This is the third morning in a row that the MC2 was tripped.
MC2 was tripped again. I think the answer is that watchdog's critical value was too small C1:SUS-MC2_PD_MAX_VAR = 10, so seismic could trip MC2. I've changed the value to 100.
I think the ETMX slow machine might be dead. All of the regular FE readbacks are fine, and the c1iscex FE computer looks fine, but the slow readbacks are all whited out.
I turned off the damping loops for ETMX, since I don't have access to the watchdog disable/enable switch. I guess checking this out will be task #1 for Monday morning.
For lack of a better idea, I keyed the crate. The computer came back up just fine, ETMX is happily damped again.
All oplevs need a little realignment, especially ETMY, which had it's lens removed (Rana has a Wall of Shame photo of this, which is why it was removed by him). Steve will look into this tomorrow, after he starts pumping.
There is no situation in which it is OK to install a mount like this. Steve had installed this flaky and shaky mount to optimize the beam size on the OL QPD.
Everyone in the lab should know better. Putting in something like this is just like sabotage - it creates extra noise in our interferometer in a sneaky way and just makes locking harder. All mounts for anything useful (including QPDs) must have highly rigid mounts.
Use the example from the PSL relayout: use the 3/4" steel mounts and the wide aluminum bases from Newport. No more art projects using home made mounting crap, Steve.
I went inside to align the beam on WFS and noticed that oscillations in yaw are ~10 times stronger then in pitch. I've plot rms of pitch and yaw measured by LID sensors and saw that MC3 yaw rms motion is a few times larger then pitch.
Also MC1 input diag matrix does not diagonalize signals for pitch and yaw. In the spectrums of these signals all 4 resonance are equally seen during the free swinging. I think we should rediagonalize MC1.
Another thing is that if MC1 and MC3 are on the same stack, pitch and yaw spectrums of these mirrors should be comparable. But MC1 signal is ~2-3 times larger then of MC3. I think we should correct calibration.
What are "LID" sensors? Do you mean the OSEM shadow sensors? I'm pretty sure that's what you meant, but I'm curious what "LID" means.
Since we upgraded the CDS system, I guess our ADC ranges have gone up but we never did anything to the OLs to match the ADC ranges. From Liz's daily summary page of the OL, I see this:
So we need a factor of 5-10 increase in the electronics gain (why isn't the BS SUM on there?). This might be accomplished in the head, but for the ones with whitening boards, might be better to do there.
(** add to Jamie's list of long term tasks **)
I've written MC123 input matrixes to the front-end.
MC1 diagonalization is poor, better then before, but still pitch is seen in pos and yaw. Either smth is malfunctioning or flags touch sensors and do not move freely. On the plot mc1_new black lines - before, red - after rediagonalization.
I've actuated on MC1 with UL, UR, LR, LL coils in turn and measured sensor readings. All coils separately work fine from the first look.
On the plot: black - free mirror, blue - UL coil actuation, green - UR, grey - LR, red - LL.
Tip Tilt pitch adjustment on existing-in vacuum suspension. This can be added by a simple installation of a 1.25" long 2-56 threaded rod with nuts.
I've manually corrected MC1 input matrix by looking at UL, UR, LL, LR transfer functions between each other. This improved pos significantly and slightly yaw.
[Koji, Steve, Den]
TT alignment is fine, yaw damping is satisfactory, pitch damping is slow. We might want to add magnets to the mirror and attach blades to the frame for pitch edge current damping.
We are moving towards electronics testing.
Atm1, TT 1.5" high adaptor base will be back from the shop in 10 days.
Atm2, There is no PITCH damping, YAW edie current damping works well at 0.5 mm gap
Atm3, Adjustable Al -disc that contains a small magnet is purely designed.
We have to come up with a solution to have damping in PITCH
We can only decide the need of pitch damping when the coils are activated.
Could you tell us why? Are you thinking about induced current damping?
I was wrong The instability will be the same when the coils are actuated.
Yuta claims he fixed the PRM oplev by centering it the other day, but no one has left it on and watched it for a long while, to make sure it's okay. We watched it now for ~2 min, and it was good, but we're leaving the oplevs off anyway for the night. Tomorrow we should restore PRM (it's currently restored), turn on the oplevs, and let it sit to make sure it doesn't go crazy.
