I estimated the transfer function of the seismic stacks using a rough model I made based on the LIGO document LIGO T000058 -00. I used a Q of 3.3 for the viton springs, and resonant frequencies of 2.3, 7.5, 15, and 22 Hz (measured in that document for the horizontal motion). I multiplied the simple mass-spring transfer function four times for each layer of metal/spring, with the respective resonant frequency for each. The pendulum suspending the test masses has a resonant frequency of 0.74 and a Q of 3, according to the same document.
When I multiply the net transfer function (pendulum included, the green line above) by the differential motion of the x arm that I measured in eLog 7186, I find the differential motion of the test mass (NOTE: I converted the differential motion to displacement by multiplying by (1/2*pi*f)).
It agrees within an order of magnitude to the seismic wall from the displacement noise spectrum hanging above the control room computers.
Finally, I looked at how the geophone and accelerometer noise spectra looked compared to the ground differential motion (any STACIS sensor signal will also be multiplied by the stack/pendulum transfer function, so I'm comparing to the differential motion before it goes through the chamber). Below about 1 Hz, it is clear from the plot below that the STACIS could never be of any benefit, even with accelerometers rather than geophones as the feedback sensors.
Koji just found the emergency exit door unlocked again. NOT GOOD.
We have determined that if you use the emergency door to enter the lab, it leaves the door unlocked, unless you go back outside and deliberately lock it. This means that someone has been using the emergency exit as a regular entrance.
It's fine to leave by that door, but you should make a habit of entering through the regular door. Using the back door as an entrance is a special case situation, when they have the main door blocked.
After Rana and Yoichi tweaked the arm locking filters, we have had some pretty awesome lock stretches. 5-day minute trend.
I made the plots a little nicer and added new sensor noises (from Brian Lantz's scripts and measurements). Click to enlarge.
The last plot shows that these other sensors' noises are lower than the differential ground motion below 1 Hz. Though 3 seismometers per STACIS is impractical, this shows that such seismometers could be used as feedforward sensors and provide isolation against differential ground motion. At these noise levels, the noise of the high voltage amplifier circuit in the STACIS would probably be the limiting factor.
Below is the bottom view of the geophone preamplifier and controller for the STACIS. It slides into the upper part of the STACIS, under the blue platform. The geophone signal goes in the bottom left, gets amplified, filtered, and otherwise pampered, and goes out from the bottom right. From there it goes on to the high voltage amplifier, and finally to the PZT stacks. Below right is a closer view of the output port for the preamplifier, top and bottom.
I suggest de-soldering and bending up the pins that carry the geophone signal (so the signals don't go directly to the high voltage amplifier), and adding the circuit below between the preamp and amplifier. The preamp connector is still attached to the high voltage amplifier connector in this setup, only the geophone signal pins are disconnected.
More on the circuit and its placement:
The first op-amp is a summing junction, and the second is just a unity gain inverter so that signal doesn't go into the high voltage amplifier inverted. I tested this with the breadboard, and it seems to work fine (amplitudes of two signals add, no obvious distortion). The switches allow you to choose local feedback, external feedforward, or both.
The geo input will be wires from the preamp (soldered to where the pins used to go), and the external input will be BNC cables, with the source probably a DAC. The output will go to the bent up pins that used to be connected to the preamp (they go into the high voltage amplifier). This circuit can sit outside of the STACIS- there is a place to feed wires in and out right near where the preamplifier sits. For power, it can use the STACIS preamp supply, which is +/- 15V. The resistors I used in the breadboard test were 10 kOhm, and the op-amp I used was LT1012 (whose noise should be less than either input, see eLog 7190).
This is visually represented below, with the preamp pin diagram corresponding to the soldering points with the preamp upside down (top right picture):
THE GOOD: SimPlants ITMX and ETMX are officially ONLINE. Damping has been instituted in both, with varying degrees of success (see Attachment 1). An overview screen for the SimPlants is up (under XARM_Overview in the sitemap - you can ignore the seperate screens for ETMX and ITMX for now, I'll remove them later), C1LSP will be online/functional by Monday.
