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?
These are trends from the past 10 days
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.
In response to yesterday's locking activity (alog 16628), I newly added the DARM->M0 damping path in the QUAD suspension models under WP 5047. This allows us for damping the bounce mode through the M0 stage using DARM signals as was done in LLO (LLO alog 16686).
(h1susi(e)tmex(y) models are modified)
Right now the modifications are completely local in the sense that I did not change the common QUAD master block but the local front end models, namely h1susetmx, h1susetmy, h1susitmx and h1susitmy. In these front end models, I disabled the link of the QUAD master block in the top layer so that they are now detached from the common QUAD master. I then added the DARM damping filters by coping the filters from Livingston's. I copied them from l1susetmx.mdl. Note that the latest-latest l1 quad suspensions are capable of routing the WFSs signals in addition to the DARM damping, but we don't have this at the moment.
I checked in all the four quad models into svn.
(some screens)
I then updated the medm screen, common/medm/quad/SUS_CUST_QUAD_OVERVIEW.adl (see the attached) which is a variant of what LLO currently has. I have not checked this screen into svn. Jeff will take care of it. Also I added a new screen, SUS_CUST_QUAD_M0_DAMP.adl which displays the filters. This is a duplication of what LLO locally has. Neither of the sites checked this screen in yet.
EY bounce filters are copied from LLO.
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.
J. Kissel, I've updated the /opt/rtcds/userapps/release/sus/common/medm/ directory to receive a few overview screen and BIO screen updates that Stuart and Joe have made, see BSFM LHO aLOG 16368 QUAD LHO aLOG 16760 jeffrey.kissel@opsws3:/opt/rtcds/userapps/release/sus/common/medm$ svn up Restored 'SUS_DRIFT_MON_SMALL.adl' U bsfm/SUS_CUST_BSFM_BIO.adl U bsfm/SUS_CUST_BSFM_OVERVIEW.adl U quad/SUS_CUST_QUAD_BIO.adl Updated to revision 9804.
Turned off earlier to allow Thomas and Elli to enter end X.
BCS9 illumintator turned off at 11:30 PT.
Due to some extenuating circumstances, Travis, Richard, and I moved the remaining hardware out of the 2 large 16' assembly cleanrooms in the west bay of the LVEA and turned them off. There is still a small cleanroom on against the West wall of the LVEA which we will turn off in a few weeks when we are finally finished kitting 3IFO hardware.
Note, we also turned the dust monitor off that was in the room since it started alarming when we turned the rooms off (was after 10am so were rushed to finish up and vacate). Of course, we should turn the monitor back on and reset the alarm thresholds...
Just getting ranges correct and consistent for display of reds & greens. All pressure lights are now Green and OK. The SERVO database is set up so restart does not affect the HEPI platforms too much. I of course would not do this if anyone was running any tests. The times are: EY 1603, EX 1619, CS 1638utc. Attached is 40 minutes of second trends with these times annotated. The corner station pressure glitch was non existent, the ends had glitches of a few PSI.
When I look at the HEPI L4Cs during this pressure glitch, it looks like it is absorbed into the normal background glitching. See the latter two attachments.
The database still has the old PID parameters. We will update these once we finish the plant analysis. Anyway, we have been running different parmeters for the LVEA Pumps and I forgot to change these (with the medm) when I restarted it. I've just now corrected this--again this should only make things better (reduce sensor noise coupling) and the transition should have been transparent.
Sheila, Dan, Daniel, Evan Jeff, Lisa, Alexa
Starting at 08:43:06 UTC Feb 11, 2015 we had a DC lock for ~1:54min. We lost lock again because of the 9 Hz bounce mode in ETMY. We had tried damping with the L2 stage, which helped a bit but still ultimately caused the lock loss. Tomorrow we should try damping with M0, as done at LLO (LLO#16686).
Sheila has pointed out that we might as well notch out the bounce mode resonances in the DHARD WFS loops. So now there is a 9.8 Hz stopband filter installed in FM9 of DHARD_P and (in an abundance of caution) in DHARD_Y.
Nice going with all the long lock segments. Once something is working you learn a great deal quickly.