PRM oplev servo was turned on with PITgain 0.5 and YAWgain -0.7
Note: gain settings were PIT 1.0 and YAW --0.5 on Jun 1, 2012 that I measured Feb 23, 2012
It is still oscillating. Gains turned down to zero.
Earthquake test our suspensions PRM damping restored. Oplev servo gains turned to zero.
The PRM damping restored. Oplev PIT gain 0.15 and YAW gain -0.3 turned to zero.
Apparently all of the ION pump valves (VIPEE, VIPEV, VIPSV, VIPSE) opened, which vented the main volume up to 62 mTorr. All of the annulus valves (VAVSE, VAVSV, VAVBS, VAVEV, VAVEE) also appeared to be open. One of the roughing pumps was also turned on. Other stuff we didn't notice? Bad.
Several of the suspensions were kicked pretty hard (600+ mV on some sensors) as a result of this quick vent wind. All of the suspensions are damped now, so it doesn't look like we suffered any damage to suspensions.
Steve has promised to fix up all of the oplevs, but it hasn't happened yet, so I've turned all of the oplev gains to zero, so that when the optics are restored we don't have to quickly click them off.
Oplev values that were changed to zero:
PRM P=0.15, Y=-0.3
SRM P=-2.0, Y=2.0
BS P=0.2, Y=-0.2
ITMY P=2.1, Y=-2.0
ITMX P=1.0, Y=-0.5
ETMX P=-0.2, Y=-0.2
ETMY P=0.5, Y=0.6
Also, PRCL was changed in the LSC input matrix from REFL33I to AS55I, since there is no REFL beam out of the IFO :(
Pitch damping solution needed! It should be in the machine shop already.
I think we can put ø2mm × 10mm long magnetic material inside 4 holes with actuation magnets. Then magnetic field on the other side of the mirror will be close to one produced by actuation magnet. Magnetic cylinder center of inertia will be in the vertical plane where mirror's center of inertia is. So this should not change alignment significantly. Eddy current dumping will be applied to the end of the magnetic cylinder opposite to the magnet using aluminium disks, we have them in the clean room.
I've tested this approach. As we do not have required cylinders with high magnetic permittivity, I replaced them with magnets simular to actuator magnets ø2mm × 3mm long. Using them and aluminium disks from other TT I've made a "pitch dumping" construction.
Pitch Q reduced but not that much as I could expect. I did a ringdown test.
yaw ringdown using original construction | yaw ringdown with added pitch damping
pitch ringdown using original construction | pitch ringdown with added pitch damping
From this data I've estimated Q factor for yaw (135 vs 88) and pitch (192 vs 77) (original vs added pitch damping). Thess results diverges with the ones obtained by designes. They measured Q~40-50 for original construction. Pitch and yaw have 2 close resonances so this time domain method can not be very precise. I've measured the same with SR785.
In these comparison plots excitation was not the same as coils are not plugged in yet, but resonance Q factors can be compared.
From this data I've estimated Q factor for yaw (135 vs 88) and pitch (192 vs 77) (original vs added pitch damping).
I've made a more precise measurement of pitch damping using spectrum analyzer.
Measurements confirm that damping using small actuation magnets reduces pitch Q by a factor of 4 and is not enough.
I've tested the idea to use coils as eddy current dampers. I terminated them with a wire and measured Q factor during the ringdown test. Sadly, I did not see any significant damping and Q was ~150. We need stronger magnets if we want eddy current dumping down to Q~1.
We need stronger magnets if we want eddy current dumping down to Q~1.
I've inserted 10mm * 10mm magnets to the 4 corner holes on the front side of the mirror frame according to actuation magnets polarity. I realigned TT and measured Q factor for pitch and yaw, it was 5-10.
I was able to do it for 1 TT only, because others have smaller (~0.1 mm) hole diameter and magnets can't go inside. I tried to warm holes up to 850 F but still was not able to insert a magnet.
Too bad - I thought it would at least give a little damping. Since we want the viscous-like energy loss to be ~49x larger, we need to have the field modulation in the damper (not dumper) increase by ~7.
I've made SolidWorks models of damping bracket and eddy current disk. They will me manufactured and used instead of old ones. New bracket will be mounted in exactly the same place where the old one was. Drawings might not be complete but all dimensions are in the models so we can fix drawing tomorrow before going to machine shop.
