After we broke the 2+ hour lock, I got greedy and tried to re-lock the IFO myself (at least to RF), after having been shown the ropes by Sheila and Evan earlier in the day. - I could get past finding the IR steps in the ALS COMM guardian when the COMM vco failed or needed some hand holding, - Could get past tweaking of the H1:ALS-C_DIFF_PLL_CTRL_OFFSET when ALS DIFF couldn't find IR, - tried tweaking the Beam Splitter alignment while stuck in the DRMI lock acquisition, and - managed to survive a few quick breaks of the DRMI during the initial 1F to 3F transition ~ 10 seconds after catching a DRMI lock - Can get all the way through the CARM offset reduction, but on of the first steps of the "RF DARM" state breaks the lock consistently. The last example of which I'd stayed for was at Feb 12 2015, 09:23:57 UTC I feel like I'm playing a 1980's Atari game, and can't get past a mid-level boss! Ah well. Good night all! I've left the ISC LOCK guardian in the requested state "RF_DARM."
Today I measured the balancing of the OMC DCPDs, using an excitation at 103Hz into the OMC length servo, and measuring the height of the second harmonic in the nullstream channel. The DCPDs are only, as far as I can tell, 1% misbalanced. In the attached plot data are in red, the blue is a by-eye fit. I have set the balance to be 50.5% PDA, 49.5% PDB (1% towards PDA on the slider).
Evan, Dan, Jeff, Peter, Daniel, Lisa2+ hours lock on DC readout, this time for real!
* Feb 12, 5:33 UTC lock on DC readout, engaged ISS loops shortly afterwards * Feb 12, 7:00 UTC improved low frequency noise by turning off ETMs optical lever damping * Feb 12, 7:35 UTC still lock on DC readout, starting alignment tests (intentionally changing BS alignment; also reduced the BS optical lever damping gain by a factor of 10 * Feb 12, 7:48 UTC unlocked by closing the AS beam diverter Positive news of the day - Thanks to the improved bounce mode damping , we can now reliably damp the bounce mode, and it is not a limiting problem anymore; - ETMX and ETMY optical lever PITCH damping loops have been reduced by a factor of 100; it turned out that these loops were responsible for the huge excess of noise that we saw yesterday below 40 Hz, and that was causing the OMC transmission to shake painfully. Now the OMC is quiet and happy (the Guardian has been updated to reflect this change). - We turned off the QPD alignment of the OMC, and replace it with dither alignment; - We turned on the ISS first and second loops: the positive news is that we improved the high frequency noise by a factor of 10. Negative news of the day - While we have improved noise at low and high frequency, we now have a new bump of noise around 100 Hz which was not there yesterday . - Our wonderful BS WFS loops, so effective yesterday, were not working today. However, today the BS alignment was not critical, and we have barely had to touch the BS anyway, but we need to figure out what happened. Right now we commented out the BS WFS in the locking sequence; - Yesterday the locking sequence was very reliable, and worked 5 times in a raw..today it has been less robust, despite similar environmental conditions.. - The RF of in-vac POP is somehow broken - no signal there. It is probably not a big deal right now at low power. - We also closed the OMC REFL beam diverter (level 2 of "Valera's levels of awesome": it works, but it doesn't do anything)
Attached are some plots of coherences and OMC noise.
Fig 1: Coherence between DARM and LSC, ISS - the excess noise at 70-400Hz, much worse than last night (grey), is coherent with the common DOFs (PRCL, SRCL, and CARM [not plotted]). Also the ISS 2nd loop out of loop PD.
Fig 2: DARM and ASC - there is coherence between IMC yaw WFS error signals and DARM, implying that the noise is due to some beam jitter coupling
Fig 3: OMC noise - note that we are shot noise / dark noise limited above ~1kHz
In figure 1, the grey trace is yesterday's almost-two-hour lock, the green is today before the oplev damping was turned downand without ISS second loop, the blue is at the end of the lock. There was a substantial improvement in many bands due to the ISS 1st loop and loosening up the oplevs. The second ISS loop didn't change much, although we did notice it reduced the intensity noise on, for example, ASC-POP_A_SUM.
