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  SUS Lab eLog, Page 35 of 37  Not logged in ELOG logo
ID Date Author Type Category Subjectup
  1572   Thu Jul 14 08:38:30 2016 GabrieleComputingCracklecymac2 restarted

At about 8:40am I restarted the cymac2 to check the BIOS configuration. Hopefully this will help me solving the issues I'm having with cymac3.

I restarted all processes.

  215   Tue May 31 17:49:47 2011 Mingyuan, TaraDailyProgressCreakdata readout

 

 

To have the ability of controlling the phase, we need adjust DC voltage of one of the PZTs independently.
We use the function generator to generate AC driving with a DC offset for one of the PZTs and use a OP270
chip to add the driving signal with another DC voltage for another PZT. By changing this DC voltage, we can
control the phase of interference signal. We adjust the voltage to put the PD intensity in the middle to have
the best sensitivity.
We did the same measurement as last time to check the peaks we observed. By use the same condition, we do see
a few extra peaks while the plates are being drovn at 2 Hz. We also changed the driving frequency to 0.7 Hz and
did the same measurement. The results looks different.
  Tara will upload the data later.

 
  216   Tue May 31 19:33:00 2011 taraDailyProgressCrackledata readout

By mingyuan, tara

We built a simple voltage summing circuit for adding DC level to the pzt. This circuit allows us to fine tune the inteferometer's differential arm length, so that we can operate at the fringe's maximum slope. Then we checked the peaks we observed from last time. It turned out to be harmonics from the common mode from driving.

 

The circuit schematic is shown below. The result Vout = Vin1 + Vin2. 

adding_circuit.png

 

The adding circuit is used as shown in the schematic (highlighted in yellow.)

crackle_choppig_2011_05_31.pdf

 *Later, we can use this summing circuit in a feedback control loop for locking the interferometer.

Then we used this circuit in the setup and repeat the measurement to check the peaks we observed last time. With the same setup, we observed the peaks again, but they probably are harmonics from 4Hz from common mode motion which was not perfectly cancelled.

 readout.png

 

 

     We repeated the measurement again with 0.7 Hz driving, and the peaks disappeared. The signal between driving and not driving the arms are very similar. The shape of the PSD changes slightly because of the lower amplitude of the driving signal, as we low pass the signal at 0.1 Hz.

readout2.png

We do need a seismic isolation and vacuum chamber. Right now, sound from people speaking in the lab can disturb the measurement.

 

 a few things we have to consider soon, before we use the maraging steel blades pulled down by a mass block in the experiment.

1) how should we push the blades?  capacitor plate? magnetic coil?

2) When can we move and get a better table, so that we can decide on seismic isolation stage.

3) We have to start looking for vacuum bell jar for the experiment.

4) lock the interferometer?

5) will we get an npro laser for the experiment?

  254   Mon Jul 25 12:33:58 2011 Larisa ThorneDailyProgressCracklediagram, with magnetic actuators

[Seiji, Larisa, Vanessa]

 

Attached is an update on the diagram for the blade crackling experiment. This includes the magnetic actuator (solenoid and Nd magnet configuration driven by a sinusoidal source), as well as a few SR560s and an SR780 which are used to modify (using filtering and gains) and test the signal produced by "shadow-blocking" the laser beam path by an oscillating mass attached a blade.

NOTE: we did not use the full Michelson set-up. This configuration uses shadow-blocking of a single mass oscillating.

  245   Mon Jul 18 11:40:24 2011 Larisa ThorneDailyProgressCracklediagrams (for reference) and update on Q calculations

 Posted below is a better picture of the Romulus blade mass-mirror configuration, where one can clearly read the dimensions.

 

With respect to Q calculations: I spend much time trying to figure out how one would best do this. Rana lent me a book ("Data Reduction and Error Analysis for Physical Sciences"), and I also tried referencing a copy of "Numerical Recipes" from the 1980s. First, I tried searching for curve fitting methods, for which both the books agreed that some 'least squares' method would work. Then I realized that it wasn't the damped motion we wanted fitted: we wanted an equation to describe a line going through all the local maxima data points of the damped spring motion. That's when I got stuck and neither of the books proved helpful....much Internet research ensued...

I finally came across something called the "log decrement" method, which looked promising, and calculated my Q (~10^4). The only problem I have now is wondering whether the calculated result is reasonable; there are no tables or charts I could find that would tell me what range of Q values I should be expecting. The only useful information I could find said that tuning forks have a Q~10^3. The highest Q values I could find (in an attempt to get some idea of what the range of Q values are) was in high Q lasers and atomic clocks valued at Q~10^11. 

 

I would really appreciate some feedback, as I have been looking for Rana or Tara since this morning and can't find them.

  549   Fri Jul 20 21:17:47 2012 janosch the refinedDailyProgressCrackledrive and damping

We don't see the 0.1Hz blade displacement from the low-f drive in our data. However, increasing the voltage amplitude of the low-f drive, and with the interferometer out of lock, one can see that the low-f drive is strong enough to periodically change the interferometer contrast by a large amount. Next week we can try to drive the blades at a higher frequency closer to the blade resonance frequencies and see what happens.

The damping circuit works for both blades. I don't know what the problem was the last days. I am almost sure that the gain was set too high.

 

  366   Sun Oct 23 23:39:10 2011 neat freakLab InfrastructureGeneraldump?

see entry here

  257   Tue Jul 26 02:16:54 2011 haixingSummarySUSforce measurement

Yi and Haixing,

In the afternoon, we made a force measurement between the 1" diameter magnet and 1/2" diameter magnet.
The experimental setup goes as follows:

By adjusting the distance between the two magnets, we can obtain force as a function of distance. We measured
the repelling force instead of attracting force, which avoids two magnets getting stuck to each other. The measurement
data are listed below:

weight (g)         distance (mm)
   0.05                    95.53
   0.06                    90.92
   0.07                    88.00
   0.08                    84.60
   0.09                    82.29
   0.10                    79.39
   0.11                    77.27
   0.15                    75.27
   0.17                    71.61
   0.23                    68.29
   0.27                    64.86
   0.33                    61.59
   0.40                    57.15
   0.48                    56.33
   0.60                    53.21
   0.75                    50.22
   1.01                    47.11
   1.20                    43.40
   1.38                    40.90
   1.59                    39.50
   1.90                    38.00
   2.32                    35.89
   2.78                    33.61

We made a fit with the analytical expression for the force between two current loops, which is a
good approximation for the force between two thin disk magnets (separation larger than their thickness).

