OSEM damping gains were adjusted by observing real time dataviewer to get Q of 5
OSEMs were kicked up one by one with 200 counts ~1sec. The error signal was optimized to get 1/2 of exitation amplitude at the 5th sinusoid wave.
C1: SUS-ITMX_SUSPOS_N1 gain 111 -> 65, PIT 7.2 -> 8, YAW 12 -> 6, SIDE 280
ITMY 277 -> 120, 19.2 -> 7, 24 -> 19, 420 -> 470
ETMY 10 -> 32, 20 -> 3, 20 -> 10, 50
ETMX 22 -> 25, 3, 3, -170
ETMX having problems: 1, YAW can not be excited
2, SIDE has no error signal in dataviewer. Sensing voltage on MEDM screen 0.142V
In preparation for tomorrow's drag wiping and door closing, I have clamped ITMX, ITMY, and ETMX with their earthquake stops and moved the suspension cages to the door-edge of their respective tables. They will remain clamped through drag wiping.
ETMY was left free-swinging, so we will clamp and move it directly prior to drag wiping tomorrow morning.
I have at taken photos and added arrows which signify the beam paths for ITMX, ITMY, and Vertex Oplev tables.
After the X and Y arm naming conventions were changed, the labelling of the electronics in the eurocrates was not changed 😞 😔 😢 . This meant that when we hooked up the new Acromag crate, all the slow ITMX channels were in fact connected to the physical ITMY optic. I ♦️fixed♦️ the labelling now - Attachments #1 and #2 show the coil driver boards and SUS PD whitening boards correctly labelled. Our electronics racks are in desperate need of new photographs.
The "Y" arm runs in the EW direction, while the "X" arm runs in the NW direction as of April 29 2018.
ITMX was freed. ITMY is being worked on is also free..
We locked Xarm/Yarm and manually alignmed ITMX/ITMY/BS/ETMX/ETMY/PZT1/PZT2.
ITMY OPLEV was largely misaligned ==> The beam was centered on the QPD.
Then we aligned PRM using SB locking PRMI.
We noticed that OPLEV servo does not work. It made the PRM just noiser.
We went into the PRM table and found that the OPLEV beam was clipped in the vacuum chamber.
We tried to maximize the reflected beam from the window by touching the steering mirrors at the injection side.
Then the reflected beam was introduced to the center of the QPD.
After the alignment, the OPLEV QPD SUM increased to 4000ish from 200ish.
According to the OPLEV trend data, this is a nominal value of the QPD SUM.
Now the OPLEV servo does not go crazy.
BS OPLEV beam was centered on the QPD.
We restored the good state of the ITMY camera and neatened both the MC2 and ITMY camera.
The MC2 camera was driving a triple T jungle into some random cables and spoiling the image. We removed all T's and the MC2 camera now drives only The Matrix.
The ITMY camera was completely unmounted and T'd. So it was misaligned just by the force of gravity acting on its BNC cable. We swapped the lens for a reasonable sized one and remounted it in its can. We then used orange cable ties to secure the power and BNC cable for the MC2 and ITMY cameras so that tugging on the cables doesn't misalign the cameras. This is part of the camera's SOP.
No more driving 50 Ohm cables and T's with video cables, Steve! If you need a portable video, just use a spigot of the Matrix and then you can control it with a web browser.
I also wiped out the D40's memory card after uploading all of the semi-useful files to the Picasa page.
Koji requested current state of BHD 3D model. I pushed this to Box after adding the additional SOSs and creating an EASM representation (also posted, Attachment 1). I also post the PDF used to dimension this model (Attachment 2). This process raised some points that I'll jot down here:
1) Because the 40m CAD files are not 100% confirmed to be clean of any student license efforts, we cannot post these files to the PDM Vault or transmit them this way. When working on BHD layout efforts, these assemblies which integrate new design work therefore must be checked for most current revisions of vault-managed files - this Frankenstein approach is not ideal but can be managed for this effort.
