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 40m Log, Page 71 of 341 Not logged in
ID Date Author Type Category Subject
2285   Tue Nov 17 21:10:30 2009 KojiConfigurationSUSETMY suspension conencted to megatron ADC/DAC

Koji, Rana

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

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

The ETMY was restored to the usual configuration.

2290   Wed Nov 18 11:27:33 2009 Koji, josephbConfigurationSUSETMY suspension conencted to megatron ADC/DAC

 Quote: Koji, Rana The megatron DAC was temporaly connected to the suspension electronics for the DAC test. We went down to ETMY as we could not excite the mirror. The DAC is putting correct voltages to the channels. However, the anti imaging filter test output does not show any signal. This means something wrong is there in the DAC I/F box or the cables to the AI circuit. We will check those things tomorrow. The ETMY was restored to the usual configuration.

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

2291   Wed Nov 18 12:33:30 2009 Koji, josephbConfigurationSUSETMY suspension conencted to megatron ADC/DAC

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

The DAC channnel swapping was the last key!

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

Quote:

 Quote: Koji, Rana The megatron DAC was temporaly connected to the suspension electronics for the DAC test. We went down to ETMY as we could not excite the mirror. The DAC is putting correct voltages to the channels. However, the anti imaging filter test output does not show any signal. This means something wrong is there in the DAC I/F box or the cables to the AI circuit. We will check those things tomorrow. The ETMY was restored to the usual configuration.

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

Attachment 1: Untitled.png
2293   Wed Nov 18 16:24:25 2009 peteConfigurationSUSETMY suspension conencted to megatron ADC/DAC

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

This starts the FB.

Now the dataviewer and DTT work!

Quote:

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

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

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

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

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

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

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

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

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

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

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

15661   Fri Nov 6 11:36:37 2020 gautamUpdateGeneralETMY suspension eigenmodes

Attachment #1 shows the main result - there are 4 peaks. The frequencies are a little different from what I have on file for ETMY and the Qs are a factor of 3-4 lower (except SIDE) than what they are in vacuum, which is not unreasonable I hypothesize. The fits suggest that the peak shape isn't really Lorentzian, the true shape seems to have narrower tails than a Lorentzian, but around the actual peak, the fit is pretty good. More detailed diagnostic plots (e.g. coil-to-coil TFs) are in the compressed Attachment #2. The condition number of the matrix to diagonalize the sensing matrix (i.e. what we multiply the "naive" OSEM 2 Euler basis matrix by) is ~40, which is large, but I wouldn't read too much into it at this point.

I see no red flags here - the PIT peak is a little less prominent than the others, but looking back through the elog, this kind of variation in peak heights doesn't seem unreasonable to me. If anyone wants to look at the data, the suspension was kicked every ~1100seconds from 1288673974, 15 times.

 Quote: I'm measuring the free-swinging spectra of ETMY overnight.
Attachment 1: ETMY_pkFitNaive.pdf
Attachment 2: ETMY.tar.bz2
15671   Tue Nov 10 15:13:41 2020 ranaUpdateGeneralETMY suspension eigenmodes

For the input matrix diagonalization, it seemed to me that when we had a significant seismic event or a re-alignment of the optic with the bias sliders, the input matrix also changes.

Meaning that our half-light voltage may not correspond to the half point inside the LED beam, but that rather we may be putting the magnet into a partially occluding state. It would be good to check this out by moving the bias to another setting and doing the ringdown there.

15673   Thu Nov 12 14:26:35 2020 gautamUpdateGeneralETMY suspension eigenmodes

The results from the ringdown are attached - in summary:

• The peak positions have shifted <50 mHz from their in-air locations, so that's good I guess
• The fitted Qs of the POS and SIDE eigenmodes are ~500, but those for PIT and YAW are only ~200
• The fitting might be sub-optimal due to spurious sideband lobes around the peaks themselves - I didn't go too deep into investigating this, especially since the damping seems to work okay for now
• There is up to a factor of 5 variation in the response at the eigenfrequencies in the various sensors - this seems rather large
• The condition number of the matrix that would diagonalize the sensing is a scarcely believable 240, but this is unsurprising given the large variation in the response in the different sensors. Unclear what the implications are - I'm not messing with the input matrix for now
Attachment 1: ETMY.tar.bz2
14433   Mon Feb 4 20:13:39 2019 gautamUpdateSUSETMY suspension oddness

I looked at the free-swinging sensor data from two nights ago, and am struggling with the interpretation.

[Attachment #1] - Fine resolution spectral densities of the 5 shadow sensor signals (y-axis assumes 1ct ~1um). The puzzling feature is that there are only 3 resonant peaks visible around the 1 Hz region, whereas we would expect 4 (PIT, YAW, POS and SIDE). afaik, Lydia looked into the ETMY suspension diagonalization last, in 2016. Compared to her plots (which are in the Euler basis while mine are in the OSEM basis), the ~0.73 Hz peak is nowhere to be seen. I also think the frequency resolution (<1 mHz) is good enough to be able to resolve two closely spaced peaks, so it looks like due to some reason (mechanical or otherwise), there are only 3 independent modes being sensed around 1 Hz.

[Attachment #2] - Koji arrived and we looked at some transfer functions to see if we could make sense of all this. During this investigation, we also think that the UL coil actuator electronics chain has some problem. This test was done by driving the individual coils and looking for the 1/f^2 pendulum transfer function shape in the Oplev error signals. The ~ 4dB difference between UR/LL and LR is due to a gain imbalance in the coil output filter bank, once we have solved the other problems, we can reset the individual coil balancing using this measurement technique.

