Bubba and crew craning at End-Y. Done by 9:30. Maggie to End-Y Corey at HAM3 for SEI cabling Alex and others to End-Y to power a microphone Eric A. - installing HEPI valve plates 12:45 - Hanford call testing sirens Craning and work with cabling inside HAM3 for Seismic
Common mode board A at H2 EY (S/N S1102638) (Jax S., Daniel S.) We changed the common generic filter to a double pole 100kHz/Q=0.85. This is to replace the Pomona box that was used to suppress the PZT resonance around 250kHz-300kHz. R129 -> 2.67K R130 -> 1.30K R131 -> 0 R132 -> 0 C207 -> 1.5n C206 -> 470p This allowed us to push the ugf to just above 30kHz with a phase margin of 45 degrees. We backed off with the gain set to -6dB in the input section which leaves us with a ugf around 28kHz and a phase margin of close to 50 degrees. Common mode board B at H2 EY (S/N S1102637) We also changed the fast monitor into the Beckhoff on the cavity locking servo to be unity gain rather than 10. R271 -> 0 R272 -> NL
As I mentioned on Friday, I noticed a coherent shift of the HEPI platform on HAM3 as I was locking it up in preparation for ISI measurements. Hugo gave me a window this morning so I unlocked the HEPI again and very thoroughly looked for interferences that might be pushing it out of our aligned location. I could find no non-suspended elements touching suspended portions aside from a few of the temporarily run in-air cables. I can't imagine that these contacts could pull the system around. Once it was all released I pushed on the crossbeams to 'see' knocking. I could not detect anything that looked like something running into something else but I did notice that the vertical moved fairly easily whereas horizontal motion was very stiff. I'm trying to understand why this would be but nothing is so far revealed. Thoughts? For the record, based on the dial indicators, I see a CCW rotation of about 250urad caused by a shift to the east of the south side of about 0.5mm.
Issue with watchdog tripped - Richard, Filiberto, Hugo
Corrected, can now actuate
We managed un-tripping the coil driver chassis bio watchdog of HAM3 by:
In Vacuum cabling - Corey, Hugo
CPS H3 and CPS V3 were swapped - corrected
I took spectra on our sensors this morning and noticed H3 and V3 were swapped. Corey went looking at it and located it on the in-vaccum side of the feedthrough.
The binary word that should be used for HAM3, in ISI_CUST_CHAMBER_BIO.adl is:
65535
Replaced ISI Coil Driver SN S1103567 with SN S1103321 in Rack H1-SEI-C2 for HAM3 . Driver seems to have internal wiring issues with the outputs. When you drive CH1 (coarse1), it would drive CH4 (coarse 2). Same with CH2 (fine1) and CH3 (fine2). Unit also has a ±18V type connector for the input power of ±24V. Filiberto Clara
Using the PT-410B vacuum gauge, we looked at the pressure in End-Y volume since its pumpdown began in early June 2012 (see attached plot). The first ~10 days is before the gate-valve that opens to the cryo pump was opened. Opening to the cryo pump reduced the pressure by a factor of 10. The start time for the plot (i.e., the offset that we subtracted from the time stamp) was adjusted (at the 0.1 day level) by hand so that the pre-GV opening segment was a striaight line in the log-log plot.
The two black lines are by-eye fits to the pumpdown curves. The slope of the first segment is 1/t^{0.68}; since the GV opening, the pumpdown is a little faster, at 1/t^{0.88}.
