Overview
A synchronized oscillator was added to QUAD_MASTER
model test mass stage (L3). After re-compiling the SUS-ETMY
model there will be two synchronized ossilators in L3 stage that will be used for driving calibration lines: *_L3_CAL_LINE
and *_L3_CAL2_LINE
.
Removed channel LKIN_P_LO
from the list of DQ channels and added L3_CAL2_LINE_OUT
into the list.
The h1susetmy
model must be recompiled in order for the changes to take effect.
Details
For one of the two calibration lines that we needed to run during ER9 we used a pitch dither oscillator, SUS-ETMY_LKIN_P
(see LHO alog 28164). After analyzing the ER9 data we found two problems with this line (see LHO alog 29108):
CAL-CS
model that calculates the time-dependent parameters rely on an oscillator that is synchronized with the ones in the SUS-ETMY
and CAL-PCALY
models. Since SUS-ETMY_LKIN_P
is not a fixed phase (synchronized) oscillator, the phases have to be adjusted by hand every time the oscillator gets restarted. With synchronized oscillators this is will not be necessary.
The second synchronized oscillator was added at L3_CAL2_LINE_OUT
and the list of DQ channels was modified accordingly. The L3_CAL2_LINE_OUT
was added with sampling rate 512 Hz. LKIN_P_LO
was removed from the list of DQ channels.
The changes were commited to USERAPPS repository, rev. 14081.
Dave, TJ, Jeff K, Darkhan,
H1:SUS-ETM(X|Y)
were recompiled and restarted, DAQ was restarted (see LHO alog 29245, WP 6117).
The QUAD MEDM screen was updated to show the new oscillator settings.
The MEDM screen updates were committed to userapps repository (rev. 14088):
common/medm/quad/SUS_CUST_QUAD_ISTAGE_CAL2_LINE.adl
common/medm/quad/SUS_CUST_QUAD_OVERVIEW.adl
After making corrections to the FSS front end model to reflect the hardware connections for signals involving temperature stabilisation of the reference cavity, the filter gain(s) and offset(s) for the ambient temperature and the average reference cavity temperature have been changed. These are for: H1:PSL-FSS_DINCO_REFCAV_TEMP offset = 344582.9468 gain = 9.011805496E-4 H1:PSL-FSS_DINCO_REFCAV_AMBTEMP offset = 328418.8499 gain = 9.650437381E-4 With these settings, these channels now read out the temperature in Kelvin.
Weekly Xtal - tiny decreases in amp diode powers. No surprise there. All other powers seem nominally steady. Still have a bad current reading at OSC DB3.
Weekly LASER - Osc box humidity down considerably after the internal water event. It appears to even be lower than it was in then days prior to the event. PMC temp output seems to be lower by a couple of degrees, I'm going to call this a good thing. All other power outputs seem nominally stable.
Weekly Environment - I see a decrease in all relative humidity counts. Also there seems to be a marginal drop in temps except for the LVEA and the PSL anteroom.
Weekly Chiller - Trends are zoomed in for high resolution. All flow and pressure trends show downward tendencies except for OSC head2 which trended slightly higher in flow.
Summary - all around, everything seems to be in good shape. There doesn't seem to be any immediate cause for alarm at this time.
Concur with Ed's analysis, everything looks to be running OK.
FAMIS # 6428 - Checked the chillers and filters. Added 125ml to Crystal chiller. Added 250ml to diode as a preventative measure. Both filters are clean. No debris; no discoloration. Trends of chiller flows, pressures, and temperatures are all OK.
SEI - All good. Progress was made with the shutter last week; different filter, too high gain settings (see alog29149).
SUS - All good.
CDS - Running.
Pulling chasis at ends for Beckhoff tomorrow.
PSL - All good.
Vac - HAM6 still coming down slowly.
Tomorrow terminate the cables for the ion pumps. Software needs an update. RGA baking.
Facilities - HVAC system contractors here.
Tomorrow moving items around in LVEA.
Interview and PNNL tour tomorrow in LVEA
Please finish maintenance by NOON tomorrow.
Sheila Terra Evan
This afternoon we made some progress on things that were making locking difficult, and only a little progress on getting to low noise.