 

The fitted curve is shown by the figure below [the right one is the zoom-in version of the left one]:

We will make a similar measurement for other three pairs of magnets tomorrow morning, which allows us to calibrate the mismatch
and calculate how much DC biased current in the control coil is needed to counteract the mismatch.
 

 

  111   Thu Dec 20 11:38:46 2007 aivanovComputingOMCframe builder fixed
I put the things back the way they were before we borrowed the ADC board. I can see the TPT data now. Alex
  632   Fri Apr 26 16:04:56 2013 taraNoise HuntingNoise Budgetfrequency noise requirement for laser used in crackle experiment

I made an estimate for frequency noise requirement for a laser that can be used in crackle experiment. With some assumptions, I came up with df = 3x102 [Hz/rtHz ] for the requirement.

 The two beams from both arms are recombined at the output port of a Michelson interferometer. If it is operated at dark port, the output signal will be linear with the differential length between the two arms.

some assumptions in the calculation:

  • Operating at darkport
  • The laser has frequency = f0 + df  (carrier + noise)
  • mismatch between the two arms is ~ 1mm
  • aim for SNR = 1, no integration time.
  • crackle signal is ~10-15 m/rtHz, this is actually the shot noise limit of the current setup.

 crackle_df_req.JPG

This will be a requirement for the planned ecdl.

Is a HeNe laser good enough? I'm not sure about HeNe frequency noise level, and I haven't found it in literature that much. I checked here,see fig 5, HeNe f noise is not so bad compared to NPRO noise (10^4 /f Hz/rtHz).This feels a bit counter intuitive. But if it is real, it should be ok for the measurement around 100 Hz and above.

  620   Mon Jan 21 22:33:26 2013 haixingSummarySUSfront and rear panels for signal conditioning boxes

Here are the front and rear panels for the signal conditioning boxes. The front-panel files are attached.

For the coils:

coil_front_panel.png

coil_rear_panel.png

For the QPD:

 QPD_front_panel.png

QPD_rear_panel.png

For the Hall-effect sensors:

 hall_sensor_front_panel.png

hall_sensor_rear_panel.png

For the linear motors [using simple DC control]:
Small panel-mounted voltage meter reads out the force gauge signal that indicates the weight of the floating plate, from which we know roughly how far we are away from the working point where the gravity is balanced by the DC magnetic force. We use two on-mom switches to control the linear motor (up and down).

linear_motor_front_panel.png

 linear_motor_rear_panel.png

  399   Thu Feb 2 18:59:20 2012 ZachDailyProgressCoating Qfront-end noise budget

I took the liberty of making my own plot. This was both in the interest of time and also to better illustrate how the plot should be made by example:

CQ_frontend_electronics_NB_2_2_2102.png

Comments:

  • "NEP" is a relatively useless term. Manufacturers use it so they can report the smallest possible intensity noise level for a given electronic noise level. Also, it would be in W/rHz, not V/rHz.
    • It is useful to plot the intensity noise level for our particular setup (i.e., wavelength) alongside the electronic noise level in volts. This is best accomplished by putting another axis on the right side with the proper scale factor with respect to the other one. For this, you use the PD's transimpedance gain [V/A], its responsivity [A/W], and your brain [?].
    • The only tricky part, really, comes when you have to plot the manufacturer's quoted noise level. For this, you have to go from their NEP [W/rHz], to the corresponding electronic noise level [V/rHz], using the proper responsivity at the peak wavelength. In this case, the peak responsivity (@ lambda = 970 nm) is 0.65 A/W, while for us (@ lambda = 633 nm), it's ~0.41 A/W. A good check to make sure you've done all the calibrating correctly is to make sure that the manufacturer's spec that you've plotted---in W/rHz on the right side---is equal to their NEP number times the ratio of the two responsivities.
  • I'm not sure how you got things to end up out of whack in yours, but the calibration should be simple: take the raw voltage noise level we measured with the spectrum analyzer, then divide by our preamp gain of 500. This is the input-referred noise level, as we have discussed. That means that even though the input noise level of the spectrum analyzer is actually higher than the dark PD noise in an absolute sense, it actually looks much lower, since we've amplified our signal with the SR560.
  • The trace names should be clear and make sense:
    • PD1 dark: The electronic noise measured out of the first PD with no laser light on it
    • PD2 dark: The electronic noise measured out of the second PD with no laser light on it
    • PD1 - PD2, dark: The differential noise of the two PDs, with no laser light on them.
      • Notice how this is roughly sqrt(2) times the level of the previous two traces. This is what we expect from the incoherent sum of the two random signals.
    • Dark noise floor: The self-noise (shorted input) of the spectrum analyzer, while on the input range setting we used for the dark measurements.
      • We saved this as "PD1NFL", but since the input range never changed throughout the first 3 measurements, and the noise spectrum of the analyzer is stationary, this is a valid noise floor measurement for all three.
    • PD1 - PD2, balanced: The differential noise of the two PDs, with the laser on and the DC difference zeroed out (hence "balanced").
      • Notice how this measurement is significantly noisier than all the others. This means that, despite the large common-mode rejection we get of intensity noise from the laser (since the PDs are balanced), there is still a strong enough differential component that we see noise from the laser. This is a crucial thing to take home.
      • As of right now, this level (~25 nV/rHz --OR-- ~50 pW/rHz) sets the ultimate noise floor of the measurement in this configuration. Once we have figured out how to calculate an achievable signal size, we can calculate the sort of SNRs we can expect. This requires the following knowledge:
        • Using our ESD, to how large of a strain amplitude can we drive up the samples' modes?
        • How do we get from a strain amplitude to a rotation of polarization?
        • How do we get from a polarization rotation to a differential power signal in W at the PDs? (This last one is easy, and you should work it out ASAP)
    • Bright noise floor: Measured in the same way as the dark noise floor, but using the input range setting we used for the measurements with the laser on
    • Preamp noise (SR560): The well known---and visually re-measured---high-gain-setting input noise of the SR560 preamp (4 nV/rHz above ~10 Hz)
    • PD manufacturer spec (PDA36A): Calculated in the above-described way using the "NEP" figure. It seems strange that our actual measurement should be so far below this (~10x, not 100x), but it turns out that this is an over-estimated number by the manufacturer to save their a$$es. Depending on the quality of the 3rd-party components that go in, some units might be closer to this level than others. Considering the transimpedance gain of 1510 V/A and knowing that the opamp used is an AD829, the measured output noise value of ~7.5 nV/rHz is totally reasonable.

Also, some general plotting tips:

  • Use a linewidth of 2 for your plots. It gives them an air of confidence
  • The same applies for the fonts. The axis ticks, etc, should be ~12-14pt, the labels should be 14-16pt, and the title should be closer to 20pt. Otherwise, you just can't read anything. Legend font sizes depend on what you can fit in.
  • Use a grid so that you don't have to break out a ruler to interpolate
  • Set your axis limits so that you make good use of the plot space. All that whiteness is just a waste. Dynamic range rules.