Some important times from the lock:
Lock sequence started at ~8:17 UTC when arms locked on green
Handoff to POPAIR at 8:27 UTC (this is the last step in the ISC Guardian before the handoff to DC readout - see LSC matrix element 3_10 in the attached plot)
DARM offset applied and OMC locked at 8:40
DARM handoff to DC readout at 8:44
Lock lost at 10:36 UTC
J. Kissel, B. Abbott Over the past few weeks, I've been building up understanding of the HEPI pump servo -- more than I ever wanted to know. The conclusions from all this? (1) The EPICs calculation of the PID loop (documented loosely in the EPICs manual here) (a) uses backwards differentiation approximation and velocity formalism to compute the *change* in control output value, which it then adds it to the previous cycle's control output value -- which turns it back into a "position" algorithm -- i.e. one *doesn't* have to differentiate the pole and two zeros of the P, I and D. Other good references I found are here, here, and here. (b) expects the "I" and "D" terms in [cycles / min] or [mins / cycle], respectively, i.e. it depends on the sampling rate / clock cycle turn-around time of the PID calculation. If you want to do any sane prediction of the filter shape, you've got to convert these to [rad/s] or [s/rad], again respectively, by multiplying by 60/(2*pi*Ts) [(min/sec).(rad/cycle)] or (2*pi*Ts)/60[(cycle/rad).(sec/min)]. (2) The EPICs turn-around time, or clock cycle, for the discrete PID controller calculation is longer than the requested sampling frequency, which means the sampling rate is determined by the clock-cycle. Further, it's slower in the corner station than the end stations. We should lower the EPICs record's demand of the sampling frequency from 10 [Hz] to 1 [Hz] (and check again if the PID can turn around the calculation fast enough). (3) The HEPI Pump servo contains a second-order, 16 [Hz], Sallen-Key, anti-aliasing filter before the input to the ADC on all pressure sensor channels (see D0901559, pg 2) (3) We should lower the PID parameters such that the UGF of the loop is ~ 1 [mHz]. Why? (a) The pressure sensors were never meant to be used as AC sensors. LHO aLOG 16500 hints that they shouldn't be used in a loop above a few [mHz]. (b) The ADC noise of the Athena II, PC 104 computer is an abysmal 1e-2 [V/rtHz]. As they are currently amplified, the pressure sensor's signal gets buried in this ADC noise by ~10 [mHz]. (c) Adding an EPICs "smoothing" parameter (a.k.a. SMOO) to the EPICs version of the pressure sensor channels adds a single-pole low-pass filter into the control loop. If sufficiently low in frequency, it'll start to creep in on your already-small phase margin. We should use this with caution, or at least be cognizant of its impact. ------------- Details. I attach 5 plots per pump station: Pg 1: On the EPICs turn around time defining the sampling rate In my perusing of the EPICs manual, I found that the PID channel, e.g. H1:HPI-PUMP_EX_PID, has sub records, one of which is "DT," which one can query with a simple caget: jeffrey.kissel@opsws8:/$ caget H1:HPI-PUMP_EX_PID.DT H1:HPI-PUMP_EX_PID.DT 0.312006 This is "the time difference in seconds between processing steps." Consequently, I caget'd this sub record 5000 times. This turned out to be faster than the EPICs calc record would update the number by 3, so I took every third report. Then I histogrammed the results, to find that the clock cycle is 0.55 and 0.28 [sec] (!!) for the corner station and both end stations, respectively. The end stations show some clock jitter, but I took the mode of the 1667 points and used that as the clock cycle. This immediately informs us that the features seen in all ASDs that happen at 1.8 [Hz] and 3.5 [Hz] at the corner and end stations are just a function of the terribly slow sampling rate -- even slower than the EPICs 16 [Hz], and the request calc record rate of 10 [Hz]. Pg 2: On EPICs Implementation Discrete PID Control It's too difficult in a simple text editor to really do the explanation any justice, but check out all of the references I show above, while you wait for coherent presentation version of this aLOG. One of the many reasons why my initial guess at what the servo was doing (in LHO aLOG 16447) was incorrect was because I wasn't accounting to the time delay of the discretization. As I found out later, it turned out that the discretization was much slower that was defined in the EPICs calc record. Pg 3: Modifying the measured plant (see LHO aLOG 16601) with the anti-aliasing filter, and an EPICs smoothing filter On the SMOOOOOOO at EY Hugh's initial instinct to combat the newly-noisy differential signal was to add some EPICs sub-record defined "smoothing factor" to the supply and return channels which form the differential pressure signal. Again, from the EPICs manual, "The converted data value is subjected to the following algorithm: val = newvalue * (1 - smoo) + oldvalue * smoo SMOO should be a value between 0 and 1, with 0 meaning no smoothing and one meaning ultimate smoothing (in fact the data will never change)." *sigh* who writes these manuals? Thank god they wrote out the algorithm. This is just the discrete realization of a first order low-pass filter. The pole frequency of which is defined by f_{pole} = 1/(2*pi*Ts) * ln(1 / (1 / alpha)) Hugh had entered in a SMOO of 0.75, which at a dismal sampling rate of Ts = 0.28 [sec], means the pole frequency is at 0.159 [Hz], which explains *some* of the excess gain peaking that we see at EY. Pg 4: Loop Design figures of merit given the now-(mostly)-understood plant and controller Pg 5: Model of closed loop ASD noise Clearly I'm still missing some phase loss term that increases the gain peaking, but at least I get the suppression correct. I could hunt around for several more days as to why this is, and find some other nasty EPICs trickery. But I'm not gunna.
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.