Summary: The interventions in late July and early August to disable blinking LEDs and isolate timing system power supplies have made some difference in the periodicities that emerge when folding magnetometer data from the end stations, with the largest difference seen with the initial firmware updates done in late July. Details: Weigang Liu has been cumulatively applying his folding algorithm to magnetometer data from January through early August, including periods before, during and after recent attempts to mitigate leakage of periodic (1 Hz and 0.5 Hz) transients seen in magnetometer channels into DARM. [Recent clogging of the Caltech cluster nodes with sufficient memory has delayed the automatic production of these plots, so Weigang did a bunch of jobs manually on head nodes for this report.] Summary of recent interventions:
Channel / link to 2016 web pages | Figure attachments | July 16 to July 21 changes | July 21 to August 6 changes | August 6 to August 18 changes
H1:PEM−EX_MAG_EBAY_SUSRACK_X | 1-4 | Improved | Higher peaks | Similar
| H1:PEM−EX_MAG_EBAY_SUSRACK_Y | 5-8 | Improved | Higher peaks | 1-Hz structure different (not better)
| H1:PEM−EX_MAG_EBAY_SUSRACK_Z | 9-12 | 1-Hz structure worse | Similar | 1-Hz structure reduced
| H1:PEM−EY_MAG_EBAY_SUSRACK_X | 13-16 | Improved | Similar | Similar
| H1:PEM−EY_MAG_EBAY_SUSRACK_Y | 17-20 | Worse | Even worse | Similar
| H1:PEM−EY_MAG_EBAY_SUSRACK_Z | 21-24 | 2-Hz structure smaller, 1-Hz structure worse | Similar | Improved
| |
PI damping working, though all gains required a sign flip. Successfully damped ETMX mode while ETMX ESD was in HV mode thanks to recent mod.
Modes 17 (ETMX), 25, 26, 27 (all ETMY) rang up. All four have been in guardian and were damped tonight with a sign flip of the gains. I was able to check some phase optimizing but locks were too short for much investigation. I've saved these changes to the guardian and they auto damped the next lock successfully.
Title: 08/19/2016, Evening Shift 23:00 – 07:00 (16:00 – 00:00) All times in UTC (PT) State of H1: Relocking after PSL back in operation. Commissioning: Outgoing Operator: Ed Activity Log: All Times in UTC (PT) 23:00 (16:00) Start of shift 23:12 (16:12) Filiberto – Powered on ITM HV power supply 00:11 (17:11) Kyle – Into LVEA to adjust RGA in Vertex 00:19 (17:19) Kyle – Out of the LVEA 04:58 (21:58) Sheila & Terra – Going to IOTC1 to work on camera alignment 05:20 (22:20) Sheila & Terra – Out of the LVEA Title: 0819/2016, Evening Shift 23:00 – 07:00 (16:00 – 07:00) All times in UTC (PT) Support: Sheila, Terra, Evan Incoming Operator: N/A Shift Detail Summary: Commissioning work continuing.
This week we were put h1fw0 back into an unstable configuration by asking it to write out all the frames (full, science, strend, mtrend). We were able to extract some useful information from the crashes. The main point is that for some reason IO starts to become unstable and the raw frames end up taking too long to write. This eats up all the internal buffers, and the system crashes. I did some tweaking of nfs settings which brought the frame writing threads to have more stable write times. Even with that a hiccup was observed which allowed the science and full frame to get a cycle out of sync, with the full frame writer being unable to catch up. Today after looking at the code I have a new build of the framewriter running on h1fw2. This splits the framewriting thread into two parts, to allow parallel execution and allow the full frame writing threads the chance to catch up if they fall behind. So far h1fw2 is stable. We will test it on h1fw0 next week.
Kyle, Chandra Isolated turbo on top of HAM 6 and spun it down, turned off scroll pump, decoupled foreline piping. Left turbo energized until bearing if fully de-levitated. NOTE: climbed on top of HAM 6 to do this work. Will de-energize turbo by Monday.
I had intended to shut down the pump cart pumping the Vertex RGA (also de-energize the HAM6 turbo controller) on Saturday morning, decouple it and then combine (valve-in) the RGA to the Vertex volume. However, I forgot to get a Work Permit approved for this prior to people exiting for the weekend. I confirmed with Keita, Sheila and Terra that their activities would not be hindered by leaving this noise source running over the weekend so, I will do this on Monday morning.
P. King, J. Oberling
Short Version: The PSL is now up and running following the HPO water leak (first reported here, repairs reported here).