I think we can use ring magnets for passive damping. Then we won't have the vent problem. I've found some at K&J Magnetics, we can get them any time. Magnets are Ni-Cu-Ni (fine for vacuum?) Diameter is 3/8'' with advertised tolerence 0.004'', so they should fit the holes.
We should check that their sus wire diameter are 0.0017" All 2-56 hardware are in and Bob is cleaning them.
Koji and Steve pointed out that previous design of a damping bracket was a bit complicated to manufacture. So I made it simpler and also added a tap hole for original yaw damping. We'll give drawing to Mike in the machine shop tomorrow morning.
I've purchased K&J magnets for eddy current damping, they should be here in 2 days.
Den mentioned that the disks will have threaded holes, and that he has made a note to that effect on the paper copy of the drawing that he will bring to Mike at the shop. Also, all threaded holes in the new plate are marked on the paper copy.
Wow... This is even more complicated than the original "Y" design...
The thinner wire has a history that it did not improve the hysteresis (ask Jenne). Nevertheless, it's worth to try.
If you flip the clamp upside-down, you can lift the clamping point up. This will make the gravity restoring torque stronger.
(i.e. Equivalent effect to increasing the mass)
Luckily (or unluckily) the clamp has no defined location for the wire as we have no wire fixture.
Therefore the clamp will grab the wire firmly even without milling.
The wire clamps should be taken off at the top and at the mirror holder. They need a mill touch up. It would be nice to have the centering jig from LLO for the 0.0017"
The clamps in this condition are really bad. It can sleep, it is not adjustable.
Jamie and I spent some time with tip tilt SN001 this afternoon. This was installed as SR3, so I was going to put a new LaserOptik mirror in there. I accidentally snapped one of the wires (I forgot how strong the magnets are - one zipped from the mirror holder and captured the wire). Jamie and I put the new LaserOptik mirror in, with the wedge correct, but we need to re-resuspend it with the 0.0036" wire tomorrow. We'll also keep working on re-pitch aligning the other optics.
PR2 needs to be put back as a G&H, and we need to put a LaserOptik mirror into PR3.
We resuspended SN001 this morning with 0.0036" wire. We did as Koji suggested, and flipped the wire clamp so the suspension point is a little higher, so we'll see if that helps. We put LaserOptik mirror SN1 into this TT001.
We put the G&H mirror back into TT004, which is PR2. We also put a LaserOptik mirror (SN5) into TT005, which is SR3.
Jamie is working on re-pitch aligning TT004 and TT005 (we already did 001), then we can re-install them in the vacuum system later this afternoon.
The tip tilts have all been pitch-adjusted now, and they have all been put back onto the tables, with the same serial numbers in the same places as we took them out. Jamie also re-leveled the BS table.
Raji and I will align things after I finish measuring the MC spot positions.
We've received all parts that we need for eddy current damping. I've made an estimate of Q with dirty tip-tilt. It looks fine (Q~1)
We need to check ring magnets for vacuum compatibility. Bob start baking on Friday.
People complained about the MC instability: If we aligned the MC, it locked nicely for a while.
Then suddenly you find that it got totally misaligned with the order of 0.2 with the alignment slider.
This misalignment usually happens for MC2, but it happend on MC3 once.
Surprisingly to me, this instability happened even without MCL and WFS, not only once but at least three times.
This suggests that the suspensions are the cause of the trouble.
I played with the MC2 suspension for a while in the afternoon. It seems that it has a hysteresis (or say, bistablity).
And the nominal alignment of MC2 seems close to the point where the transition happens. (Dunno why)
I further played with MC2 and found that a step of POS actuation by +/-10000 induces this transition go and back.
When the POS kick is in the negative direction (-10000), the MC2 seems to return to the preferrable
position. Therefore, I applied DC position force of -5000 to pull the mirror a bit from the nominal position.
I let the MC locked for ~4hours without MCL and WFS, it kept good alignment and the lock was stable
except for unlocks because of the activties by Den and Ayaka.
All of them has been done without previous monitor data as the tools were available.
The MC2 situation is not conclusive but we should check how we can prevent the bistable transition
by restricting MCL/WFS.