[Attachment #3] - Downsampled time-series of the data used to make Attachment #1. The ringdown looks pretty clean, I don't see any evidence of any stuck magnets looking at these signals. The X-axis is in kilo-seconds.

We found that the POS and SIDE local damping loops do not result in instability building up. So one option is to use only Oplevs for angular control, while using shadow-sensor damping for POS and SIDE.

Attachment 1: ETMY_sensors_1_Feb_2019_2230_PST.pdf
Attachment 2: ETMY_UL.pdf
Attachment 3: ETMY_sensors_timeDomain.pdf
14441   Thu Feb 7 19:34:18 2019 gautamUpdateSUSETMY suspension oddness

I did some tests of the electronics chain today.

1. Drove a sine-wave using awggui to the UL-EXC channel, and monitored using an o'scope and a DB25 breakout board at J1 of the satellite box, with the flange cable disconnected - while driving 3000 cts amplitude signal, I saw a 2 Vpp signal on the scope, which is consistent with expectations.
2. Checked resistances of the pin pairs corresponding to the OSEMs at the flange end using a breakout board - all 5 pairs read out ~16-17 ohms.
3. Rana pointed out that the inductance is the unambiguous FoM here: all coils measured between 3.19 and 3.3 mH according to the LCR meter...

Hypothesising a bad connection between the sat box output J1 and the flange connection cable. Indeed, measuring the OSEM inductance from the DSUB end at the coil-driver board, the UL coil pins showed no inductance reading on the LCR meter, whereas the other 4 coils showed numbers between 3.2-3.3 mH. Suspecting the satellite box, I swapped it out for the spare (S/N 100). This seemed to do the trick, all 5 coil channels read out ~3.3 mH on the LCR meter when measured from the Coil driver board end. What's more, the damping behavior seemed more predictable - in fact, Rana found that all the loops were heavily overdamped. For our suspensions, I guess we want the damping to be critically damped - overdamping imparts excess displacement noise to the optic, while underdamping doesn't work either - in past elogs, I've seen a directive to aim for Q~5 for the pendulum resonances, so when someone does a systematic investigation of the suspensions, this will be something to look out for.. These flaky connectors are proving pretty troublesome, let's start testing out some prototype new Sat Boxes with a better connector solution - I think it's equally important to have a properly thought out monitoring connector scheme, so that we don't have to frequently plug-unplug connectors in the main electronics chain, which may lead to wear and tear.

The input and output matrices were reset to their "naive" values - unfortunately, two eigenmodes still seem to be degenerate to within 1 mHz, as can be seen from the below spectra (Attachment #1). Next step is to identify which modes these peaks actually correspond to, but if I can lock the arm cavities in a stable way and run the dither alignment, I may prioritize measurement of the loss. At least all the coils show the expected 1/f**2 response at the Oplev error point now. The coil output filter gains varied by ~ factor of 2 among the 4 coils, but after balancing the gains, they show identical responses in the Oplev - Attachment #2.

Attachment 1: ETMY_sensors.pdf
Attachment 2: postDiag.pdf
7429   Sat Sep 22 01:03:30 2012 DenUpdatePEMETMY table

I've installed Guralp readout box back and it turned out that it does not work with voltage provided from the rack (+13.76 0 -14.94).  +/-12 voltage regulators inside the box convert it to -0.9 0 -12. I've connected the box to +/-15 DC voltage supply to measure seismic motion at the ETMY table. Readout box works fine with +/- 15.

Seismic noise on the ETMY table measured to be a few times higher then on the floor in horizontal direction in the frequency range 50 - 200 Hz. Attached are compared spectrums of X, Y and Z motions.

Attachment 1: X.pdf
Attachment 2: Y.pdf
Attachment 3: Z.pdf
7539   Fri Oct 12 22:44:49 2012 DenUpdatePEMETMY table

 Quote: Seismic noise on the ETMY table measured to be a few times higher then on the floor in horizontal direction in the frequency range 50 - 200 Hz. Attached are compared spectrums of X, Y and Z motions.

Accelerometers were installed on the ETMY table and nearby ground to measure amplification of the seismic noise due to the table. During this experiment ground and table motions were measured simultaneously.

Attachment 1: etmy_x_psd.pdf
Attachment 2: etmy_y_psd.pdf
Attachment 3: etmy_z_psd.pdf
Attachment 4: etmy_coh.pdf
7540   Sun Oct 14 11:41:42 2012 DenUpdatePEMETMY table

 Quote: Accelerometers were installed on the ETMY table and nearby ground to measure amplification of the seismic noise due to the table. During this experiment ground and table motions were measured simultaneously

I've added xml file with measurement settings and data to 40m svn at directory 40m_seismic/etmy.

Attachment 2: 14OCT2012.pdf
Attachment 3: 14OCT2012.xml
<?xml version="1.0"?>
<!DOCTYPE LIGO_LW [
<!ELEMENT LIGO_LW ((LIGO_LW|Comment|Param|Time|Table|Array|Stream)*)>
<!ATTLIST LIGO_LW Name CDATA #IMPLIED Type CDATA #IMPLIED>
<!ELEMENT Comment (#PCDATA)>
<!ELEMENT Param (#PCDATA)>
<!ATTLIST Param Name CDATA #IMPLIED Type CDATA #IMPLIED Dim CDATA #IMPLIED
Unit CDATA #IMPLIED>
<!ELEMENT Table (Comment?,Column*,Stream?)>
<!ATTLIST Table Name CDATA #IMPLIED Type CDATA #IMPLIED>

... 231759 more lines ...
8330   Thu Mar 21 17:06:34 2013 SteveUpdate40m UpgradingETMY table is out

 Quote: Yes! We are swapping. I'll be there very soon!

