40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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ID Date Author Type Categoryup Subject
  13923   Wed Jun 6 17:22:23 2018 KojiBureaucracyGeneralSalvaged junk from yend

While Keerthana and johannes were working at the end, I made a little cleaning at the yend. I salvaged large amount of hardware inclding optics, optomechanics. We all together should work on returning them to appropriate locations.

Attachment 1: DSC_0661.JPG
DSC_0661.JPG
  13939   Mon Jun 11 13:55:33 2018 keerthanaUpdateGeneralProject Updates

As of now, I have made the codes needed to sweep the marconi frequency for taking the cavity scan data, the photo diode at the y-end is conected to the spectrum analyser already and I also have the finesse simulation of the Ideal Fabry-perot cavity. By seeing my last elog entry, Gautam suggested me that I need to take a different approach for estimating the FSR and TMS value from the Finesse graph. That is, by using least square fit models. Now I am trying to do that and get a better estimate of the error values. Based on my understanding I am dividing this project into various tasks.

1. Getting a better estimate of the error value by using least square fits. Also plotting a graph of frequency Vs mode number and finding the value of Free Spectral Range from its slop.

2. Inserting zernike polynomials to the Finesse simulation and with the help of least square fit, plotting the graph of frequency Vs mode number. Understanding the shifts from the Ideal graph we obtained from step 1. Using this data, plotting the phase map corresponding to this.

3. Repeating step 2 by taking different zernike polynomials and creating a data base which will be useful for the analysis of the real data. This will also prepare me to do the fitting models easily.

4. Collecting data from the IFO and applying these fitting models to it. Finding the set of zernike polynomials which are similar to the actual fugure error of the mirror. Plotting the Phase map corresponding to those zernike polynomials.

If you feel that there is some mistake in the steps, please correct me. It will be really helpful!

  13949   Tue Jun 12 14:47:37 2018 gautamBureaucracyGeneralUnlabelled components from EX moved to SP table and labelled

Steve mentioned two unlabelled optics were found at EX, relics from the Endtable upgrade.

  • One was a 1" 45 deg p-pol optic (Y1-1025-C-45P), it looks a bit scratched.
  • The other was a Beam Sampler (BSF10-C).

These are now labelled and forked down on the SP table.

  13950   Tue Jun 12 15:32:15 2018 SteveBureaucracyGeneralSalvaged junk from Xend

Koji's collection of Yend components put away. I cleaned up the  Xend bench today.

Loadcells, leveling wedge mounts  and related items placed under flowbench cabinet next to Guralp staff.

 

  13962   Thu Jun 14 13:29:51 2018 gautamUpdateGeneralPSL shutter closed, all optics misaligned

[jon, gautam]

Jon is doing some characterization of the AUX laser setup for which he wanted only the prompt retroreflection from the SRM on the AS table, so the PSL shutter is closed, and both ITMs and ETMs are misaligned. The prompt reflection from the SRM was getting clipped on something in vacuum - the ingoing beam looked pretty clean, but the reflection was totally clipped, as I think Johannes aligned the input beam with the SRM misaligned. So the input steering of the AUX laser beam into the vacuum, and also the steering onto AS110, were touched... Also, there were all manner of stray, undumped beams from the fiber on the AS table noJon will post photos.

Before we began this work, we found that c1susaux was dead so we rebooted it.

  13967   Thu Jun 14 19:30:12 2018 gautamUpdateGeneralIFO alignment restored

All optics have been re-aligned. Jon/Johannes will elog about the work today.

  13968   Thu Jun 14 22:45:05 2018 johannesUpdateGeneralAUX beam SRC alignment

[Jon, Gautam, Johannes]

Jon spent some time trying to align the AUX beam to the SRC today, I got to the game kind of late so maybe others can add more detail.

The AUX beam that is reflected by the SRM looks terribly misshapen - it is quite elongated in vertical direction. Unfortunately I didn't snap a picture of it - anybody? It seemed at first as if this could be clipping - but after confirming the alignment of the AUX beam with the PSL output beam with aligned SRM, a slow dither of the SRM just moved the ugly pattern on the AS camera with no change to its shape - so clipping is unlikely. I'm now thinking that this is just the output beam of the fiber coupler after propagating ~15 meters to the SRM and back - even though this aspheric lens triplet coupler is supposed to be super-duper. I found that if I loosen the fiber slightly and pull it back just a bit at least the spot on the AS camera becomes nice and round - so maybe the fiber just doesn't sit well in this collimator? Not sure why that would be. I checked the fiber tip with the microscope, and while there was some gunk present, the central region and the core were clear (still cleaned using the fiber cleaning kit, which got rid of the debris). Either way, before switching to a different collimator I think we should give the Guoy phase measurement a shot - after all there was plenty of RF signal present on both AS110 and the PDA10CF placed at the YEND.

Looking for rogue beams on the AS table, I started placing some beam dumps. There was one particularly strong source of stray beams - a lens that was labeled with KPX094AR.33_F100. It became apparent after alignment efforts to the IFO had moved the AUX beam signifcantly off-center on this lens. According to the label it should have an AR coating for 1064nm, however judging by the amount of reflected light, it was certainly NOT AR-coated for 1064nm. I replaced it with a bi-convex f=100mm lens with confirmed AR-behavior.

The AUX laser is currently shuttered.


Per our Wednesday meeting, some items to work on are

  • Align the zero-order AUX beam into a second collimator on the PSL table, so we can switch the fiber output and look for RF signals at the offset-phaselock frequency without the additional frequency shift from the AOM. This will simpligy the mode spectroscopy scheme significantly
  • Abandon the R10/T90 beamsplitters in favor of R90/T10 beamsplitters. We'll swap the large mirror in front of the AS camera with an R90/T10 BS, and follow it up with a second R90/T10 BS that sends the AUX beam to the IFO. This way we'll have identical power levels on AS110 and AS55, and still 90% of the current AUX light going into the IFO, but without strong secondary beams from R10/T90 optics.
  13970   Fri Jun 15 08:09:15 2018 SteveBureaucracyGeneralcleaning up at the PSL enclousure

The cabeling was cleaned up a little bit yesterday morning. The upper back side is still massy.

Attachment 1: before.jpg
before.jpg
Attachment 2: after.jpg
after.jpg
Attachment 3: back_side.jpg
back_side.jpg
  13971   Fri Jun 15 09:14:42 2018 SteveUpdateGeneralOplev sums

Oplev sums of 240 days.