Try to let this stuff soak in, as we'll probably have to make this whole measurement again. Next time, you will plot it!

Another thing: our whole noise budget will get a little more complicated once we add in the lockin, but this analysis of the front-end (the very place where physics meets measurement apparatus) is extremely important.

Quote:

[Giordon, Zach]

 The last post we discussed the noise measurements with a noticeable peak around the 50kHz. This time, we've set the preamp gain to 500 and retook the measurements. The attached image shows the result of said measurements.

One thing we noticed is that the photodetector noise is roughly two orders of magnitude smaller than our best estimates for this. Zach thinks it's not real, I think it's pretty awesome. Here some explanations of the measurements.

  • A-B output means that the output comes from the preamplifier on an AC coupled setting amplified at 500. This either came with the laser on or off. We fixed the range here and then ran a noise floor measurement where we grounded the input.
  • PDA and PDB mean Photodetector A and Photodetector B as listed in the experimental set up drawing in an eLog post some days ago. PDA has a Noise Floor (NFLR) measurement like before as we noticed that the range of it was significantly different from the A-B output range [this is not true of PDB].
  • Theoretical PD and Theoretical Preamp are values highlighted from the rough noise calculations made about a week ago. (Same place as the inclusion of the experimental set up).

I've also noticed that the plot doesn't make complete sense to me. For example, the noise floor of PD1 seems to be higher than PD1 itself - but maybe Zach can re-explain to me the difference between fixed range and auto range here.

For lazy people, I've reattached the experimental set up and noise calculations.

 

 

  289   Tue Aug 9 18:28:27 2011 Larisa ThorneDailyProgressCracklefull Michelson pictures

I call it: "Michelson on a Seismic Stack with Two Magnetic Actuators".

 

The second picture is of the result (a Bode plot) of testing to see if the servo/feedback loop designed did what was expected. That is, the transfer function resembles what was expected (see the transfer function portion of my second progress report for what these expectations look like).

  348   Thu Sep 8 21:55:46 2011 haixingSummarySUSfull levitation

The levitated plate is finally fully levitated without any physical touch of the tuning screws, but
with Eddy-current damping
for gaining enough phase margin [we need to modify the circuit to
remove the aluminum plates].

levitation.png

The error signal of the OSEM and the control signal for the coils are indicated in the following
figure of the Labview front panel (the fourth channel is not used, as we only have three degrees
of freedom to control right now):

labview_front_panel.png

The procedure for this levitation goes as follows: we first lock the magnet 1, and then magnet 3.
After the steady state is reached, we slowly increase the proportional gain of magnet 4 up to 0.5.
When the error signal from the OSEM approaches to zero, we gradually detach the tuning screw.
The changes have to be made very slow such that the control has time to response,
as our control bandwidth is quite small.  

config.png

Somehow, we are lucky in the sense that the three degrees of freedom [pith, yaw and vertical]
are weakly coupled to each other
. We realize the levitation, by simply using three independent
controllers.

To realize this, I made few small improvements of the maglev device:

1. The bottom fixed plate is adjusted such that it gives less constraint on the position of the OSEM to
    avoid the flags to touch the edge of OSEM (my newly designed ones do not work due to crappy
    hand-making by myself).

2. The tuning screws are wrapped with Teflon tapes to make them firm. Previously, the tapped holes
    are slightly larger than the screw size, and we cannot use them for a very fine tuning. Especially,
    they drift around during the transient times, as they are hit by the vibrating levitated plate.

3. We reattached those aluminum plates for Eddy-current damping.

We now need to fully characterize the system.

PS: The video for this levitation does not look awesome, so I did not post it ;-)

  418   Thu Feb 23 02:06:21 2012 ZachDailyProgressCoating Qgetting started with the HV setup

[Giordon, Alastair, Zach]

Alastair dropped by today and showed us how to use the HV amplifier.

When we got to the lab, we turned on the ion gauge and the pressure reading in the tank was ~10-7 Torr, which Alastair reckoned was pretty good for one day of pumping with the large tank-mounted turbo (Giordon thought he turned this on over the weekend but it looks like a cable was unplugged). Alastair instructed us on how to rig things up and then safely turn things on and off. We tested the ESD with a maximum DC offset of 3 kV and AC amplitude of 1.5 kV @ 1 kHz, and nothing seemed to spark or explode. 

Giordon and I then did some initial sweep testing by driving the amp with an Agilent function generator. Using the frequency estimates he posted before, we set up some narrow-band, slow sweeps across some of the modes and then monitored the spectrum of the PD difference signal on a spectrum analyzer in FFT mode. Alastair recommended doing it this way instead of taking a swept sine with the analyzer alone in order to better distinguish between a real signal and a spurious EM coupling.

All in all, we weren't that successful. We did see some cases of what appeared to be modes, roughly where his COMSOL model predicted, but they each had their own problems. The differences in measured vs. predicted eigenfrequencies were all at the high end or slightly beyond the bounds that he put on them by varying sample dimensions. It could be that some other material properties are off.

Here is a list of a few modes we sought to measure (if Giordon sees this perhaps he can upload his fancy animations so we can see what the modes physically look like):

  • ~5 kHz
    • This mode was completely swamped by some sort of intermittent glitching, which was apparent up to ~10 kHz or so
  • ~25 kHz
    • This was the most promising one we looked at today, but we saw some sort of strange double-peaking at some FFT spans and then not when we zoomed in to lower span. The model doesn't predict two nearly degenerate modes here, so there should in fact only be one. A common feature to all of the modes we actually resolved was broadening or sidebands from low-frequency solid-body motion of the sample (e.g., pendulum, torsional, tilting).
    • I think the next step should be to look at this mode in particular but with the proper lock-in readout
    • I very roughly measured its linewidth to be ~2 Hz. If in fact the measurement is valid then it places a lower bound on the mode Q of ~104
  • ~44 kHz (x2)
    • The model DOES predict two nearly degenerate modes here, and we saw some very broad peaks in this region. I'm not sure yet what the degeneracy means for our measurements.
  • ~80 kHz and above
    • It appears that modes of this high a frequency are too quiet for us to see, and any attempts to drive them were fruitless. Of course, the lock-in readout might help us to find them.

Lots more to come on Friday.

