setup is portable, used to synchronize the end stations.  The 1PPS leading edge of the portable 4310 lags the leading edge from the NTP server by 28-32nS, providing a difference of about 90nS between the two standards, where the TDS 1PPS leads the portable 4310.  Both the TDS 1PPS and portable 4310 1PPS were left connected to the timing comparator in the MSR overnight to monitor the stability, which was good.

Today, the portable 4310 was loaded into a van and taken to EY to compare with the 1PPS output of the time code translator (TCT) which is connected via fiber to the TDS in the MSR. The delay adjustment of the TCT was set to have the leading edge of the TCT be 90nS before the leading edge of the portable 4310, the 90nS being the time difference of the portable 4310 to the TDS.  The adjustment is to the nearest 10nS, and ended up at about 85nS.  The procedure was repeated at EX, and the adjustment ended up at 90nS.  This leaves the TCT units at the end station with 1PPS signals synchronized to the corner station TDS.  The 1PPS signals for each unit is connected to input 1 of the timing comparators at EX, EY, and the MSR, allowing the timing differences to be monitored as EPICS channels.

EX - H1:SYS-TIMING_X_FO_A_PORT_9 SLAVE_CFC_TIMEDIFF_1
EY - H1:SYS-TIMING_Y_FO_A_PORT_9 SLAVE_CFC_TIMEDIFF_1
MSR - H1:SYS-TIMING_C_MA_A_PORT_2 SLAVE_CFC_TIMEDIFF_1
H1 CDS (DAQ)
david.barker@LIGO.ORG - posted 16:26, Tuesday 12 May 2015 - last comment - 16:34, Tuesday 12 May 2015(18388)
CDS Maintenance Summary

Timing Calibration

Jeff, Jim, Dave:

Jim synced up the atomic clock system to the NTP GPS receiver and then used it to sync the MCA unit which in turn drives the end station TCT units. The 1PPS originating from the MCA was connected to the first input of the MSR comparator. Jim also synchronized the original atomic clock to the same source, and we transported this unit (continually powered via UPS) to both end stations. At the end stations the time offset dip switches on the TCT units were changed to compensate for the TOF to the end stations. At the end stations the 1PPS coming from the TCT are being fed into the comparators, first channel.

We also connected the 1PPS from the NTP GPS to the second comparator input in the MSR.

A more detailed alog of these procedures is in the works.

PSL ISS model change:

Sudarshan and Jeff.

A new h1psliss model was created. This is a "stand alone" model, no common PSL parts are being used. Full details in Jeff and Sudarshan's alog.

HWS Beckhoff gain setting

Aidan, Elli, Nutsinee, Patrick

A HWS gain setting was incorrectly set as a read-only channel and therefore could not be changed from zero. Patrick has made this changeable and it is now 1.0

DMT channel list changed

John Z and Dave

John Zweizig requested a new DMT channel list be applied to the DAQ broadcaster, this was done at 15:00 local time.

LDAS Tape Robot Move

Greg, Dan, Jim, Dave

The LDAS tape robot was moved from the computer users room to the warehouse. Fiber optics cabling was added in the MSR between the warehouse patch panel and the Q-Logic switches in the DAQ racks.

Comments related to this report
david.barker@LIGO.ORG - 16:34, Tuesday 12 May 2015 (18389)

Attached is a minute trend plot for 4 hours (midday to 4pm PDT) showing the MCA and TCT 1PPS time differences measured by the timing system comparators (which are clocked by the aLIGO timing system). In all three locations (MSR, EX and EY) the MCA and TCT 1PPS signals are connected to the first comparator channels.

All variations seen are due to the timing system itself (all three locations vary in the same way). At each station the range of variation is about 25-30nS over the 4 hours time period.

Both end stations are synchronized to within the 10nS resolution of the TCT.