2) Because the current files reflect the 40m as built state (as far as I can tell), I shared the files in a zip directory without increasing the revisions. It is unclear whether revision control is adequate to separate [current 40m state as reflected in CAD] from [planned 40m state after BHD upgrade]. Typically a CAD user would trust that we could find the version N assembly referenced in the drawing from year Y, so we wouldn't hesitate to create future design work in a version N+1 assembly file pending a current drawing. However, this form of revision control is not implemented. Perhaps we want to use configurations to separate design states (in other words, create a parallel model of every changed component, without creating paralle files - these configurations can be selected internal to the assembly without a need to replace files)? Or more simply (and perhaps more tenuously), we could snapshot the Box revisions and create a DCC page which notes the point of departure for BHD efforts?
Anyway, the cold hard facts:
- Box location: 40m/40m_cad_models/Solidworks_40m (LINK)
- Filenames: 3002.zip and 3002 20211001 ITMY BHD for Koji presentation images.easm (healthy disregard for concerns about spaces in filenames)
Kiwamu and Koji
Some tools and the level gauge were removed from the table.
BAD news: I could clearly see scatter of the green beam path because of the dusts in the arm tube. Also many dusts are seen on the ITM surface.
Picture of the ETM - reflection from the ITM is hitting the mirror and the suspension structures.
1. Shoot the ITM center with the green beam.
- Two persons with walkie-talkies required for this work.
- Turn on the end green pointer. We could see the long trace of the beam sliced by the beam tube wall.
- Look at the tube peeping mirror for the CCD.
- Adjust yaw such that the beam trace on the tube wall is parallel to the arm.
- Adjust pitch such that the beam trace on the tube gets longer. This means that spot gets closer to the ITM.
- Continue pitch adjustment until some scatter appears on the ITM tower.
- Once the spot appears on the tower, you can easily adjust it on the mirror
2. Adjust pitch/yaw bias such that the reflection hits the ETM.
- Initially the ITM alignment is totally bad. ==> You clealy see the spot on the wall somewhere close to the ITM.
- Adjust pitch/yaw bias such that the spot goes farther as far as possible.
- Once you hit the suspension tower, the scatter is obviously seen from the peeping mirror.
- You can match the incident beam and the scattering of the reflection. You also can see the reflection from the ETM towards the ITM as the spot size gets huge (1/2 tube diameter).
- We found that the bias is ~-2 for pitch and ~-6 for yaw.
3. Go into the chamber. Check the table leveling.
- Open the light door.
- I found that the table is not leveled. Probably it drifted after the move of the weight (i.e. MOS removal).
- Removed one of the round-shaped weight. Moved the other weights such that the table was leveled.
4. Remove the bias for yaw and rotate suspension tower such that the reflection hit the center of the ETM.
- Removed the yaw bias. This makes the reflected spot totally off from the ETM.
- Rotate suspension tower so that the beam can approximately hit the ETM.
- Look at the peeping mirror, the beam is aligned to the ETM.
5. Adjust OSEMs
- Push/pull the OSEMs such that we have the OSEM outputs at the half of the full scale.
6. Adjust alignment by the bias again.
- Moving OSEMs changes the alignment. The pitch/yaw biases were adjusted to have the beam hitting on the ETM.
- Bias values at the end of the work: Pitch -0.8159 / Yaw -1.2600
7. Close up the chamber
- Remove the tools and the level gauge.
- Close the light door.
[Steve and Koji]
The invac OPLEV mirrros were aligned before we get to the PMA party.
The OPLEV mirrors were adjusted in accordance with the optical layout.
Surprisingly the optical layout was enough precise such that we have the healthy red beams on the optical tables.
Steve placed the apertures at the position of the returning spots while I shook the stack to check if the range of the spot motion is sufficient.
The sole thing that has been deviated from the optical layout was that the SRM returning beam had to be reroute
as the SRM has better reflectivity on the AR surface in stead of the HR one.
The sole thing that has been deviated from the optical layout was that the SRM returning beam had to be reroute
as the SRM has better reflectivity on the AR surface in stead of the HR one.
I suppose that if we were really clever we would intentionally choose either the AR or HR surface so as to minimize the effect of the thermal lensing and/or thermal expansion from the locked interferometer absorption.
Oplev HeNe was replaced this afternoon. We did some HeNe shuffling:
Attachment #1 shows the RIN and Attachment #2 and #3 show the PIT and YAW TFs with the new HeNe.
The ITMX Oplev path is still not great - the ingoing beam is within 2mm of clipping on a 2" lens used in the POX path, and there is a bunch of scattered red light everywhere. We should take the opportunity when the chamber is open to try and have a better layout (it may be tricky to optize without touching the two in-vacuum steering optics).