The ETMY optical table 4' x 2' with all optical components was placed on two carts and rolled out of the end.  The 4' x 3' x 4" TMC 78-235-02R breadboard was placed into position and marked for anchoring bolt locations.

It will be drilled, tapped, shimmed, leveled and bolted it into final position tomorrow morning.  I'm planning to bring  the acrylic enclosure to the east end tomorrow afternoon.

Attachment 1: ETMYtableSupport.jpg
8340   Mon Mar 25 18:07:31 2013 SteveUpdate40m UpgradingETMY table is out

Quote:

 Quote: Yes! We are swapping. I'll be there very soon!

The ETMY optical table 4' x 2' with all optical components was placed on two carts and rolled out of the end.  The 4' x 3' x 4" TMC 78-235-02R breadboard was placed into position and marked for anchoring bolt locations.

It will be drilled, tapped, shimmed, leveled and bolted it into final position tomorrow morning.  I'm planning to bring  the acrylic enclosure to the east end tomorrow afternoon.

The new table is tapped and leveled, but not ready for final anchoring. The existing 8 mm shims on the top of the support legs will be moved to the bottom of the legs, where more torque is available on the 1/2" bolts

The coated tin film sheets are being installed at the shop. The table and the enclosure will be ready on Friday.

Attachment 1: shimmingEE.jpg
8355   Tue Mar 26 16:10:31 2013 JamieUpdate40m UpgradingETMY table leveling

Steve's suggestion for how to level the end table using "swivel leveling mounts":

8320   Thu Mar 21 08:11:53 2013 SteveUpdate40m UpgradingETMY table swap

Quote:

 Quote: As discussed at the 40m meeting: Koji, Manasa and Steve We are planning to remove the whole 4'x2' optical table ETMY-ISCT with optics as it is tomorrow morning. This way I can start placing the new 4'x3' table and acrylic enclosure in place.

I will be removing all cables on the ETMY endtable and labeling them today before we remove the table tomorrow morning. If there is anything else that should be done before the swapping which we might have not considered, elog it and we'll have it all done.

Also,I've attached the updated inventory.

The cables are Not disconnected. I have people coming to do the lifting at 9:45am  Email is not working. This will cause a delay. I need conformation that we still moving on with the swap

8321   Thu Mar 21 08:46:46 2013 ManasaUpdate40m UpgradingETMY table swap

Yes! We are swapping.

I'll be there very soon!

4695   Wed May 11 22:54:53 2011 JenneUpdateTreasureETMY trans QPD installed

I put the ETMY trans QPD in.

The ETMY trans beam was already going toward the TRY DC PD, and a CCD camera.  I put a beam splitter in that beam (reducing the power to TRY and the CCD by 50%), and sent my picked-off beam to the ETMY QPD.  Since there is a lens in this path to focus the beam onto TRY and the camera, I put the QPD ~the same distance from the lens as the camera.  Due to space requirements (because of all the green stuff on the table now), I had to put a Y1 turning mirror between the beam splitter and the QPD.  The beam is aligned onto the PD, although the signal isn't super strong.  When the PD is blocked, the sum is ~(-92 counts).  When the beam is on the PD, the sum is ~(-78 counts).

213   Wed Dec 26 15:00:06 2007 ranaUpdateSUSETMY tripping
Steve mentioned to me that ETMY is still tripping more than ETMX. The attached DV plot
shows the trend of the watchdog sensors; essentially the RMS fluctuations of the shadow
sensors. (note** DV can make PNG format plots directly which are much better than JPG
when making plots and much smaller than PS or PDF when plotting lots of points).
Attachment 1: etm.png
214   Wed Dec 26 15:12:48 2007 ranaUpdateSUSETMY tripping
It turned out that the ETMY POS damping gain was set to 1.0 while the ETMX had 3.8.

I put both ETMs to a POS gain of 4 and then also set the PIT, YAW and SIDE gains for
ETMY. Let's see if its more stable now.

In the next week or so Andrey should have perfected his damping gain setting technique
and the numbers should be set more scientifically.
216   Thu Dec 27 13:08:04 2007 ranaUpdateSUSETMY tripping
Here's a trend from the last 2 days of ETMX and ETMY. You can see that the damping gain increase
has made them now act much more alike. Problem fixed.
Attachment 1: Untitled.png
629   Thu Jul 3 12:36:05 2008 JonhSummarySUSETMY watchdog
ETMY watchdog was tripped. I turned it off and re-enabled the outputs.
2433   Sun Dec 20 14:34:24 2009 KojiUpdateSUSETMY watchdog tripped Sunday 5:00AM local

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

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

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

Attachment 1: Y.png
4802   Thu Jun 9 20:10:38 2011 kiwamuUpdateSUSETMY whitening filter : all off

I checked the state of the whitening filters for the ETMY shadow sensors.

Result : They've been OFF  (i.e. flat response).

(measurement and setup)

I measured the transfer functions of the whitening board (D000210) by looking at the signal before and after the whitening stage.

The whitening board handles five signals; UL, UR, LR, LL and SD, and there are five single-pin lemo outputs for each signal on the front panel.

A good thing on those lemo monitors is that their signals are monitored before the whitening stages.

Rana suggested me to use these signals for the denominator of the transfer functions and consider the sensor signals as excitation signals.

So I plugged those signals into extra ADC channels via an AA-board and measured the transfer functions.

In the measurement the coherence above 4 Hz was quite small while the suspension was freely swinging.

