I also made xfer fctns of the 4 piston coils on ETMY and ETMX with OL_PIT.  (I looked at all 4 even though the attached plot only shows three.)  So it looks ike the coils are OK.

Looks like something went nuts in late April.  We have yet to try a hard reboot.

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.

Earthquake  of magnitude 5.0  shakes ETMY loose.

MC2 lost it's damping later.

 Round 3 for the day of MC2 watchdogs tripping.

 I've watchdogged all the suspensions while I mess around with computers.  If no one else is using the IFO, we can leave them undamped for a couple of hours to check the resonant frequencies, as long as I don't interrupt data streams with my computer hatcheting.

Ops. I restored the damping of the suspensions at around 16:30.

  In this experiment, we used a feedback control to create a stable trap for a NdFeB permanent magnet. The block diagram is the following:

signal into another  SR560 as a low-pass filter with a gain of 100 above 30 Hz. We used the "DC" coupling modes in both

preamplifers. The output is then used to drive a coil. The coil has a dimension of 1.5 inch in diameter and 2 inch in length.

The inductance of the coil is around 0.5 H and the resistance is 4.7 Om. Therefore, it has a corner frequency aournd 10/2pi Hz.

The coil has a iron core inside to enhance the DC force to the permanent magnet. The low-frequency 1/f response of the magnet is produced

by the eddy current damping of the aluminum plane that is below the magnet. This 1/f response is essential for a stable configuration. In the

next stage, we will remove the aluminum plane, and instead we will use a filter to create similar transfer function. At high-frequencies, it behaves as 

a free-mass and has a 1/f^2 response. Finally, the magnet is stably levitated.

This afternoon I re-enabled the ETMY coils after I found that the watchdogs for the mirror had tripped last night at 2:06am.

MC2 damping restored,  MZ locked and the arms are flashing now.

I built a Simulink model of the magnetic levitation system and try to explain the dip in the open-loop transfer function that was observed.

One can download the model in the svn. The corresponding block diagram is shown by the figure below.

Here "Magnet" is equal to inverse of the magnet mass. Integrator "1/s" gives the velocity of the magnet. A further integrator gives the displacement of the magnet.

Different from the free-mass response, the response of the magnet is modified due to the existence of the Eddy-current damping  and negative spring in the vertical

direction, as indicated by the feedback loops after two integrals respectively. The motion of the magnet will change the magnetic field strength which in turn will pick

up by the Hall-effect sensor. Unlike the usual case, here the Hall sensor also picks up the magnetic field created by the coil as indicated by the loop below the mechanical

part. This is actually the origin of the dip in the open-loop transfer function. In the figure below, we show the open-loop transfer function and its phase contributed by both

the mechanical motion of the magnet and the Hall sensor with the black curve "Total". The contribution from the mechanical motion alone is shown by the magenta curve

"Mech" which is obtained by disconnecting the Hall sensor loop (I rescale the total gain to fit the measurement data due to uncertainties in those gains indicated in the figure). 

The contribution from the Hall sensor alone is indicated by the blue curve "Hall" which  is obtained by disconnecting the mechanical motion loop. Those two contributions

have the different sign as shown by the phase plot, and they destructively interfere with each other and create the dip in the open-loop transfer function.

In the following figure, we show the close-loop response function of the mechanical motion of the magnet.

As we can see, even though the entire close loop of the circuit is stable, the mechanical motion is unstable around 10 Hz. This simply comes from the fact that

around this frequency, the Hall sensor almost has no response to the mechanical motion due to destructive interference as mentioned.

In the future, we will replace the Hall sensor with an optical one to get rid of this undesired destructive interference.

By including a differentiator from 10 Hz to 50 Hz, we increase the phase margin and the resulting

magnetic levitation system is stable even without the help of eddy-current damping.

The new block diagram for the system is the following:

Here the eddy-current damping component is removed and we add an additional differential

circuit with an operational amplifier OP27G.

In addition, we place the Hall sensor below the magnet to minimize the coupling between

the coil and the Hall sensor.