I'll ask Chub to replace it this afternoon.
ITMX OSEMs were adjusted so as to have the right DC numbers and the more uniform response to POS excitation.
It is waiting for the free-swinging test.
- ITMX was moved from its position to the north side of the table.
- The table was rebalanced.
- We found that the output of the LR OSEM has an excess noise compared with the other OSEMs.
We tried to swap the LR and SD OSEMs, but the SD OSEM (placed at the LR magnet) showed
the same excess noise at around 10-50Hz.
- We found that one of the EQ stops was touching the mirror. By removing this friction, all of the OSEMs
come to show similar power spectra. Good!
- Then we started to use LOCKIN technique to measure the sensitivity of the OSEMs to the POS excitation.
Originally the response of the OSEMs was as follows
UL 3.4 UR 4.3
LL 0 LR 2.5
After the adjustment of the DC values, final values became as follows
UL 3.9 UR 4.4
LL 3.9 LR 3.2
- We decided to close the light door.
For my work designing a cost function, so that I can try out new feedback servo designs on the oplevs, I wanted to know what the dark noise of an oplev is. Since the pitch and yaw channels are divided by the sum channel, when the laser is off, the noise in the pitch and yaw channels looks much higher than it really is. So, I collected some data from the 4 individual quadrants of the ITMY oplev, when the laser was on (but damping was off), and when the laser was off. I used the values of the oplev input matrix to re-create the non-normalized pitch and yaw signals. What I see is that we have some kind of real signal below 1 kHz, but we're hitting the noise at around 1 kHz. So, we definitely don't want to use oplev error signal information above 1 kHz when designing new servos.
The last word in the title is "off". OSEM damping was on, but the oplev damping was off. These are uncalibrated, because the calibrations that we have to go from counts to microradians are for the normalized signals.
I tried again at plotting the ITMY_QPD noise spectra in for dark and bright operation. Before we had the strange situation where the dark noise seemed higher, but Kiwamu noticed this was caused by dividing by the SUM before the testpoint I was looking at. This time I tried just multiplying by the measured SUM for bright and dark to normalise the spectra against each other. The results looks more reasonable now, the dark noise is lower than the bright noise for a start! However, the dark noise spectrum now doesn't look the same as the one I showed in my previous post.
I took a dark noise measurement for the ITMY QPD, for comparison with measurements of the oplev noise later on. Initially I was plotting the data from test points after multiplication by the oplev matrix (i.e. the OLPIT_IN1 / OLYAW_IN1), but found that the dark noise level seemed higher than the bright noise level (!?). Kiwamu realised that this is because at that test point the data is already divided by QPD SUM, thus making the dark noise level appear to be greater than the bright level, since QPD SUM is much smaller for the dark measurements. The way around this was to record the direct signals from each quadrant before the division. I took a power spectrum of the dark noise from each quadrant, then added them in quadrature, then divided by QPD SUM at the end to get an uncalibrated PSD. Next I will convert these into the equivalent for pitch and yaw noise spectra. To calibrate the plots in radians per root Hz requires some specific knowledge of the oplev path, so I won't do this until I have adjusted the path.
ITMY oplev was nearly clipping in yaw, causing wonky behavior (POY lock popping in and out frequently). I recentered it and the arm is locking fine now.
We installed ITMYOL1 and ITMYOL2 on the ITMY chamber. We aligned the ITMY OpLev beam and closed the loop successfully, we then had a second round of YARM aligment, where we brought the Y peak transmission up from 0.04 counts to 0.09 counts (up by a factor of two). We still couldn't close the YARM loop but we have a better alignment.
I've calculated a suitable collimating telescope for the ITMY/SRM oplev laser, based on the specs for the soon-to-arrive 2mW laser (model 1122/P) available here: http://www.jdsu.com/ProductLiterature/hnlh1100_ds_cl_ae.pdf
Based on the fact that the 'beam size' value and 'divergence angle' value quoted don't match up, I am assuming that the beam radius value of 315um is _not_ the waist size value, but rather the beam size at the output coupler. From the divergence angle I calculated a 155um waist, (zR = 12cm). This gives the quoted beam size of about 316um at a distance of 8.5" away from the waist. This makes me think that the output coupler is curved and the waist is at the back of the laser, or at least 8.5" from the output coupler.