(Matt E, Peter F)
As part of gearing up for aLIGO CW and Stochastic analysis detector characterization, a number of us are developing and starting to use new or enhanced spectral line finding tools. We plan to apply these various tools to this summer's OAT data in the hope of 1) making the tools better via exposure to real data; 2) identifying spectral lines early on that can be mitigated; and 3) cataloging lines that we have to live with in aLIGO. A wiki clearinghouse for OAT spectral line studies can be found here. For now it has mostly documentation on tools and channel selections, but over time it will be populated with study results. One important tool is an enhanced version of the familiar Fscan program. Greg Mendell has started creating daily Fscan plots for locked-arm data (defined by the mean value of H2:ISC-ALS_EY_REFL_PWR_MON_OUT16 over 1 minute lying in the range 4300-8000 -- see wiki above for explanation). The Fscans generated so far cover only the days of July 16 and 20, chosen because each had more than five hours of locked-arm data. I have used the half-hour SFTs generated during the Fscanning to look at average spectra for the calibrated OAT feedback channel H2:SUS-ETMY_M0_LOCK_L_IN1_DQ for July 16 (5 hours) and July 20 (9 hours) with 0.56 mHz binning. Two different averages were computed, one being a simple arithmetic average, the other a noise weighted average that is almost, but not quite the same as a harmonic mean. (The same method was used to compute unweighted and weighted averages for h(t) for all of S5 and S6, as discussed in more detail here.) Generally speaking, one expects the weighted average to be lower than the unweighted average and to have a smaller variance. Large differences between unweighted and weighted averages indicate non-stationary bands. The figures below show the results:Some quick observations:
- Full spectrum (0-1000 Hz) for July 16 (unweighted and weighted averages)
- Full spectrum (0-1000 Hz) for July 20 (unweighted and weighted averages)
- Full spectrum (0-1000 Hz) for July 16 and 20 together (weighted only)
- Zoomed spectrum (0-2 Hz) for July 16 and 20 together (weighted only)
- Zoomed spectrum (2-10 Hz) for July 16 and 20 together (weighted only)
- Zoomed spectrum (10-100 Hz) for July 16 and 20 together (weighted only)
- Zoomed spectrum (100-200 Hz) for July 16 and 20 together (weighted only)
- Zoomed spectrum (200-800 Hz) for July 16 and 20 together (weighted only)
Here is a list of the SFT filenames from July 16. The start times are embedded in the names: H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026518956-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026520756-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026523546-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026525346-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026527146-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026528946-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026530746-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026532546-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026535786-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026538156-1800.sft Here is a list of the SFT filenames from July 20. H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026785686-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026787486-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026789286-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026791086-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026792886-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026794686-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026796486-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026798286-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026803896-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026805696-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026807496-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026809296-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026811096-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026812896-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026814696-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026816496-1800.sft H-1_H2_1800SFT_fscanH2_SUS-ETMY_M0_LOCK_L_IN1_DQ-1026818296-1800.sft
The initial entry included links but did not list the URLs. For future reference, here they are:OAT spectral line wiki page: https://wiki.ligo.org/foswiki/bin/view/DetChar/OneArmTestLineInvestigations
Daily OAT Fscans (SUS channels): https://ldas-jobs.ligo-wa.caltech.edu/~pulsar/fscan/H2_OneArm/H2_OneArm_SUS/fscanNavigation.html
Averaged S5/S6 spectra: https://ldas-jobs.ligo.caltech.edu/~keithr/spectra/
Bram took a look at the transmitted-light photodiode for the reference cavity in the optics lab (using a spectrum analyzer - no DAQ channel available). He saw strong harmonics of 2.74 Hz and 4.0 Hz. So those lines showing up in the ALS feedback signal are artifacts of the temporary light source being used for the One Arm Test and should not be relevant to future aLIGO running.
see post 3582 for the measurements of the 2.75 Hz and the 4 Hz peaks.
Patrick changed the Beckhoff channel name for the ref cav trans to H2:PSL-FSS_TPD_DC_OUTPUT and restarted the Beckhoff EPICS IOC on h2ecatey. I then added this channel to the H2EDCU_ECATEY.ini slow chans file and restarted the H2 DAQ Friday afternoon. This channel can now be trended from H2 DAQ.
This DAQ restart also picked up new fast INI files for H2SUSETMY, H2SUSITMY, H2ISCEY following work by Jeff K and Bram.
The H1.ipc and H2.ipc files were filled with historic false starts. So I rebuilt both ipc files and recompiled all H1 and H2 models which send or receive using IPC (all three types: shared mem; pcie dolphine; rfm gefanuc).
During our commissioning of the H1 HAM3 ISI I noticed I had made a copy-paste error in the IOP model h1iopseih23 which I corrected. A full code restart of this front end was done around 5pm Friday.
Attached are plots of dust counts > .5 microns in particles per cubic foot. Also attached are plots of dust counts for the two dust monitors at end Y, both > .3 microns and > .5 microns in particles per cubic foot over approximately four hours this evening ending at ~ 8:00 PM. They slowly increased and have remained high. I drove out to the end station to investigate, but did not notice anything to attribute it to.