  419   Thu Feb 23 22:06:17 2012 Giordon StarkDailyProgressCoating Qgetting started with the HV setup

Quote:

[Giordon, Alastair, Zach]

Here is a list of a few modes we sought to measure (if Giordon sees this perhaps he can upload his fancy animations so we can see what the modes physically look like):

  • ~5 kHz
    • This mode was completely swamped by some sort of intermittent glitching, which was apparent up to ~10 kHz or so
  • ~25 kHz
    • This was the most promising one we looked at today, but we saw some sort of strange double-peaking at some FFT spans and then not when we zoomed in to lower span. The model doesn't predict two nearly degenerate modes here, so there should in fact only be one. A common feature to all of the modes we actually resolved was broadening or sidebands from low-frequency solid-body motion of the sample (e.g., pendulum, torsional, tilting).
    • I think the next step should be to look at this mode in particular but with the proper lock-in readout
    • I very roughly measured its linewidth to be ~2 Hz. If in fact the measurement is valid then it places a lower bound on the mode Q of ~104
  • ~44 kHz (x2)
    • The model DOES predict two nearly degenerate modes here, and we saw some very broad peaks in this region. I'm not sure yet what the degeneracy means for our measurements.
  • ~80 kHz and above
    • It appears that modes of this high a frequency are too quiet for us to see, and any attempts to drive them were fruitless. Of course, the lock-in readout might help us to find them.

Lots more to come on Friday.

Giordon did see eLog post. Here are fancy gifs. Click an image to see it in a new tab/window for animation to happen. I've attached a zip file that contains all gifs (for properly downloading). Images shown below are in order of increasing eigenfrequency (from the first "non"-translational mode [re: no fixed point]) to the 9th mode as referenced based on the bolded line in the PDF linked to the comment I've replied to.

1st.gif2nd.gif3rd.gif4th.gif5th.gif6th.gif7th.gif8th.gif9th.gif

  567   Wed Aug 29 11:36:46 2012 nicolasDailyProgressNoise Budgetgwinc-dev BQuad model doesn't like thick ribbons

In order to accentuate the thermal noise in a silicon test cavity, it would be nice to make the ribbons a little bit thicker. Sadly, the BQuad thermal noise model seems to explode when the fibers get thicker.

The three plots I will show have the following parameters in common:

4 fibers, single pendulum silicon suspension @120K. 10g mirror mass, 5cm fiber length, 2cm cavity length. The fiber width is 2mm and the fiber thickness varies in the three plots.

The first shows a fiber thickness of 0.05mm. The second has 0.1mm, and the third is 0.2mm.

As one can see, the model sort of goes more and more nuts as the thickness is increased. I don't really understand the model enough to know why this is the case, but it seems that to have a believable noise budget we might need to make a thermal noise model from scratch, rather than using gwincdev.

  1909   Tue May 18 10:28:50 2021 PacoLab InfrastructureEquipmentLoanheimann sensor update

Heimann (HTPA80x64d) thermopile array;

- First test to grab frames was done in my personal Win10 machine, with no success. Either I was unable to configure the server correctly, or the software "ArraySoft" is not supported in Win10. Upon contacting Heimann, I received instructions to update to a newer version but was warned that it's just a new GUI, nothing really changed from v1 --> v2. So didn't even bother.

- Instead, wrote a simple python-socket UDP server to catch the video stream. Most trouble happened when using temperature mode (command "K"). The client streams a bunch of zeros... My guess is that this unit does not have an internal temperature calibration, and one could in principle be uploaded but we probably don't care. Streaming in raw voltage mode (command "t") works well, as shown by the sample frame shown in Attachment 1.

- After recovering the CTN Win7 laptop from Radhika, I gave "ArraySoft" another change just to know the frames I was getting in python were not bogus. For this I pointed a 532 nm laser pointer straight to the sensor and got an image shown in Attachment 2. The key difference is the processing of the video stream. Attachment 1 is a single frame, while Attachment 2 is the average of 30 frames with no offsets present. 

- Another issue present during this task was a faulty USB connection. Sometimes moving the sensor around would interrupt the stream (power lost). I carefully removed the case and exposed the TO-39 package and surrounding electronics to inspect and search possible failures but after seeing none, I swaped the USB power cable with my portable battery charger and had a more robust operation... So I dumped the old USB cable, and will get a new one.

- Since this one was borrowed from TCS lab, I placed an order for another one which will be set up permanently in the lab. Hopefully this will be enough for the OSA.

  256   Tue Jul 26 01:25:17 2011 haixingDailyProgressSUShistogram of magnets

Just to add a little bit more details to the previous elog:

To obtain matched magnets, we measured the magnetic field strength of the magnets. We have two type of magnets: the
first one (for fixed magnets) is 1 inch in diameter and 1/32" inch thickness; the other one (for the levitated plate) is 1/2 inch
in diameter and 1/8" inch thickness [refer to the schematic for illustration]:

config.png

In total, we bought 12 1'' ones and 12 1/2" ones [we want to get the distribution before ordering more]. We used a Gauss meter
to measure the strength [in the axial direction]. We used a plastic block to fixed the distance between the Gauss meter and
the magnets.

For the 1" ones, the measured values are {94.9, 126.3,84.6, 109.8, 117.1, 94.2, 104.8,96.5,116.3 108.5,98.0,122.6}. The histogram
is the following [normalized with respect to the total number and the horizontal axis is Gauss]:



We fitted it with a Gaussian distribution with mean of 106.1 Gauss and variance of 12.8 Gauss.

For the 1/2" ones, the measured values are {126.7,131.9,127.9,129.3,125.8,133.1,132.4,124.8,130.7,125.0,136.2,135.0}. We
fitted it with a Gaussian distribution with mean of 130.0 Gauss and variance of 3.9 Gauss.



The 1/2" ones have a much smaller variance.

Even though the quantity is small, we were able to find 4 pairs of matched ones that are differed by 5%. Interestingly, since
the force between two magnets depends on the product of their strength, we can choose the magnets in such a way that
if the fixed magnets is 5% weaker, we can compensate it by choosing the levitated magnets is 5% stronger. This needs to
be confirmed by the force measurement. Just in case, we have ordered more 1" magnets.

  160   Thu Sep 2 13:27:43 2010 Vladimir DergachevMiscSUShysteresis measurements

There is no evidence of hysteresis in the latest measurements. The plot below zooms in to the few cycles in the middle of the upper plot.

The thick black areas are created by the proper mode of the tiltmeter and air currents.