Quote:

Since there have been various software/hardware activity going on (stack weighing, AUX laser PLL, computing timing errors etc etc), I decided to do a check on the state of the IFO.

  • c1susaux, c1aux and c1iscaux crates were keyed as they were un-telnet-able.
  • Single arm locking worked fine, TT alignment was tweaked (as these had drifted due to the ADC failure in c1lsc) to maximize Y arm transmission using the dither servos.
  • Arms weren't staying locked for extended periods of time. I particularly suspected ITMX, as I saw what I judged to be excess motion on the Oplev.
  • @Steve - ITMX and BS HeNes look like they are in need of replacement judging by the RIN (although the trend data doesn't show any precipitous drop in power). If we are replacing the BS/PRM Oplev HeNe, might be a good time to plan the inejction path a bit better on that table.
  • RIN in Attachment #1 has been normalized by the mean value of the OL sum channel. There is now a script to make this kind of plot from NDS in the scripts directory (as I found it confusing to apply different calibrations to individual traces in DTT).

 

Attachment 1: opSums.png
opSums.png
  13974   Sat Jun 16 00:26:48 2018 gautamUpdateGeneralPRC modescan attempt

[Jon, Gautam, Johannes]

We did the following today:

  1. Dither align arms such that ITMs were reliable arm references.
  2. Configure the IFO such that ITMX single bounce was the only visible beam reaching the AS port from the symmetric side - ITMY, both ETMs, PRM and SRM were misaligned.
  3. Do coarse alignment on the AS table using the usual near field / far field overlap technique, with "near" and "far" dictated by arm reach on the AS table. In this way, the ingoing AUX beam and the PSL single bounce from ITMX were collimated on the AS table.
  4. Lock the AUX / PSL PLL. We expected a beatnote on AS110 at eithe (80-50)=30 MHz or (80+50)=130 MHz. 80 MHz is the AOM driver frequency, while 50 MHz is the PLL offset. (Marconi was actually set to 60 MHz, prolly Keerthana forgot to reset it after some remote experimentation).
  5. Beat was found at 30 MHz. 
  6. Input steering of AUX beam into the IFO was tweaked to maximize the beat. Johannes claims he saw -35 dBm on AS110 last week. But Jon reported a best effort of ~-60 dBm today. Not sure how to square that circle.
  7. Once we were confident that the input of the AUX and PSL beams were well aligned, we decided to do a scan. PRC was chosen as PRMI can be locked but I don't yet know the correct settings for SRMI locking, and DRMI seemed too ambitious for daytime.
    • PRMI was locked on carrier.
    • Jon can comment more here, but the measurement with AM sidebands does not rely on any beatnote on the AS110 PD, it is just looking for coupling of the AM sideband into the IFO from the AS port at resonant frequencies of the PRC.
    • For a coarse sweep, we swept from 1-60 MHz, 801 points, and the IF bandwidth was set at 30 kHz on the AG4395.
    • Transfer function being measured was the ratio of AM signal detected at AS110 PD, to RF drive applied to the AOM driver.
    • We were expecting to see dips separated by the PRC FSR (~25 MHz, since the PRC RT length is ~12.5m), when the AM sideband becomes resonant in the PRC.
    • But we saw nothing. Need to think about if this is an SNR problem, or if we are overlooking something more fundamental in the measurement setup.

This measurement seems like a fine candidate to trial the idea of looking for the FSRs (and in general, cavity resonances) of the PRC in the phase of the measured TFs, rather than the amplitude.

  13975   Sat Jun 16 01:25:29 2018 KojiUpdateGeneralPRC modescan attempt

The PRC FSR is, of course, very close to twice of our f1 moudlation frequency (11MHz x 2 = 22MHz) .

I still don't understand what response the measurement is looking for. I understood the idea of using the subcarrier as a stablized carrier to the PRC with a certain freq offset from the main carrier. I suppose what was swept was the AOM modulation frequency (i.e. modulation frequency of the AM applied to the subcarrier). If that is the case, the subcarrier seemed fixed at an arbitorary frequency (i.e. 50MHz) away from the carrier. If one of the AM sidebands hits the PRC resonance (i.e. 22, 44, 66MHz away from the main carrier), you still have the other sideband reflected back to the AS. Then the RF signal at the AS is still dominated by this reflected sideband. I feel that the phase modulation is rather suitable for this purpose.

If you are talking about ~MHz AM modulation by the AOM and scanning the PLL frequency from 1MHz to 60MHz, the story is different. And this should involve demodulation of the AS signal at the AM modulation frequency. But I still don't understand why we don't use phase modulation, which gives us the PDH type signal at the reflection (i.e. AS) port...

 

  13976   Sat Jun 16 20:57:59 2018 JonUpdateGeneralPRC modescan attempt

Here's a Finesse modeling of what we're expecting to observe with this test. It uses Gautam's base model of the 40m IFO with appropriate modifications for the needed configuration.

The idea is to lock the IFO in the SRMI configuration, with the phase-locked AUX beam injected from the AS port. The AUX beam is imprinted with AM sidebands and slightly misaligned relative to the SRC so as to transfer power into HOM1. The RF network analyzer provides the drive signal for the AOM, and its frequency is swept to coherently measure the transfer function [reflected AUX beam / drive]. The reflected AUX beam is sensed by the AS110 PDA10CF.

It is also possible to drive PM sidebands as Koji suggests, but the squeezer group has encouraged using AM for practical advantages. The SNR with AM is a bit higher (less power lost into harmonics at large modulation index), there is a broadband AOM already available aligned to the SQZ beam at LLO, and there is also concern that driving strong PM could interfere with the SQZ control loops.

Expected SRMI Response

Attachment #1 shows the expected response to swept-AM in SRMI. Resolving just the FSR and the first-order mode splitting is sufficient to extract the SRC Gouy phase.

Expected response in the SRMI configuration.

Expected DRMI Response

Since the 40m has not been opearted in SRMI since ~2016 (last done by Eric Q.), Gautam believes it may take some time to relock this configuration. However, the modeling indicates that we can likely obtain sufficient sensitivity in DRMI, which would allow us to proceed faster. Attachment #2 shows the expected response to swept-AM in DRMI. The PRC leakage signal turns out to be significantly smaller than the SRC reflection (a factor of ~30 in amplitude), so that the signal still retains its characteristic shape to a very good approximation. The tradeoff is a 10x reduction in SNR due to increased PSL shot noise reaching AS110.