Images attached to this comment
H1 General
jeffrey.bartlett@LIGO.ORG - posted 16:08, Tuesday 12 May 2015 (18387)
Ops Shift Summary
LVEA: Laser Hazard
Observation Bit: Commissioning 
  
07:00 Karen & Cris – Cleaning in the LVEA
08:16 Karen – Out of the LVEA
08:17 Karen – Cleaning at End-Y
08:30 Filiberto – Cabling work at BSC1, BSC2, BSC3 & HAM4
08:30 Elli – Hartman work at End-Y
08:35 Jason & Perter – RefCav alignment work H1-PSL
08:40 Kyle – Bake out of RGA and pump work at End-Y
08:48 Hugh – Moving HAM2 seismometer to Beer Garden area
08:54 Jim – Sensor correction work on ETM-X
08:55 Bubba – 3IFO crane work in LVEA North Bay area
09:00 Add 125ml water to Crystal chiller
09:00 Jodi – 3IFO PM work at Mid-X and Mid-Y
09:01 Elli – Back from End-Y 
09:02 Elli – Going to LVEA to work on Hartman sensor
09:16 Nutsinee – Going into the LVEA
09:18 Paradise Water - delivery on site
09:25 Elli & Nutsinee – Out of the LVEA
09:30 Kyle – Going to Mid-X 
09:31 Robert – Staging in PSL for periscope tuning
09:42 Joe – Checking batteries in the LVEA
09:50 Karen – Finished at End-Y
09:53 Cris – Finished in LVEA – Going to End-X
09:56 Mitch – Going to Mid and End Y 
10:05 Nutsinee & Elli – Going to End-Y
10:13 Joe – Out of the LVEA
10:37 Elli & Nutsinee – Back from End-Y
10:40 Mitch – Back from Mid & End stations
10:43 Dave & Jim – Going to End-Y for atomic clock calibration 
10:58 Mike – Tour of LVEA ahead of VIP tour on 05/19
11:12 Elli & Nutsinee – Checking the TCS-X laser
11:23 Kyle – Back from Mid-X
11:30 Jason & Peter – Finished in the PSL
11:30 Robert – Going into the PSL for periscope work
11:32 Elli & Nutsinee – Out of LVEA
11:33 Jim & Dave – Finished at End-Y 
11:40 Jim – Going to End-X for atomic clock calibration
11:41 Elli & Nutsinee – Checking the TCS-Y laser
11:42 Jeff – DAQ restart
11:45 Filiberto & Andres – Finished in LVEA
11:48 Truck on site for tape robot move
12:04 Elli & Nutsinee – In LVEA working on Hartman sensor at TCS-HT4
12:15 Jim – Back from End-X
12:20 Kiwamu & Jason – Finished with OpLev-PR3 alignment
13:15 Jodi & Jim – In LVEA to recover a broken computer
13:29 Nutsinee & Elli – Out of the LVEA
13:31 Jodi & Jim – Out of the LVEA
14:12 6.8 Magnitude EQ in Japan 
14:15 Robert – Finished with PSL periscope alignment
H1 SEI
hugh.radkins@LIGO.ORG - posted 15:46, Tuesday 12 May 2015 - last comment - 16:49, Tuesday 12 May 2015(18386)
CPS 71MHz Sync fanout system deployed--No obvious issues yet

See D1400363 for overall scheme and cable details.

The 71 MHz sine is ported to D1400155 in TCS-X1-R2-27 SE of BSC1.  From there sync signals go to the three BSCs corners 1 & 3 satellite racks.  At each BSC, the corner 1 signal is passed on to corner 2 with a local cable.

Attached are three plots with the three BSCs showing reference traces from early this morning before the big EQ.  Current traces are from later today.  There are no combs popping up suggesting there are no cross talking sync signals.  There is variablilty between the reference and current noise floors.  Some are lower a few are slightly higher but nothing standing out affecting an entire corner (see ITMX ST2 H2.)  I suspect when the middle of the night comparison is done with similar conditions, they will look even better and that cables are okay.