The super high low-frequency noise in my simPlant is from seismic noise and having a DC response of 1, so that the seismic noise at low frequencies is just passed as is and then amplified along with everything else in the m --> counts conversion. Not quite sure how to deal with this except by NOT having a DC response of 1 (which it technically doesn't have when you do the algebra - Rana said that "it made sense" for the optic to have unity gain at low frequencies, but the behavior is not matching up with reality).
THE BAD: It looks like the ITMX Switch from Reality to simPlant doesn't work (or some of the signals aren't getting switched). When switching from reality to simulation, it looks like the control system is receiving signals from the SimPlant, but is transmitting them to the real thing. As a result, when you flip the switch from reality to sim, ITMX goes seriously crazy and starts slamming back and forth against the stop. REALLY NOT GOOD. As soon as I saw what was going on, I turned back to reality and flipped the watch dogs on (YES THEY WERE OFF). I'll investigate the connections between the plant and control system some more in the morning (i.e. later today) (this is also probably what is causing the "lost connections" in c1sup/sus we can see in the machine status screen).
I optimized the TM views with illuminator light on quad1 It actually looks better there.
I'll post a dark- OSEM light only in jpg tomorrow. ETMY camera is malfunctioning in dark condition now.
ALL illuminator lighting are off. ITMX and ETMY looks back lighted. I will check on their apertures.
In order to focus on 1064 resonant spots I tried to restore and align the arms by script. I only got flashes.
I used the LED illuminations at ETMX and BS yesterday for a tour.
I am afraid that I left them on.
> I used the LED illuminations at ETMX and BS yesterday for a tour.
> I am afraid that I left them on.
It was turned off before the picture was taken.
All LED illuminations were turned off. I checked them a few times.
Problem with ITMX solved! The ITMX block in c1sup hadn't been tagged as "top_names". I rebuilt and installed the model, and there are no longer lost connections, :D
The problem with the glow on the ETMY face is due to the red light being scattered off of the optical table from the HeNe laser for the OL. Why is the red light hitting the table?
One way to fix the problem for the camera image is to insert a long pass filter (if Steve can find one).
Edmund Optics: NT62-874
Edmund Optics: NT65-731
Edmund Optics: NT32-759
Den and I decided to try to classify seismic signals in the frequency domain rather than the time domain. We looked at amplitude spectral density plots of all of the data in our set, and noted that there were noticeable differences in the frequency domain for midnight quiet, trucks, and earthquakes.
For example, here is the time series of quiet, midnight seismic noise as compared to the seismic noise at the peak of an earthquake - the earthquake signal is noticeably higher in the 1 - 3 Hz region. Likewise, for the truck signal, there are noticeable bumps that arise at 10 and 30 Hz during the peak of the truck's motion due to the resonant frequency of the truck bouncing on its wheels.
We investigated this potential means of classification further by considering the linear separability of the power of our signals in various frequency bands. Below is a plot of the power of a normalized signal in the 0.1 - 3.0 Hz region vs. the power of the normalized signal in the 3.0 - 30.0 Hz region - calculated by means of fft and separation of the discrete resulting frequencies (in short, an ideal filter).
There is rather clear linear separability of the normalized signals in this case, as two lines could potentially be drawn to separate trucks from quiet and earthquake in this case (with a few misclassified points due to quiet - since the lab isn't actually empty and quiet in the middle of the night, and man-made seismic disturbances to occur). The reason we have to normalize our signals lies in the fact that the data set had different gains for various seismometers at different times. Normalization not only allows us to use our data set for training effectively, but it also assures that the online classification, if the online signals are also normalized, will allow for variable seismometer gains in the future and still be able to classify signals.