Expected DRMI response. The main difference is a 10x increase in shot noise on AS110.

Based on this, we should proceed with DRMI scans instead of PRMI next week.

Quote:

The PRC FSR is, of course, very close to twice of our f1 moudlation frequency (11MHz x 2 = 22MHz) .

I still don't understand what response the measurement is looking for. I understood the idea of using the subcarrier as a stablized carrier to the PRC with a certain freq offset from the main carrier. I suppose what was swept was the AOM modulation frequency (i.e. modulation frequency of the AM applied to the subcarrier). If that is the case, the subcarrier seemed fixed at an arbitorary frequency (i.e. 50MHz) away from the carrier. If one of the AM sidebands hits the PRC resonance (i.e. 22, 44, 66MHz away from the main carrier), you still have the other sideband reflected back to the AS. Then the RF signal at the AS is still dominated by this reflected sideband. I feel that the phase modulation is rather suitable for this purpose.

If you are talking about ~MHz AM modulation by the AOM and scanning the PLL frequency from 1MHz to 60MHz, the story is different. And this should involve demodulation of the AS signal at the AM modulation frequency. But I still don't understand why we don't use phase modulation, which gives us the PDH type signal at the reflection (i.e. AS) port...

 

 

Attachment 1: 40M_SRMI_AM_annotated.pdf
40M_SRMI_AM_annotated.pdf
Attachment 2: 40M_DRMI_AM.pdf
40M_DRMI_AM.pdf
  13977   Sun Jun 17 14:20:35 2018 KojiUpdateGeneralChiara new USB 4TB DIsk

I have connected a 4TB disk to chiara via a USB-SATA adapter. This disk has been recognized as /dev/sde. A GUID Partition Table (GPT), not MBR was made with gdisk to make a partition with the size beyond 2TB.
I tried to use "dd" to copy /home/cds (/dev/sdb1) to /dev/sde1, but failed. The copy was done (taking ~12h) and the partition was not recognized as a complete filesystem.

So I decided to use rsync instead.

sudo mkfs -t ext4 /dev/sde1
sudo mkdir /media/usb4g
sudo mount -t ext4 -o rw /dev/sde1 /media/usb4g
sudo rsync -a --progress /home/cds/ /media/usb4g

Progress
14:33 Copied     33G/1831G
14:38 Copied     36G/1831G
17:02 Copied   365G/1831G (~2.2GB/min)
01:18 Copied 1449G/1831G (~2.2GB/min)
04:36 Completed
> sent 1907955222607 bytes  received 126124609 bytes  37010956.31 bytes/sec
> total size is 1907271994803  speedup is 1.00

  13980   Mon Jun 18 12:07:03 2018 KojiUpdateGeneralChiara new USB 4TB DIsk

The initial local backup with rsync was done. Now the new 4TB disk is (supposed to be) automatically mounted at boot as /media/40mBackup so that we can run the daily backup on this disk. (<- This was confirmed by "sudomount -a")

controls@chiara|~> sudo blkid
...
/dev/sde1: UUID="92dc7073-bf4d-4c58-8052-63129ff5755b" TYPE="ext4"

controls@chiara|~> cat /etc/fstab

...

UUID=92dc7073-bf4d-4c58-8052-63129ff5755b   /media/40mBackup    ext4    defaults    0   0

Here I've used UUID rather than the device name "/dev/sde1" because the device name can get altered depending on the order of the usb connection.

This new disk is just a bare HDD drive sitting on the top of the chassis. We eventually want to accommodate this disk in the chassis so that we can recover the function only with the modification of /etc/fstab.  We need to wait for a next chance to have chiara down. In fact, when we can isolate chiara, we want to use this disk as the main disk and install another 4TB disk as a backup.

  13984   Mon Jun 18 19:47:02 2018 gautamUpdateGeneralMICH actuator calibration

Summary:

The actuator (pendulum) gains for the Beam Splitter and the two ITMs were measured to be:

BS: 9.54 +/- 0.05 nm/ct [100 ohm series resistor in coil driver board]

ITMX: 2.44 +/- 0.01 nm/ct [400 ohm series resistor in coil driver board]

ITMY: 2.44 +/- 0.02 nm/ct [400 ohm series resistor in coil driver board]

Counts here refers to DAC counts at the output of the coil filter banks (as opposed to counts at the LSC servo output). The dominant (systematic) uncertainty (which isn't quoted here) in this measurement is the determination of the peak-to-peak swing of the dark port sensor, AS55_Q. I estimate this error to be ~1ct/33cts = 3%. These values are surprisingly consistent with one another once we take into account the series resistance.

Details:

The last time this was done, we used ASDC to do the measurement. But I don't know what signal conditioning ASDC undergoes (in PD or in readout electronics). In any case, in my early trials yesterday, ASDC was behaving unpredictably. So I decided to do redo the measurement.

[Attachment #1]- Flowchart describing the calibration procedure.

[Attachment #2] - AS55_Q output while the Michelson was freeswinging. I had first aligned the ITMs using ASS. The peak-to-peak value of this corresponds to \lambda/4. So we know AS55_Q in terms of cts/m of MICH displacement.

[Attachment #3] - Magnitudes of transfer function from moving one of the MICH optics, to the now calibrated AS55_Q. Fits are to a shape a/f^2, with a being the fitted parameter. Coherence during the measurement is also plotted.

  • Note that the excitation is applied to the channels C1:SUS-<optic>_LSC_EXC, for <optic> in [BS, ITMX, ITMY]. But since my de-whitening board re-work to remove the analog x3 gain, there is a digital x3 gain in the coil driver filter banks. So while the calibration numbers given above are accurate, be aware that when using them for sensing matrix measurements etc, you have to multiply these by x3.
  • Furthermore, moving the BS by x results in a Michelson length change of \sqrt{2}x, and this has been factored into the above number.

Next Steps:

  1. Now that I have a calibration I trust more, re-analyze my DRMI sensing matrix data. Actually the sensing response numbers aren't significantly different from what I have been assuming. It's just that in terms of counts applied at the LSC input of a suspension, there is a digital x3 gain that has to be explicitly factored in.
  2. Calibrate POX and POY by locking the arms and driving the now calibrated ITMs by a known number of counts.
  3. Calibrate the ETMs, and MC1/MC2/MC3 by looking at calibrated POX/POY.
  4. Lock DRMI, and calibrate SRM and PRM.

