Y-arm length
e-log    length [m]
-----------------------------
 556(2008-Jun-24)  38.70    +/- 0.08    Cavity swinging measurement
 556(2008-Jun-24)  38.67    +/- 0.03    Tape & photo
 776(2008-Jul-31)  38.640   +/- 0.007   Beam injection, poor PLL, Transmitted DC
 782(2008-Aug-02)  38.6455  +/- 0.0012  Beam injection, independent PLL, Transmitted DC
 787(2008-Aug-04)  38.64575 +/- 0.00037 Beam injection, independent PLL, Transmitted RF
this(2008-Aug-04)  38.6462  +/- 0.0003  Beam injection, independent PLL, Transmitted RF, five FSRs, freq calibrated
-----------------------------

FSR1:  3879251.9 Hz +/-  8.8 Hz
FSR2:  7757968.1 Hz +/- 10.8 Hz
FSR3: 11636612.9 Hz +/- 10.2 Hz
FSR4: 15515308.1 Hz +/-  8.7 Hz
FSR5: 19393968.7 Hz +/-  8.4 Hz

Last night something happened on the beat between the PSL beam and the auxiliary NPRO beam, that spoiled the quality of the beating I had before. As a result the PLL has become unable to lock the two lasers.

The amplitude of the beat at the spectrum analyzer has gone down to -40 dBm from -10 that it was earlier. The frequency has also become more unstable so that now it can be seen writhing within tens of KHz.

Meanwhile the power of the single beams at the PLL photodiode hasn't changed, suggesting that the alignment of the two beam didn't change much.

Changes in the efficiency of the beating between the two beams are not unusual. Although that typically affects only the amplitude of the beat and wouldn't explain why also its frequency has become unstable. Tuning the alignment of the PLL optics usually brings the amplitude back, but it was uneffective today.

It looks like something changed in either one of the two beams. In particular the frequency of one of the two lasers has become less stable.

Another strange thing that I've been observing is that the amplitude of the beat goes down (several dBm) as the beat frequency is pushed below 50 MHz. Under 10 MHz it even gets to about -60 dBm.

I noticed the change yesterday evening at about 6pm, while I was taking measurements of the PLL open loop tranfer function and everything was fine. I don't know whether it is just a coincidence or it is somehow related to this, but Jenne and Sanjit had then just rebooted the frame builder.

 I confirm what I said earlier. The amplitude of the beat is -10 dBm at 300MHz. It goes down at lower frequencies. In particular it gets to-60 dBm below 20 MHz. For some strange reason that I couldn't explain the beating efficiency has become poorer at low frequencies.

Problem found. Inspecting with Koji we found that there was a broken SMA-to-BNC connector in the BNC cable from the photodiode.

Yesterday I measured the Open Loop Gain of the PLL in the absolute length experiment. The servo I used was that of the old Universal PDH box.

The OLG looks like this:

The UGF is at 10 KHz.

In the revival of the experiement length measurement for the recycling cavities, I turned the auxiliary NPRO back on. The shutter is closed.

I also recollected all the equipment of the experiment after that during the summer it had been scattered around the lab to be used for other purposes (Joe and Zach's cameras and Stephanie and Koji's work with the new EOM).

X Arm
FSR     =  (3897627 +/- 5 )   Hz
L       = (38.45833  +/- 0.00005) m
g2x     =   0.31197  +/- 0.00004
g2y     =   0.32283  +/- 0.00004
R-ETM_x = (55.8957   +/- 0.0045) m
R-ETM_y = (56.7937   +/- 0.0038) m

Y Arm
FSR     = ( 3879252 +/- 30 )  Hz
L       = (38.6462   +/- 0.0003) m
g2x     =   0.31188  +/- 0.00004
g2y     =   0.32601  +/- 0.00004
R-ETM_x = (56.1620   +/- 0.0013) m
R-ETM_y = (57.3395   +/- 0.0011) m

So far, this is just preliminary, because I haven't done full error analysis to determine the error on my measurements.  That will hopefully be done by tomorrow afternoon (so before we start taking off doors).

I find that the length of the Xarm is:  37.5918 meters.

I find that the length of the Yarm is:   37.5425 meters.