I looked at the linear separability of our training set using various combinations of frequency bands, and deduced that the current separation in the BLRMS preforms best (coincidentally, since the BLRMS separations are just decades), which meant that we could use the current BLRMS system we have for online classification of seismic noise.
Thus, I built a neural network which performed classification with the following parameters:
- One hidden layer of 20 neurons
- Gradient descent backpropagation with learning parameter mu = 0.175
- Sigmoidal activation functions for each neuron (computationally achieved by a parametrized hyperbola rather than an actual hyper-tangent in order to save on computation time).
- 5 inputs - the normalized fft^2 of the signal (since the root of a signal doesn't add linearly to 1) in the following frequency regions: 0.1 - 0.3, 0.3 - 1.0, 1.0 - 3.0, 3.0 - 10.0 and 10.0 - 30.0 Hz. Since this division was done through the (frequency, fft value) return in Matlab, the signal was essentially filtered ideally into these frequency bands.
- 3 output neurons representing an output vector, with desired output vectors of [1, 0, 0] for earthquake, [0, 1, 0] for truck, and [0, 0, 1] for quiet.
- 1,600,000 training epochs (batch backpropagation on all of the data)
Below is the best learning curve for this network, representing the total amount of inputs misclassified out of 224. The best result achieved was 30 misclassified signals out of 224. Obviously this is not ideal, but our data is not totally linearly separable. This could, however, be reduced with further iterations, but given the close to 0 slope of the learning curve between iteration number 1,000,000 and number 1,500,000, this could take a very long time.
Thus, I trained the network, generated the weight vectors and optimal activation function parameters, and was ready to implement a feed-forward neural network (with no online training). My next e-log (Part 2) will be about this system and will be posted shortly.
ACAD files of the 40m optical layout have been updated as per the vent in Aug 2011.
Files are available at the 40m svn docs-->Upgrade12-->Opt_Layout2011.
To ease the pain of hunting files, optical layout ACAD files have been moved to a new directory 40M_Optical Layout in the repository. Relevant files from directories Upgrade12 and upgrade 08 will be moved to "40M_Optical Layout" very soon and eventually these old directories will be removed.
Changes mentioned by Koji and Steve have been updated to the files (except for the cable connector which have been added but whose part number has to be found to match accurately with the current layout). The file in the directory should now match the current setup after the last vent Aug 2011.
Let me know if you find any mismatch between the current setup and the layout.
Plans about new installations/reconfiguration during the new vent will be carried out in a separate file.
C1LSP has been added to the site map. I'll work on filling in the structure some more today and tomorrow (as well as putting up PDH and REFL/AS MEDM screens).
NOTE: Does anyone know how to access channels (or if they're even there) for straight Simulink inputs and outputs (i.e. I have some sort of input, do something to it in the simulink model, then get some output)? I've been trying to add ADC MEDM screens to c1lsp, but channels along the lines of C1LSP-ADC0_0_Analog_Input or C1LSP-ADC0_A0 don't seem to exist.
I've put EM 172 microphones inside Steve's isolation box to measure their noise. I've attached mics to each other and aligned them using the tape.
At low frequencies (below 1 Hz) the noise is limited by ADC as there is a 10 Hz high-pass filter inside mic readout box.
ADC noise is measured by splitting the signal from 1 mic into 2 ADC channels.
NVM. Figured out that I can just look in dataviewer for the channels. It looks like there aren't any channels for ADC0...I'll try reinstalling the model and restarting the framebuilder.
Since the classification finally works (or seems to work..), I wrote triangulation scripts in Python which triangulate the signals, and a plotting script in Matlab which generates a heat map of seismic noise source locations. I switched the ADC Streckeisen and Trillium connections in order to better triangulate with the current channels, and will return them either tomorrow, or when I come back from Livingston so that we can have weekday data as well.
There was a 5.6 Earthquake that occurred near Tofino, Canada about 30 minutes ago. It showed up rather strongly on the BLRMS.