The beam jitter into the IMC, as measured by DOF1_{P,Y}, hasn't changed from last night. The working hypothesis is that the alignment has drifted into a place where beam jitter couples more strongly into the length DOFs. We checked many PEM channels for coherence with DARM in case, for example, someone had left a fan on in the LVEA, but found no coherence with environmental channels.
A plot of POP vs. POPAIR demodulated signals is attached. Evidently, there is nothing meaningful in the in-vacuum signals, even though there is about 1.7 mW of dc power. This is roughly what we expect; with 2.8 W incident on the IMC, an IMC transmission of 90%, a power-recyling gain of 33 W/W, 250 ppm of transmission through PR2, and 10% transmission through mirror M12 on HAM1, we get 2.1 mW.
Also attached are some short videos of the AS port and the OMC transmission during full lock.
The Box is Checked, and the Advanced LIGO Project has delivered on its prime instrument performance goals. Congratulations to the entire aLIGO team for making this happen! and thanks again to the Hanford All-nighters.
Congratulations and happy noise hunting.
Once again, congratulations from your LLO colleagues! Allow yourselves a moment to enjoy this sweet success before having good luck with the noise hunting…
Fantastic! Noise hunting licenses for everyone! Curious as to what the wind conditions were like.
Dave -- wind conditions were around ~10 [mph]. Microseism was ~5e-1 [m]. Pretty quite night! May we have MANY more. Just like tilt meters.
PeterF, Kiwamu
We found that the RF cables from POP_A were unplugged at the front panel of the demodulation board by the PSL enclosure. We hooked them back in. Confirmed that the demodulated signal showed some interferometer fringes.
J. Kissel, S. Dwyer After both Keita and Sheila had recited the H1 SUS ETMY's measured highest vertical, "bounce," mode frequency was 9.7305+/-0.0002 [Hz], I was glancing around at the various notching done in the control filters for H1 SUS ETMY. I'd found that the optical lever's pitch loop had a bandstop filter of ellip("BandStop",4,1,60,9.7,9.9)ellip("BandStop",4,1,40,13.4,14.2)gain(1.25893) i.e. just missing the ETMY frequency. Thus, we adjusted the filter to better match 9.7 [Hz], i.e. ellip("BandStop",4,1,60,9.6,9.8)ellip("BandStop",4,1,40,13.4,14.2)gain(1.25893) This reduces the gain of the loop at 9.73 [Hz] by a factor of 76.9231 (37.7 dB). This was done well before locking activity go started this evening. The pitch loop remains on. As with the DARM DAMP filters, this change was individually loaded into the bank.