Images attached to this report
Comments related to this report
hugh.radkins@LIGO.ORG - 16:49, Tuesday 12 May 2015 (18391)

Oh yes, of course.  I added the jumper on P2 of the Master Card for BS Stage1 H1 to make it too a Slave like all the others.

LHO VE
kyle.ryan@LIGO.ORG - posted 15:32, Tuesday 12 May 2015 (18385)
Ran pump cart at BSC6 for a few hours this morning
Low temp baking RGA on BSC6 during maintenance periods -> Also, temporarily shut off instrument air to X-mid VEA while re-routing copper line
H1 PSL (PSL)
jason.oberling@LIGO.ORG - posted 14:17, Tuesday 12 May 2015 (18383)
PSL FSS RefCav Realignment & PMC Alignment Tweak

J. Oberling, P. King

Summary

We tweaked the beam alignment into the PMC in the horizontal direction using both mirrors M06 and M07.  Final PMC transmitted power was 22.3 W with a visibility of 91.5%.  This did not recover the FSS RevCav TPD voltage, so we transitioned to realigning the FSS RefCav.  We found the beam clipped between mirror M26 and the 21.5MHz EOM.  We corrected this using mirror M25 and the used mirror M26 and the top input periscope mirror to tweak the alignment into the FSS RefCav.  Final RefCav TPD was 1.37V.  Still unclear where the drift in the RefCav TPD is coming from.

Details

We measured the power before the FSS AOM, after the AOM (single pass), and at the base of the RefCav input periscope.  Peter also measured the power between M34 and L05 (after the 35W pickoff for the DBB)

According to Peter this is all reasonable, so we moved on to the PMC.  Motive here is to make the reflected beam shape more concentric, thereby improving the beam alignment into the PMC, and increasing the transmitted power (and hopefully the FSS RefCav TPD in the process).  We tweaked the horizontal alignment using mirrors M06 and M07, and ended with a final transmitted power of 22.3 W, an improvement of about 0.3 W.  We then had to adjust the alignment into the PMC Refl PD, PD03, by adjusting mirror M20 and thin film polarizer TFP03 (to keep the unlocked voltage reading of the PD at ~-1.5V).

This gives a PMC visibility of 91.5%.  Unfortunately this did not significantly increase the FSS RefCav TPD, so it seems we really do have an alignment issue.

This first thing we did was to check the beam position on various irises in the beam path.  We found the beam clipping on the iris high and to the west between M26 and the 21.5 MHz EOM.  We corrected this with M25, and then used M26 and the top periscope mirror to tweak the RefCav TPD.  While a small bit of lateral adjustment was needed, the majority of the adjustment was to pitch.  The final TPD voltage was 1.37 V, and the RefCav Refl PD read 0.060 V while the RefCav was locked.  Unfortunately we are still unclear where the RefCav drift is coming from...

H1 AOS (ISC, SUS)
kiwamu.izumi@LIGO.ORG - posted 13:28, Tuesday 12 May 2015 (18382)
PR3 oplev found to be clipped; fixed and recalibrated

Jason, Kiwamu (WP 5199)

PR3 oplev is now back to functional.

As reported in the last week (alog 18246), PR3 was found to be not functional. This morning we took a look at the PR3 oplev and found that the beam had been clipped. We fixed it by steering the launcher telescope and recalibrtated both pit and yaw signals.

 


[Unclipping]

Looking at the returning beam, we found that the beam was largely clipped on the west side and its bottom side. Apparently this was causing the nonideal cross-coupled behavior as reported in alog 18246. We could not identify what object was occulting the returning beam, but according to Jason, it could be somewhere around the viewport for the return beam. We decided to steer the launcher telescope to unclip the beam. The unclipping went smooth and no major issue was found. Since we moved the beam toward the East, we had to recenter the QPD stage afterwards. The beam is now about 1 cm away from the clipping edge, meaning we can move PR3 by several 100 urads until clipped. This is good enough.