The neural network classification system also picked up on it, but oscillated from Earthquake (1.0) to Quiet (0.5) perhaps due to the filters we currently have installed. Here is a shot of the GUR1X classification channel at the time of the EQ:
Data from PEM now goes directly to OAF without using RFM. Transmission RFM -> OAF errors are gone as RFM has to read 30 channels less now.
Again kernel "protection error" occured as before with PEM model so OAF model could not start. I changed optimization flag to -02, this fixed the problem.
I made the signal box as described in eLog 7210. It adds the geophone signal and an external signal.
It has six switches, for x, y, and z signals from both an external and local (geophone) source. The x signals add if both x switches are flipped down (and the same for the other directions). For example, if you want to feed in only an external signal in the x direction, flip down the external x direction switch (it's labeled on the box), leaving all others flipped up.
The x, y, and z outputs are wired to the pins from the preamplifier that go to the high voltage board. These I disconnected from the preamplifier by cutting at their base (there are spare connectors if this wants to be undone, or, a wire can just be soldered from the pin to its old spot on the board). The power (plus/minus) and ground are wired to the respective pins from the geophone preamplifier (naturally, the STACIS must be turned on for the box to work since the box shares its power source). Below, the front (switches and geophone/external inputs) and back (power, ground, outputs) of the box are shown:
The preamplifier can plug into its regular connectors- the x,y,and z signals will all be redirected to the signal box with these modifications. The box sits outside the STACIS, there is room to feed the wires out from underneath the STACIS platform.
NOTE: The geophone z switch is a little different than the others, just make sure it's flipped all the way down if you want that signal to be seen in the z output.
Atm1, condition: all oplev lasers are off or blocked, green shutters are closed at the ends, PSL out put shutter is closed, all outside LED illuminating are off, all room lights are off
Only the OSEMs are on. ETMY and ITMX are still look like illuminated.
Atm2, condition: open PSL shutter. ETMY at 11 o'clock and ETMX 1 o'clock bright scattered spot of 1064 nm are visible
Atm3, condition: closed PSL shutter and restored all oplev He/Ne lasers, it is visible at ETMY
Next: I will disconnect power to OSEMs at ETMY
ETMX has some periodic oscillation. It's damping was found tripped this morning.
Static filter was adjusted to filter 1 Hz resonance in MCL and it could do it. Stack is not great in this experiment due to the phase mismatch. I'll fix it.
We tracked this down to the power normalization stuff that Yoichi added over the weekend.
With a non-zero normalization factor, and a small TRX transmission, the input the XARM controller gets really big. When XARM is then triggered, a huge impulse is sent into the SUS_ETMX_LSC input, which causes the Vio2 filter in FM0 to ring like crazy. This probably also explains why Yoichi was seeing trouble locking the arm when the normalization is on
The solution, as Yoichi also mentions, is probably to trigger the normalization like we trigger the rest of the boost filters.
The videocapture.py script is now in ...../scripts/general/ , along with the videoswitch.
Also, there's a button gui on the VIDEO medm screen to capture different camera views.
Rana points out that we haven't had fast channels for PMC (trans, refl, pzt), input laser things, more FSS things since the upgrade. Bad.
I (for the first time personally) locked the FPMI. I have data for the POX11I, POY11I, AS55Q error signals for each arm and the Michelson (JenneLockingDTT/FPMI_error_signals.xml), but I haven't calibrated the data yet - Self: do this! FPMI with arms locked using IR has been happily locked for a long time now - this is good.
From elogs / my old MICH calibration script, I have the plant calibrations of:
POY: 1.4e12 cts/m
POX: 3.8e12 cts/m
AS55: 9.4e9 cts/m
MICH has FM 5 on, Xarm has FM4-10 all on, Yarm has FM3-10 all on.
Post note: FM 3 - the integrator - for Xarm wasn't triggered. It turns on just fine, so I've got it triggered just like Yarm.