S. Dwyer, J. Kissel, K. Kawabe After installation of the infrastructure (LHO aLOG 16655), and copying of LLO's filters (and adjusting for the specific frequency of 9.7305 [Hz]; LHO aLOG 16658), we tried damping the H1 SUS ETMY's highest vertical mode (a.k.a. "bounce" mode). For the first attempt, the IFO was locked only using ALS diff, with Sheila in the driver's seat. At the time, the mode had been rung up to ~7e-12 (DARM) [m/rtHz] @ 9.7 [Hz]. We had tried a few configurations of the filter bank, and only adjust the gain. We'd found how to ring *up* the mode with a positive gain, with the +60 [deg] (FM2) and bp9.73 (FM4) filters engaged -- then flipped the gain sign (i.e. flipped the phase 180 [deg]), and immediately could see reduction. We had the gain as high as -64, using ~50% of the DAC range, after which took about ~10 [min] for the mode to cool down to the ALS DIFF noise floor of ~1e-12 [m/rtHz] @ 9.7 [Hz]. After a lock loss of two, we were able to get as high the IFO guardian state "RESONANCE," with CARM controlled using digitally normalized RELFAIR9, and DARM has been transitioned to AS45 Q. At this point we saw the mode was still quite run up, so we again turned on the DARM DAMP V filter -- same filter combo, and we could see just as quick a reduction with a gain of -64. This time however, we were using much less of the DAC range, so I went up to a gain of -100, and the mode was quickly damped to the RESONANCE noise floor of ~1e-13 [m/rtHz] @ 9.7 [Hz] within a minute or three. With these two victories, I'm reasonably confident that this will be our ticket to future bounce-free success. Design strings: FM1 "+60dg" zpk([0],[2.16667+i*12.8182;2.16667-i*12.8182],1,"n")gain(0.0523988) FM2 "-60dg" zpk([0],[1.21667+i*7.1979;1.21667-i*7.1979],1,"n")gain(0.0911865) FM4 "bp9.73" butter("BandPass", 4, 9.3, 10.4)gain(120, "dB") with all filters set to an input switching of "zero history" and output switching of "immediately." Attached is a bode plot of the final good set of filters together, FM2 and FM4. Note that these filters were loaded individually from each bank, Keita did *not* load the the whole foton file.
Why local damping does not work:
Before the DARM bounce damping was implemented, I started playing with the BOSEM damping at the top stage, and concluded that it will not work even though the bottom stage bounce mode is clearly visible in the top BOSEM.
The reason for this is that the feedback only sees the top to top transfer fuction.
This TF at the bottom bounce resonant frequency (9.7305 something something Hz) is not that different from that at off-the-resonance proximity (e.g. 9.7Hz). I confirmed this by various things like injecting band limited white noise, injecting sine wave tuned to the resonance as good as possible (9.7305 something level), injecting sine wave at proximity frequency, feeding back with a band pass filter and turning up the gain until it does something.
This means that, since the coupling from the top to the bottom is small, the top mass starts oscillating at proximity before the feed back can do something significant to the bottom motion.
The decay time (1/e) for the bottom bounce mode, measured by the top BOSEMs, was measured to be 13000 to 14000 seconds (Q of 4E5 or so).
I was able to reduce this to 8000 to 9000 seconds by top mass local feedback, which is useless.
Why DARM to top mass damping works:
The feedback loop sees the top to the bottom TF, which has a very sharp peak (as in Q of 4E5 sharp) at the resonance. Therefore you can touch the resonance without touching anything else.
Note that DARM to top mass bounce damping affects the calibration, so there will be a calibration hole at 9.7Hz if the damping filter is on.
When the bounce motion measured by DARM was on the order of 10^-11m, we needed to use the full range of DAC to damp the motion using DARM bounce damping path.
J. Kissel, J. Betzweiser, K. Izumi, M. Fays Integration Issue 913, ECR E1400257, Work Permit #5048 Dave and my initial install of the h1calcs.mdl (for H1 CALibration [model]; Corner Station -- to avoid confusion with the PCAL models at the end station, which are h1calex.mdl and h1caley.mdl) model did not have the latest and greatest updates from LLO. After speaking with Joe Betz, he committed work he'd recently done with the l1calcs.mdl model, which now uses the following library part and c-code: /opt/rtcds/userapps/release/cal/common/models/CAL_CS_MASTER.mdl /opt/rtcds/userapps/release/cds/common/src/RING_BUFFER.c As such, I updated the appropriate corners of the userapps repo, copied over /opt/rtcds/userapps/release/cal/l1/models/l1calcs.mdl and search and replaced l1calcs>h1calcs, l1oaf0>h1oaf0, llo>lho, L1:>H1:,=L1>=H1. The model is now re-compiled, re-installed, and restarted. Kiwamu is working on filling in the infrastructure, but we're waiting for more information from LLO. The CAL overview has been added to the sitemap, and relevant screenshots of the model and medm screens are attached. Max stresses that the MEDM screens are preliminary, and I agree.