Therefore I had to excite the ETMY suspension by putting random noise in a frequency band from 5 Hz to 35 Hz to obtain better coherence.

(results)

The response is flat over frequency range from ~ 0.2 Hz to ~40 Hz, see the plot below.

According to the spectrum of each signal the measurements above 10 Hz are just disturbed by the ADC noise.

If the whitening filters are ON, a pole and zero are expected to appear at 30 Hz and 3 Hz respectively according to the schematic, but no such features.

4065   Thu Dec 16 15:10:18 2010 josephb, kiwamuUpdateCDSETMY working at the expense of ETMX

I acquired a second full pair of Host interface board cards (one for the computer and one for the chassis) from Rolf (again, 2nd generation - the bad kind).

However, they exhibited the same symptoms as the first one that I was given.

Rolf gave a few more suggestions on getting it to work.  Pull the power plugs.  If its got slow flashing green lights, just soft cycle, don't power cycle.  Alex suggested turning the IO chassis on before the computer.

None of it seemed to help in getting the computer talking to the IO chassis.

I finally decided to simply take the ETMX IO chassis and place it at the Y end.  So for the moment, ETMY is working, while ETMX is temporarily out of commission.

We also made the necessary cables (2x 37 d-sub female to 40 pin female and 40 pin female to 40 pin female) .  Kiwamu also did nice work on creating a DAC adapter box, since Jay had given me a spare board, but nothing to put it in.

15607   Fri Oct 2 10:29:49 2020 gautamUpdateOptical LeversETMY, BS and ITMX HeNes degrading

Attachment #1 shows that the ITMX, ETMY and beamsplitter Oplev light levels have decayed significantly from their values when installed. In particular, the ETMY and ITMX sum channels are now only 50% of the values when a new HeNe was installed. ELOG search revealed that ITMY and ETMX HeNes were replaced with newly acquired units in March and September of last year respectively. The ITMX oplev was also replaced in March 2019, but the replacement was a unit that was being used to illuminate our tourist attraction glass fiber at EX.

We should replace these before any vent as they are a useful diagnostic for the DC alignement reference.

Attachment 1: OLsum.png
7729   Mon Nov 19 23:14:31 2012 EvanUpdateCamerasETMYF focus

Adjusted focus on ETMYF camera so that the IR beam is in focus.

8145   Sat Feb 23 14:52:03 2013 JenneUpdateLSCETMYT camera back to normal

 Quote: 3. Replaced Ygreen REFL camera with ETMYT camera to see transmitted beam mode.

The camera that Yuta means in his elog from last night/this morning is the scattering camera at the Yend.  The reason (I think) that he had to do this is that Manasa and Jan took the cable for the ETMYT camera, and were using it for their scattering camera.  They mention in elog 8072 that they installed a camera, but they didn't say anything about having taken the ETMYT cable.  This is the kind of thing that is useful to elog!

Anyhow, I have removed the Watec that belongs with the scattering setup, that Yuta borrowed, and put it back on the scattering table-on-a-pedestal. I then realigned the usual ETMYT camera (that Yuta moved out of the way to install the borrowed Watec), and put the ETMYT cable back to its usual place, connected to the Sony camera's box on the floor.

tl;dr: ETMYT camera is back to original state.

EDIT later:  I put the Watec back, since it is more sensitive to IR, so now we have a Watec in the regular ETMYT place.

12424   Fri Aug 19 22:51:12 2016 gautamUpdateSUSETMs first-contacted

I've applied first contact to both the ETMs. They're now ready to be suspended. I've also cut up some lengths of the new wire and put them in the oven for a 12 hour 70C bake.

• For both ETMs, I first applied first contact to the bulk of the HR and AR surfaces (all the way out to the edge for the HR, for the AR as large an area as possible without getting too close to the magnets). Calum recommended pouring first contact onto the horizontal optic, but since I had no practise with this method, I opted not to try it out for the first time on our ETMs
• After allowing this to dry for 24 hours, I peeled this layer off. Visual inspection suggests that the whole film came off cleanly.
• I then applied first contact to a smaller area around the center of the optic for only the HR surface. This will only be peeled off once the suspended optic is back in the vacuum chamber. This way, we keep the HR face protected for as long as possible.
• Even though we applied F.C to both faces of the ITMs, I don't think its so important to keep a film on the AR side of the ETMs till we take it in. So I didnt re-coat the AR side with a smaller area of F.C. This way, if we want, we can do the OSEM assembly in the cleanroom without having to worry about peeling the F.C off with limited access to the rear of the optic.
• I also opted to bake some lengths of the newly arrived steel wire for suspension. Not sure how important/useful this bake will be.

Unless we want the AR surface to also have a small F.C coat until the optic is in the vacuum chamber, I think I will proceed with re-suspending the ETMs..

1608   Tue May 19 16:08:03 2009 ranaSummarySEIEUCLID
From Stuart Aston, I've attached a picture of the EUCLID position sensor:
Attachment 1: Picture_6.png
1810   Wed Jul 29 19:41:58 2009 ChrisConfigurationGeneralEUCLID-setup configuration change

David and I were thinking about changing the non-polarizing beam splitter in the EUCLID setup from 50/50 to 33/66 (ref picture).  It serves as a) a pickoff to sample the input power and b) a splitter to send the returning beam to a photodetector 2 (it then hits a polarizer and half of this is lost.  By changing the reflectivity to 66% then less (1/3 instead of 1/2) of the power coming into it would be "lost" at the ref photodetector 1, and on the return trip less would be lost at the polarizer (1/6 instead of 1/4).