Also, just remembered - I turned off the XARM TRX power normalization, since it was causing crazy numbers in the xarm servo. The XARM locked pretty easily after that.
The green beam for the Xarm is flashing a pretty nice 00 mode, but isn't catching lock.
The green beam for the Yarm isn't flashing at all that I can tell from just the camera views. I don't have energy to start this sometimes monumental task tonight, so I leave it for Future Jenne to work on.
Oplevs centered in flashing condition, except PRM and SRM. IP POS centered also,
I like this new summing screen of Jenne.
I installed pyepics version 3 (http://cars9.uchicago.edu/software/python/pyepics3/overview.html) in ..../scripts/pylibs . I also added an "epics.conf" file to /etc/ld.so.conf.d/ , which points to the place in /ligo/apps/epics/base/lib/linux-x86_64/ where the DLLs live. All .conf files in /etc/ld.so.conf.d/ get included in the path, so python should always automatically be able to use epics now, after you "import epics" in a script.
This is supposed to give us direct channel access to all epics channels, rather than using Yuta's wrapper scripts for ezca stuff. I was going to write a tdsavg equivalent using camonitor, since it's unclear whether tds tools are being supported anymore.
However, I'm not getting it to connect to the server that serves epics, so I can't get the values of any channels. All of the info in the link above assumes that you automatically get a connection, and I'm out of ideas right now of things to try. Does anyone else have any ideas?
Temperature sensor for vacuum. How many : 2 or 3 ? $350 each
Glass encapsulated thermistor #55007 with Ceramabond 835-m glued onto spade connector and hooked up to controller DP25-TH-A with analoge output.
This zero to 10Vdc can go to ADC
Optical layout of the current endtable at ETMX has been updated in the svn repository (directory: 40M_Optical Layout). This layout will help in redesigning the table for the proposed replacement.
Some part numbers of mounts/optics are missing and will be updated once I find them. If you find anything wrong with the layout, do let me know.
POY was looking funny, and the YARM wasn't locking. It looked like POY wasn't seeing any light at all. I went to check, and it looks like a beam dump got accidentally placed in the POY path during oplev adjustments this morning. POY is back, locking continues.
While meditating on other things, I have noticed / found the following today:
YARM ASS works okay. Yesterday I measured the sensing matrix for the ASS for both arms (although I forgot to copy one of the matrix elements to my text file for Xarm - needs remeasuring). I put the Yarm matrix in (after appropriate inversion, only non-zero pitch-to-pitch, yaw-to-yaw elements). I turned on the Yarm ASS, and the yaw converged pretty quickly (couple of minutes), with gains of -1 in the servos, overall gain of anywhere between 0.005 and 0.010. The pitch took much longer, and I had to 'pause' several times by turning off the overall gain for the yarm ass when the MC lost lock (which has happened several times tonight - unknown cause). Eventually, the pitch settled out, and quit changing, but the lockin outputs weren't zero, even though the error signal for the servos were almost zero (gains for the pitch servos were -0.5, overall gain ~0.005 was better than 0.01 - higher gain caused oscillations in the lockin outputs). I think this means that I need to remeasure the yarm pitch ass matrix. It's still much, much faster to just turn on the dithers, watch the striptool of the lockin outputs, and align the cavity by hand.
I think the ETMX Trans camera view is clipped a little bit. I went down there, and it doesn't seem to be on the last optic before the camera, and moving the spot on the camera doesn't change the shape of the image, so I don't think it's on the camera. We should look into this, since it's either clipping on the BS that separates some camera beam from the TRX beam, or TRX is getting a clipped beam too. If the clipping is any earlier in the Trans path, the Trans QPD could also have some clipping. This requires investigation. The xarm trigger needs to be reset/disabled so we don't lose lock every time we block the TRX beam (as was happening to me).