Reference:

[1] - http://www.phys.ufl.edu/~bernard/papers/CQG20_S903.pdf

Attachment 1: AS55cal_process.pdf
AS55cal_process.pdf
Attachment 2: AS55cal.pdf
AS55cal.pdf
Attachment 3: MICH_act_calib.pdf
MICH_act_calib.pdf
  13987   Tue Jun 19 18:56:55 2018 JonUpdateGeneralAUX beam alignment issues

Not much progress today with the AUX cavity scans. I've determined there still are some alignment issues.

At the start of today a large AUX/PSL beat note was visible on the AS110 sensor, at a similar power as where we left off last night (-60 dBm). Proceeding from there, I attempted to reproduce Johannes' measurement of the cavity transmission resonances. I misaligned the X-arm, locked the Y-arm cavity, and scanned the AUX RF offset approximately 8 MHz in 2 kHz steps. This should have swept through two FSRs, but nothing was visible.

Further inspection revealed that none of the PSL light was making it back to through the AUX fiber to the PSL table. I take this to mean that the beam seen earlier on AS110 was the ITMY reflection, and that the AUX injection axis was no longer reaching ETMY. I also found that the AUX beam size just after the 90/10 beasmsplitter looks anomolously large. Maybe a lens was recently changed? In any case, the mode-matching looks like it is going to need to be readjusted.

  13989   Wed Jun 20 00:57:04 2018 johannesUpdateGeneralAUX beam alignment issues

We did swap a lens as discussed in elog 13968, but they both had f=100mm specified, the difference being one was AR-coated for 1064 and bi-convex, while the other one was plano-convex and had a different coating. The reason for the large beam spot was something else: The fiber wasn't sitting in the coupler properly. When reconnecting the fiber after taking it out make sure to align the key on the fiber end with the notch in the coupler before tightening. After discovering this the following was done:

  • Fixed fiber mounting situation
  • Tested AUX alignment into fiber on PSL table, was still good
  • The AUX polarization was aligned to the wrong fiber axis. I fixed this. The coupler on the PSL table has it's noth oriented vertically since we're using s-polarized light. The AS-table coupler is rotated by 90 degrees, such that the notch points to the side. This way we technically don't need any halfwaveplates for rotation. However, there are still current HWPs installed.
  • Locked both arms and ran dither alignment until satisfactory
  • Misaligned ITMX and ETMX, and further set the ITMX pitch offset to 0.0
  • Started overlapping the expectedly misaligned beams by eye. For this I turned the power of the deflected beam down to 50mV bias voltage, which gives the PSL and AUX lasers similar card-brightness on the shared path
  • Misaligned SRM more because there was still the strong prompt reflection coming out the AS port.
  • Restored phaselock between AUX and PSL, with beat at 30MHz between 1st-order diffracted in fiber and PSL
  • Immediately saw STRONG 30MHz RF signal on AG4395. Disappeared when blocking AUX, and optimized alignment brought the signal up to -10dBm, as shown in attachment #1
  • Checked YEND PDA10CF and saw a -80dBm RF signal at 30 MHz (#2), compatible with earlier observations.

Before leaving I restored the XARM alignment. SRM remains misaligned, LSC off. Alignment shouldn't change drastically over night, so I suggest when picking this work up tomorrow to directly look for the beats after phaselocking AUX and PSL

Attachment 1: as110_rf_30MHz.pdf
as110_rf_30MHz.pdf
Attachment 2: yend_rf_30MHz.pdf
yend_rf_30MHz.pdf
  13996   Thu Jun 21 14:23:22 2018 Udit KhandelwalSummaryGeneralA summary of the Tip-TIlt Mirror Holder design changes

Here’s a quick summary of the Tip-Tilt Design updates (all files are in the dropbox in [TipTiltSus>TT_New]) that I have been working on with Koji and Steve's help.

1. Plate on top to hold mirror in place:

The plate is 0.5 mm thick. I did a rough FEA with 10 N force on the point of pressure on it, and it bent easily.

2. Weighted screw rod at the bottom for tilting the mirror-holder:

I did a very simplified free body analysis to calculate the required length of the rod to achieve a +/- 15 mRad tilt, and got around 1.5 inches.

3. Set-screws on both side of wire clamp to adjust its horizontal position:

  • Front view (showing set screws on either side of the clamp to push it into the desired position, and the clamp in the middle with screws on top and bottom to fix its position):

  • Exploded view showing protrusion in clamp that sits in the mirror holder inset:

 

  • Exploded view showing inset in the mirror holder to slide protrusion in:

 

 

Comments:

1. Used the same screw size in most places to reduce complexity.

2. The mirror holder I have worked on is a little different from the actual piece I have on my table. Which one do you prefer (Koji)?

  13997   Thu Jun 21 14:57:59 2018 KojiSummaryGeneralA summary of the Tip-TIlt Mirror Holder design changes

> 2. Weighted screw rod at the bottom for tilting the mirror-holder:

Too long. The design of the holder should be check with the entire assembly.
We should be able to make it compact if we heavier weights.
How are these weights fixed on the shaft?
Also can we have options for smaller weights for the case we don't need such a range?
Note the mass of the weights.

> 3. Set-screws on both side of wire clamp to adjust its horizontal position:

How much is the range of the clamp motion limited by the slot for the side screws and the slot for the protrusion? Are they matched?
Can you show us the design of the slot made on the mirror holder?

>>

Where is the center of mass (CoM) for the entire mirror holder assy and how much is the height gap between the CoM and the wire release points. Can you do this with 3/8" and 1/2" fused silica mirrors?

  14002   Fri Jun 22 00:06:13 2018 shrutiUpdateGeneralover-head fluorescent lights down

Two out of the four over-head fluorescent lights in the X end of the interferometer were flickering today.

  14013   Sun Jun 24 23:13:46 2018 johannesUpdateGeneralAUX beam alignment issues

At some point we want to change the AUX injection on the AS table to interfere less with the normal interferometer path, and avoid 10/90 beamsplitters which produce a fair amount of ghosting. The plan is to replace the 99/1 BS whose reflection goes to AS110 and AS55, while the transmission goes to the AS camera, with a 90/10 BS as shown in the attachment. This results in ~10% less light on the PDs compared to the pre-AUX era. Between this BS and the AS camera there will be a second 90/10 BS that sends the AUX light into the IFO, so we end up with marginally less AUX power into the IFO and the same PSL power on the AS cam. We're short optics, so this has to wait until two new beamsplitters arrive from CVI.