  412   Sat Feb 11 13:47:08 2012 ZachDailyProgressCoating Qin-vac setup

Here are some notes and pictures of what was done yesterday for the in-vac setup:

Giordon has already reported on the ESD support. To make this, I drilled the Teflon bars I had made up in the appropriate way. The two side bars have oblong holes near the center (but shifted aft a bit), so that the crossbar holding the ESD can be adjusted finely in depth. The crossbar has several holes across the middle (perpendicular to the holes that mount it to the side bars), spaced so that the ESD can be moved left or right a bit as necessary to combat cancellation from symmetry. See his entry for a good picture.

While he worked on actually attaching it to the suspension, I was working on the HV connection. I decided the best way to do it was to mount the PEEK connector to a Teflon spacer, which is mounted to the base of the chamber via 1/4-20 vented and silvered cap screw. I countersunk the hole in the Teflon for the PEEK-mounting 8-32 screw so that I could fit the nut underneath. Here's a shot:

HV_connector.png

On one side of the connector, we have the HV supply provided by cable from the SHV connection on the side of the chamber, and the ground is provided by a cable that is screwed directly into the chamber base via 1/4-20 vented and silvered cap screw. Of course, I verified that the entire tank is indeed grounded with respect to the HV amp. Here is the whole assembly in the chamber:

connector_in_chamber.png

I'm not crazy about the angles of the cables coming out of the connector, so I may choose to shorten them.

I also connected the other cables (which will go into the PEEK connector from the other side) to the real ESD---which I also drilled beam holes into---with silver epoxy. The stuff is a bit of a pain in the ass, and I had to apply a good bit of it just to make sure the wire would be (mostly) submerged. I left it drying under foil.

epoxy_on_ESD.png

With this, we should be pretty much ready to weld in the sample and pump everything down on Monday.

  727   Sun Sep 8 21:51:14 2013 haixingMiscSUSissue of matlab function "margin()" with an unstable plant

I used the matlab function margin() to plot the phase and gain margins for the open-loop transfer function for maglev. It seems to give an incorrect answer. Here is what I got:

margins.png

As the gain margin is negative, this indicates that the system (plant + controller) is unstable. However, this is not the case.

I used the matlab function nyquist() to make a Nyquist plot, and this is what I got:

nyquist.png
The contour circles -1 counter-clock wise once, and this satisfies the Nyquist stability criterion, as the plant (in my case the plate can be modeled as a mechanical object attached to a negative spring) has one pole on the right-half complex plane. Basically, my plant together with the controller in indeed stable, which is also the reality.

Therefore, this seems to indicate that nyquist(), instead of margin() is the right way to examine the stability in the case with an unstable plant in matlab.

  321   Thu Aug 18 15:48:46 2011 Yi and HaixingDailyProgressSUSissues in digital control of single DOF

To better understand the digital control system, we first tried to control a single degree of freedom (DOF) with Labview
and NI DAQ system yesterday. We relaxed the constraint on the angular motion of the levitated plate [it was constrained
by mechanical springs originally]. This allows us effectively to have a single DOF system to work with [as shown by the
figure below]:



The experimental setup and its schematic goes as follows:

17082011(005).jpg

We used SR560 as a low-pass filter for anti-aliasing. The corner frequency for the low-pass filter is 100Hz.

After adjusting the working point, we get the error signal. In the figures below, we showed the error signal (orange curve) from the OSEM and the control
signal (cyan curve) from the analog output of the national instrument (NI) card, before (left figure) and after (right figure) the low-pass filter is turned off

17082011(004).jpg17082011(006).jpg

From the signal we can see that the system is oscillatory. It does not decrease when we apply the derivative control. From the control signal, we can
see that the sampling rate is very low, and the control signal is clearly discrete with a rate around 50ms.
Probably this is why we can not have a stable
control. Can someone give us some suggestions on how to proceed? Thanks.
 

  322   Thu Aug 18 20:27:21 2011 KojiDailyProgressSUSissues in digital control of single DOF

 - The previous entry showed that the sampling rate is 1ms.

If the loop is really running at 50ms, you should see an error output from the "timed-loop structure".

If the timeout error is found, the servo does not make sense anymore.

 

- Why don't you take the transfer function of the digital servo filter separately from the closed loop?

 

  323   Thu Aug 18 21:38:41 2011 HaixingDailyProgressSUSissues in digital control of single DOF

Thank you very much for your reply.

>> - The previous entry showed that the sampling rate is 1ms.

Yes, indeed it was. Actually, even in the current setup, the sampling rate for the channel is set to be 1kHz.
Jan told me the highest sampling frequency that we can get is of the order of 100kHz.

>> - If the loop is really running at 50ms, you should see an error output from the "timed-loop structure".

When we changed the loop time constant from 1ms to 100ms, it seems that there is no change at all. The control signal
still behaves like that. Maybe we do not know how to set it up correctly. However, there is no error output from the "timed-loop structure".
We will look into this more carefully.  Right now, we really have very poor knowledge of the digital system. I will come up to 40m
to bother you with few more questions tomorrow, if you will be around.

  725   Fri Sep 6 17:07:39 2013 haixingSummarySUSissues to be investigated

Since the plate is levitating, we are now in the position for real work. Here are the two major issues to investigate in the plan.

1. TF of the plate and cross coupling among different degrees of freedom (important in order to optimize the control servo)

We will measure various transfer functions to characterize the plate TF and cross couplings. We will build six degrees of freedom simulink model based on Georgios's work of three DOFs, and try to make a match between the model and the system.

2. Noise budget (to pin down the major noise source)

(a) sensing and actuation noise

We will calibrate the noise from the hall effect sensor. If it is confirmed to be the major noise, we can switch to the optical lever sensing scheme as planned. The coil is quite weak, in terms of voltage to force conversion factor, and it is 5mN/V. The thermal noise of the coil may not be important (to be confirmed with more rigorous analysis).

(c) acoustic noise

Right now the system is exposed in air, and it is anticipated that the acoustic noise is quite significant. To mitigate this noise, we can use a bell jar to cover it which can give a reasonable level of noise isolation.

 

(b) seismic noise

We will make a correlation measurement between the sensor output and the seismometer (or accelerometer) to see where the seismic noise dominates.

(d) ambient magnetic field noise

We will use two low-noise honeywell hall effect sensors [link] to measure the ambient magnetic field. To get a better sensitivity, we will use differential measurement by shielding one (together with instrumentation amplifier for amplifying the readout).

(e) thermal noise of the magnet

The major noise source comes from the random jitering of the magnetic moments due to thermal excitation. We can find the literature on how to analyze this kind of noise.

(f) long-term drift

We know little about the long stability of the magnets and also how the temperature drift affects the magnets. This needs to be investigated.

 

  603   Mon Nov 5 03:25:01 2012 ranaDailyProgressCracklejitter -> intensity noise

  This is a great find! The laser power fluctuations are limiting the interferometer noise. Now all you have to do is fix that.