The resulting levitation system is shown by the figure below:

I have connected ETMY sus electronics to megatron ADC/DAC.
We continue this state until 15:00 of today. (Restored 13:00)

0) Now the connection for the ETMY suspension was restored in a usual state. It damps well.

1) I thought it would be nice to have dataviewer and DTT working.
   So far, I could not figure out how to run daqd and tpman.
   - I tried to configure
    /cvs/cds/caltech/target/fb/daqdrc
    /cvs/cds/caltech/target/fb/master
    /cvs/cds/caltech/chans/daq/C1TST.ini (via daqconfig)

   - I also looked at
    /cvs/cds/caltech/targetgds/param/tpchn_C1.par
   but I don't understand how it works. The entries have dcuids of 13 and 14 although C1TST has dcuid of 10.
   The file is unmodified.

   I will try it later when I got a help of the experts.

2) Anyway, I went ahead. I tried to excite suspension by putting some offset.

It seems to have no DAC output. I checked the timing signal. It seems that looks wrong clock.

   I looked at DAC output by putting 5000,10000,15000,20000,25000cnt to UL/UR/LR/LL/SD coils.
   I could not find any voltage out of the DAC in any channels.

   Then, I checked the timing signal. This clock seems to have wrong frequency.
   What we are using now is a clock with +/-4V@4MHz. (Differential)
   Maybe 4194304Hz (=2^22Hz)?

   I went to 1Y3 and checked the timing signal for 16K. This was +/-4V@16kHz. (Diffrential)

   The possible solution would be
   - bring a function generator at the end and try to input a single end 4V clock.
   - stretch a cable from 1Y3 to 1Y9. (2pin lemo)

OK. Now, Timing/ADC/DAC are working. It's almost there.

1) As a temporaly clock, I put a function generator at the back side of the ETMY.
Set it to the rectangular +/-4V@16384Hz. Connect it to D060064 PCIX Timing Interface Board in the IO Chasis.
That is a line receiver to feed the TTL signal into ADCs/DACs.

I confirmed the actual sampling clock is supplied to the ADC/DAC boards by looking at the SMB output of the D060064.

2) Restarted the realtime code.

3) I looked at DAC output by putting 5000,10000,15000,20000,25000cnt to UL/UR/LR/LL/SD coils again.
Yes! I could see the DAC channels are putting DC voltages.

4) Then I connected DAC CH0 to ADC CH0 using SCSI breaking up boards.
Yes! I could see the coil output switching change the ADC counts!

Now, we are ready to see the suspension damped. Check it out.

Koji, Rana

The megatron DAC was temporaly connected to the suspension electronics for the DAC test. We went down to ETMY as we could not excite the mirror.

The DAC is putting correct voltages to the channels. However, the anti imaging filter test output does not show any signal.
This means something wrong is there in the DAC I/F box or the cables to the AI circuit. We will check those things tomorrow.

The ETMY was restored to the usual configuration.

Had been disconnected for about two weeks.  I found a partially seated 4-pin LEMO cable coming from the OSEM PD interface board. 

It appears the front panel for the DAC board is mis-labeled.  Channels 1-8 are in fact 9-16, and 9-16 are the ones labeled 1-8.  We have put on new labels to reduce confusion in the future.

Hurraaaah!
We've got the damping of the suspension.
The Oplev loops has also worked!

The DAC channnel swapping was the last key!

DataViewer snapshot to show the damping against an artificial excitation was attached

/cvs/cds/caltech/target/fb/daqd -c daqdrc

This starts the FB.

Now the dataviewer and DTT work!

I added an integrator to increase the gain at low frequencies (below 5 Hz). In addition, I increased

the band of the differentiator. The schematics for both integrator and differentiator are the following:

The magnetic is stably levitated.

I turned off the light to get rid of 60Hz noise on the photodiode. I tried to measured the

open-loop transfer function of this setup, but somehow the SR560 is always saturate

when I injected the signal from SR785, which produces some weird results at

low-frequencies.

In addition, I found out that when the light is turned on, the levitation

can be stable even when I inverted the sign of the control loop. The control signal

on the osciloscope is the following:

This oscillator is around 120 Hz, which should be  the harmonics of 60 Hz from light pollution.