Attachment 1: EUCLID.png
13998   Thu Jun 21 15:32:05 2018 gautamUpdateElectronicsEX AA filter range change

[steve, gautam]

I took this opportunity of EX downtime to change the supply voltage for the AA unit (4-pin LEMO front panel) in 1X9 from +/-5V to +/-15V. Inside the AA board are INA134 and DRV135 ICs, which are rated to work at +/-18V. In the previous state, the inputs would saturate if driven with a 2.5Vpp sine wave from a DS345 func. gen. After the change, I was able to drive the full range of the DS345 (10Vpp), and there was no saturation seen. This AA chassis is only used for the OSEM signals and also some ALS signals. Shadow sensor levels and spectra are consistent before and after the change. The main motivation was to not saturate the Green PDH Reflection signal in the digital readout. The steps we took were:

1. Confirm (by disconnecting the power cable at the back of the AA box) that the power supplied was indeed +/- 5 V.
2. Remove DIN fuse blocks from DIN rail for the relevant blocks.
3. Identify a +15 V, -15 V and GND spot to plug the wires in.
4. Effect the swap.
5. Re-insert fuses, checked supply voltage at connector end of the cable was now +/- 15 V as expected.
6. Re-connect power cable to AA box.
14128   Fri Aug 3 14:35:56 2018 gautamSummaryElectronicsEX AUX electronics power restored

Steve and I restored the power to the EX AUX electronics rack. The power strip on the lowest shelf of the AUX rack now goes to another power strip laid out vertically along the NW corner of 1X9. The EX green locks to the arm just fine now.

14523   Mon Apr 8 18:28:25 2019 gautamUpdateALSEX Green PDH checkout

I worked on characterizing the green PDH setup at EX, as part of the ALS noise budgeting process. Summary of my findings:

1. Green doubling efficiency is ~ 1.5 %/W (3mW of green for 450mW of IR). This is ~half of what was measured on the PSL table. There are probably large errors associated with power measurement with the Ophir power meter, but still, seems like a big mismatch.
2. The green REFL photodiode is a Thorlabs PDA36A
• It is being run on 30 dB gain setting, corresponding to a transimpedance of 47.5 kohm into high impedance loads. However, the PD bandwidth for this gain setting is 260 kHz according to the manual, whereas the PDH modulation sidebands on the green light are at twice the modulation frequency, i.e. ~560 kHz, so this is not ideal.
• There was ~250 uW of green light incident on this photodiode, as measured with the Ophir power meter.
• The DC voltage level was measured to be ~2.7 V on a scope (High-Z), which works out to ~280 uW of power, so the measurements are consistent.
• When the cavity is locked, there is about 25% of this light incident on the PD, giving a shot noise level of ~25 nV/rtHz. The dark noise level is a little higher, at 40nV/rtHz.
• Beam centering on the PD looked pretty good to the eye (it is a large-ish active area, ~3mmx3mm).
• The beam does not look Gaussian at all - there are some kind of fringes visible in the vertical direction in a kind of halo around the main cavity reflection. Not sure what the noise implications of this are. I tried to capture this in a photo, see Attachment #1. Should an Iris/aperture be used to cut out some of this junk light before the reflection photodiode?
3. The in-going beam was getting clipped on the Faraday Isolator aperture (it was low in pitch).
• I fixed this by adjusting the upstream steering, and then moving the two PZT mounted green steering mirrors to recover good alignment to the X arm cavity.
• GTRX level of ~0.5 was recovered.
4. To estimate the mode-matching of the input beam to the cavity axis, I looked at the reflected light with the cavity locked, and with just the prompt reflection from the ETM:
• DC light level on the reflection photodiode was monitored using the High-Z input o'scope.
• Measured numbers are Plocked ~ 660 mV, Pmisaligned ~ 2.6V, giving a ratio of 0.253.
• While locked, there was a ~ 10 Hz periodic variation in the DC light level on the green REFL photodiode - not sure what was causing this modulation.
• However, this is inconsistent with a calculation, see Attachment #2. I assumed modulation depth of 90 mrad, round-trip loss of 100 ppm, and Titm = 1.094%, Tetm = 4.579%, numbers I pulled from the core-optics wiki page.
• Not sure what effect I've missed out on here - to get the model to match the measurement, I have to either assume a higher cavity finesse, or a much higher round-trip loss (5000ppm), both of which seem implausible.

The main motivation was to get the residual frequency noise of the EX laser when locked to the X arm cavity - but I'll need the V/Hz PDH discriminant to convert the in-loop error signal to frequency units. The idea was to look at the PDH error signal on a scope and match up the horn-to-horn voltage with a model to back out said discriminant, but I'll have to double check my model for errors now given the large mismatch I observe in reflected power.

Attachment 1: IMG_7393.JPG
Attachment 2: greenModeMatch.pdf
14527   Tue Apr 9 18:44:00 2019 gautamUpdateALSEX Green PDH discriminant measurement

I decided to use the more direct method, of disconnecting feedback to the EX laser PZT, and then looking at the cavity flashes.

Attachment #1 shows the cavity swinging through two resonances (data collected via oscilloscope). Traces are for the demodulated PDH error signal (top) and the direct photodiode signal (bottom). The traces don't look very clean - I wonder if some saturation / slew rate effects are at play, because we are operating the PD in the 30 dB setting, where the bandwidth of the PD is spec-ed as 260 kHz, whereas the dominant frequency component of the light on the PD is 430 kHz.