XARM really doesn't like to relock unless the POX whitening is turned off. Good flashes, doesn't really catch (10+ min waiting (while working on Yarm stuff) ). After turning off the whitening, it catches almost immediately. Even though it's on the to-do list to rethink the tuning of our whitening, we should probably implement the whitening triggering now anyway. It'll make things easier.
The double integrator that Rana implemented in the X and Y arm servo filters last week take 8 seconds to turn off (due to Foton settings), so even though they are triggered to turn off immediately upon lockloss, they sit around and integrate for 8 seconds, so have huge signals. If the cavity flashes and the locking trigger engages during that 8 seconds, we send a huge kick to the ETMs. I'm modeling the response of the filters to an impulse and noise, particularly in the case of ramping on the double integrators. The problem is that a flat filter has 0deg phase, but the double integrator has 180deg phase at low frequencies, so there's some weird sign flipping that can happen as we ramp - this is part of what I'm modeling.
MC is losing lock unusually often tonight. Everything on the servo board screen looks normal (which is good since that's all set by the autolocker). I just disabled the test exc in, but that's been left enabled for a while now, and it hasn't (I think?) been a problem since there shouldn't be anything connected to the board there. PMC transmission is a little low, 0.816, and FSS is starting to get near -1 on the slow actuator adjust, but we've seen locking of the PMC problems around -1.5 or -2 of the FSS, and the adjust value was at -0.8 earlier tonight and we still had MC locking problems. I have had the seismic channels open on Dataviewer for the last several hours, and I'm not seeing any spikes in any of the Guralp channels which correspond to the times that the MC loses lock. BLRMS don't seem particularly high, so MC lockloss cause is still a mystery for today.
The ETMX monitor selector on the VIDEO screen seems not to be switching the actual camera that's shown on the monitor. Using the script command itself works, so my screen is wrong.
Reinforced concrete grout plate for existing carbon steel stands at the ends.
Last week, Rana changed the integrators in the arm LSC servo filters to be double integrators with complex poles.
Yesterday, I found that using the "timeout" feature of Foton (at filter ON/OFF request, waits for zero crossing, or T seconds, whichever comes first) is useful for turning on the integrators, but bad for turning them off. When we're locked, the error signal is oscillating around zero, so there is often a zero crossing. When we lose lock, we want to turn off the filter immediately. But, as soon as lock is lost, the input signal gets large, and doesn't often cross zero, so the filter waits 8 seconds until actually turning off. If the arm flashes any time during that 8 sec, we send a big kick to the optics.
An alternative option could be ramping the filter on. However, since the double integrator has -180deg phase at low frequencies (until the poles at ~5Hz), the transition between no filter (0deg phase) and integrator on could be problematic. I simulated this, and find that for the very beginning of the ramping process, we would have a problem.
The filter is defined as: NoFilter * (1 - R) + Integrator * (R), so for R=0, the integrator is off, and for R=1, the integrator is fully on. R can be any value [0,1].
The first figure is the time series (1 second, 16kHz), ramp goes from 0->1 or 1->0 in 1 second:
The second figure is bode plots for selected values of R:
As R gets smaller and smaller, the notch goes to lower frequency, and becomes higher Q. So perhaps ramping is not a good answer here.
What if we go for single or triple integrator, to get rid of the (+1) + (-1) problem?
It seems as though there is something funny going on around ~1.5 Hz, starting a little over an hour ago.
We see it in the BLRMS channels, the raw seismometer time series, as well as in various suspensions and LSC control signals. It's also pretty easy to see on the camera views of all the spots (MC, arms, transmissions....AS is a little harder to tell since it's flashing, but it's there too).
The plots I'm attaching are only for ~10min after the jump happened, but there has been no change in the BLRMS since it started. Usually, we'd see an earthquake in all the channels, and even big ones ring down after a little while. This is concentrated at a pretty narrow frequency (some of Den's plots for later have this peak), and it's not ringing down, so it's not clear what is going on.