I am not sure exactly why it is stable when the control-loop sign is flipped. This could

be similar to the Pauli trap in the iron trap, because the coil not only provides a force

but also provides the rigidity. The sign of such rigidity depends on the sign of the control

current. If such oscillating rigidity changes at a frequency much higher than the response

frequency of the magnet, it will stablize  the system simply by significantly increasing

the inertial of the magnet.More investigations are essential to completely understand it.

For information about Pauli trap, one can look at the wikipedia:

http://en.wikipedia.org/wiki/Quadrupole_ion_trap

I've changed the watchdog rampdown script so it brings the SUS watchdogs to 220, instead of the 150 it previously targeted.  This is to make tripping less likely with the jackhammering going on next door.  I've also turned off all the oplev damping.

 Saturday's special event of braking up the large concrete pieces in CES bay was un event full.

Just felt a big "kerplunk" type ground-shaking, presumably from all the antics next door.  MC2's watchdog tripped as a result.  The watchdog has been reenabled.

In this night, I checked the free swinging spectra of ETMX to make sure nothing wrong with ETMX by the wiping.

Compared with the past (Aug.6 2008), the spectra of ETMX doesn't show significant change.

Successfully the wiping activity didn't change its configuration so much and didn't bring bad situations.

(bad situation means for example, the suspended components hit some others).

 The spectra of ETMX by DTT are attached. Also you can see the past spectra in Yoichi's entry.

Yoichi's data was taken during the air-pressure condition, so it's good for comparing.

Actually I compared those data by my eyes, because I could not get the past raw data somehow.

The resonant frequencies and their typical height changed a little bit, but I think those are not significant.

NOTE: In the figure, pitch and yaw modes (~0.57Hz and ~0.58Hz) look like having a smaller Q-factor than the past.

The free swinging spectra of ETMY and ITMX were taken after today's wiping, in order to check the test masses.

These data were taken under the atmospheric pressure condition, as well as the spectra of ETMX taken yesterday.

Compared with the past (see Yoichi's  good summary in Aug.7 2008), there are no significant difference.

There are nothing wrong with the ETMY and ITMX successfully.

 --

By the way I found a trend, which can be seen in all of the data taken today and yesterday.

The resonances of pitch and yaw around 0.5Hz look like being damped, because their height from the floor become lower than the past.

I don't know what goes on, but it is interesting because you can see the trend in all of the data.

Where is the plot for the trend?
It can be either something very important or just a daydream of you.
We can't say anything before we see the data.

We like to see it if you think this is interesting.

... Just a naive guess: Is it just because the seismic level got quiet in the night?

P.S.

You looks consistently confused some words like damping, Q, and peak height.

• Q is defined by the transfer function of the system (= pendulum).
   
• Damping (either active or passive) makes the Q lower.
   
• The peak height of the resonance in the spectrum dy is determined by the disturbance dx and the transfer function H (=y/x).

dy = H dx

As the damping makes the Q lower, the peak height also gets lowered by the damping.
But if the disturbance gets smaller, the peak height can become small even without any change of the damping and the Q.

Please do not touch the watchdogs for all SUSs except for MCs,

because I am going to measure the free swinging spectra for ITMs, ETMs, BS, PRM, SRM tonight.

Today, it is good chance to summarize those data under atmospheric pressure.

thank you.

Okay, now the data are attached. At that time I just wanted to say like the follower.

- - -

In the free-swinging spectra around ~0.5Hz, you can see the two resonances, which come from pitch and yaw mode of the pendulum.

Note that, the vertical and the horizontal axis are adjusted to be the same for the two plots in the figure .

And I found that

* the floor levels are almost the same (the factor of about 1.5 or something like that) compared to the past.

* however the peak heights for two resonances are several 10 times smaller than the past.

* this tendency are shown in all of the data (ITMX, ETMX, ETMY).

If such variation of the peak heights is cased by the seismic activity, it means the seismic level change by several 10 times. It sounds large to me.
 

Well, I get the point now. It could be either seismic or change in the suspension Q.