Attachment 1: AS_AUX_SETUP.pdf
AS_AUX_SETUP.pdf
  14014   Mon Jun 25 19:14:02 2018 UditSummaryGeneralRe: A summary of the Tip-TIlt Mirror Holder design changes

2. Weighted screw rod at the bottom for tilting the mirror-holder:

The screw length selected here (2") is not interfering with any part of the assembly.

The 'weights' I have here are just thumb nuts from Mcmaster, so their weight is fixed (1.65g each, btw).

Problem I'd like to solve: Find an assortment of weighted, symmetric nuts with caps on one end to fix position on shaft. 

3. Set-screws on both side of wire clamp to adjust its horizontal position:

Thanks for pointing out the mismatch in travel distance of protrusion and clamp screws. To match them, the clamp screw slot now sticks out of the profile (by 1.5mm). The range of the clamp motion is +/- 3 mm.

Also, here's a screenshot of the slot in the mirror holder:

--

- Excluding the weighted screw rod assembly, the height gap between assembly COM and wire release point is 3.1 mm.

Quote:

> 2. Weighted screw rod at the bottom for tilting the mirror-holder:

Too long. The design of the holder should be check with the entire assembly.
We should be able to make it compact if we heavier weights.
How are these weights fixed on the shaft?
Also can we have options for smaller weights for the case we don't need such a range?
Note the mass of the weights.

> 3. Set-screws on both side of wire clamp to adjust its horizontal position:

How much is the range of the clamp motion limited by the slot for the side screws and the slot for the protrusion? Are they matched?
Can you show us the design of the slot made on the mirror holder?

>>

Where is the center of mass (CoM) for the entire mirror holder assy and how much is the height gap between the CoM and the wire release points. Can you do this with 3/8" and 1/2" fused silica mirrors?

 

  14015   Mon Jun 25 21:14:08 2018 KojiSummaryGeneralRe: A summary of the Tip-TIlt Mirror Holder design changes

3.
- Do we need this much of extended range of the clamp location? How much range will we need if we use either 3/8 or 1/4 inch mirrors?
- This slot on the mirror holder ring is not machinable.

About the CoM height
- Include the angle adjustment screw and adjust the wire releasing point to have comparable pitch resonant freq to the SOS suspension.

 

  14042   Fri Jul 6 19:39:37 2018 Udit KhandelwalSummaryGeneralCAD drawings of cantilever suspension required

Request to Koji to acquire the drawings or 3D CAD of the cantilever suspensions of the Tip-Tilt Assembly!

  14046   Mon Jul 9 12:36:32 2018 poojaUpdateGeneralProjector light bulb blown out

Projector light bulb blown out today.

  14048   Tue Jul 10 14:20:09 2018 steveUpdateGeneralprojector light bulb replaced

Bulb replaced at day 110  We have now spare now.

 

  14055   Thu Jul 12 11:13:39 2018 gautamUpdateGeneralOMC revival

Aaron and I are going to do the checkout of the OMC electronics outside vacuum today. At some point, we will also want to run a c1omc model to integrate with rtcds. Barring objections, I will set up this model on one of the spare cores on the physical machine c1ioo tomorrow.

  14056   Thu Jul 12 12:26:39 2018 aaronUpdateGeneralOMC revival

We found a diagram describing the DC Readout wiring scheme on the wiki page for DC readout (THIS DIAGRAM LIED TO US). The wiring scheme is in D060096 on the old DCC.

Following this scheme for the OMC PZT Driver, we measured the capacitance across pins 1 and 14 on the driver end of the cable nominally going to the PZT (so we measured the capacitance of the cable and PZT) at 0.5nF. Gautam thought this seemed a bit low, and indeed a back of the envelope calculation says that the cable capacitance is enough to explain this entire capacitance.

Gautam has gone in to open up the HV driver box and check that the pinout diagram was correct. We could identify the PZT from Gautam's photos from vent 79, but couldn't tell if the wires were connected, so this may be something to check during the vent.

UPDATE:

Turns out the output was pins 13 and 25, we measured the capacitance again and got 209nF, which makes a lot more sense.

  14061   Thu Jul 12 23:59:14 2018 gautamUpdateGeneralVent objectives and prep

Vent objectives:

  1. Install radiative heater setup in EY chamber.
  2. Re-direct 50% of AS beam to OMC
    • First, we need to check if the OMC trans PDs work. Else, we have to consider using some in-air PDs for the transmon.
    • Check that OMC length PZT works.
    • Check that OMC steering PZTs work (Koji and I have used this in 2016 to check AS beam clipping so they should work).

We only anticipate opening up the IOO chamber and the EY chamber.


Vent preparation: see here.

  14063   Fri Jul 13 02:52:11 2018 gautamUpdateGeneralVent objectives and prep

[KA, GV]

  1. Arm scan setup moved from West side of PSL table to North side of AP table
    • Marconi is now providing the LO for the loop. A ~5m 50ohm BNC cable needs to be laid out from the PLL area to the NW corner of the AP table where the Agilent is for the TF measurement scheme which allows phase discrimination.
    • We took this opportunity to characterize/improve the setup a bit, and also clean up the 10s of cables around the PSL table. There were some Video cables (75ohm instead of 50ohm no) that were part of the scanning setup which we excised.
    • Mode matching onto beat PD on PSL table was improved - beat signal Vpp increased by factor of 2. PLL gain was adjusted accordingly. 
    • AUX power @AP table ~37mW (before recombination BS), ~3.7mW onto SRM, ~200uW onto ITMY.
    • We got a beatnote in transmission of ~120uV (rms?) after optimizing alignment into Y arm cavity with the AUX frequency on an arm FSR.
    • From Sandrine's calculations, I expected ~20mV of beat signal. We leave it to Annalisa and Terra to square that circle. Probably the MM into the arm isn't stellar either, and we didn't check the polarization of the aux beam (that it is matched to the IFO's p-pol).
    • The entire AUX injection chain needs careful characterization before
  2. Vent prep
    • Both arms were locked to IR, TRY maximized using ASS, TRX maximized by hand.
    • GTRY and GTRX were also maximized.
    • All test mass/PRM/SRM oplevs were centered with this "good" alignment.
    • PSL power into the IMC was cut from 1.07 W (measured after G&H mirror) to 97 mW, by rotating the waveplate immediately after the PSL (original angle 180deg, new angle 216 degrees).
    • PMC was locked. I did not need to change any of the gain settings.
    • 2" R=10% BS in the IMC REFL path was replaced with a Y2, so there is no MCREFL till we turn the power back up.
    • IMC was locked. I touched up my IMC low power autolocker, but this probably needs a bit more touching up tomorrow. MC has remained locked at low power for ~25mins, but as I typed this, I jinxed it and it lost the lock. anyway we have good alignment references.
    • PSL shutter will remain closed.