I used the mass-kicking technique, as summarized by Kiwamu, and fully described by Alberto.  More words / description to follow with the full error analysis.

The accelerometer power supply / preamp board has been OFF because of exciting new accelerometer measurements.  It's now on, so watch out and make sure to turn it back off before plugging / unplugging accelerometers.

We are done taking accelerator huddle test data. So I moved back all six accelerometers and cables to MC1 and MC2. I also relabel each of the accelerometers properly since the labels on them were confusing.

QED

Koji, Steve, and Kevin looked into calibrating the Wilcoxon accelerometers. Once calibrated, the accelerometers will be used to monitor the motion of the PSL table.

We want to use the shaker to shake each accelerometer and monitor the motion with an OSEM. We will make a plate to attach an accelerometer to the shaker. A flag will also be mounted on this plate.The OSEM will be mounted on the table next to the shaker and positioned so that the flag can block the LED light as the plate moves up and down. We will then measure the motion of the accelerometer as it is shaken from the OSEM signal. The OSEM signal will be calibrated by keeping the plate and the flag still and moving the OSEM down along the flag a known distance with a micrometer.

[Ian, Torrey Cullen, Sander Vermeulen]

We are trying to calibrate one of the Wilcoxon accelerometers from the cryo lab to do a seismic study of campus. To calibrate it, we took data on Friday afternoon until about 6 pm for the Wilcoxon in the X, Y, and Z orientations and took cross-spectra with the seismometer down the end of the X arm from the channels C1:PEM-SEIS_EX_X_IN1, C1:PEM-SEIS_EX_Y_IN1, C1:PEM-SEIS_EX_Z_IN1. For the Wilcoxon, we used the channel from [17717] that was not being used. In the image of the panel in [17717] we tried channel 5, with the channel name C1:X01-MADC0_EPICS_CH28 but it was a slow channel. We asked Koji if there was a fast channel we could use, and he lent us channel 4 on that board with the channel name C1:ALS-X_SLOW_SERVO1_IN1. We took data from this channel to do our measurements. nothing was plugged into this channel when we started using it so we left it that way when we were done. 

I have attached our data.

NOTE: As it turns out the seismometer down the x end is not calibrated. We will recalibrate using the seismometer at the vertex

There is a version of this on the McCuller Logbook. It includes some plots. More non-40m related posts will continue there.

I was able to get this accelerometer going for the next Lab tours. I want to get this guy up on a big screen to give people a nice "wow". I found this accelerometer on the Y end cabinet and there is 1 more available if anyone needs it at 40m. It is a Brüel & Kjær 8318. It contains a PZT so there is no need to input a signal. The accelerometer seemed to only put out roughly 2 mV max, so i had to amplify with an SR560 to get a good looking signal. 

RXA: link to Manual

[C1:PEM-ACC_MC1_X]
chnnum=15014
gain = 10

etc.

[Jenne and Koji] 

In order to characterize the seismic vibration of the PSL table, we put the accelerometers on and below the PSL table.

On the PSL: MC2 Accelerometers (X, Y, Z) - being connected to CH1-3 of the preamps
East side of the PSL table. X, Y, and Z is directed to North, East, and Up.

On the ground: MC1 Accelerometers (X, Y, Z) - being connected to CH4-6 of the preamps
Beneath the West side of the PSL table. X, Y, and Z is co-aligned to the MC2 ACC.

I found that the C1:PEM-ACC_MC1_Z has large noise in the low freq (~1Hz) region. I tracked down the noise source
and found the noise is still present in the down stream even when the CH17 (C1:PEM-ACC_MC1_Z) of the ADC IF BNC
(@1Y7) was terminated.

I consulted with Jenne and decided to connect this channel to CH14, which is vacant and has name
C1:PEM-AUDIO_MIC2 (16k).
(for the details of the channel configurations, see /cvs/cds/caltech/chans/daq/C1ADCU_PEM.ini)

I first tried magnetometer channels to steal, but they didn't seem reacting (and the connected to the wrong channels).
I am feeling that we should once entirely check the I/F box.

Note that there looks the difference of the gain by x10 between C1:PEM-ACC_MC* channels and C1:PEM-AUDIO_MIC2.