You should maximize the output of the fiber after pump down. If its very sensitive to the knobs, maybe get more sensitive knobs. You will need to reduce the jitter -> intensity coupling by a factor of 1000 in order to get to the level that they had before.

Then remember that the sensitivity of the Michelson to intensity noise goes down as you reduce the Michelson offset. Instead of operating at mid-fringe, if you are able to turn up the loop gain you should be able to go to 1/100 of mid-fringe and get a nice noise reduction.

  606   Fri Nov 9 14:03:03 2012 ericqDailyProgressCracklejitter -> intensity noise

By tightening the hell out of the coupler and laser mount posts, and mounting them on an optics breadboard resting on some squishy rubber I had laying around, I am able to get better RIN coming out of the fiber.

LaserRINprogress.pdf

There is still plenty of room for improvement. The coupler alignment is kind of tricky; there are little screw to lock the adjustment stage in place which I hope would reduce the amount of jitter, but when I tighten them, it hurts my coupling, probably by affecting the alignment.

Today, I'm going to try and align and take some data to check out my noise performance and try to get an upper limit (again), since I don't really trust my last attempt. We'll see how alignment goes, seeing as I spent an inordinate amount of time yesterday trying to align to no avail. 

 

  246   Tue Jul 19 15:56:07 2011 Larisa ThorneDailyProgressCracklelab 050

 Lab room phone: (626) 395-3877

 

Also, does anyone know the password for the lab room computer? It's the one that says "controls for dhcp-123-221.caltech.edu"

  255   Mon Jul 25 15:07:56 2011 Larisa ThorneLab InfrastructureGenerallab 050

 The lab floor is being mopped tomorrow. Perhaps this would be a good time to clean/put stuff away? (I did start on this a little last week, but much can still be done)

  251   Fri Jul 22 12:47:54 2011 Larisa ThorneLab InfrastructureGenerallab equipment

I took the liberty of tidying up the Crackling table a bit.

The Cryo people left us a friendly reminder to "get our own shit": they had found many parts from their own experiment being used or lying around on our Crackling table. Parts belonging to the Cryo experiment are labeled with a dot of gold nail polish. I'm fairly sure I found, switched out and put away all these gold-dotted parts that were lying around on our Crackling table as I was cleaning up.

  334   Mon Aug 29 11:25:24 2011 Yi and HaixingSummarySUSlevitation of one degree of freedom

After modifying the digital and analog part, we demonstrated levitation of a single degree of freedom [one corner of the
the levitation plate (as explained in the previous Elog 321)]. This time, we again use the trick of eddy-current damping
by placing an aluminum plate above the levitated magnet to obtain enough phase margin. Because we have a poor modelling
of our plant, the circuit we design [the details will be shown below] cannot provide enough phase margin. We are now
trying to measure the plant transfer function [only possible if it is levitated] and modify our circuit. In the next stage, we will try
to levitate two corners of the plate, which has two degrees of freedom, before we jump to levitate the entire plate (three degrees
of freedom that need to be controlled in the current scheme).

We took a photo of the plate corner and also the control and error signals from the oscilloscope.

levitation.png control_signal.png

(the yellow curve shows the error signal from the sensor and the blue curve shows the control signal).

Yesterday, we try to measure the entire open-loop transfer function [especially to get the TF for the plant part] by
injecting signal after the sensor with preamplifier SR560 as a summing amplifier (as shown by the figure below). Due to
the transient signal (before reaching the steady state) from the OSEM always saturate the SR560, we cannot get the right
control signal to achieve a stable levitation. We then try to use Labview to measure the transfer function by using the
build-in vi: "response function measurement. vi", but the resulting curve is very bumpy and we cannot make any sense out
of it. The possible solution is to make our own summing amplifier which allows a large voltage input and output.


___________________________________________________________________________________________________

During the last few days, we have modified both the digital and analog parts of our system. The detailed modifications and
related issues are shown as follows:

>> Digital part:

[TF measurement] We change the time-loop structure, and now the sampling rate becomes higher than what has been shown
in Elog 321. To tell the new sampling rate and the time delay of the digital path, we use SR785 to make a direct frequency
measurement, instead of using oscilloscope. We can tell the time delay from the phase. The bode plot of the TF for the digital path
[a direct path with 2-order low pass filter around 170 Hz] is shown by the figure below:

From this curve, we learn that the sampling rate is around 300Hz (from the dip of the spectrum?), and the time delay is 4.6ms
---not a very decent DAQ, but sufficient at this preliminary stage.

[issue in computational power] We found a very critical problem in our digital system---the computer does not work properly (the computer is
a quite old one) and screws up the gain if we run other programs simultaneously (even open IE) or other graphic processes. Below we show the
difference in TF of the digital part between turning on and off the waveform chart in Labview for showing real-time control signal.

TF_difference.png
As we can see that the gains at high frequencies (above 5Hz) go down significantly.

[issue in PID controller] Initially, we used the build-in "PID.vi" in the Labivew to try the digital control. As it turns out that the derivative part of the
PID does not work properly
. We can clearly see many spikes in the control signal if we set the gain of the derivative control to be nonzero. This is
partially because the discreteness of the signal from the ADC, and the simply derivative control in the "PID.vi" is not band-limited. The high frequency
part of the signal screws up the derivative controller. Instead, we realize lead compensation by using an analog circuit. In the mean time, we will
try to add lead compensation by using a digital filter which is band-limited.

>> Analog part:

circuit_board.png

We have made many small changes to the analog circuit [as shown by the figure above]. Initially, channel two and three are coupled, as we want their signal difference.
Now we decouple them. We then have four parallel channels for the feedback control. We replaced many components to realize the following transfer function
[left panel shows the amplitude and the right panel shows the phase in degree (red cure is the calculated one and blue curve is measured one)]:



Initially, we thought that we have a reasonable good understanding of the plant, and the above circuit can provide a stable levitation
by using the Nyquist stability criterion, which turns out to be not the case. The design open-loop transfer function has a unit gain
frequency at 8Hz with a phase margin of 20 degree, as shown by the figure below:



The transfer function that we assumed for the plant goes as follows [based on our measurement]:

* coil to levitated magnet: 7.7 x 10^{-3} N/V
* magnet itself is modelled by a negative spring---the negative spring constant is -50N/m with mass equation to 240g
* the flag to the sensor (i.e., the displacement to the sensor output): 71 V/m

Now by using the stably-levitated system, we will be able to have more accurate measurements of the plant TF, and we can then
figure out what is the right filter for the lead compensation.