Robert, Alastair, Dave:
Robert noticed ADC comb noise on a corner station microphone PEM channel. We power cycled the h1oaf0 IO Chassis with the procedure:
Unfortunately we forgot to tell Alastair his TCS DAC outputs will go to zero volts, which in the case of the chiller setpoints causes laser issues if it is zero for more than 5 minutes. After the front end models were back up and running Alastair recoverted the TCS lasers. I am now starting the effort to write restart instructions to capture these dependencies.
Good news, Robert reports the restart fixed his noise problem.
On a slightly unrelated note, Jeff had installed a new version of h1calcs model which required a DAQ restart.
Related to my post 16497, all test mass ISI's are now running all St1 loops (w/ T750 blends on RZ) and X,Y,Z and RZ loops on St2. I've also edited the guardians to restore these dofs on these ISI's. I've left the BS alone, if it is transitioned to fully isolated, it will only bring up X and Y on St2 and no RZ loops. Otherwise BSC's are in nominal configs, SC, FF01, LLO blends, &c.
Jeff K, Dave WP5048
We created the first install of the h1calcs model on the front end computer h1oaf0.
We ended up restarting the DAQ twice: first to resync with Kiwamu's QUAD SUS changes; and then to add the new h1calcs.
The appropriate EDCU and overview MEDM files were updated.
All of the ISI have a script, connected to a button on the commands screen that controls the state of the analog gain of the GS-13s, but this script didn't control the whitening (see 16606 and comment, as well as 16425). Ryan dR has edited this script, such that it now controls the dewhitening filters. The configuration we think we want to run is with the analog gain on and no analog whitening (studies forthcoming), which means the Gain and Dewhitening filter lights off. Not all chambers have been to the "correct" configuration, this something Hugh and I will take care of over the next few days. The first two images show where to launch the command screens from on HAM and BSC ISI overviews, the second two show the gain switch buttons on the command screens.
This morning Dave and Alastair reported one of the TCS AA chassis in the CER was found powered off. Switched unit back on and found the -15V led was flickering. Took chassis S1300387 to lab and found two buffer IC's (AD8622) had had failed on board S1300387 on CH3 and CH4. Replaced IC's and ran transfer functions. Unit was replaced back in rack.
07:51 Karen and Cris in the LVEA 07:58 Jim W. turning off HEPI to ISI feedforward on all BSC chambers to run measurement for ~ 20 min. 08:03 Hugh restarting end Y HEPI pump servo 08:15 Aidan going through the LVEA on the way to the high bay 08:18 Jeff B. to LVEA to look at dust monitors, work with Mitchel in West bay on bag and tag 08:21 Rick to end Y 08:40 Christina driving forklift from LSB to high bay 08:45 Sudarshan and Thomas to end Y for PCAL work 08:49 Cris to mid X 08:50 Alastair to LVEA to check on TCS laser 08:57 Aidan working on 3IFO near HAM6 09:01 Rick back from end Y 09:12 Betsy and Travis to the West bay 09:19 Andres moving 3IFO parts from the LVEA to the staging building 09:28 Doug to LVEA to take pictures 09:51 Richard to LVEA 09:56 Jeff B. and Doug out of LVEA 09:58 Jim W. running measurement on ETMY 10:00 Mitchel out of LVEA 10:03 Thomas and Nutsinee back from end Y 10:14 Travis and Betsy out of LVEA 10:45 Dave B. to CER to check on TCS AA chassis 10:51 Dave B. and Aidan to CER to power on TCSY AA chassis, does not work, Filiberto and Aidan investigating 11:37 Thomas and Elli back from end X 11:41 Thomas and Elli to end Y 11:42 Bubba to mid X to check on possible noisy air handler 11:54 Kiwamu starting WP 5047 11:56 Bubba back from mid X 12:09 Thomas and Elli back from end Y 12:16 Kiwamu restarting SUS ETMY model Bubba back to mid X 13:39 DAQ restart for new CALCS model 15:03 Jim W. to HAM5 to read serial number off box
model restarts logged for Mon 09/Feb/2015
2015_02_09 01:44 h1fw0
2015_02_09 02:28 h1fw1
2015_02_09 14:36 h1fw1
all unexpected restarts of frame writers.