J. Kissel, T. Vo After finally getting the optical levers aligned while the optics were aligned in a good state for the cavity, I've taken a spectra of both H2 SUS ITMY and H2 SUS ETMY in the quiet time mentioned in the isolationist data miner's dream. There're lots of fun features, differences, and similarities between the two test mass spectra, that will be good to noodle over. This will be excellent material to try to reproduce via models! If anyone wants to gather future data, this calibrated template lives here: /ligo/svncommon/SusSVN/sus/trunk/QUAD/Common/Data/2012-07-27_H2OAT_Oplev_ASDs.xml
Please disregard the calibration in this plot. As commented by Thomas in LHO aLOG 3713, we've discovered flaws in the data analysis, in addition to some non-linearities in a step of the calibration originally posted in LHO aLOG 3614. These flaws result in the calibration scale factor being off by more than an order of magnitude in some cases. We're working on getting accurate numbers this week, thanks for your patience! Note, since there is no frequency dependence to the calibration (all analog whitening is compensated for in real time digitally), it is *only* the scale factor that is off. Details: -------- For future reference, and to give credit where credit is due, suspicion was originally raised by M. Evans and P. Fritschel, who sanity checked the numbers in the spectra with the following calculation: - The data I show here was for the cavity unlocked. They say the P motion (and even Yaw motion) of both test masses, but ETMY specifically, is "just too damn high". - I walked them through our extensive calibration technique, and they believe the methods in principle: - You've got a signal in [cts], from which you read a known translation, in [m]. - You've turned it into [rad] using the lever arm, L to (or from) from test mass. - The ratio of those two numbers, [rad] / [ct] is the calibration to which you should multiply your signal in order to get [rad] of test mass motion. But it practice, something has gone astray. - Thinking the motion was large just because the cavity was unlocked, I re-measured the cavity motion using the optical levers with our current calibration and the cavity locked (2012-08-02 04:00 UTC = 2012-08-01 9:00p PDT, a little after Alberto said he locked the cavity for the night), and compared it against cavity unlocked on 2012-07-27 02:51 UTC. See first attachment, 2012-08-02_H2OAT_Oplev_ASDs.pdf. - The motion is about the same, maybe different by a factor of 2 at most. Let's say the ETMY is moving dTheta_E = 50 urad, and ITMY is moving at dTheta_I = 5 urad at the QUADs first modes at 0.43 and 0.56 Hz, which dominate the time series (which has been confirmed, but is not shown, by *look* at the time series that formed these spectra in DTT). - Using the calculation attached from Seigmann, "LASERS" pg 768 and 769, (CavityMisalignment.pdf) and assuming the cavity stability parameters g1 = g2 = g g = 1 - L/R = 1 - (length of the cavity) / (radii of curvature of cavity mirrors) = 1 - 4e3 [m] / 2.2e3 [m] = -0.8 [ ] then that means that (from Eq 32) of attached (taking the ETM as mirror 1), the spot is jiggling on the face of the test mass by a distance, | dx | = | dTheta_E * L * g / (1 - g^2) + dTheta_I * L / (1 - g^2) | = | 50e-6 [rad] * 4e3 [m] * -0.8 [ ] / (1 - (-0.8 [])^2 ) + 5e-6 [rad] * 4e3 [m] / (1 - (- 0.8 [ ])^2) | = 0.38889 [m] ... that's 38 [cm], which is about as big as the diameter of the test mass (34 [cm])! - When you look at the spot on the ETM with the camera, while the cavity is locked, one sees the the spot moving *at most* 1 [cm] peak-to-peak in Pitch, and it *certainly* not from the top to bottom of the test mass.