The collimating telescope gives a waist of size 1142um (zR=6.47m) at a distance of 1.427m away from the original laser waist, using the following lens combo:
L1 f=-0.15 @ 0.301m
L2 f=0.3 @ 0.409m
This should be fine to get a small enough spot size (1-2mm) on the QPDs.
Looking at Steve's plot, I was reminded of the ITMY UL OSEM issue. The numbers don't make sense to me though - 300um of DC shift in UL with negligible shifts in the other coils should have made a much bigger DC shift in the Oplev spot position.
We had a redo of elog entry 975 tonight. The noisy OSEM was fixed by jiggling the rack end of the long cable. Don't know exactly where--I also poked around the OSEM PD interface board.
In the attached PDF the reference trace is the noisy one.
I've noticed that the glitchy behaviour in ITMY UL shadow sensor readback is back - as mentioned above, I looked at the Sat. Box and could not find anything wrong with it, perhaps I'll plug the tester box in over the Thanksgiving weekend and see if the glitches persist...
I left the tester box plugged in from Thursday night to Sunday afternoon, and in this period, the glitches still appeared in (and only in) the UL channel.
So yesterday evening, I pulled the Sat. Box. out and checked the DC voltages at various points in the circuit using a DMM, including the output of the high current buffer that supplies the drive current to the shadow sensor LEDs. When we had similar behaviour in the PRM box, this kind of analysis immediately identified the faulty component as the high current buffer IC (LM6321M) in the bad channel, but everything seems in order for the ITMY box.
I then checked the Satellite Amplifier Termination Board, which basically just adds 100ohm series resistors to the output of the PD readout, and all the resistors seem fine, the piece of insulating material affixed to the bottom of this board is also intact. I then used the SR785 in AC coupled mode to look at the high frequency spectrum at the same points I checked the DC voltages with the DMM (namely the drive voltage to the LEDs, and the PD readout voltages on the PCB as well as on the pins of the connector on the outside of the box after the termination board (leading to the DAQ), and nothing sticks out here in the UL channel either. Of course it could be that the glitches are intermittent, and during my tests they just weren't there...
I am hesitant to start pulling out ICs and replacing them without any obvious signs of failure from them, but I am out of debugging ideas...
One possibility is that the problem lies upstream of the Sat. Box - perhaps the UL channel in the Suspension PD Whitening and Interface Board is faulty. To test, I have now hooked up ITMY Sat. Box. + tester box to the signal chain of ETMY. If I can get the other tester box back from Ben, I will plug in the ETMY sat. box. + tester to the ITMY signal chain. This should tell us something...
400 days plot. Satelite amp ITMY has been swapped with ETMY
Unlabeled sat.amps are labeled. This plot only makes sense if you know the Cuh-Razy sat amp locations.
We fixed the issue of ITMY ULCOIL not driving ITMY by replacing one of the 64pin ribbon cable in the satellite amplifier box.
We thought the coil driver and the sat amp box are OK by checking the voltage change at the output of the sat amp box by giving an offset to UL coil driver, but it was not giving a current change, probably due to too much contact resistance in the cables.
It was sneaky because it was not completely disconnected.
All the coils for our suspensions are now working!
What we did:
- Using breakout boards, the output current of sat amp box was measured using FLUKE multimeter. It turned out that UL is not giving measurable current. We also confirmed that UR coil driver can drive UL by re-directing the current from UR coil driver to UL. This means that the UL magnet was not de-magnetized!
- Measured the coil resistance from at the coil driver output and found that UL coil seen from there has too high resistance which cannot be measured with the multimeter, whereas UR coil was measured to be ~30 Ohms.
- Went back to the feedthru and measured the resistance of UL coil. Upto the output of the Satellite Amp Terimator, the resistance was measured to be ~16 Ohms, but not at the input of the Satellite Amp Terimator (Attachment #1,2).
- It turned out that #16 pin of 64pin ribbon cable in between the Satellite Amp Terimator (LIGO-D990021) and the Satellite Amp board (LIGO-D961289) at the Satellite Amp Terimator side was not good (Attachment #3).