Here is a whole pile of plots. Recall that the T-240 is plugged into the "STS_3" channels, and we don't have BLRMS for it, so you can look at the time series, but not any frequency specific stuff.
Jenne and I did adaptive filtering of MC_L and measured how X and Y ARM control signals change compared to non-filtered MC_L. We did the test during 1.5 Hz seismic noise activity and adaptive filter was able to subtract it. However, it adds noise at high frequencies, It is not seen in MC_L but it is present in the ARMs control signals.
I'll investigate this problem. May be we need to reduce adaptation gain. In this experiment it was 0.1 and adaptive filter convergence time was equal to 1-2 mins.
Atm1, I'm not sure about the seismic data. Baja earthquake magnitude 3.0 at yesterday morning.Seismometers do not see them !
Atm2, No posted seismic activity. Someone is jump walking in the lab? Why are there time delays between the suspensions?
We are discussing venting first thing next week, with the goal of
diagnosing what's going on in the PRC.
Reminder of the overall vent plan:
Since we won't be prepared for tip-tilt installation (item 2), we should
focus most of the effort on diagnosing what's going on in the PRC. Of
the other planned activities:
(1) dichroic mirror replacement for PR3 and SR3
Given that we'll be working on the PRC, we might consider going ahead
with this replacement, especially if the folding mirror becomes
suspect for whatever reason. In any case we should have the new
mirrors ready to install, which means we should get the phase map
(3) black glass beam dumps:
Install as time and manpower permits. We need to make sure all needed
components are baked and ready to install.
(4) OSEM mount screws:
Delay until next vent.
(5) new periscope plate:
Delay until next vent.
(6) cavity scattering measurement setup
Delay until next vent.
Bob is back. Cleaning and baking all our posts and clamps. They will be ready for use Tuesday next week. Therefore beam dumps will be available for installation.
The ringdown measurements are in progress. But it seems that the MC mirrors are getting kicked everytime the cavity is unlocked by either changing the frequency at the MC servo or by shutting down the input to the MC. This means what we've been observing is not the ringdown of the IMC alone. Attached are MC sus sensor data and the observed ringdown on the oscilloscope. I think we need to find a way to unlock the cavity without the mirrors getting kicked....in which case we should think about including an AOM or using a fast shutter before the IMC.
P.S. The origin of the ripples at the end of the ringdown still are of unknown origin. As of now, I don't think it is because of the mirrors moving but something else that should figured out.
It is HIGHLY unlikely that the IMC mirrors are having any effect on the ringdown. The ringdowns take ~20 usec to happen. The mirrors are 0.25 kg and you can calculate that its very hard to get enough force to move them any appreciable distance in that time.
I found this entry in the old 40m ilog which describes the STACIS performance. It shows that even though the STACIS is bad for the differential arm motion below 3 Hz. It has quite a big and positive effect at 10-30 Hz. The OSEMs show a bigger effect than what the single arm does. I think this is because the single arm is limited by the MC frequency noise above 10 Hz.
We should figure out how to turn on the STACIS but set the lower UGF to be ~5 Hz.
The huge kick observed in the MC sus sensors seem to last for ~10usec; almost matching the observed ringdown decay time. We should find a way to record the ringdown and the MC sus sensor data simultaneously to know when the mirrors are exactly moving during the measurement process. It could also be that the moving mirrors were responsible for the ripples observed later during the ringdown as well.
* How fast do the WFS respond to the frequency switching (time taken by WFS to turn off)? I think this information will help in narrowing down the many possible explanations to a few.
We took a look at the Xend green, and we weren't able to make it lock. We improved the alignment a little bit, and when we looked at the error signal, it looked nice and PDH-y, but for whatever reason, the cavity won't catch lock.