model restarts logged for Tue 10/Feb/2015
2015_02_10 10:03 h1tcscs
2015_02_10 10:08 h1pemcs
2015_02_10 10:10 h1pemex
2015_02_10 10:10 h1pemey
2015_02_10 10:12 h1pemmx
2015_02_10 10:12 h1pemmy
2015_02_10 11:32 h1susetmx
2015_02_10 11:36 h1dc0
2015_02_10 11:38 h1broadcast0
2015_02_10 11:38 h1fw0
2015_02_10 11:38 h1nds0
2015_02_10 11:42 h1fw1
2015_02_10 11:42 h1nds1
2015_02_10 13:01 h1iopoaf0
2015_02_10 13:03 h1oaf
2015_02_10 13:03 h1odcmaster
2015_02_10 13:03 h1pemcs
2015_02_10 13:03 h1tcscs
2015_02_10 19:32 h1fw1
2015_02_10 20:23 h1fw1
2015_02_10 22:30 h1fw1
Maintenance Day. New code for TCS and PEM with associated DAQ restart. SUS ETMX restart to clear error. ADC timing glitch required restart of h1oaf0. Unexpected restarts of frame writer.
Attached are plots of coherence between DARM and other channels during last night's lock.
In the 100-200Hz region, there is some coherence with the other LSC DOFs, and the OMC ASC control signals (OMC-ASC_{ANG, POS}_OUT_DQ).
Above 300Hz there is coherence with the input intensity noise.
In the 20-40Hz band there is some coherence with the OMC ASC.
Below 10Hz there is a lot of alignment noise.
Question for DetChar people: does this agree with other coherence tools?
Dan, Evan
We measured the dark noise of the OMC DCPDs with the IMC unlocked and MC2 misaligned. (We also trimmed the dark offsets.)
The attached xml file & plot has measurements of OMC-DCPD_{A,B}_IN1 and _OUT with zero, one, and two stages of analog whitening enabled (and the corresponding digitial dewhite filters). The y-axis units are in cts/rt[Hz] for the IN1 channels, mA/rt[Hz] for the OUT channels.
With zero whitening (the case for the locks last night), the ADC noise is about 7x10^-3 cts/rt[Hz] at IN1. Last night our noise was about 10x larger than this (see upper left plot here).
Some notes about the conversion of the DCPD signals from counts to milliamps in the DCPD filter banks:
In the noise budget, we have
These agree with each other.
The attached PDFs show the resistance measurements for all RHs and the relative resistance vs time for the RHs as 1W is applied to each segment. All segments are operating within nominal parameters.
The resistances for the segments are:
Segment | Resistance (Ohms) |
ITMX UPPER | 44.0 |
ITMX LOWER | 42.4 |
ITMY UPPER | 40.7 |
ITMY LOWER | 42.5 |
ETMX UPPER | 41.9 |
ETMX LOWER | 41.0 |
ETMY UPPER | 42.2 |
ETMY LOWER | 43.6 |
Just for reference, here is the transient thermal lens in ITMX, as measured by the HWS, from this morning's 2W RH test (~1800s of applied power).
A follow-up. The data from the RTD temperature sensors for each RH is plotted in the attaced PDF.
The ETMY and ITMX RH RTDs are non-responsive.
Attached is spectra from WHAM6 looking at the GS-13 INF IN1s--before the digital filters.
The Red traces where taken at 1417utc (~6am local) with the FM4 & FM5 ON, my understanding and based on the plots here, this is analog low gain and whitening.
The Blue traces are from 1550utc with FM4 ON and FM5 OFF--analog low gain but not whitened.