The pendulum memorizes its own state for a period of ~ Q T_pend. (T_pend is the period of the pendulum)
If the pendulum Q is very high (>10⁴), once the pendulum is excited, the effect of the excitation can last many hours.

On the other hand, in our current case, we turned on the damping once, and then turned off the damping.
Again it takes ~Q T_pend to be excited. 

In those cases, the peak height is not yet before in equilibrium, and can be higher or lower than expected. 

So, my suggestion is:
Track the peak height along the long time scale (~10hrs) and compare between the previous one and the current one.
This may indicate whether it is equilibrium or not, and where the equilibrium is.

The free swinging spectra of ITMs, ETMs, BS, PRM and SRM were measured last night in order to make sure that nothing wrong have happened by the wiping.

I think there are nothing wrong with ITMs, ETMs, BS, PRM and SRM successfully.

For the comparison, Yoichi's figure in his elog entry of Aug.7 2008 is good, but in his figure somehow PRM spectrum doesn't look correct.

Anyway, compared with his past data, there are no significant changes in the spectra. For PRM which has no counterpart to compare with, its shape of spectra looks similar to any other spectra. So I think PRM is also OK. The measured spectra are attached below.

The free swinging spectra of ITMs, ETMs, BS, PRM and SRM were measured under the vacuum-condition. The attachment are measured spectra.

It looks there are nothing wrong because no significant difference appear from the past data and the current data (under atmosperic pressure).

So everything is going well.

It seemed that the ETMY watchdog tripped early Sunday morning.
The reason is not known. I just looked at ETMX, but it seemed fine.

I called the control room just in case someone is working on the IFO.
Also I did not see any elog entry to indicate on going work there.

So, I decided to reset the watchdog for ETMY. And it is working fine again.

MC2 is having a bad day, and I'm not yet sure why.  It's to do with the damping though.  When the damping is off, after a little while it will settle to ~30mV or so on the Watchdog screen.  When I enable all of the outputs and then turn on the damping, the optic gets kicked up.  It's like there's a minus sign error somewhere, maybe in a bad burtrestore?  This has been going on since I did my morning bootfest.

It's started to sit down and play nicely now.  Is someone doing magic remotely that is fixing things that I hadn't figured out yet?

The MCL path of MC2 was in a strange state as the filters were activated as if it is in lock even though we had no lock. So I manually ran "mcdown". This reset the filters of the MCL path.

I have assembled the circuit and the control box for the quadrant magnetic levitation yesterday. The final setup is shown

in the figure below:

Due to my carelessness, I I connected the wrong ends of the power supply. I damaged 4 op-amp and one voltage 

regulator during this assembly. This stupid mistake spent me several hours to fix, and I got a bitter lesson;-(

Afterwards, I replaced those op-amps and reconnected the power supply . Kiwamu helped me and we measured

the transfer function of this circuit.  The transfer function agrees with  the specification in the schematics which

has a integrator below 1 Hz and a differentiator from 5 to 20 Hz. The bode plot for the measured transfer function

is the following:

Today I tested the photodetector parts and found that there is a mysterious oscillation. Whenever I connect the

photodector input A of the circuit (as indicated in the figure below),

the output of the op-amp has a 500k Hz oscillation shown up in the oscilloscope.This happens even A is disconnected from

the photodetector and connected to an open end wire. I don't know how to eliminate it, and its amplitude is so large (peak to

peak is around 2.5 V) which completely dominates the photodetector output. Does anybody has some ideas? Thanks.

1. Why do all of the BNCs have no GND connection? Each should have the individual cables to the ground. Each signal line and the corresponding ground line should be twisted together.

2. This looks the (usual) oscillation of the V-I conversion stage but I can't tell anything as I don't have the circuit diagram of the whole circuit.

3. In a certain case, putting some capacitance at the feedback may help. Read P.11 of the data sheet of LT1125. Try to put some capacitors from 20pF to some larger one whether it changes the situation or not. I suppose the bandwidth of your sensor can be ~1kHz. So putting a capacitance less than 10nF still has no effect to the servo.