Long Version: This morning, after giving the HPO ~48 hours to completely dry, we inspected the HPO optical surfaces. The only thing found was some water spots on the head 1 4f lens (this was drag wiped clean); all other optical surfaces look good. We then slowly brought up each head individually to ensure no contamination was causing the optical surfaces to glow; all good here as well. The HPO was then successfully powered up an allowed to warm up for several minutes. The front end came on without issue and the injection locking locked immediately. After allowing the system to warm up for ~1 hour, I attempted to lock the PSL subsystems (PMC, FSS, ISS). The PMC did not want to lock; according to Peter this was likely due to a slight horizontal misalignment (this is seen in a trend of the QPD that lives in the ISS box. I unfortunately don't have a copy of it). I returned to the enclosure and tweaked the beam alignment into the PMC and it locked without issue. I then tweaked the PMC alignment further to maximize the power throughput. PMC now has a visibility of ~80% with ~122W transmitted (with ISS on). The FSS and ISS both locked without issue. The PSL is now operational and fully recovered from the water leak.
Information about the mis-alignment was obtained from the reflected spot CCD image, not the ISS QPD.
[Alastair, Jason, Ben, Vern, Dave]
Thanks to everyone for their help getting this work done. The Y-arm TCS laser is now running full power, and the table is fully aligned. The in-loop photodiode is also now working again. Details below.
Tuesday we discovered the laser on the table (SN 20306-20419D) had previously been paired with the driver that went with the spare laser ( 20816D-20510). The laser had been outputing 40W at the time. When the Hanford team had swapped in the 'spare' driver they actually were putting in the one that matched up with the laser (SN 20419D-20306) and the power went down to 16W. First thing we did on Tuesday was to add irises to the table to define the optical axis after the laser. We added blocks to the table to define laser position We then swapped in the spare laser (20510-20816D) and aligned to the blocking, and we found the power outputs were ~14W with its mating driver, and ~40W with the driver SN20419D-20306.
Checks on as much of the electronics as we could test showed no problems (RF distribution system, controller voltages, power etc).
Wednesday we decided the fastest way to diagnose the drivers was to swap them in to the working X arm table. Driver SN 20419D-20306 gave a power output of 58W. Driver 20816D-20510 gave 42W. Swapping back to the original X arm laser (SN 20706-21015D) and driver combo gave 60W so at this point we left the X-table in its previous working condition. Conclusion was that driver SN 20816D-20510 has now given output of ~40W on three separate lasers and appears to have some issue.
Moving back to the Y-table, two issues were noticed. Firstly there was very minor discoloration on one pin of the power cable for the laser. Ben also said that the pin looked badly seated and did some corrective work on this (we should check with him if he thinks this needs further work). Secondly the power meter height was adjusted to make sure the aligment to the laser gave the largest apeture possible - this could with a little misalignment oclude part of the beam.
We repeated measurement of spare laser SN20510-20816D with driver 20419D-20306 getting 49W output. We then completed the cycle of tests by putting in laser 20306-20419D with its matching driver 20419D-20306 and getting 58.6W output. It's not clear what fixed the problems - the power cable seems a likely candidate but behavior of the laser still doesn't seem totally consistent with this (if one half of the driver was getting no current we would expect ~25W output). We also might want to test driver SN 20816D-20510 to check whether the power connector (which looked okay when visibly inspected) might be a cause for its performance drop.
After the laser swaps the final laser configuration was aligned to the blocking on the table and then to the optical axis with some minor tweaking of the actuators on the first mirror on the table. The laser was aligned through the whole table. At the mask we aligned by maximizing transmitted power, then using the FLIR camera on remote desktop (yes this works now - thanks Dave Barker) we tweaked the alignment to make the beam symmetrical after the mask. We then aligned to the irises at the output of the table which define the optical axis into the vacuum system. We changed the alignment onto the power meter that gives the power output to the CP because the head was too close to a focus. We checked the calibration of the power output to the CP and this was confirmed accurate. Finally we aligned to the two photodiodes on the table. Inloop was not giving an output but we swapped cables with outofloop and were able to get a signal to align to.
The problems with the in-loop photodiode were traced to being a bad ADC board which has now been swapped for the spare (thanks Ben & Jason for tracking this down).
The Y-table will have the output to the vacuum system unblocked so the system is ready to go. The laser will be left keyed off, with the rotation stage set to minimum power. When the system is needed it just needs keyed on at the rack in the LVEA, and then power increased at the rotation stage.