After the unclipping, Jason checked the beam shape and confirmed that there was no sign of clipping. We also briefly checked the responsivity of each segment by placing the beam on each segment by steering PR3. This convinced us that the responsivity is almost the same among the four segments. We physicallyt locked the launcher telescope as a part of the normal procedure so that it is not going to move.

[Recalibration]

After the unclipping, I recalibrated the oplev. Here is a summary of the new calibration:

  old calibration [urad/cnts] new calibration [urad/cnts]
PR3 pit  38.86  26.90
PR3 yaw  38.53  29.60

I also updated the SDF accordingly. The data and fitting code are attached as a zip file.

One thing I found during the calibration is that there is still some cross-coupling between pitch and yaw at 10% level. I don't think this is a big issue, but those who use PR3 oplev should be aware of it. I am not sure what part of it is causing the cross-coupling.

Non-image files attached to this report
H1 PSL (PSL)
sudarshan.karki@LIGO.ORG - posted 12:46, Tuesday 12 May 2015 (18381)
PSLISS model changes

SudarshanK, DaveB, JeffK,

We made changes to psl iss model to include the DC signal from the eight photodiodes on the array.  These  DC signals are acquired before the whitening in the transimpedance amplifier. This psliss model restart  didnot affect the psl itself, which we were afraid it might. Good to know for future restartts. The DAC restart was made around 11:30 local time. These 8 additional channels will be available to  trend via epics channel. These signals are also used to normalize the ISS PD signals to obtain the RPN.  The channel names are as follows:

H1:PSL-ISS_SECONDLOOP_PD1_DC

........

H1:PSL-ISS_SECONDLOOP_PD8_DC

Attached is the new front end model that includes the changes.

Images attached to this report
H1 CDS
patrick.thomas@LIGO.ORG - posted 12:15, Tuesday 12 May 2015 (18380)
Updated Conlog channel list
Had to add H1:TCS-ITMX_HWS_POSITIONDETECTOR2SUM and H1:TCS-ITMY_HWS_POSITIONDETECTOR2SUM to the exclude list. Looks like we may need to change the HartmannSensor library again at some point to make these read only. They change (rapidly) now that the gain is no longer 0.

Added 242 channels. Removed 45 channels.
H1 CDS (CDS, TCS)
patrick.thomas@LIGO.ORG - posted 11:33, Tuesday 12 May 2015 (18377)
Updated TwinCAT HartmannSensor library, h1ecatc1 PLC1
Daniel, Elli, Patrick, Nutsinee

I changed the OPC_PROP_RIGHTS of PostionDetector2SUMGain from 1 (read only) to 3 (read/write) in the HartmannSensor library code. I checked the change into SVN. I updated from source, recompiled and restarted PLC3 on h1ecatc1.

Yesterday Nutsinee made a code change to PLC1 on h1ecatc1 and checked it into SVN. This was to fix the picomotor labels. I updated from source, recompiled and restarted PLC1 on h1ecatc1.

I restarted the EPICS IOC on h1ecatc1. I did caputs to H1:TCS-ITMX_HWS_POSITIONDETECTOR2SUMGAIN and H1:TCS-ITMY_HWS_POSITIONDETECTOR2SUMGAIN to change them from 0 to 1.

WP 5199, 5200
H1 CDS
patrick.thomas@LIGO.ORG - posted 11:14, Tuesday 12 May 2015 - last comment - 11:48, Tuesday 12 May 2015(18375)
restarted h1ecatx1 computer
Did before its expected biweekly crash. Burtrestored to 10:10 am.
Comments related to this report
patrick.thomas@LIGO.ORG - 11:42, Tuesday 12 May 2015 (18378)
Well, it still crashed anyway. Restarted the computer again. This time the IOC failed to start. The IOC reports 'Failed to start', 'Failed to open ADS ports' for each PLC.
patrick.thomas@LIGO.ORG - 11:48, Tuesday 12 May 2015 (18379)
Logged into h1ecatx1. Opened the LIGO TwinCAT Target Configuration. Selected h1ecatx1, PLC1, PLC2, PLC3. Hit Restart EPICS database. This time it worked. Burtrestored again to 10:10 am.
H1 General
thomas.shaffer@LIGO.ORG - posted 10:21, Tuesday 12 May 2015 (18374)
ESD driver medm update and SYS_DIAG user guide

The ETMX ESD driver medm screen 'Active light' has been flickering when it is OFF. To fix this issue, I pushed this lower threshold to +/-325 from +/-200.