- Replaced the cable and confirmed that ULCOIL can kick ITMY (Attachment #4).
- C1:SUS-ITMY_TO_COIL matrix was reverted to default values.
- We might have to re-commission Yarm ASS again since pitch-yaw coupling have changed. -> EDIT: Checked that it works (except for ITM PIT L), including offloading offsets (writeASS_offsets.py), 18:30 local.
- Now that LO1 LLCOIL issue is solved and LO2 stuck is solved, we should do the free swing test again to identify the resonant frequencies.
- OSEM sensor diagonalization (input matrix), coil balancing (and F2A)
We investigated the ITMY ULCOIL issue (40m/16873).
ULSEN is sensing the optic motion but ULCOIL cannot move the optic.
We confirmed that the coil input is there upto satellite amplifier output.
We also checked that ULCOIL have 3.3 mH and 16 Ohms, which are consistent with other coils.
We need to investigate ITMY ULCOIL in the next vent.
What we did:
- Checked again that C1:SUS-ITMY_ULCOIL_OFFSET does not kick ITMY using OSEM sensor signals and oplev signals. ULSEN moves when ITMY is kicked by other coils.
- Checked that kick gives voltage changes at coil driver and satellite amplifier output. We unplugged J1 DB25 cable from the feedthru flange and checked the signals sent to coil with oscilloscope.
- Measured inductance (using BK PRECISION LCR meter) and resistance (using Fluke) of coils for ITMY. Below is the result. UL coil seems to be consistent with other coils. (It seems like BK PRECISION one wil give wrong resistance if the dial is set to the resistance value which is too low compared with the one you want to measure. If you want to measure 16Ω, set the dial to larger than 20Ω, not 2Ω)
Feedthru connector: ITMY1
Pin 3-15 / R = 16.3Ω / L = 3.32 mH (UL)
Pin 7-19 / R = 16.4Ω / L = 3.30 mH (UR)
Pin11-23 / R = 16.2Ω / L = 3.31 mH (LL)
Feedthru connector: ITMY2
Pin 3-15 / N/A
Pin 7-19 / R = 16.3Ω / L = 3.30 mH (SD)
Pin11-23 / R = 16.4Ω / L = 3.33 mH (LR)
- UL is the only short OSEM in ITMY OSEMs.
- ITMY have dumbells for magnets.
- If UL magnet is off, ULSEN would not work. Something not magnetic is working for shadow sensing for UL? Dumbells?
- ULSEN just sensing some coupling from other OSEMs?
To see if the ULCOIL channel of the ITMY coil driver is working or not, I swapped ITMY coil driver and ITMX coil driver by swapping DB15 cable (see Attachment #2).
With this swap, I confirmed that ITMX can be kicked with C1:SUS-ITMY_ULCOIL_OFFSET, but ITMY cannot be kicked with C1:SUS-ITMX_ULCOIL_OFFSET (see Attachment #1).
This means that the issue is not the in-air electronics.
Mystery remains again...
We need to investigate ITMY ULCOIL in the next vent.
I revereted the swap and confirmed that damping loops work fine again.
what was the result of the inductance measurement? should be ~3.3 mH as measured from the flannge or cable that goes to the flange from sat amp.
ITMY ULCOIL was measured to have ~3.3 mH as measured from the flange. RTFE 40m/16896 .
Its good that the inductance test passed. This means that the coil is OK. How does the inspection photo look? This is the one you guys took of the ITM OSEM that shows the position of the magnet w.r.t. the coil. Also, how does the free swinging spectra look? Either one of these might indicate a broken magnet, or a sticky EQ stop.
We checked the photos we have, but we didn't have the photos which show ULCOIL situation clearly.
Free swing of ITMY (and others) will be done this weekend to see the OSEM spectra and resonant frequencies.
For good measure:
While doing initial measurements for the new global damping infrastructure I discovered that the ETMY loop between the OSEM actuation and the OSEM sensors has a gain that is 2.5 times greater than the ITMY. The result is that to get the same damping on both, the damping gain on the ETMY must be 2.5 times less than the ITMY. I do not know where this is coming from, but I could not find any obvious differences between the MEDM matrices and gains.