I turned on the TCS Y laser and restored the TCS settings to their ER9 values (0.5 W for X, 0.3 W for Y).
The TCS Y rotation stage needs to be recalibrated.
Terra, Sheila
Tonight we had trouble engaging the ASC again.
Losing optical gain in POP X
We rang up what we think is a PR3 bounce mode when engaging the ASC the same way as last night. We found that we could avoid ringing this mode up by keeping the PRC2 gain low (digital gains of -500). Right before the OMC damage/vent, the POP X path was reworked and the optical gain seemed suspiciously low.
Tonight we found that the optical gain has decreased even more. Terra changed the demod phase by dithering PR3 pit (500 counts to M3) and rotated the phase positive 65 degrees, (Q1, Q2, Q3, Q4 from 55, 53, 54, 51 to 120, 118, 119, 116 ) to maximize the signal in I (minimize the Q signal). The 2 attached figures show Terra's before and after OLG measurements (excitation gain of 50), both with Jenne's gain of -5000, showing a 10dB increase in optical gain which is about what we expected based on the dither amplitude change.
After optimizing the phase, we did not see the 28 Hz mode get rung up, but this seems to come and go because we also didn't see it yesterday. We quickly tried moving L2 on the POP X path, while watching the amplitude of the PR3 dither line in the POP X signal. We moved the lens about 4 inches closer to POP X and about 3 inches further away, and didn't find any location that had more signal for PR3 so we replaced it as we found it.
We are going to leave the IFO locked in DC readout 2 Watts with the request set to down so that it will not try to relock. The noise is bad as expected.
POPX whitening gain is 0dB but should be odd, see alog 26307. FRS 6057 filed.
The whitening gain on POP X was changed from a gain step of 7 (21 dB) to 0 (0dB) on August 12th. This whitening chassis has a problem and we must use odd gain settings, or else it will return an error and not set the gains equally on all quadratns, as Keita and Hang noted 26307
The change in gain probably happened during a beckhoff restart for the shutter code, but we could have been saved from this problem by SDF. I cannot find a record for these whitening chassis in any SDF table.
Also, this does not explain the drop in gain that Jenne saw, which happened before the whitening settings changed.
The stuck whitening gain bit is the LSB of the Q3 channel. In the past this was typically an indication of a cable problem (short).
Sheila Daniel Terra
Connected the AM laser to the POP X head, and saw that we have very similar response in the electronics to what Evan measured in 27069
we had 3.3 mW out of the AM laser with a whitening gain of 21 dB, used -40 dBm of RF drive at 45.501150 MHz. We saw about 600 counts on each quadrant (except quadrant 3 which had 350 counts and also the least amount of DC light because of way the laser was mis centered on the diode).
We saw that there are rather large offsets when we changed the whitening gain, so Daniel reset the offsets. The large offsets might have contributed to problems last night, along with confusion about the whitening gain.
Also, we remembered that a factor of 6.7 of the mystery gain loss was due to adding a beamsplitter and forgetting to comensate for it on July 11.
(Edit: Actually, Haocun and I did remember to correct for this gain change, we just compensated for it in the digital loop gain. )
So to summarize:
loops were intially commisioned with a whitening gain of 21, a digital gain of -21, a 1 Hz ugf, and electronics gain similar to what we have now. (late may)
Edit: loops were originally commisioned with a filter gain of -200 for pit, -0.1 in the input matrix, an analog gain of 21 dB, and the WFS head electronics performing in a way simlar to what we have now. This is when the reference that I think Jenne used was saved, and within a few days the pit input matrix was reduced by a factor of 2.
Edit: Around June 16th, we had difficulty staying locked when these loops were engaged, which was noted in the alog. Terra and I just looked at trends of the filter gains, and it seems like we also reduced the digital gain from -220 to -3.4 although this was not noted in the alog. This, together with the input matrix change explains most of the missing gain that Jenne found.
On July 11th I forgot to compensate for the beamsplitter causing a gain reduction of 6.7 that no one noticed.
On July 26th, Evan and Keita relocated POP X and Jenne noticed that the digital gain had to be increased by a factor of 250 (or 500 for yaw) to keep the ugf the same.
August 12th the whitening gain was reduced to 0 dB from 21 dB by mistake in a beckhoff reboot.