  331   Thu Aug 25 02:23:17 2011 DanDailyProgressCracklelock attempt

I could lock the Michelson for several seconds.
When I try to lock the Michelson, it seems that a noise at 200Hz grows up and breaks the lock. (Oscilloscope signal)
I measured a noise spectrum over a short time when the Michelson was locked. (Graph)
There are peeks at 53Hz and 214Hz.

I had tried to lock the Michelson by tow masses.
I hung another mass in a same way. (Fig)
I adjusted the filter, but I could not control.
It seems that a noise at 200Hz disturbs the control.

I measured the transfer function of the current buffer. (Graph)
It shows this circuit has gain 10.

 

  294   Wed Aug 10 12:58:30 2011 Larisa ThorneDailyProgressCracklelock attempt 1

 Here are the sample waveform results (best I could find) from the oscilloscope for my first attempt to lock the Michelson current constructed.

  296   Wed Aug 10 15:06:03 2011 Larisa ThorneDailyProgressCracklelock attempt 2

 [Seiji, Larisa, Vanessa]

 

Unsure why we weren't getting a good signal in the oscilloscope, we went over the criteria of a good/functional servo:

  1. Stability (around unity gain frequency)
  2. Actuator range (in terms of force and displacement)
  3. Gain (is there enough?)
  4. Lock acquisition

It was determined that the fourth point, lock acquisition, was the most likely cause for error. On rough estimate, we were getting about 1-2 orders of magnitude less work energy than was needed to control the mass' motion. 

One solution to this problem was to decrease the speed at which the mass was moving, which would in turn decrease the amplitude of motion. This meant we needed damping in addition to the damping that is already taking place in the configuration: something Seiji called "eddy current damping". 

 

Attached is one of the ways we hoped to improve our results: by shorting the actuator coils (both). As you can see, the signal is still pretty crappy...

  297   Wed Aug 10 15:44:34 2011 Larisa ThorneDailyProgressCracklelock attempt 3

While shorting the actuator coils, magnets have been set up close to the edges of the masses. This is part of a new scheme to use "eddy current damping", which we are using to try to lock the Michelson (one arm only, at the moment). The loop was no on.

 

First picture is the small Nd magnet close to the Romulus mass.

Second picture is the small Nd magnet close to the Remus mass.

Neither magnet is touching its respective mass, but it is on the order of 10-3m closeness. We have no had any problems with the masses touching the magnets: they were successful at damping the motion quickly enough to prevent touching.

 

The resulting waveform was starting to looking a bit cleaner...it showed many more points where the masses were changing direction of motion (inflection points?), and this corresponds to much smaller displacement amplitude. Still no locking, but we are much closer now.

  298   Wed Aug 10 17:33:18 2011 Larisa ThorneDailyProgressCracklelock attempt 4

Next attempt involved "killing" the seismic isolation stack, as well as one of the blades (I can't post pictures of this because they might be a liability to Seiji's professorship). Even with the box on top of the configuration and playing with the gains, our results mysteriously did not improve.

 

Perhaps more (Nd?) magnets for eddy camping?

 

------------------------------------------------------------------------------------------------------------------------------------------------------------

TO DO:

Lock the Michelson by the end of Thursday!

  299   Wed Aug 10 18:20:03 2011 Larisa ThorneDailyProgressCracklelock attempt 5

Quote:

 [Seiji, Larisa, Vanessa]

 

Unsure why we weren't getting a good signal in the oscilloscope, we went over the criteria of a good/functional servo:

  1. Stability (around unity gain frequency)
  2. Actuator range (in terms of force and displacement)
  3. Gain (is there enough?)
  4. Lock acquisition

It was determined that the fourth point, lock acquisition, was the most likely cause for error. On rough estimate, we were getting about 1-2 orders of magnitude less work energy than was needed to control the mass' motion. 

One solution to this problem was to decrease the speed at which the mass was moving, which would in turn decrease the amplitude of motion. This meant we needed damping in addition to the damping that is already taking place in the configuration: something Seiji called "eddy current damping". 

 

Attached is one of the ways we hoped to improve our results: by shorting the actuator coils (both). As you can see, the signal is still pretty crappy...

Nothing new. More fiddling around got us nowhere. As proof, I've attached the waveform. 

Better luck next time.

  300   Wed Aug 10 18:44:28 2011 Larisa ThorneDailyProgressCracklelock attempt 6

Quote:

Quote:

 [Seiji, Larisa, Vanessa]

 

Unsure why we weren't getting a good signal in the oscilloscope, we went over the criteria of a good/functional servo:

  1. Stability (around unity gain frequency)
  2. Actuator range (in terms of force and displacement)
  3. Gain (is there enough?)
  4. Lock acquisition

It was determined that the fourth point, lock acquisition, was the most likely cause for error. On rough estimate, we were getting about 1-2 orders of magnitude less work energy than was needed to control the mass' motion. 

One solution to this problem was to decrease the speed at which the mass was moving, which would in turn decrease the amplitude of motion. This meant we needed damping in addition to the damping that is already taking place in the configuration: something Seiji called "eddy current damping". 

 

Attached is one of the ways we hoped to improve our results: by shorting the actuator coils (both). As you can see, the signal is still pretty crappy...

Nothing new. More fiddling around got us nowhere. As proof, I've attached the waveform. 

Better luck next time.

 Maybe we just need to wait for the blades to damp longer? This is the same waveform after a few minutes of "chilling out"...

  302   Thu Aug 11 17:18:31 2011 Larisa ThorneDailyProgressCracklelock attempt 7

Trip to the 40m yielded these really cool magnets (see below).

We were hoping for many smaller magnets, like the ones used for the magnetic actuator set-up, but Steve Vass informed me that for masses of the magnitude we were using, the larger magnets would be more effective for eddy current damping. There was some difficulty finding a good angle/elevation to affix them so that they wouldn't attract the steel plates or the screws being used, so they were on the order of 10-2m away, instead of 10-3m with the smaller magnets. 

Conclusion: with these much larger magnets contributing to the eddy current damping, there was only a very marginal change. The masses are still moving too much.

  303   Thu Aug 11 17:26:32 2011 Larisa ThorneDailyProgressCracklelock attempt 8

 This time, we tried simplifying the configuration a lot. Changes include:

  • Only one seismic stack, no rubber isolation remains
  • One of the mirror-masses has been eliminated and replaced with a stationary mirror, so only one arm of the Michelson will move (when driven by actuator)

No significant changes to the oscilloscope output. It's still as crappy as before

  1897   Tue Jan 26 11:47:12 2021 PacoDailyProgressGenerallow quality PDH error signal

After getting what looked like a decent cavity reflection signal, installed RFPD yesterday. For this, removed the lens that was right before the PD because the RFPD area is large enough, but keep ND filter in place. Powered with +- 18 VDC and monitor DC out on the scope, and RF out is sent to the IF of the mixer in the PDH box. For the LO, split the Marconi RF output and connected the demodulated signal into Ch2 of the scope in hopes that there was an error signal.