I've set up the ITMY and ETMY chambers in (what I *think* is) their current best-performance state, such that we can get a nice long quiet stretch of data over the weekend. I say *think* because I never nailed down Fabrice enough to tell me the exact blend configuration of the ISIs that was best for the cavity. Also unfortunately, I didn't catch the ISC team in time to request a lock of the cavity, and I don't know how to do it myself :- (which naturally means there's no ISC control going to either chambers). ANYWAYS, Here's the setup, as of Jul 28 2012 02:00 UTC (7:15p PT, 1027476016): HPIs - ITMY - ISO Loops ON; X, Y, Z, RX, RY, RZ (No HP or VP) - No boost - 800 mHz Blend on all DOFs - (No sensor correction or feed-forward) - ETMY - ISO Loops ON; X, Y, Z, RX, RY, RZ, HP, VP - No boost - 800 mHz Blend on all DOFs - (No sensor correction or feed-forward) ISIs - ITMY - Stage 1 - Damping ON - Isolation ON; X, Y, Z, RX, RY, RZ - In X & Y: 250 mHz blend of L4Cs and CPSs only (no T240s) - In Z RX RY RZ: 750 mHz blend of L4Cs and CPSs only (no T240s) - (No ST1-ST2 feed-forward) - Stage 2 - Damping ON - Isolation ON; X, Y, Z, RX, RY, RZ - In X & Y: 100 mHz blend of GS13s and CPSs - In Z RX RY RZ: 750 mHz blend of GS13s and CPSs - ETMY - Stage 1 - Damping ON - Isolation ON; X, Y, Z, RX, RY, RZ - In X & Y: 250 mHz blend of L4Cs and CPSs only (no T240s) - In Z RX RY RZ: 750 mHz blend of L4Cs and CPSs only (no T240s) - (No ST1-ST2 feed-forward) - Stage 2 - Damping ON - Isolation ON; X, Y, Z, RX, RY, RZ - In X & Y: 100 mHz blend of GS13s and CPSs - In Z RX RY RZ: 750 mHz blend of GS13s and CPSs QUADs - ITMY - M0 (TOP) - Damping ON; [zeros:poles] - L: FM1 [0:15,15], FM3 [0.43Boost2], FM10 [Ellip50], G = -20.0 - T: FM1 [0:50,50], FM3 [0.43Boost2], FM10 [Ellip50], G = -20.0 - V: FM1 [0:20,20], FM10 [Ellip50], G = -6.0 - R: FM1 [0:20,20], FM10 [Ellip50], G = -0.3 - P: FM1 [0:25,25], FM2 [0.54Boost],FM3 [1.13Boost], FM10 [Ellip50], G = -0.1 - Y: FM1 [0:20,20], FM2 [0.6Boost], FM10 [Ellip50], G = -1.0 - L1 (UIM) - Damping ON: - L: FM1 [0:50,50], FM9 [Ellip20], G = -5.0 - P: FM1 [0:50,50], FM2 [0.6boost], FM9 [Ellip20], G = -3.0 - Y: (OFF) - ETMY - M0 (TOP) - Damping ON; [zeros:poles] - L: FM1 [0:15,15], FM3 [0.43Boost2], FM10 [Ellip50], G = -20.0 - T: FM1 [0:50,50], FM3 [0.43Boost2], FM10 [Ellip50], G = -20.0 - V: FM1 [0:20,20], FM10 [Ellip50], G = -6.0 - R: FM1 [0:20,20], FM10 [Ellip50], G = -0.3 - P: FM1 [0:25,25], FM2 [0.54Boost],FM3 [1.13Boost], FM10 [Ellip50], G = -0.1 - Y: FM1 [0:20,20], FM2 [0.6Boost], FM10 [Ellip50], G = -1.0 - L1 (UIM) - Damping ON: - L: FM1 [0:50,50], FM9 [Ellip20], G = -5.0 - P: FM1 [0:50,50], FM2 [0.6boost], FM9 [Ellip20], G = -3.0 - Y: (OFF) FMY - M1 (TOP) - Damping ON: - L: FM1 [0:15,15], FM10 [Ellip50], G = -5.0 - T: FM1 [0:20,20], FM10 [Ellip50], G = -10.0 - V: FM1 [0:20,20], FM10 [Ellip50], G = -2.0 - R: FM1 [0:20,20], FM10 [Ellip50], G = -0.3 - P: FM1 [0:25,25], FM10 [Ellip50], G = -0.05 - Y: FM1 [0:20,20], FM10 [Ellip50], G = -1.0 TMTS - M1 (TOP) - Damping ON - L: FM1 [damp30], FM2 [boost450m], FM10 [ELF10], G = -20.0 - T: FM1 [damp30], FM2 [boost450m], FM10 [ELF15], G = -7.0 - V: FM1 [damp30], FM10 [ELF10], G = -10.0 - R: FM1 [damp30], FM10 [ELF10], G = -20.0 - P: FM1 [damp30], FM10 [ELF10], G = -10.0 - Y: FM2 [dampYaw], FM10 [ELF10], G = -10.0 AND, the Optical lever beams are on the QPDs for both test masses. I've made copies of each of the above mentioned systems Foton Filter files, and stuck them in the userapps repository under, hpi/h2/filterfiles/H2HPIETMY.txt hpi/h2/filterfiles/H2HPIITMY.txt isi/h2/filterfiles/H2ISIETMY.txt isi/h2/filterfiles/H2ISIITMY.txt sus/h2/filterfiles/H2SUSETMY.txt sus/h2/filterfiles/H2SUSFMY.txt sus/h2/filterfiles/H2SUSITMY.txt sus/h2/filterfiles/H2SUSTMSY.txt and committed to revision 2718.
Assembly/In-vacuum cabling - Hugh, Jim, Greg, Hugo
ready
It appears that communication was lost to the end X weather station at around 16:44 7/27/2012 UTC. Restarting the IOC did not re-establish communication. I have not driven out to the end station to investigate further yet.