The asymmetric horns corresponding to the sideband resonances were also puzzling. Doing the modeling, Attachment #2, I think this is due to the fact that the demodulation phase is poorly set. The PDH modulation frequency is only ~5x the cavity linewidth, so both the real and imaginary parts of the cavity reflectivity contribute to the error signal. If this calculation is correct, we can benefit (i.e. get a larger PDH discriminant) by changing the demod phase by 60 degrees. However, for 230 kHz, it is impractical to do this by just increasing cable length between the function generator and mixer.

Anyway, assuming that we are at the phi=30 degree situation (since the measurement shows all 3 horns going through roughly the same voltage swing), the PDH discriminant is ~40 uV/Hz. In lock, I estimate that there is ~60 uW of light incident on the PDH reflection photodiode. Using the PD response of 0.2 A/W, transimpedance of 47.5 kohm, and mixer conversion loss of 6dB, the shot-noise limited sensitivity is 0.5 mHz/rtHz. The photodiode dark noise contribution is a little lower - estimated to be 0.2 mHz/rtHz. The loop does not have enough gain to reach these levels.

 Quote: PDH discriminant (40 uV/Hz, see this elog)
Attachment 1: cavityFlashes.pdf
Attachment 2: modelPDH.pdf
14524   Mon Apr 8 23:52:09 2019 gautamUpdateALSEX Green PDH error monitor calibrated

Some time ago, I had done an actuator calibration of ITMX. This suspension hasn't been victim to the recent spate of suspension problems, so I can believe that the results of those measurement are still valid. So I decided to calibrate the in-loop error signal of the EX green PDH loop, which is recorded via an SR560, G=10, by driving a line in ITMY position (thereby modulating the X arm cavity length) while the EX green frequency was locked to the arm cavity length. Knowing the amount I'm modulating the cavity length by (500 cts amplitude sine wave at 33.14159 Hz using awggui, translating to ~17.2 kHz amplitude in green frequency), I demodulated the response in C1:ALS-X_ERR_MON_OUT_DQ channel. At this frequency of ~33 Hz, the servo gain should be large, and so the green laser frequency should track the cavity length nearly perfectly (with transfer function 1/(1+L), where L is the OLG).

The response had amplitude 5.68 +/- 0.10 cts, see Attachment #1. There was a sneaky gain of 0.86 in the filter module, which I saw no reason to keep at this strange value, and so updated to 1, correcting the demodulated response to 6.6 cts. After accounting for this adjustment, the x10 gain of the SR560, and the loop suppression, I put a "cts2Hz" filter in (Attachment #2). I had to guess a value for the OLG at 33 Hz in order to account for the in-loop suppression. So I measured the OLTF using the usual IN1/IN2 method (Attachment #3), and then used a LISO model of the electronics, along with guesses of the cavity pole (18.5 kHz), low-pass filter poles (4x real poles at 70 kHz), PZT actuator gain (1.7 MHz/V) and PDH discriminant (40 uV/Hz, see this elog) to construct a model OLTF. Then I fudged the overall gain to get the model to line up with the measurement between 1-10kHz. Per this model, I should have ~75dB of gain at ~33Hz, so the tracking error to my cavity length modulation should be ~3.05 Hz. Lines up pretty well with the measured value of 4.7 Hz considering the number of guessed parameters. The measured OLG tapers off towards low frequency probably because the increased loop suppression drives one of the measured inputs on the SR785 into the instrument noise floor.

The final calibration number is 7.1 Hz/ct, though the error on this number is large ~30%. Note that these "Hertz" are green frequency changes - so the change to the IR frequency will be half.

Attachment #4 shows the error signal in various conditions, labelled in the legend. Interpretations to follow.

Attachment 1: errMonCalib.pdf
Attachment 2: errMon.png
Attachment 3: OLTF.pdf
Attachment 4: EX_frequencyNoises.pdf
14525   Tue Apr 9 00:16:22 2019 ranaUpdateALSEX Green PDH error monitor calibrated

G=10 or G=100?

14526   Tue Apr 9 00:18:19 2019 gautamUpdateALSEX Green PDH error monitor calibrated

wrong assumption - i checked the gain just now, it is G=10, and is running in the "low-noise" mode, so can only drive 4V. fixed elog, filter.

Note: While working at EX, I saw frequent saturations (red led blinking) on the SR560. Looking a the error mon signal on a scope, it had a pk-to-pk amplitude of ~200mV going into the SR560. Assuming the free-swinging cavity length changes by ~1 um at 1 Hz, the green frequency changes by ~15 MHz, which according to the PDH discriminant calibration of 40 uV/Hz should only make a 60 mV pk to pk signal. So perhaps the cavity length is changing by 4x as much, plausible during daytime with me stomping around the chamber I guess.. My point is that if the SR560 get's saturated (i.e. input > 13000 cts), the DQ-ed spectrum isn't trustworthy anymore. Should hook this up to some proper whitening electronics

 Quote: G=10 or G=100?
13751   Fri Apr 13 11:02:41 2018 gautamUpdateALSEX fiber polarization drift

Attachment #1 shows the drift of the polarization content of the light from EX entering the BeatMouth. Seems rather large (~10%). I'm going to tweak the X end fiber coupling setup a bit to see if this can be improved. This performance is also a good benchmark to compare the PSL IR light polarization drift. I am going to ask Steve to order Thorlabs K6XS, which has a locking screw for the rotational DoF. With this feature, and by installing some HWPs at the input coupling point, we can ensure that we are coupling light into one of the special axes in a much more deterministic way.

Attachment 1: EX_pol_drift.png
14740   Tue Jul 9 18:42:15 2019 gautamUpdateALSEX green doubling oven temperature controller power was disconnected

There was no green light even though the EX NPRO was on. I checked the doubling oven temperature controller and found that its power cable was loose on the rear. I reconnected it, and now there is green light again.