A hint of the error signal is present (blue trace below), although deeply buried in line noise (and harmonics up to ~180 Hz) so there really are two things to optimize now -->

  1. Line noise (hunting for ground loops or equipment, e.g. power supplies, analyze LO spectrum before/after splitters, mixers, etc...)
  2. Mode matching (this was the first reaction, as improving the cav refl SNR by means of mode matching makes a better pdh err signal)

Other things attempted so far -->

  • Switched mixers, splitter, and RF cables
  • Bypass the phase shifter completely
  • Scan LO phase
  • Floated RFPD power supply
  • Floated PDH box power supply (really only affecting the phase shifter if anything, though unlikely to matter at this point)
  581   Wed Oct 10 00:06:36 2012 haixingDailyProgressSUSmaglev

Updates:

Yesterday, I stuffed the pcb boards for the hall-effect sensors (Allegro A1301 A1301-2-Datasheet.pdf),
and also one quadrant photodiode circuit for testing.


hall_effect_sensor_board.jpgQPD_board.jpgQPD_board_stuffed_front.jpg
   [Hall effect sensor]             [QPD (before stuffed)]          [QPD stuffed (front side)]

The photodiode used is Hammatsu Si Pin photodiode S4349, and the operational amplifier
is Analog Device ADA4004-4 1.8 nV/√Hz, 36 V Precision Amplifiers. Here I attached the
schematics and the pcb layout for the QPD, which might be useful for others in other applications.
The zip file goes as follows:
QPD_Altium_files.zip

Issues found (some small modifications are needed):

  1. The 1/4-20 tapped holes of the fixed plate is too tight and the screws cannot go through.
  2. The 0.5inch hole on the floating plate is a little bit too small and the reflector cannot be fitted in.
  3. There is also a tiny problem with the slot (wrong sizing) for fixing the magnet.

Things to be done this week:

  1.  Design Signal conditioning circuits (some simple filtering and amplification) for the hall-effect sensors,
    coils and also the linear DC motors.
  2. Stuff the chassis power board for the binary input and output.

List of items needed (or to be ordered):

  1. A rack for fixing various chassis [the analogy and digital parts].
  2. Three 1-u chassis boxes for the signal conditional circuits, the front panel (BNC connectors)
    and the back panel (D-sub connectors slots).
  286   Tue Aug 9 10:25:25 2011 HaixingDailyProgressSUSmaglev circuit board

In order to use Labview for maglev, we need to have an analog interface for the input (OSEM) and output (coil).
I have designed a new board based upon the old circuit design we had previously for the maglev. Here we only
keep the LED drive and coil drive part. The LED drive is a second-order low pass filter with Sallen-Key topology
with a corner frequency around 4.5Hz, designed by Rana.The coil drive is a voltage follower with Gain of 2 where
we use BUF634 to boost the current of quad opamp L1125.

The schematics for the LED drive is given by the figure below:


LED_drive.png

The schematics for the coil drive is given by the figure below:

coil_drive.png

The final board is

circuit_board.png

The Altium file for this board is in the attachment titled: analogy_circuit.zip

 

  240   Wed Jul 13 13:05:30 2011 Vanessa AconDailyProgressCracklemagnetic actuator notes

 A quick calculation of the force from a solenoid on a small magnet (which we approximate as a dipole), from which we can find the dimensions and the number of coils for the solenoid we need (not sure if it is correct; will think more on it later).

  243   Fri Jul 15 10:12:01 2011 Vanessa AconDailyProgressCracklemagnetic actuator notes

The magnet should be placed so that it is half out of the coil. At the mouth of the coil, you get a strong field gradient so you ought to calculate the force at that point. Then remember that the max current we can supply is 100 mA before the coil starts getting warm.

  244   Fri Jul 15 14:04:27 2011 Vanessa AconDailyProgressCracklemagnetic actuator notes

 Fixed my calculations from my previous post.  Hopefully they are correct now.

Calculated the magnetic force on a small magnet at the end of a solenoid (approximating the magnet as a dipole with magnetic moment mu).

  250   Fri Jul 22 12:36:49 2011 Larisa ThorneDailyProgressCracklemagnetic actuator set-up notes

 Attached is the promised circuit diagram, describing what was done yesterday in terms of configuration. 

A few notes on the diagram:

  • The oscilloscope was hooked up in order to see the physical signal that was coming from the source and the signal that was seen by the photodetector (produced by the motion of the mass moving across the laser beam path)
  • The laser used in the experiment was one of the two HeNe lasers on the Crackling table (so lamda~633nm)
  • For those of you not familiar with what the SR780 is: a network signal analyser. This is an older machine taken from the (defunct?) LIGO lab in the High Energy Physics building, which Tara retrieved for the use of crackling experiments. It was used to measure the transfer function (of signal inputs B/A), using the Bode window type over the range of frequencies 1-10Hz.
  • Again, for those of you not familiar with the SR560: we used it to get rid of the DC offset in the signal. The SR560 contains a bandpass filter with corner frequencies 0.03-300Hz (well outside the frequency range of interest by a factor of 30 on each extreme), boosts the output signal by a gain of 10, and uses DC coupling.

 

New magnetic actuator configuration notes:

  • I soldered the wire ends of the solenoid to a couple of wires that had a BNC connector on the other end (see last image in this last post)
  • We calculated the resistance of the solenoid to be R=11.3 Ohms (11.7 total - 0.3 for the cables on the multimeter)
  • The inductance of the solenoid was found to be L=254uH

More to come later this afternoon...

 

  252   Sat Jul 23 17:22:01 2011 haixingDailyProgressSUSmatching the magnets

Yi Xie and Haixing,

We used the Gauss meter to measure the strength distribution of bought magnets, which follows a nice Gaussian distribution.
We pick out four pairs--four fixed magnets and four for the levitated plate that are matched in strength. The force difference is
anticipated to be within 0.2%, and we are going to measure the force as a function of distance to further confirm this.

In the coming week, we will measure various transfer functions in the path from the sensors to the coils (the actuator). The obtained
parameters will be put into our model to determine the control scheme. The model is currently written in mathematica which can
analyze the stability from open-loop transfer function.

  568   Wed Aug 29 11:43:55 2012 nicolasDailyProgressNoise Budgetmatlab source

The source for what I've been using to calculate thermal noise.

ELOG V3.1.3-