I uploaded a screenshot of measured transfer functions of the damped ITMY and ETMY sus's. Notice that the ETMY measurement is 2.5 times higher than the ITMY. The peak also has a lower Q, despite having the same damping filters running because of this mysterious gain difference. Lowering the damping gain of the ETMY loop by this 2.5 factor results in similar Q's.
Just to find out where we are currently, I plotted the ITMY and SRM oplev spectra along with the ETMY oplev spectra. ETMY seems to be very good, so comparing with this seemed useful, so we know how much we have to improve by. The SRM power spectrum appears to be around 2 orders of magnitude higher than ETMY over pretty much the whole measurement band. The ITMY power spectrum is not so bad as the SRM above about 60Hz. Next thing to do is to check the dark noise level for the ITMY and SRM QPDs.
The title of this post should of course have been " ... - comparison with ETMY" not " ... - comparison with ITMY"
Today I worked on getting the ITMY and SRM oplevs back in working order. I aligned the SRM path back onto the QPD. I put excitations on the ITMY and SRM in pitch and yaw and observed the beam at the QPDs to check for clipping. They looked clean from clipping.
I divided the open loop transfer functions by the filter response and the sensor responses (previously measured calibration factors) to leave just the actuator responses. I've attached the actuator responses plotted in radians/count and phase over frequency.
Next step: fit the actuator response with poles and zeros.
EDIT: I divided by the wrong filter function earlier - the plots there now are divided by the correct filter function
Here are the results of the complex fitting. The residuals are bigger this time, but still probably small enough to be ok(?), with the possible exception of ITMY PITCH (due again I think to the data points straddling the resonance).
ITMY YAW actuator response complex fit
-- Fit completed after 282 iterations--
I used an fminsearch function to fit the SRM and ITMY actuator response magnitudes. The testfunction was just that for a single second order pole, but it gave what I consider to be good fits for the following reasons:
*for 3 of the 4 fits the residuals were less than 0.5% of the summed input data points. The worst one (ITMY pitch) was about 2.7%, which I think is due to the resonance happening to be right in the middle of two data points.
*the tolerance of 1 part in 10^9 was reached quickly from not very finely tuned starting points.
The test function was: G=abs(Gp./(1+1i.*f./fp./Qp-(f./fp).^2)), where G(f) is the actuator response magnitude, Gp is the pole gain, fp is the pole frequency, and Qp is the pole Q factor.
In the end I just fitted the response magnitude. I was initially fitting the complex response function, but ran into problems which I think were cased by overall phase offsets between the data and test function. Can I canvass for opinion if fitting the magnitude is OK, or should I try again fitting the phase too?
Anyway, here are the results of the fits, and I've attached plots of each too (each one in linear and log y axis because each on its own might be misleading for fits):
EDIT - I added more points to the otherwise sparse looking fitted curves
ITMY PITCH actuator response fit
-- Fit completed after 190 iterations--
Started with: Gain = 3e-06,
Q factor = 5,
Pole frequency = 1,
Fit results: Gain = 1.32047e-06,
Q factor = 4.34542,
Pole frequency = 0.676676
Residual (normalised against the sum of input datapoints) = 0.0268321
ITMY YAW actuator response fit
-- Fit completed after 156 iterations--
Fit results: Gain = 1.14456e-06,
Q factor = 8.49875,
Pole frequency = 0.730028
Residual (normalised against the sum of input datapoints) = 0.00468077
SRM PITCH actuator response fit
-- Fit completed after 192 iterations--
Fit results: Gain = 7.94675e-06,
Q factor = 7.16458,
Pole frequency = 0.57313
Residual (normalised against the sum of input datapoints) = 0.00301265
SRM YAW actuator response fit
-- Fit completed after 156 iterations--
Fit results: Gain = 3.34179e-06,
Q factor = 9.57601,
Pole frequency = 0.855322
Residual (normalised against the sum of input datapoints) = 0.000840468
Here are the open loop transfer functions for ITMY and SRM. The various settings for the OLTFs were as follows:
Oplev filter used for all OLTFs: 300^2:0
Gains for oplev servos (for each OLTF only the 1 servo for the measured TF was on. They are all set back to 0 now):
SRM yaw gain = 1
SRM pitch gain = -1
ITMY yaw gain = -1
ITMY pitch gain = 1
measurement band = 0.2Hz to 200Hz
points = 33
swept sine magnitude envelope: amp = 2 for f > 60Hz, amp = 0.1 for f < 60Hz
Measurement points were from e.g. C1-SUS-ITMY-OLPIT-IN2 to C1-SUS-ITMY-OLPIT-IN1 to give a TF of -(loop gain).