13635   Fri Feb 16 01:09:55 2018 gautamUpdateALSEX green locking duty cycle

I have been puzzled as to why the duty cycle of the EX green locks are much less than that of the EY NPRO. If anything, the PDH loop has higher bandwidth and comparable stability margins at the X end than at the Y end. I hypothesize that this is because the EX laser (Innolight 1W Mephisto) has actuation PZT coefficient 1MHz/V, while the EY laser (Lightwave 125/126) has 5MHz/V. I figure the EX laser is sometimes just not able to keep up with the DC Xarm cavity length drift. To test this hypothesis, I disabled the LSC locking for the Xarm, and enabled the SLOW (temperature of NPRO crystal) control on the EX laser. The logic is that this provides relief for the PZT path and prevents the PDH servo from saturating and losing lock. Already, the green lock has held longer than at any point tonight (>60mins). I'm going to leave it in this state overnight and see how long the lock holds. The slow servo path has a limiter set to 100 counts so should be fine to leave it on. The next test will be to repeat this test with LSC mode ON, as I guess this will enhance the DC arm cavity length drift (it will be forced to follow MCL).

Why do I care about this at all? If at some point we want to do arm feedforward, I thought the green PDH error signal is a great target signal for the Wiener filter calculations. So I'd like to keep the green locked to the arm for extended periods of time. Arm feedforward should help in lock acquisiton if we have reduced actuation range due to increased series resistances in the coil drivers.

As an aside - I noticed that the SLOW path has no digital low pass filter - I think I remember someone saying that since the NPRO controller itself has an in-built low pass filter, a digital one isn't necessary. But as this elog points out, the situation may not be so straightforward. For now, I just put in some arbitrary low pass filter with corner at 5Hz. Seems like a nice simple problem for optimal loop shaping...

gautam noon CNY2018: Looks like the green has been stably locked for over 8 hours (see Attachment #1), and the slow servo doesn't look to have railed. Note that 100 cts ~=30mV. For an actuation coefficient of 1GHz/V, this is ~30MHz, which is well above the PZT range of 10V-->10MHz (whereas the EY laser, by virtue of its higher actuation coefficient, has 5 times this range, i.e. 50MHz). Supports my hypothesis.

Attachment 1: GreenLock8hrs.png
13752   Fri Apr 13 16:59:12 2018 gautamUpdateALSEX green mode-matching

THIS CALCULATION IS WRONG FOR THE OVERCOUPLED CAV.

Summary:

Mode-matching efficiency of EX green light into the arm cavity is ~70*%, as measured using the visibility.

Details:

I wanted to get an estimate for the mode-matching of the EX green beam into the arm cavity. I did the following:

1. Locked arm cavities to IR. Ran dither alignment servos to maximize the transmission of IR on both arms. The X arm dither alignment servo needs some touching up, I can achieve higher TRX by hand than by running the dither.
2. Aligned green PZT mirrors so as to maximize GTRX. Achieved level as 0.47.
3. Went to EX table and tweaked the two available mode-matching lens positions on their translational stages. Saw a quadratic maximum of GTRX about some equilibrium position (where the lenses are now).
4. Measured average value of the green PDH reflection DC level whiel green TEM00 mode was locked. $P_{\mathrm{locked}} = 716 \mathrm{cts}$.
5. Misaligned ITMX macroscopically. Measured the average value of the green PDH reflection DC level again. P_{\mathrm{misaligned}} = 3800 \mathrm{cts}.
6. Closed EX Green shutter. Measured the average value of the green PDH reflection DC level. $P_{\mathrm{dark}} = 30 \mathrm{cts}$.
7. Modulation depth of the EX PDH was determined to be 90mrad. Based on this, power in sideband is negligible compared to power in the carrier, so I didn't bother correcting for sideband power in reflection.
8. Mode-matching efficiency calculated as \frac{P_{\mathrm{misaligned}} - P_{\mathrm{locked}}}{P_{\mathrm{misaligned}} + P_{\mathrm{locked}} - 2P_{\mathrm{dark}} }.

This amount of mode-matching is rather disappointing - using a la mode, the calculated mode-matching efficiency is nearly 100%, but 70% is a far cry from this. The fact that I can't improve this number by either tweaking the steering or by moving the MM lenses around suggests that the estimate of the target arm mode is probably incorrect (the non-gaussianity of the input beam itself is not quantified yet, but I don't believe this input beam can account for 30% mismatch). For the Y-arm, the green REFL DC level is actually higher when locked than when ITMY is misaligned. WTF?? Only explanation I can think of is that the PD is saturated when green is unlocked - but why does the ADC saturate at ~3000cts and not 32000?

This data is almost certainly bogus as the AA box at 1X9 is powered by +/-5VDC and not +/-15VDC. I didn't check but I believe the situation is the same at the Y-end.

3000 cts is ~1V into the ADC. I am going to change the supply voltage to this box (which also reads in ETMX OSEMS) to +/-15V so that we can use the full range of the ADC.

gautam Apr 26 630pm: I re-did the measurement by directly monitoring the REFLDC on a scope, and the situation is not much better. I calculate a MM of 70% into the arm. This is sensitive to the lens positions - while I was working on the EX fiber coupling, I had bumped the lens mounted on a translational stage on the EX table lightly, and I had to move that lens around today in order to recover the GTRX level of 0.5 that I am used to seeing (with arm aligned to maximize IR transmission). So there is definitely room for optimization here.