J. Kissel, D. Barker Recently, the ${userapps}/release/sus/common/models/SIXOSEM_F_STAGE_MASTER.mdl had been updated in order to include signal exchange and CART2EUL and EUL2CART transformation with the ISI signals. Because the TMTS models use this library part, the ${userapps}/release/sus/common/models/TMTS_MASTER.mdl main library part, and the top level model, ${userapps}/release/sus/h2/models/h2sustmsy.mdl needed to be updated to handle these new input and output ports. I've done so on both the above mentioned models, and recompiled to ensure functionality (and was successful). Since this is an unimportant change, at the advice of Alberto, Dave and I agreed to just reinstall, restart, and restore the model during next Tuesday's (July 31 2012) maintenance period. Further Notes: --------------- - the original motivation and discovery of the problem was because Dave has noticed that the /opt/rtcds/lho/h2/chans/ipc/H2.ipc (the file that stores the channel mapping for inter-process communication) had a whole bunch of old crap in it, so he deleted it, and wants to recompile all models that use IPC in order to refill it. - These changes were made in parallel with other changes to top level models. Unfortunately, the commit log message that was intended for the h2susitmy commit - I've also added EPICs output channels which capture the IPC receive errors, called H2:SUS-TMSY_ISC_IPC_PIT_ERR H2:SUS-TMSY_ISC_IPC_YAW_ERR which eventually can/should be included somewhere in MEDM screens.
I've added the following channels to the framebuilder: $(IFO):SUS-$(OPTIC)_L3_OPLEV_SEG1_IN1 2048 $(IFO):SUS-$(OPTIC)_L3_OPLEV_SEG2_IN1 2048 $(IFO):SUS-$(OPTIC)_L3_OPLEV_SEG3_IN1 2048 $(IFO):SUS-$(OPTIC)_L3_OPLEV_SEG4_IN1 2048 which required adding these channels to the ${userapps}/release/sus/common/models/QUAD_MASTER.mdl then recompiling, reinstalling, restarting, and restoring the QUAD test mass models: ${userapps}/release/sus/h2/models/h2susitmy.mdl ${userapps}/release/sus/h2/models/h2susetmy.mdl Before restarting, I created new safe.snap files, in /opt/rtcds/userapps/release/sus/h2/?tmy/h2sus?tmy_safe.snap in order to capture the new optical lever calibration. After restarting, I restored to the following snap files: /ligo/cds/lho/h2/burt/2012/07/27/14:00/h2sus?tmyepics.snap
While bringing things back up on ITMY, we noticed rather large motions around the BSC8 chamber, as noted in Thomas' LHO aLOG 3634. We were concerned that it had to do with the restart of the model (a la March 2012), but as Thomas shows the large motions had started to occur prior to our model restarts. Bram also reports that the cavity had been behaving poorly for an hour or so prior to this computer work. Finally, because we were scared, we manually triggered the entire chambers IOP watchdogs, so we were confident it was not any excitations from any DAC. We further confirmed this by checking both the SUS coil-driver monitor signals, and noted that the ISI's "rogue excitation" monitor also remained green. The large motion dissipated after ~ 5 minutes of just waiting (we would have turned everything back on, with damping loops running -- which is more safe that with everything turned off, if we trust CDS infrastructure to be functional -- but the the GS-13s were saturating, which would not allow ISI watchdogs to be reset). It should be noted that though these motions were large, they were not extreme. The QUAD's top-stage OSEMs were visibly wobbling, but only by a few thousand counts. ISI GS13s were railing, but they're extrememly sensitive, and ISI position sensors on both stages indicated that were not hitting the locker-limiter mechanical range of motion. Also worthy of note -- the recompile, reinstall, restart, and restore of H2 SUS ETMY went smoothly, without trouble. Because adding the channels to the DAQ list is part of the QUAD_MASTER library part, the change was literally identical in both models.
The ISC signals have been added to the ETMY HEPI model. Changes have been committed to the svn. The model has been successfully compiled and installed. We should be ready to offload.
To offload to HEPI we need to low pass the cavity signal before to add it to the HEPI longitudinal super-sensor. We made preliminary measurements this morning to check the Cavity and HEPI signs and units, but we need to refine the drive parameters. The template is saved in: /ligo/svncommon/SeiSVN/seismic/HEPI/H2/ETMY/Misc/DTT_Cavity_offload What we need to do next week: - adjust the measurement parameters to get good coherence - tune the gains and check the signs to put the signals in the same unit - design the low pass filters. We plan to make a very low frequency one, to reject tidal motion. And a higher frequency one to reject the motion amplification due to ISI gain peaking (around 30 mHz) - measure the open loops (ISC, HEPI, and the sum of the two)