@SV, we are ready to vent tomorrow. Aaron is supposed to show up ~830am to assist.

Attachment 1: preVentStatus.png
preVentStatus.png
  14067   Fri Jul 13 17:13:45 2018 KojiUpdateGeneralVent objectives and prep

Notice: I removed these 75Ohm video cables.

Attachment 1: P_20180713_020603.jpg
P_20180713_020603.jpg
  14068   Fri Jul 13 18:01:13 2018 gautamUpdateGeneralLow power MC

After getting the go ahead from Steve, I removed the physical beam block on the PSL table, sent the beam into the IFO, and re-aligned the MC to lock at low power. I've also revived my low power autolocker (running on megatron), seems to work okay though the gains may not be optimal, but it seems to do the job for now. Nominal transmission when well aligned at low power is ~1200cts. I briefly checked Y arm alignment with the green, seems okay, but didn't try locking the Y arm yet. All doors are still on, and I'm closing the PSL shutter again while Keerthana and Sandrine are working near the AS table.

  14069   Fri Jul 13 20:36:33 2018 KojiSummaryGeneralIn vac/In air heater wiring

I went to the Y-end and took more photos of the cable stand. These revealed that in-vac pin #13 is connected to the shield of the cable (P.2). This in-vac pin #13 corresponds to  in-air pin #1. So in the end, we bunch the pins in the following order.

In Air In Vac
Pin #2-7 Pin #12-7
Pin #8-13 Pin #6-1
Pin #14-19 Pin #25-20
Pin #20-25 Pin #19-14

 

Attachment 1: heater_wiring.pdf
heater_wiring.pdf heater_wiring.pdf heater_wiring.pdf
  14076   Tue Jul 17 12:46:28 2018 ranaUpdateGeneralsome notes from yesterday

For the EY, instead of balancing the table, I just moved the weight approximately so that the ETMY OSEMS were at half light, but didn't check the level since ETMY is the only optic.

 

Some notes on OMC/AS work (Aaron/Gautam can amend/correct):

- Beam is now well centered in OMC MMT. Hits input coupling mirror and cleanly exits the vacuum to the AS table.

- Didn't see much on OMC trans, but PDs are good based on flashlight test.

- just before closing, re-aligned beam in yaw so that it gets close to the east screw on the input coupler. Aaron and I think we maybe saw a flash there with the OMC length PZT being driven at full range by a triangle wave.

- with OMC Undulators (aka tip/tilt PZT mirrors) energized, the beam was low on PZT1 mirror. We pitched ITMY by ~150 micro-rad and that centered the beam on PZT1 mirror. ITMY-OL is probably not better than 100 urad as a DC reference?

- We checked the range of Undulator 1 and we were getting ~5 mrad of yaw of the beam for the full range, and perhaps half of that in pitch. Rob Ward emailed us from Oz to say that the range is robably 2.7 mrad, so that checks out.

Even if the ITMY has to be in the wrong position to get the beam to the OMC, we can still do the heater tests in one position and then do the OMC checkout stuff in the other position.

Gautam suspects that there is a possible hysterical behaviour in the Undulators which is related to the MC3 glitching and the slow machine hangups and also possibly the illuminati.

[aaron]

-We noticed a ghost beam that from MC REFL (MMT2) that should be dumped during the next vent--it travels parallel to the OMC's long axis and nearly hits one of the steering mirrors for OMC refl.

-We measured the level of the table and found it ~3 divisions off from level, with the south end tilted up

-Gautam rotated and slightly translated OM5 to realign the optic, as expected. No additional optics were added.

-Gautam and I tested the TT piezo driver. We found that 3.6V on the driver's input gave 75V (of 150V) at the output, at least for yaw on piezo 1. However, as Gautam mentioned, during testing it seemed that the other outputs may have different (nonzero) offset voltages, or some hysterisis.

  14077   Tue Jul 17 12:55:45 2018 KojiSummaryGeneralStarted pumping

[Steve, Koji, Gautam]

We started pumping down at ~12:15PM.

Vent finalization ~ YEND

  • The table leveling was way off. This was adjusted by the balancing weight. (Attachment 1~3)
  • The alignment of ETMY was not too much off. Just aligned it with the oplev spot on MEDM and this already made the green flashing.
  • The Green TEM00 was maximized with ITMY and ETMY. This made the PSL IR flashing.
  • The heater wires were checked. I found that one of the heater wires was touching the optical table via the cable shield. This is because the upper pins were shifted to the left side (Attachment 4&5). The pins were shifted and now all 4 cables are isolated form the table. I also checked the mutual resistance between the 4 terminals. They were measured to be isolated except two pairs that showed 4.4 Ohms and 4.0 Ohms (Attachment 6)
  • The tools were removed from the chamber. The Y arm was still flashing.
  • We closed the ETMY door.

Vent finalization ~ Vertex

  • Found the ITMX stuck. Gautam came in and showed us his black magic to release the optic...
  • This allowed us to align X arm. The green flash was found and the TEM00 flash was seen. This allowed us to see the PSL IR flash at the X end.
  • PRM Refl was aligned. SRM was aligned with the oplev.
  • The beam on the AS port was checked. The AS beam came out from the window.
  • Closed the OMC chamber.

Pumping

  • Started pumping with RP1 and RP3. (~12:15PM)

Attachment 1: IMG_5408.JPG
IMG_5408.JPG
Attachment 2: IMG_5400.JPG
IMG_5400.JPG
Attachment 3: IMG_5401.JPG
IMG_5401.JPG
Attachment 4: IMG_5402.JPG
IMG_5402.JPG
Attachment 5: IMG_5403.JPG
IMG_5403.JPG
Attachment 6: IMG_5404.JPG
IMG_5404.JPG
  14081   Wed Jul 18 03:14:48 2018 AnnalisaUpdateGeneralVent 80 recovery

[Gautam, Johannes, Koji, Annalisa]

Tonight we increased the power of the PSL laser and we achieved the lock of both arms with high power.

The AUX beam alignment to the Y arm was recovered and the PLL restored (using the Marconi as LO).