12532   Wed Oct 5 16:28:10 2016 gautamUpdateendtable upgradeEX laser power monitor PD installed

I installed a 10% BS to pick off some of the light going to the IR fiber, and have added a Thorlabs PDA55 PD to the EX table setup. The idea is to be able to monitor the power output of the EX NPRO over long time scales, and also to serve as an additional diagnostic tool for when ALS gets glitchy etc. There is about 0.4mW of IR power incident on the PD (as measured with the Ophir power meter), which translates to ~2500 ADC counts (~1.67V as measured with an Oscilloscope set to high impedance directly at the PD output). The output of the PD is presently going to Ch5 of the same board that receives the OL QPD voltages (which corresponds to ADC channel 28). Previously, I had borrowed the power and signal cables from the High-Gain Transmon PD to monitor this channel, but today I have laid out independent cabling and also restored the Transmon PD to its nominal state.

On the CDS side of things, I edited C1SCX to route the signal from ADC Ch28 to the ALS block. I also edited the ALS_END library part to have an additional input for the power monitor, to keep the naming conventions consistent. I have added a gain in the filter module to calibrate the readout into mW using these numbers. The channel is called C1:ALS-X_POWER_OUT, and is DQed for long-term trending purposes.

The main ALS screen is a bit cluttered so I have added this channel to the ALS overview MEDM screen for now..

14984   Tue Oct 22 15:32:15 2019 gautamUpdateALSEX uPDH electronics checkout

Summary:

The EX PDH setup had what I thought was insufficient phase and gain margins. So I lowered the gain a little - the price paid was that the suppression of laser frequency noise of the end laser was reduced. I actually think an intermediate gain setting (G=7) can give us ~35 degrees of phase margin, ~10dB gain margin, and lower residual unsuppressed AUX laser noise - to be confirmed by measurement later. See here for the last activity I did - how did the gain get increased? I can't find anything in the elog.

Attachment 1: uPDH_X_OLTFs.pdf
14986   Wed Oct 23 10:23:26 2019 ranaUpdateALSEX uPDH electronics checkout

During our EX AM/PM setups, I don't think we bumped the PDH gain knob (and I hope that the knob was locked). Possible drift in the PZT response? Good thing Shruti is on the case.

Is there a loop model of green PDH that agrees with the measurement? I'm wondering if something can be done with a compensation network to up the bandwidth or if the phase lag is more like a non-invertible kind.

14987   Wed Oct 23 11:11:01 2019 gautamUpdateALSEX uPDH electronics checkout

The closest thing I can think of is here.

 Quote: Is there a loop model of green PDH that agrees with the measurement? I'm wondering if something can be done with a compensation network to up the bandwidth or if the phase lag is more like a non-invertible kind.
13947   Mon Jun 11 23:22:53 2018 gautamUpdateCDSEX wiring confusion

[Koji, gautam]

Per this elog, we don't need any AIOut channels or Oplev channels. However, the latest wiring diagram I can find for the EX Acromag situation suggests that these channels are hooked up (physically). If this is true, there are 12 ADC channels that are occupied which we can use for other purposes. Question for Johannes: Is this true? If so, Kira has plenty of channels available for her Temperature control stuff..

As an aside, we found that the EPICS channel names for the TRX/TRY QPD gain stages are somewhat strangely named. Looking closely at the schematic (which has now been added to the 40m DCC tree, we can add out custom mods later), they do (somewhat) add up, but I think we should definitely rename them in a more systematic manner, and use an MEDM screen to indicate stuff like x4 or x20 or "Active" etc. BTW, the EX and EY QPDs have different settings. But at least the settings are changed synchronously for all four quadrants, unlike the WFS heads...

Unrelated: I had to key the c1iscaux and c1auxey crates.

13958   Wed Jun 13 23:23:44 2018 johannesUpdateCDSEX wiring confusion

It's true.

I went through the wiring of the c1auxex crate today to disentangle the pin assignments. The full detail can be found in attachment #1, #2 has less detail but is more eye candy. The red flagged channels are now marked for removal at the next opportunity. This will free up DAQ channels as follows:

 TYPE Total Available now Available after ADC 24 2 14 DAC 16 8 12 BIO sinking 16 7 7 BIO sourcing 8 8 8

This should be enough for temperature sensing, NPRO diagnostics, and even eventual remote PDH control with new servo boxes.

Attachment 1: c1auxex_channels.pdf
Attachment 2: XEND_slow_wiring.pdf
13961   Thu Jun 14 10:41:00 2018 gautamUpdateCDSEX wiring confusion

Do we really have 2 free ADC channels at EX now? I was under the impression we had ZERO free, which is why we wanted to put a new ADC unit in. I think in the wiring diagram, the Vacuum gauge monitor channel, Seis Can Temp Sensor monitor, and Seis Can Heater channels are missing. It would also be good to have, in the wiring diagram, a mapping of which signals go to which I/O ports (Dsub, front panel BNC etc) on the 4U(?) box housing all the Acromags, this would be helpful in future debugging sessions.

Quote:

 TYPE Total Available now Available after ADC 24 2 14

13965   Thu Jun 14 15:31:18 2018 johannesUpdateCDSEX wiring confusion

Bad wording, sorry. Should have been channels in excess of ETMX controls. I'll add the others to the list as well.

Updated channel list and wiring diagram attached. Labels are 'F' for 'Front' and 'R' for - you guessed it - 'Rear', the number identifies the slot panel the breakout is attached to.

Attachment 1: XEND_slow_wiring.pdf
Attachment 2: c1auxex_channels.pdf
ELOG V3.1.3-