Green traces are from 1650utc with both FM4 & 5 OFF--analog high gain and not whitened; The brown traces start at 1722utc with FM4 OFF and FM5 ON, that is, analog whitening and high gain.
Again, based on the plots, the switches appear to be doing what I thought and expect.
Do we have saturations when in whitened high gain? No, based on the H1:FEC-51_ACCUM_OVERFLOW, no saturations accumulated during any of the measurements.
What about being ADC limited in low gain without whitening. Included on the traces are the ADC noise from the svn. It certainly looks like in low gain without analog whitening, we approach the ADC limit at 100Hz and very likely about a few 100Hz.
Conclusion--Leave FM5 ON all the time--we are not saturating in high gain and we are near the ADC noise in low gain without whitening...but wait:
But what about those ugly lumps between 200 and 400Hz? They do not show up on the unwhitened hi gain signal but are evident on the other three configurations. The ringing is exactly 1Hz and the beating is about 45Hz. Maybe this suggests a problem with the whitening filter? Maybe we should not whiten the signal when in high gain.
I added a zoom in of the high frequency beat stuff.
From JeffK's 16425, while I'm a bit confused as to Jeff's language I think i understand:
These two states are compensated for digitally in FMs 4 and 5 of the GS13INF banks, by the difference between the two states (the overall gain of 2 is folded into the calibration filter). FM4 is the switchable gain compensation, FM5 is the switchable compensating de-whitening filter. The front-end code for the HAMs and BSCs is set up that these digital banks control the analog switching. - When FM4 is ON, the gain switch is HI (or a binary output of 1), so the analog gain is 2, and FM4 compensates the gain of 10 difference. - When FM4 is OFF, the gain switch is LO (or a binary output of 0), so the analog gain is 20. - When FM5 is ON, the analog whitening is LO (or a binary output of 0), so there is no whitening, and FM5 compensates the z:p = 50:10 difference. - When FM5 is OFF, the analog whitening is HI (or a binary output of 1), so the whitening is engaged.
and I think the FM5 states are backwards as to the above verbeage. The digital DWH filter certainly looks like a De-Whitening and the above traces bare out the FM5 enables the analog whitening.
dtt template is in /ligo/svncommon/SeiSVN/seismic/HAM-ISI/H1/HAM6/HAM6_GS13_GAIN_DWH.xml
So just to be absolutely clear, I restate the conditions in the two desired states (originally defined, as Hugh says, in LHO aLOG 16425): - When FM4 is ON, the gain switch is HI (or a binary output of 1), so the analog gain is 2, and FM4 compensates the gain of 10 difference. - When FM4 is OFF, the gain switch is LO (or a binary output of 0), so the analog gain is 20. - When FM5 is ON, the analog whitening is HI (or a binary output of 1), so the analog whitening is engaged, and FM5 compensates the analog whitening of z:p = 10:50 [Hz] with a de-whitening z:p = 50:10 [Hz] filter. - When FM5 is OFF, the analog whitening is LO (or a binary output of 0), so the analog whitening is is OFF, and no FM5 means no compensation. Attached is the corrected version of the State Machine diagram I'd originally posted. (it's also copied as a comment to 16425).
The first attachment is a time series of the HAM6 Watchdog, the Fastshutter State, and a GS-13 trace on HAM6. The switch to low Gain is clear on this last trace. This is a 5 day trend and the ~20 minutes needed to get the below .005Hz BW data is comfortably unmolested by the ISI or the fastshutter--the start times of the Spectra calculations begin at the vertical black lines. As for ISI trips and shutter fires--there were none.
The High Gain Spectra period begins at 0800utc on 29 Jan, the Low Gain Spectra begins at 0800utc 1 Feb.
The second attached graph has Horizontal GS13s on HAM6 in High and Low Gain on the upper plot. The Verticals are in the lower plot. High Gain Spectra is Dashed, Low Gain traces are Solid. Also shown is our ADC noise in counts.