Ayaka and I restored all of the oplev gains to these values. The exception is ETMY, which has both gains negative. I am unsure if this is a transcription error on my part, or if something physical has changed. The layout of the ETMY oplev was modified (since Rana took out the offending lens) but that shouldn't affect the sign of the gains.
This week I've got all TT stuff baked and today was testing eddy current damping and electronics.
In the beginning everything was good: ring magnets fit mirror holder holes and their interaction with actuation magnets is strong enough to keep damping magnets in the wholes. I've put the frame horizontally and kicked it, magnets were still in the whole. Brackets also fit to the TT frame.
I've tested eddy current dumping during ring down measurements, it was strong enough.
Then I started to test electronics. I've provided signal to TT1 channels and could see it in the clean room. But then things went terrible. I just could not connect TT cables to OSEMS, there is not enough space in the OSEM for the connector to plug in.
Connector should be machines to be more narrow. There is actually no reason for a connector to have this shape. I think it was designed to fit perfectly the OSEM frame but turned out to be ~0.5 mm wider then it should be.
PRM oplev gains set to zero from PIT 0.15 and YAW -0.3 and damping restored
Using instructions from Bram and Suresh, I was able to plug in connectors to BOSEMs. Today I've tested electronics, everything works good. Jamie made an medm screen and channels for TTs. Sliders for pitch and yaw go from -100 to 100 counts. Calibration to angle is 1e-5 rad / count.
TTs are in the clean room waiting for installation.
Please leave here what was the instruction by Bran and Suresh so that the other people can redo it sometime later!
Please leave here what was the instruction by Bran and Suresh so that the other people can redo it sometime later!
The connectors can be plugged into the BOSEMs if we loosen the two screws which hold down the mini-D connector and the flex circuit. Tighten the screws after the connector is pluged in.
We've provided acoustic excitation using speakers on the AS table and saw that PSD of YARM feedback signal increased in the frequency range 50 - 100 Hz. Meanwhile, XARM feedback signal did not change. Moreover, YARM noise is much higher at these frequencies compared to XARM.
The problem was with YARM oplev servos. Both ITMY and ETMY produced noise to YARM length. ITMY oplev signal had a huge resonance at 55 Hz. We measured coherence with accelerometers, it was 0.8. It turned out that one of the mirror mounts was not fixed in the oplev path. When we fixed it, noise has gone.
Note: speakers were on AS table but mirror mounts could steel feel it on ITMY table.
Then we had a look on ETMY table. We saw a mirror on suspiciously long mirror mount that was used in the ETMY oplev path. We slightly kicked long mount with a small screwdriver and YARM control signal went up with resonance at 100 Hz.
I will just leave the picture of spectrum that shows the injected acoustic sound effects due to the oplevs.
red line: POY error without oplev feedback nor acoustic noise
blue line: POY error without oplev feedback but with acoustic noise
brown line: POY error with oplev feedback but without acoustic noise
green line: POY error with oplev and acoustic noise
You can see there is noise only at green line around 70 - 100 Hz. And it does not look like the acoustic signal is injected directly to the arms but the acoustic sound couples to the original noise source.
I think the angle of incidence on TT inside BSC will be too large because of eddy current damping brackets. I've measured max possible angle of incidence
This means that we do not have too much range and there is a probability that 45 degree incident beam will start clipping. I think we should just cut off the central part of the bracket. We do not need it anyway, our eddy current damping due to corner magnets is good enough.
I've left the brackets near the laptop in the clean room.
Tonight we've noticed that ITMX local damping was kicking the optics. This happened because LR shadow sensor was not working. In ~30 minutes it started to work again. Evan and I were working on installation, moving and focusing cameras and locking prcl and mich. We've installed a camera on BSC and plugged it in to PSL_SPARE input.
I'm not sure that this can be correlated to ITMX LR shadow sensor behaviour.
I've estimated max possible angle of incidence on TT if we allow 20mm tolerance for the beam size and 5 mm tolerance for spot location on the mirror. It turns out to be
alpha = 43 degrees
So we need to cut the central part of the bracket. Then the max possible angle of incidence will be
alpha = 63 degrees
We can start the vent on Monday and use TT with an old bracket for yaw damping and later during the week we can install the brackets after they will be baked.
At least, we don't want to use Al-coated mirrors. We should use multilayer dielectric mirrors.