August 16th Terra and I noticed this further reduction in gain, which is explained by the whitening gain. We also changed the demod phase which increased the gain by about 10 dB. We checked that small movements of the L2 don't change the optical gain much, and moving it by a few inches can decrease the signal.
So, we are missing about a factor of 40 gain, which we cannot explain with electronics.
In the end only a factor of 2 of Jenne's gain change in unexplained. It seems that we have had stable high power locks with both the high gain and low gain settings for PRC2, so we can decide which we want to use. We also should have a factor of 3 increase in gain because of the phasing Terra and I did.
More complicated than that.
Whitening (dB) |
POPX digital gain before rotation |
Input matrix | PRC2_P_GAIN |
BS |
Overall gain relative to original |
alog | |
Originally | 33 | 1 | -1 | -220 | none | NA | |
May 24 ~1:02 | 33 | 1 | -0.05 | -220 | none | 0.5 | |
Jun. 17 | 33 | 1 | -0.05 | -3 | none | 6.8E-3 | |
Jun. 22 ~noon | 21 |
2.8 |
-0.05 | -3 | none | 4.8E-3 | 27901 |
Jul. 11-12 | 21 | 2.8 | -0.05 | -21 | inserted | 5.0E-3 | 28324 |
Jul. 27 ~4:20 | 21 | 2.8 | -0.05 | -5000 | inserted | 1.2 | 28666 |
No mystery optical/electronic gain reduction any more. Maybe a factor of 1.2 came from the rework on the table.
It's not clear to me why the PRC2 filter gain was reduced by a huge amount on Jun. 17 but I haven't searched through alog.
Typo in the above table, originally the input matrix was -0.1, not -1.
HEPI BS Tripped few minutes before ITMX ISI. This is the only HEPI that tripped in the neighborhood of the large quake.
ITMY ISI tripped--timing (H1:ISI-ITMY_ST2_WD_MON_GPS_TIME) indicates stage2 tripped on ACTuators 1 second before Stage1 on T240s but looking at the plots, the Actuators have only registered a few counts, nothing near saturation/trip level. But the T240s hit their rail almost instantly. It seems the Stage2 Last Trip (H1:ISI-ITMY_ST2_WD_MON_FIRSTTRIG_LATCH) should be indicating ST1WD rather than Actuator. On ETMY, the Trip Time is the same for the two stages and Stage2 notes it is an actuator trip but again, there are only a few counts on the MASTER DRIVE; seems this too should have been a ST1WD trip[ indication trip on Stage2--I'll look into the logic.
On the BS ISI, the Stage1 and Stage2 trip times are the same, and the Last Trip for Stage2 indicates ST1WD. The Stage2 sensors are very rung up after the trip time but not before unlike the T240s which are ramping to to the rail a few seconds before trip. ETMX shows this same logical pattern in the trip sequence indicators.
On the ITMX ISI, Stage1 Tripped 20 minutes before the last Stage2 trip. This indicates the Stage1 did not trip at the last Stage2 trip.
No HAM ISI Tripped on this EQ.
Bottom line: the logical output of the WDs are not consistent from this common model code--needs investigating. Maybe I should open an FRS...
Attachment 1) Trip plots showing Stage2 trip time 1 second before the stage1 trip where the stage2 actuators do not go anywhere near saturation levels.
Attachment 2) Dataviewer plot showing the EQ on the CS ground STS and the platform trip times indicated.
It seems this is not a problem with the watchdog but a problem with the plotting script. It seems for ST2 Actuators, it misses a multiplier on the Y axis. It works correctly for ST1 Actuators and all the sensors; it does not work for other chambers as well for ST2 ACT. FRS 6072.
Actually, the plotting script is working fine. When the spike is so large that the plotting decides to switch to exponential notation, the exponent is hidden by the title until you blow up the plot to very large size.
I removed the 300 Hz and 600 Hz stopband filters in DARM, along with the 950 Hz low-pass filter.
I increased the gain from 840 ct/ct to 1400 ct/ct, giving a UGF of 55 Hz. This seems to have improved the gain peaking situation around 10 Hz (see attachment).
The new settings have been added to the guardian (in the EY transition state), but have not been tested. The calibration has not been updated.
Tagging CAL Group. Evan Goetz has also been working on a better PUM roll-off. He'll be installing those improvements soon as well, and a full loop design comparison.