 1. They are all connected to the box which has a single connection to the board ground. If I connect each of them to the ground, there would be many small loops

of ground. Of course, I should have replaced all the connectors such that the they are disconnected to the box as point out by Robert.

2. The oscillation disappears after I add 5 nF capacitor in parallel to the existing resistor. Thank you very much for pointing this out.

1. Yes. That is the bad. You should eventually replace the BNCs to the isolated ones.

2. OK. I like to emphasize again that everyone works on electronics should read data sheets more carefully and seriously because they have many important practical instructions to exploit full performance of the components. 

I have tried to make the quadrant magnetic levitation work but unfortunately I did not succeed. During the experiment, I have made

the following changes to the circuit and setup:

(1) I added small resistors (6K) in parallel to R11, R23, R35 and R47 (indicated in the following schematics)  to increase

the control bandwidth from 20 Hz  to 80 Hz.

(2) I changed RLED1, RLED2, RLED3, RLED4 from 2.2K to 1.5K  in the LED driver such that the current of the

LED increases and in turn the displacement sensitivity increases.

(3) I changed R51 and R51 (in the differencing block for PD1 and PD2) from 5K to 1 K. Correspondingly,

I increased R52 and R54 from 5K to 50K. This changes increase the gain in the differential control by a

factor of 50, which compensates the gain loss after increasing the control bandwidth.

 (4) The trim pots in the coil drive block have the following values: 100K for pot1 and pot4, 1K fro pot 2 and pot3.

To increase the gain, I replaced R17, R30, R31, R41 by 102 Om resistors (we run out of 100 Om chip resistors.)

(5) I wrapped the OSEM flags by plastic tubes to block the light from the LED more efficiently. This also removed

the changes of the photocurrent in the photodetector when the levitated plate moves horizontally.

Possible issues that cause the setup not working at the moment:

(1) The feedback gain could be probably still not enough. During the experiment, I can't feel any force changes when the

flags crossing the zero point. The error signals and control signal has the right sign.

(2) The levitated weight may be not enough and the working point is below the extremum of the DC attracting force.

This could give rise to a large negative spring which requires unreasonable feedback gain to compensate.

(3) The DC attracting force between the magnets are differing each other too much (mismatch) and can't

be compensated by the coil driving force.

(4) The control bandwidth may be still not  large enough. Initially my design was 100 Hz, but I forgot to divide

the angular frequency by 2pi and the resulting circuit has a bandwidth of 20 Hz. Later I increase it up to 80 Hz

by changing the resistors as mentioned before.

(5) The polarization of the coil could have a wrong sign. I have checked with Gauss meter, but still the absence

of zero-point crossing force change makes me worry about this.

For continuation of this work, I will finish writing my document and summarize all the results and outline what

needs to be done in the future. If everything goes well, I will be back in June and can spend more time on this

experiment. I can also work with the summer students together on this project.

[Jenne, Kiwamu]

The 2 SOS towers for the ITMs have been assembled, and are on the flow bench in the cleanroom.  Next up is to glue magnets, dumbells, guiderods and wire standoffs to the optics, then actually hang the mirrors.

Koji, Steve

ITMX OSEM CONFIGURATION

Jenne and Koji

We successfully hung ITMX on the SOS. Side magnet is ~2mm off from the center of the OSEM. ITMX aligned using the QPD. The OSEMs changes the alignment. It looks that something magnetic is inside the OSEM PD or LED.

Reguled ITMY side magnet.

Cleaned up the lab for the safety inspection.

 Some details on the side magnet situation from today: 

To glue the magnets+dumbbells to the optics, we use the magnet-dumbbell gluing fixture.  This fixture is supposed to have teflon 'pads' for the optic to sit on while you align it in the fixture, however the fixture which we received from MIT (it's Betsy's....but it came via MIT) only had one of the 4 teflon pads. 

Kiwamu and I decided (last week, when we first glued ITMX's magnets) that it would be bad news to let the AR face of the optic sit on bare metal, so we fashioned up some teflon pads using stock in a cabinet down the Yarm.  We were focused on thinking about the face magnets, and didn't think about how the thickness of the teflon affected the placement of the side magnet.  We chose some teflon that was too thin by ~1mm, so the optic sat too low in the fixture, resulting in the side magnet being glued too close to the HR side of the optic (this is all along the Z - axis, where Z is the direction of beam propagation). 