Next step is to divide this through by the sensor reponse (i.e. the calibration factor measured earlier) and the filter response to get just the actuator response.
I replaced the lenses that were there with a -150mm lens followed by a +250mm lens. This gave a significantly reduced beam size at the QPDs. With the beam analyzer up and running it should be possible to optimize this later this afternoon. Next I will remove the SRM QPD from the path and make measurements of the beam spot position movement and corresponding OSEM values for different DC mirror offsets. I will then repeat the process for ITMY.
The measured calibration factors for the oplevs are as follows:
Kiwamu noticed that the 1/L in the counts per radian should have just been L, which accounts for most of the discrepancy. We checked the input filters on the OSEMs, and they have 10dB of gain at DC. Accounting for this, estimates on the order of 20urad/count, which is much more reasonable!
I found that some of the Optical Lever Servos were ON today and injecting nonsense into the interferometer optics. I have set all of the gains = 0 to save us more headaches.
I had previously set the gains to zero, see the first line of my entry on Monday 5468. I should have the servo and noise characterisation done today for these oplevs today, so we can review it soon.
ITMY gets new Tamron M118FM50 that has improved close focusing. It is a small fixed focal length camera so the video tube cover can be put on.
The Watec LCL-902K 1/2" ccd camera was losing it power supply voltage because of bad connection. It was replaced.
We did the following things in the ITMY chamber today:
1) We tried to get the ITMY stuck again by adjusting the coil gains so that it goes into the orientation where it used to get stuck. We (reassuringly) failed to get it stuck again. This, as we came to know later, is because kiwamu had rotated the side OSEM such that the optic does not get stuck . However the OSEM beam is at about 30 deg to the vertical and the SD is sensitive to POS motion now resulting in the poorer separation of modes as noted by Jenne earlier (5439)
2) We checked the earthquake stops and repositioned two at the bottom (towards the AR side of the optic) which we had backed out earlier.
3) We took pics of all the OSEMS.
4) Checked to see if there are any stray beams with an IR card. There were none.
5) I obtained the max values of the OSEMS by misaligning the optic with the coil offsets. These values are in good agreement with those on the wiki
OSEM UL UR LR LL SD
Max 1.80 1.53 1.68 1.96 2.10
Current 0.97 0.79 0.83 0.97 1.02
We can close the heavy doors tomorrow morning.
[Paco, Anchal, Yuta]
Today, in short we:
C1:SUS-BS_ULSEN_OUT16 = 599
C1:SUS-BS_LLSEN_OUT16 = 575
C1:SUS-BS_URSEN_OUT16 = 602
C1:SUS-BS_LRSEN_OUT16 = 636
C1:SUS-BS_SDSEN_OUT16 = 669
C1:SUS-ITMX_ULSEN_OUT16 = 403
C1:SUS-ITMX_LLSEN_OUT16 = 609
Since UL coil actuation is lost, we modified the output matrix of ITMY to use only UR, LR and LL face coils for POS, PIT and YAW actuation. The output matrix was changed to following:
After this change, the damping was still working as good as before. I took PIT to POS/PIT/YAW and YAW to POS/PIT/YAW coupling measurements by exciting C1:SUS-ITMY_ASCPIT[YAW]_EXC and seeing effect at C1:SUS-ITMY_SUS[POS/PIT/YAW]_IN1 when the damping loops were off. Attached are the results. We were able to reduce PIT to YAW and YAW to PIT coupling by 10 dB by this simple change in output matrix. More coil balancing or off-diagonal termsmight help more and should be attempted if required. The coupling to POS did not change much.
Note that attachment 1 shows transfer functions from excitation point to the DOF sensing inputs while attachment two looks at ratio of C1:SUS-ITMY_SUS[POS/PIT]_IN1 to C1:SUS-ITMY_SUSYAW_IN1 which is the actual quantity of interest. I didn't repeat the PIT measurement due to lack of time.
Also note that all such measurements are being recorded in our new measurements git repo. We'll populate this repo with diaggui template+data files as we do measurements.