Since we spend a nontrivial amount of time commissioning at high powers (>20 W) with DARM controlled by EX, I moved the DARM gain increase so that it comes on once the PSL power reaches 20 W.
This is a quick summary of today's TCS joy. I ran another differential lensing test today. I went to the other side of the differential lensing (CO2X goes higher power).
The highest cavity pole was 352 Hz in this test.
This time, I also took many measurements of the intensity and frequency noise couplings periodically throughout the test using Evan's automated measurement script (20470). I will analyze and post them later. The second attachment is trend of some relevant channels.
This is a report on the intensity noise coupling measurement to DARM during the same TCS testing period.
The below is an animated plot showing how the intensity noise coupling evolved as a function of time during the test. The transfer function was measured from ISS-SECONDLOOP_SUM14_REL to CAL-DELTAL_EXTERNAL. DELTAL_EXTERNAL is unwhitened.
As shown in the above animated plot, the intensity noise increased at the beginning and then went back down to where it was. The overall spectral shape almost did not change, but the scaling factor has changed roughly by a factor of two comparing the minimum and maximum. The magnitude of the coupling rises in proportion to frequency -- if I plotted them for a coupling to DCPDs, they would be almost flat due to the cavity pole correction taken out.
Here is another plot showing the evolution of coupling as a function of time.
The upper plot shows the transfer coefficient at 2500 Hz (in arbitrary unit) as a function of time. The bottom plot shows the CO2 lensing from the same period. The transfer coefficient shows a clear correlation with the defocus of ITMs. I can not say for sure if the differential was a dominant cause of this effect because I had a few uD defocus as well in the same fashion.
Here is the same analysis for the frequency noise coupling to DARM. The variation in the coupling is more drastic than that of intensity noise.
The below is a same type of animated plot. The transfer function was measured from REFLA_RF9_I_ERR to CAL-DELTAL_EXTERNAL. Note that DELTAL_EXTERNAL is properly unwhitend.
It seems that the coupling has two different mechanisms, one for the coupling below 300 Hz and the other for the above. As the CO2 setting changed, the high frequency part increased at the beginning and decreased later while keeping the same spectral shape. On the other hand the low frequency part varied in an opposite fashion; it decreased as the high frequency part increased. The slope of the high frequency coupling seems to be almost proportional to f. If we convert it into [OMC DCPDs [A] / laser frequency [Hz]], it will be more like 1/f due to the cavity pole and REFL's transfer functinon against the laser frequency.
Here is another plot showing the evolution of the transfer coefficient at 2500 Hz. The coupling coefficient changed by a factor of 15 at this frequency. This is much more drastic than that of the intensity noise coupling which varied by a factor of two or so.
A preliminary conclusion:
With the 2 W PSL, the DARM cavity pole prefers a high CO2 differential lensing while the laser noise couplings prefer a low differential lensing.
This is a belated analysis on the intensity noise coupling. The punch lines are:
[Noise coupling v.s. differential lensing]
As seen in the plot above, the coupling coefficient shows a linear relation to the differentianl lensing. This likely indicates that the differential lensing is not optimized to minimize the intensity noise coupling. I should note that this measurement had used the badly clipped COY beam (27433) which was later fixed in May 2016; a smaller differential lensing means less power in CO2Y than CO2X.
[Intensity noise coupling]
Here is a plot showing the intensity noise coupling of the various TCS settings. This time the coupling coefficient is converted to OMC power [W] / input RIN. The dashed line in the magnitude represents the expected value calculated by
(coupling) = 2 * J1^2 * Pin * Tomc * Tifo [W/RIN] = 5.5e-6 [W/RIN],
where Pin = 2 W is the PSL input power, Tomc = 61.4 ppm is the OMC transmission for the 45 MHz RF sidebands, and Tifo is the transmission of the intereferometer for the 45 MHz RF sidebands which I have assumed to be 1 for quick calculation. As seen in the plot, the expected noise level (limited by the 45 MHz RF sidebands) is lower then the measurement by roughly a factor of 10. These two plots support the hypothesis that we are far from the optimum point.
Here are the beamsplitter angles as a function of differential lensing. (There are some data dropouts in the trends).
This seems to indicate that a differential lens change of a few tens of microdiopters causes the beamsplitter yaw to change by a few hundreds of nanoradians, presumably via changes in the 36 MHz angular plant. In pitch it is less clear whether we are seeing angular control effects or simply drift over time.