One caveat is that the ground motion is different at the two times. The third attachment shows the Cartesian DOFs for the HAM6 GS-13s in the upper two plots and the ground noise in the bottom plot. We've had a ground motion decrease in the microseism frequencies and below during the low gain period. You can see the Low Gain Spectra are at the ADC level below 50mHz. And the 10x signal reduction expected is more like 5x below these frequencies. If this conclusion passes mustard, we'll have to revisit the GS13 triggering delays/levels.
DTT template is /ligo/svncommon/SeiSVN/seismic/Common/MatlabTools/HAM6_GS13_GainNoiseTest.xml
J. Kissel, H. Radkins Which GS13 gain/whitening configurations are the "right" gain configurations? How many times have we asked this? Hugh is trying to settle this once-and-for-all with quantifiable results like the above entry, but I relay the history and current problems with the GS13 gain / whitening switching below. The GS13 Interface Board (D1002706), used for both HAM and BSC ISI GS13s (in D1000067 and D1002432, respectively), has two *independent* switches: one for an analog whitening filter (switching between a flat gain of 1, or a zero:pole filter of 10:50 [Hz] -- a gain of 1 at low-frequency, 5 at high frequency), and one for analog gain (switching between a flat gain of). Thus, there are four possible gain/whitening states for this interface board. See attached visual aide. These two states are compensated for digitally in FMs 4 and 5 of the GS13INF banks, by the difference between the two states (the overall gain of 2 is folded into the calibration filter). FM4 is the switchable gain compensation, FM5 is the switchable compensating de-whitening filter. The front-end code for the HAMs and BSCs is set up that these digital banks control the analog switching. - When FM4 is ON, the gain switch is HI (or a binary output of 1), so the analog gain is 2, and FM4 compensates the gain of 10 difference. - When FM4 is OFF, the gain switch is LO (or a binary output of 0), so the analog gain is 20. - When FM5 is ON, the analog whitening is LO (or a binary output of 0), so there is no whitening, and FM5 compensates the z:p = 50:10 difference. - When FM5 is OFF, the analog whitening is HI (or a binary output of 1), so the whitening is engaged. A long time ago, Brian had performed a design study (see G1000412) that had suggested (on pg 24-25) that "Low Gain Mode [is] good enough to get close to requirements at all [frequencies] above 300 [mHz], tilt[-horizontal] coupling [from vertical GS13 noise turning into RX & RY, which causes X & Y]. [In] High Gain Mode, ADC noise is at least 2x below the sensor noise at all frequencies." where he defines "Low-gain is DC gain of 2, with a zero at 10 [Hz], pole at 50 [Hz]" and "High-gain is fixed gain of 12 (input stage of 6)." Clearly the later statement is now out-of-date with respected to the current revision of D1002706, but the intention is clear -- HI Gain = analog gain ON, analog whitening OFF (FM4 OFF, FM5 ON) LO Gain = analog gain OFF, analog whitening ON (FM4 ON, FM5 OFF) Indeed -- that a "Gain of 10" and "No Whitening" is the "nominal" configuration is now written directly surrounding the circuit in the schematic D1002706. Why? Because - having *no* whitening or additional gain (i.e. FM4 and FM5 ON, or an overall interface response of a flat gain of 2), you'll likely be buried in the ADC noise floor at all relevant frequencies, and - having *both* whitening and additional gain (i.e. FM4 and FM5 OFF, or an overall interface response of low-frequency gain of 20 and high-frequency response of 100, with a z:p pair at 10:50 [Hz]) will likely saturate the ADC. Further, this was solidified in a SEI team summit at the March 2011 meeting, notes were taken (see T1200373) that say the following: " FM4 - Switchable Readout Gain: - Gain of 10 (7) [113] (cancels fixed gain in FM1) - FM4 is ON when analog gain is OFF - FM4 is ON in "low gain" mode (analog x10 gain is OFF) - FM4 is hooked to analog gain via BIO, such that when FM4 is turned OFF, the analog gain is