We made a quick measurement of the phase noise and the results will be posted tomorrow.

The beam on the PSL has been blocked, as well as the AUX beam on the AS table. The Marconi has been switched off.


gautam:

  1. Before turning up PSL power, I placed a block in front of MC refl to avoid any PD burning. Replaced HR Y1 2" optic with the usual 10% reflective BS to direct MC REFL to the locking PD.
  2. Waveplate was rotated back to 180 deg (original position before the vent). After optimizing PMC transmission, I measured 1.05 W going into the IMC (pre-vent value was 1.07 W, prolly within power meter absolute accuracy).
  3. IMC autolocker restored to usual high power version on megatron.
  4. There seems to be some kind of vacuum interlock in effect that prevents me from opening the PSL shutter via EPICS - I had to toggle the position on the shutter controller under the table. After tonight's work, I returned the controller to the NC state, to avoid any further interference with this interlock code that may prevent pumping in the AM.
  5. PLL gain was re-adjusted to achieve maximum stability (judged by eye) of the beat-note in lock triggered on the Marconi LO signal. Alignment onto the NF beatPD was also tweaked to squeeze out as much beat as possible.
  6. The main objective tonight was to send AUX beam in, recover transmission beat, scan the AUX frequency, and resolve some peaks (MAX HOLD scanning technique, magnitude only for now, no phase info). Thanks to JE's expert fiber alignment and beatnote maximization, we achieved this yes. Annalisa will post a plot tmr. 
  7. For unknown reasons, the Y arm ASS does not maximize TRY. So we are in the unfortunate situation of neither arm having a working ASS servo. To be worked on later.
  14084   Wed Jul 18 23:43:50 2018 KojiUpdateGeneralVent 80 recovery

Is the reflector too close to the beam and causing clipping?

Quote:

For unknown reasons, the Y arm ASS does not maximize TRY. So we are in the unfortunate situation of neither arm having a working ASS servo. To be worked on later.

Attachment 1: IMG_5868.JPG
IMG_5868.JPG
Attachment 2: IMG_5382.JPG
IMG_5382.JPG
  14106   Thu Jul 26 15:11:18 2018 SteveUpdateGeneral Viewports & coating of 2001

New optical quality BK-7 windows in 2001 [4 substrates ] AR coated R<0.75 % for 630-1064nm " Azury BLue" broadband : TRX, TRY, ITMY-Oplev &  ITMX-Oplev viewports.

The BS-Oplev and PRM-Oplev 10" CF with 5.38" diameter view was coated the same way. The window here is Corning 7056 Borosilicate

5 more BK-7 substrates were coated R <0.1% of 1064 nm "Golden Orange" Their location: IMC-IN, IFO-REF and OMC   The next vent we have to confirm optical quality window locations.

All other conflat flange viewports are 7056 Kovar sealed .

Technical notes of 2001 40m upgrade can be seen at LIGO-T010115- 00- R  ....page 14

Attachment 1: BK7window_Coatings.PDF
BK7window_Coatings.PDF BK7window_Coatings.PDF
  14107   Fri Jul 27 02:30:51 2018 gautamUpdateGeneralGlitchy MC

Kevin and I saw some weird IMC / PEM BLRMS behaviour today - see Attached screenshot. Not sure what was happening with the IMC, but MCtrans was oscillating at ~3Hz for a good 20 minutes or so. I just killed the lock, and restarted MCautolocker on megatron. There was a strange feature in the 3-10Hz BLRMS around that time as well. All seems back to normal now...

Attachment 1: 38.png
38.png
  14176   Wed Aug 22 08:44:09 2018 SteveUpdateGeneralearth quake

6.2M Bandon, OR did not trip any sus

 

Attachment 1: yesterday_EQs.png
yesterday_EQs.png
  14182   Fri Aug 24 08:04:37 2018 SteveUpdateGeneralsmall earth quake

 

 

Attachment 1: small_EQ.png
small_EQ.png
  14191   Wed Aug 29 14:51:05 2018 SteveUpdateGeneraltomorrow morning

Electrician is coming to fix one of the fluorenent light fixture holder in the east arm tomorrow morning at 8am. He will be out by 9am.

The job did not get done. There was no scaffolding or ladder to reach troubled areas.

  14284   Wed Nov 7 19:42:01 2018 gautamUpdateGeneralIFO checkup and DRMI locking prep

Earlier today, I rebooted a few unresponsive VME crates (susaux, auxey).

The IMC has been unhappy for a couple of days - the glitches in the MC suspensions are more frequent. I reset the dark offsets, minimized MCREFL by hand, and then re-centered the beam on the MC2 Trans QPD. In this config, the IMC has been relatively stable today, although judging by the control room StripTool WFS control signal traces, the suspension glitches are still happening. Since we have to fix the attenuator issue anyways soon, we can do a touch-up on IMC WFS.

I removed the DC PD used for loss measurements. I found that the AS beam path was disturbed - there is a need to change the alignment, this just makes it more work to get back to IFO locking as I have to check alignment onto the AS55 and AS110 PDs.

Single arm locking worked with minimal effort - although the X arm dither alignment doesn't do the intended job of maximizing the transmission. Needs a checkup.

PRMI locking (carrier resonant) was also pretty easy. Stability of the lock is good, locks hold for ~20 minutes at a time and only broke because I was mucking around. However, when the carrier is resonant, I notice a smeared scatter pattern on the ITMX camera that I don't remember from before. I wonder if the FF idea can be tested in the simpler PRMI config.

After recovering these two simpler IFO configurations, I improved the cavity alignment by hand and with the ASS servos that work. Then I re-centered all the Oplev beams onto their respective QPDs and saved the alignment offsets. I briefly attemped DRMI locking, but had little success, I'm going to try a little later in the evening, so I'm leaving the IFO with the DRMI flashing about, LSC mode off.

  14303   Sun Nov 18 00:59:33 2018 gautamUpdateGeneralVent prep

I've begun prepping the IFO for the vent, and completed most of the IFO related items on the checklist. The power into the MC has been cut, but the low-power autolocker has not been checked. I will finish up tomorrow and post the go ahead. PSL shutter is closed for tonight.