While aligning the green to the arm, Jamie noticed that the reflection from the intracavity power (not the prompt reflection) was not overlapping with the input beam or prompt reflection. This means that the cavity axis and the input green beam were not co-linear. I adjusted the BS and ITMX to get the IR transmitted beam (which had been near clipping on the top edge of the first (2 inch) optic it sees out of the vacuum) back near the input green beam spot on the combining beam splitter. Then we continued tweaking the green alignment until we saw nice TEM00 flashes in the cavity. The SNR of the error signal increased significantly after this work, since the cavity buildup was much higher. But alas, still no lock.
The MC1 accelerometer cube (3 accelerometers arranged in x,y,z) is under the PSL table, as I found it at the beginning of the summer.
The MC2 accelerometer cube is on the table where I worked on the STACIS, right when you walk into the lab from the main entrance. Their cables are dangling near the end of the mode cleaner, so the accelerometers are ready to be placed there if wanted.
All accelerometers are also plugged into their ADC channels.
MC Autolocker was updated. (i.e. mcup and mcdown were updated)
# Turn on MCL servo loop
echo mcup: Turning on MCL servo loop...
ezcaswitch C1:SUS-MC2_MCL INPUT OUTPUT ON
ezcawrite C1:SUS-MC2_MCL_GAIN -300
ezcaswitch C1:SUS-MC2_MCL FM2 FM5 FM7 ON
# Offset to take off the ADC offset of MC_F
ezcawrite C1:SUS-MC2_MCL_OFFSET 42
ezcaswitch C1:SUS-MC2_MCL OFFSET ON
# Turn on MCL servo loop
echo mcup: Turning on MCL servo loop...
ezcaswitch C1:SUS-MC2_MCL INPUT OUTPUT ON
ezcawrite C1:SUS-MC2_MCL_GAIN -300
ezcaswitch C1:SUS-MC2_MCL FM2 FM5 FM7 ON
# Offset to take off the ADC offset of MC_F
ezcawrite C1:SUS-MC2_MCL_OFFSET 42
ezcaswitch C1:SUS-MC2_MCL OFFSET ON
This offset of 42 count is applied in order to compensate the ADC offset of MC_F channel.
The MCL servo squishes the MC_F signal. i.e. The DC component of MC_F goes to zero.
However, if the ADC of MC_F has an offset, the actual analog MC_F signal, which is fed to FSS BOX,
still keep some offset. This analog offset causes deviation from the operating point of the FSS (i.e. 5V).
# Turn off MCL servo loop
echo mcdown: Turning off MCL servo loop...
ezcawrite C1:SUS-MC2_MCL_GAIN 0
ezcaswitch C1:SUS-MC2_MCL INPUT OUTPUT OFFSET FMALL OFF FM1 FM8 FM9 ON
# Remove Offset to take off the ADC offset of MC_F
ezcawrite C1:SUS-MC2_MCL_OFFSET 0
The FSS Slow DC servo was turned off.
As MCL stabilizes the MC_F (Fast PZT), we no longer need to use the laser temp to do so.
In other word, if you like to turn off the MCL servo for some reason, we need to turn it on in order to keep the MC locked.
I tweaked the alignment of ITMX and ETMX a teeny bit to get the TEM00 flashes back (the work in the previous elog was pre-dinner, so it had been a few hours), then took a screenshot of the error signal and refl dc power on the photodiode for the green xend setup.
The error signal is certainly noisy, although I think when Jamie and I were looking at it earlier this evening, the SNR was a little better.
I need to look at the modulation depth, to see if it's correct, ... maybe lock the Xarm on IR and scan the green laser PZT to check the sideband heights.
I should also check to make sure that the PD is powered, and the gain is high enough (currently the PD gain is set to 20dB). Earlier today, when I set the gain to 30dB, Jamie said that it was saturating, so I put it back down to the 20dB where we found it.
Still no lock of the green though :(
Edit: realized I was bad and didn't label the traces on the plot: green is refl dc power, blue is demodulated error signal.