turned ON - Choose for analog switch to happen at zero crossing (a bit you can flag in the foton .txt file) FM5 - Switchable Whitening (for GS13s only): - Filter matches analog whitening (cancels fixed dewhitening in FM1) - FM5 is ON when analog whitening is OFF - FM5 is OFF in "low gain" mode (analog whitening is ON) - FM5 is hooked to analog whitening via BIO, such that when FM5 is turned ON, the analog whitening is turned OFF - Choose for analog switch to happen at zero crossing (a bit you can flag in the foton .txt file) " Seems clear, right? Great. Here's the problem: (1) The front end does not restrict the user from the ADC-noise-swamped state, lets call it "ultra-lo gain mode," of FM4 and FM5 ON (additional analog gain and whitening OFF) or the ADC saturating state, let's call is "ultra-high gain mode," of FM4 and FM5 ON (additional gain and whitening ON). (2) The python command script used to switch between the modes is ${userapps}/isi/common/scripts/sensor_hilo and IT ONLY SWITCHES FM4. This (and the name "hi gain" and "low gain") has confused users who only use this command script into thinking that the difference between the two relevant states is *only* the x10 gain and FM4. This had resulted in chaos and confusion during LHO's period of revolving commissioners, and ingrained a long-standing, almost superstitious, confusion about what "low gain" and "high gain" states mean. Thankfully, I think after 15 discussions on SEI calls, 20 individual-to-individual email chains, and some LLO spy sessions via remote log-in over the past few years, Jim and Hugh have settled on what Brian thought was right answer for GS13s back in 2010: - All* HAMs are in high-gain mode (with FM4 OFF and FM5 ON, i.e. additional analog gain of 10 and no whitening.) - All* BSCs are in high-gain mode ("") Why do I have asterisks next to ALL in both cases that continue to add to the confusion? Because of blasts from lock-acquisition / lock-loss. From experience with DRMI lock-acquisition, LLO has found that ISI BS ST2 GS13s saturate regularly if in (nominal, not ultra) hi-gain mode. If the GS13s are in the (nominal, not ultra) low gain configuration, they don't saturate. As such, for the ISI BS only, we use the nominal lo-gain mode. For experience with the Fast Shutter closing and opening on HAM6, LLO has found that the ISI HAM6 GS13s saturate regularly even in the nominal lo-gain mode. Thus, we've changed the configuration of the HAM6 ISI to the ultra-low gain mode (FM4 and FM5 ON, no additional analog gain or whitening). So here's my suggestions: - we rewrite the python script sensor_hilo to be a FOUR state system instead of a TWO state system, and make sure that FM5 gets toggled as well as FM4. - we use either GUARDIAN or the new SDF system to keep track of these FMs. If the chamber needs to switch gains after lock acquisition or lock loss, it should be controlled by guardian. - we continue to measure the performance of all platforms to find out where we're ADC noise limited in all possible states of the GS13 interface.
"Trust, but verify." Always! Hugh has caught an error in the above description of the GS13 interface's state machine which didn't obey reality. Thankfully, he was able to confirm this with real data from HAM6 -- see LHO aLOG 16606. I've added the following [clarification of / correction to] the above to Hugh's entry, and I repeat it here for completeness: - When FM4 is ON, the gain switch is HI (or a binary output of 1), so the analog gain is 2, and FM4 compensates the gain of 10 difference. - When FM4 is OFF, the gain switch is LO (or a binary output of 0), so the analog gain is 20. - When FM5 is ON, the analog whitening is HI (or a binary output of 1), so the analog whitening is engaged, and FM5 compensates the analog whitening of z:p = 10:50 [Hz] with a de-whitening z:p = 50:10 [Hz] filter. - When FM5 is OFF, the analog whitening is LO (or a binary output of 0), so the analog whitening is is OFF, and no FM5 means no compensation.
Here's a corrected drawing to indicate the state of the FMs in each HI and LO states.