Why it ended up being 2mm off instead of only 1mm I don't really have an explanation for, other than perhaps tightening the set screws to hold the optic (by the barrel) in the fixture pushes the optic up.  I observed this happening when I didn't put any effort into keeping the optic flat on the teflon pads, but I thought that I made sure the optic was seated nicely in the fixture before starting to glue.  When I glued the new ITMY side magnet tonight I tried to make sure that the optic was seated nicely in the fixture.  We'll see what happens.

Before gluing the new ITMY side magnet (and now it's set for all future magnet gluings....), I found 4 teflon pads of all the correct thickness.  It turns out that we have a magnet gluing fixture of our own, which I found in the cabinets in the clean room.  This fixture had all 4 teflon pads, so I stole them and put them into the one that we're using for this round of upgrade / suspension hangings.  The height of all future side magnets should be correct. The thickness of the pads in the 'spare' fixture matched the one which came with the fixture from MIT as closely as I could feel by putting them on the same flat surface next to each other and feeling if there was a step. 

A side note about this magnet gluing fixture that I found:  It has the word "TOP" etched into it, to prevent exactly my problem with the ITMY side magnets in the first place.  Unfortunately the threads for the set screws which hold the optic are shot (or something is funny with them), so we can't just use this fixture. 

Gluing notes regarding the standoffs and guiderods:

There's more glue than I'd like on the guiderods / standoff for ITMX.  The glue was starting to get a little tacky when I glued the standoff in place after we balanced the optic, so it was hard to get it in the right place.  I'm confident we have a good epoxy contact, and we don't have much glue that I think it'll be a big problem.  Certainly I'll be a lot better at manuvering my glue-stick a.k.a skinny piece of wire around the suspension tower to get to the standoff for the rest of the optics that we're hanging, and I won't have glued something like ITMY side magnet immediately beforehand, which took enough time that the glue started to get tacky (not very tacky, just barely noticeably tacky).

I'd say that most gluing activities should be completed within ~10-15min of mixing the glue, after spending ~2min stirring to make sure it's nice and uniform.  It doesn't dry fast enough to be a huge rush, but you should get right on the gluing once the epoxy has been mixed. 

 The brand new OSEM LED and PD can be picked up with a weak magnet. These ferrous metals of LEDs and PDs will be magnetized by sitting in the sus next to the

magnets for years. I hanged optics with new OSEMs and never saw this effect before.

We have to demagnetize them.

The OSEM LEDs and PDs from Honeywell have always had some ferromagnetic material in them. These are the same OSEMs we had since 2000.

You must be thinking of the really old 20th century plastic OSEMs.

Jenne, Koji

Recent status of SOSs:

We completed one of the suspension (ITMY).

ITMX: 6 Magnets, standoffs, and guide rod glued / balance to be confirmed / needs to be baked
ITMY: 6 Magnets, standoffs, and guide rod glued / balance confirmed / needs to be baked
SRM: 6 Magnets, one standoff, and guide rod glued,  / waiting for the release from the gluing fixture.
PRM: one standoff, and guide rod glued / waiting for the magnet gluing. 

We think we solved all the problems for hanging the suspensions.

--- Magnet gluing fixture ---

• There is the two kinds of fixtures. Neither does work propery in the original form!
• The height of the side magnets should be finely adjusted by changing the teflon sheets beneath the optics in the fixture.
• Be aware of the polarity of the fixture in terms of the side magnets
• Wrongly glued magnets (and others) can be removed by a razor blade with some amount of acetone.
• The pickle picker frequently knocks the magnets down during the release. Don't s be down in the dumps too much.

--- Suspending the mirror ---

• The wire winches must be carefully attached to the suspension tower such that the wires are not streached during fastening the clamps.
• There are a couple variations of the drawings for SOS. The one we have has #4-40 for the earthquake stops at the bottom.
  Zach and Mott made the EQ stops with the right size.