I also changed this in SYS_DIAG.

 

While talking about SYS_DIAG, I have made a wiki page for troubleshooting the usermessages that it will bring up. This is a page mainly to help operators find the source of the problem and how to resolve it.

It can be found here:  https://lhocds.ligo-wa.caltech.edu/wiki/SYS_DIAG%20Guardian

H1 AOS
keita.kawabe@LIGO.ORG - posted 18:40, Monday 11 May 2015 - last comment - 09:40, Tuesday 12 May 2015(18366)
SR3 really physically moves in PIT during a long lock. Why? (Stefan, Evan, Sheila, Kiwamu, Keita)

Related alog: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=18269

Summary:

During long lock stretches where POPAIR_B_RF90 slowly drifts up, SR3 pitches up, and this seems to be a real PIT motion, not some bogus signal, even though SR3 is not touched by ASC nor LSC.

Turning SR3 back to the original angle when in lock doesn't restore POP90 (see the above alog by Evan), so this PIT is not the cause of POP90 drift, but rather the result of something else affecting both SR3 and POP90.

The time constant of SR3 drifting in-lock is much slower than the time constant of SR3 getting back after lock loss as was pointed out by Evan. The former looks as if it could be the mirror heating, and the latter could be the wire cooling.

The power buildup in the SRC itself is about 120mW or so according to Kiwamu and probably is not enough to cause wire heating by some scattered light.

Based on these, one possibility that Stefan came up with is that the heating of the ITMs changes the amount of higher order mode spilling over on the SR3 wires, causing PIT. Since wire heating is much quicker than the mirror, the time constant is equial to that of the mirror. Once the lock is lost, the power is lost immediately, and the cooling is determined by the wire alone.

We could play with TCS during a long lock to see how POP90 responds, and/or scan OMC to see the mode change during a long RF lock.

Details:

The two plots show the same set of signals. The first one is from last night and the second one is when Evan changed SR3 PIT manually while in lock.

If you look at POP90 (ch2), SR3 OPLEV PIT (Ch6) and SR3 M3 witness BOSEM PIT signal (ch9) in the first plot, they are almost perfectly correlated, and in this case SR3 moved by 0.7 urad. The fact that the motion is seen by oplev and bosem suggests that this is real.  Also, if the oplev signal is caused by e.g. some scattered light caught by oplev, the oplev sum (ch.8) should change at least 2% over the lock stretch, but in reality it changed by less than 0.2%.

SR2 PIT (Ch. 13) and SRM YAW (Ch.12) are also coherent with POP90.

SR2 PIT should be the result of ASC feeding back to SR2. In the second plot, when Evan turned SR3 back, SR2 also moved back.

SRM YAW might be the similar effect as SR3.

Images attached to this report
Comments related to this report
suresh.doravari@LIGO.ORG - 21:20, Monday 11 May 2015 (18368)

How about using the SR3 oplev as a reference and feed back to the mirror to hold alignment as the mirror pitches forward?  It might serve to obtain longer locks during which you could tune the TCS to reduce this effect.  At present the SR3 oplev does not glitch and can be used during lock.   It has less than 0.01 microrads in pitch drift over 1000 seconds as shown in the LLO alog 18097.  The mirror motion and microseismic motion are also clearly visible above the noise floor.

keita.kawabe@LIGO.ORG - 09:40, Tuesday 12 May 2015 (18373)

Maybe it was not clear, but the point is that the SR3 motion itself isn't probably a serious problem, but the differential heating of ITMs might be, causing something funny in SRC, eventually causing the IFO to unlock.