  14304   Sun Nov 18 17:09:02 2018 gautamUpdateGeneralVent prep

Vent prep

Following the checklist, I did these:

  • Both arms were locked to IR, TRY and TRX maximized using ASS.
  • GTRY and GTRX were also maximized.
  • ITM/ETM Oplevs centered with TRX/TRY maximized, PRM/SRM/BS Opelvs were centered once the DRMI was locked and aligned.
  • Attachment #1 summarizes the above 3 bullets.
  • Sensoray was made to work with Donatella (Raspberry Pi video server idea is good but although the sensoray drivers look to have installed correctly, when the Sensoray unit is plugged into the RPi USB port, the red light doesn't come on, so I opted to not spend too much time on it for the moment).
  • Photos of all ports in various locked configurations are saved in /users/sensoray/SensorayCaptures/Nov2018Vent
  • PSL power into the IMC was cut from 1.07 W (measured after G&H mirror) to 97 mW. I opted to install a new HWP+PBS after the PMC to cut the power, so we don't have to fiddle around so much with the PMC locking settings [Attachment #3, this was the only real candidate location as the IMC wants s-polarized light].
  • 2" R=10% BS in the IMC REFL path was replaced with a 2" Y1 HR mirror, so there is no MCREFL till we turn the power back up.
  • IMC was locked.
  • Low power MC autolocker works [Attachment #2]. The reduction in MCREFL is because of me manually aligning the cavity, WFS servos are disabled in low power mode since there is no light incident on the WFS heads.
  • Updated the SUS driftmon values (though I'm not really sure how useful this is).
  • PSL shutter will remain closed, but I have not yet installed a manual beam block in the beam path on the PSL table.

@Steve & Chub, we are ready to vent tomorrow (Monday Nov 19). 

Attachment 1: VentPrepNov2018.png
VentPrepNov2018.png
Attachment 2: MCautolocker_lowPower.png
MCautolocker_lowPower.png
Attachment 3: IMG_7163.JPG
IMG_7163.JPG
  14316   Mon Nov 26 10:22:16 2018 aaronUpdateGeneralprojector light bulb replaced

I replaced the projector bulb. Previous bulb was shattered.

  14324   Thu Nov 29 17:46:43 2018 gautamUpdateGeneralSome to-dos

[koji, gautam, jon, steve]

  • We suspect analog voltage from N2 pressure gauge is connected to interfacing Omega controller with the 'wrong' polarity (i.e pressure is rising over ~4 days and then rapidly falling instead of the other way around). This should be fixed.
  • N2 check script logic doesn't seem robust. Indeed, it has not been sending out warning emails (threshold is set to 60 psi, it has certainly gone below this threshold even with the "wrong" polarity pressure gauge hookup). Probably the 40m list is rejecting the email because controls isn't a part of the 40m group.
  • Old frames have to be re-integrated from JETSTOR to the new FB in order to have long timescale lookback.
  • N2 cylinder pressure gauges (at the cylinder end) need a power supply - @ Steve, has this been purchased? If not, perhaps @ Chub can order it.
  • MEDM vacuum screen should be updated to have gate valves be a different color to the spring-loaded valves. Manual valve between TP1 and V1 should also be added.
  • P2, P3 and P4 aren't returning sensible values (they should all be reading ~760torr as is P1). @ Steve, any idea if these gauges are broken?
  • Hornet gauges (CC and Pirani) should be hooked up to the new vacuum system.
  • add slow channels of   foreline pressures of TP2 & 3   and    C1:Vac-IG1_status_pressure
  14325   Fri Nov 30 15:53:52 2018 JonOmnistructureGeneralN2 pressure gauge fix

I've made a repair to the N2 pressure monitor. I don't believe the polarity of the analog signal into the controller actually was reversed. I found the data sheet (attached) for the transducer model we have installed. Its voltage should read ~0 at 0 PSI and 100mV at 100 PSI. As wired, the input voltage reads +80 mV as it should.

The controller calibrates the sensor voltage to PSI (i.e., applies a scale and offset) based on two settable reference points which appeared to be incorrect. I changed them to:

  1. 0 mV = 0 PSI (neglecting the small dark bias)
  2. 100 mV = 100 PSI

After the change, the pressure reads 80 PSI. Let's see if the time history now shows a sensible trend. 

Quote:

[koji, gautam, jon, steve]

  • We suspect analog voltage from N2 pressure gauge is connected to interfacing Omega controller with the 'wrong' polarity (i.e pressure is rising over ~4 days and then rapidly falling instead of the other way around). This should be fixed.

 

Attachment 1: N2_transducer_datasheet.pdf
N2_transducer_datasheet.pdf
  14331   Tue Dec 4 18:24:05 2018 gautamOmnistructureGeneralN2 line disconnected

[jon, gautam]

In the latest installment in this puzzler: turns out that maybe the trend of the "N2 pressure" channel increasing over the ~3 day timescale it takes a cylinder of N2 to run out is real, and is a feature of the way our two N2 cylinder lines/regulators are setup (for the automatic switching between cylinders when one runs out). In order to test this hypothesis, we'd like to have the line pressure be 0 initially, and then just have 1 cylinder hooked up. When we went into the drill-press area, we heard a hiss, turns out that one of the cylinders is leaking (to be fair, this was labelled, but i thought it isn't great to have a higher N2 concentration in an enclosed space). Since we don't need any actuation ability, I valved off the leaky cylinder, and disconnected the other properly functioning one. Attachment #1 shows the current state.

Attachment 1: IMG_7195.JPG
IMG_7195.JPG
  14333   Thu Dec 6 17:33:33 2018 JonOmnistructureGeneralN2 line disconnected

I believe I finally have the N2 gauge working correctly. The wiring is unchanged from its original state and the controller has been recalibrated.

After letting the line pressure drop to 0 PSI as indicated by the analog gauge in the drill-press room, I recorded the number of counts read by the Omega controller. Then I pressurized the line to 80 PSI, again indicated by the analog gauge, and recorded the Omega counts again. I entered these two reference points into the controller (automatically determines the gain and offset from these), then confirmed the readings to agree with the anaog gauge as I varied the line pressure.

The two reference points are:

0 PSI  :  13 counts
80 PSI : 972 counts

 

Quote:

[jon, gautam]

In the latest installment in this puzzler: turns out that maybe the trend of the "N2 pressure" channel increasing over the ~3 day timescale it takes a cylinder of N2 to run out is real, and is a feature of the way our two N2 cylinder lines/regulators are setup (for the automatic switching between cylinders when one runs out). In order to test this hypothesis, we'd like to have the line pressure be 0 initially, and then just have 1 cylinder hooked up. 

 

ELOG V3.1.3-