H1 ISC (CAL, ISC)
sudarshan.karki@LIGO.ORG - posted 14:54, Monday 11 May 2015 - last comment - 19:23, Thursday 14 May 2015(18361)
Cavity Pole monitoring using Pcal Lines

SudarshanK, DarkhanT

We introduced two Pcal lines at 240 Hz and 310 Hz on photon calibrator at Y end.  The Pcal lines are about a factor of 10 above the DARM sensitivity at those frequencies. We will look into any changes in the amplitude and phase of these lines to determine the the position of cavity pole frequency. The cavity-pole has been observed at frequencies listed in  alog LHO #18360.

Images attached to this report
Comments related to this report
gabriele.vajente@LIGO.ORG - 16:24, Monday 11 May 2015 (18364)

Since the pole frequency is at about 300 Hz, it would be useful to have a high frequency line, for example at about 1 kHz. This will allow a better reconstruction of the pole frequency.

peter.fritschel@LIGO.ORG - 19:46, Monday 11 May 2015 (18367)

If you haven't already, I recommend also putting a notch in the DARM loop at 310 Hz. That way any phase change that occurs at 310 Hz in DARM should be a direct measurement of changes in the sensing phase (which would presumably come from a chang in cavity pole). I probably would have gone a little higher with the 2nd line, closer to 400 Hz. Why did you choose what you did?

sudarshan.karki@LIGO.ORG - 22:51, Monday 11 May 2015 (18369)CAL, ISC

Gabriele, We also have a permanent Pcal line at around 540 Hz. We thought it should be enough. Is there any advantage of going close to1 KHz?

Peter, I will have to talk to Jeff about putting a notch on the DARM loop, I am not sure how to go about it. Regarding the choice of 240 Hz and 310 Hz, knowing we already had one line at around 540 Hz we picked a pair of line between one of the non-vetoed frequency band of pulsars. We could easily shift the second line to 400 Hz. 

jameson.rollins@LIGO.ORG - 11:20, Tuesday 12 May 2015 (18376)

Larry Price did an analysis of just this situation, i.e. at what frequencies should you measure the transfer function to most optimally extract the features in the frequency response.  His analysis showed that the most optimal place is at the feature itself.  In other words, the best place to put your calibration line to most efficiently measure the cavity pole is at the expected cavity pole frequency.  See: LIGO-G1400084

evan.hall@LIGO.ORG - 04:15, Wednesday 13 May 2015 (18401)CAL

In light of this optimal, Fisher-matrix-based approach, Kiwamu and I have installed a notch in DARM at 322.1 Hz (actually an 80 dB elliptic bandstop from 321 Hz to 323 Hz). The goal is to inject a calibration line digitally into DARM control, so that we can use an LSC lock-in to demodulate the line.

We have set up LSC oscillator #3 to take OMC DC and demodulate it at 322 Hz. Both I and Q have 4th order butterworth low-pass filters. The lock-in output drives ETMX and ETMY differentially. The lock-in drive is currently 0 ct. It has not been set yet.

christopher.wipf@LIGO.ORG - 14:04, Wednesday 13 May 2015 (18411)

Better check the assumptions here. Doesn't Larry's result assume an open-loop measurement, white actuator strength, and white measurement noise (none of which holds in this case)?

kiwamu.izumi@LIGO.ORG - 19:23, Thursday 14 May 2015 (18439)

Chris,

Thank you for pointing it out. We also noticed that the assumptions were not quite valid in our case. On the other hand, Larry's analysis still gives us a good idea of what frequency we should excite. According to his Fisher matrix analysis, the measured transfer coefficient exhibits a maximum response to change in the cavity pole frequency when the excitation is at the exact pole frequency. This led us to a frequency at around 322 Hz. If you take the spectral shape of sensor noise (or DARM residual) and the actuator transfer function into account, probably a slight lower frequency than the current choice may be better, but since we wanted to have a notch in DARM far from the UGF, we chose it to be close to the cavity pole.

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