[From Jenne:  The gain difference is because the C1:PEM-ACC_MC* channels have gain=10 in the .ini file, while C1:PEM-AUDIO_MIC2 uses the default gain=1. ]

Result of the accelerometer measurement

Introduction

We wanted to characterize the PSL table before the work before its lifting up.
We put a set of three-axis Wilcoxon accelerometers on the ground and another set on the PSL table through the weekend.

Result

- The data at 9th Aug 00:00(UTC) is used. This was Sunday 5PM in the local time.
- The freq resolution was 0.01Hz. The # of avg was 50.

- The accelerometer signals were calibrated by the value 1.2e-7 V/(m/s^2). We use this absolute value of the spectrum for the comparison purpose.

- The accelerometers were aligned to North(X), East(Y), and Up(Z). There was the coherence observed from 2~20Hz.
  The transfer functions are valid only this frequency region although we still can set the lower bound of them.

- The transfer functions in the horizontal directions show huge peaks at around 20Hz. The Q of the peaks are ~30 to ~100.
  The vertical transfer function shows somewhat lower peak at around 50Hz with Q of ~10.

Some thoughts

- The low resonant freq and the high Q of the horizontal mode comes from the heaviness of the table.

- We are going to raise the table. This will usually mean that we get the lower resonant freq. This is not nice.

- So, the decision to use 6 tripods rather than 4 was right.
- The steel tripods are expected to give both more rigidity and more damping than the chep-looking hollow Newport legs.
- Concrete grouting of the tripods will also lower the effective height and will benefit for us.

The MC1 accelerometer cube (3 accelerometers arranged in x,y,z) is under the PSL table, as I found it at the beginning of the summer.

The MC2 accelerometer cube is on the table where I worked on the STACIS, right when you walk into the lab from the main entrance. Their cables are dangling near the end of the mode cleaner, so the accelerometers are ready to be placed there if wanted.

All accelerometers are also plugged into their ADC channels.

MC1 accelerometer has been plugged in. The modecleaner locking has been intermittent today, but I looked at a 15 minute lock in DTT, looking at the STS1 seismometer and both accelerometer triplets. Plot and DTT xml attached.

For the sake of not cluttering up everything with legends, the coherence plots are organized by direction (x, y, z), and include the coherence of each of the three sensors (sts, acc1, acc2) with the IMC control signal and the IMC transmitted RIN. 

Some remarks:

• The 1 Hz pendulum motion is about equal amounts of X and Y, which makes sense, as MC1 and 3 are at an angle
• The ~3 Hz stack motion seems to be entirely in the X direction. Why?
• The bounce/roll bands are strongly coherent with Z motion at MC2. 
• The STS does not appear to have any low frequency advantage over the accelerometers, in terms of coherence, contrary to what I would expect even without a thermal enclosure. 
• The control signal and RIN RMSs are clearly dominated by noise in the 1-3Hz band, where we have reasonable coherence. Good prospects for noise subtraction...

The accelerometers have been installed at MC1 and MC2. MC2 data is live, I haven't yet run the cables from the MC1 set to the preamp yet, though. 

Today, I installed the Wilcoxon accelerometers in the table near the end of the mode cleaner. I only set three of them up instead of all six. They were set up just as Rana suggeted we should have them properly set up, i.e. cables being tighten up, and a box on top to prevent any airflow introducing any disturbances. We are planning on running the huddle test on these guys once the upgrade? to the interferometer is done.

The cables were tightly clamped to the table as shown below, I used a thick piece of shock absorbing rubber to do this.

 A small piece of thin rubber was used to hold each of the accelerometers tightly to the table in order not to damage them.

We had to borrow Megan's and Kate's piece of black foam in order to seal one of the sides properly, as the cable had to come out through somewhere. We didn't want to mess with drilling any holes into the box! 

There was a small crack even after using the foam. I sealed it up with duck tape.

The box isn't perfect, so there were multiple cracks along the bottom and top of it that could potentially allow for air to flow to the inside. Eric suggested that we should be super careful this time and do it right, so every crack was sealed up with ducktape.

Finally, we needed something heavy to be placed on top of the box to hold everything well. We used Rana's baby to accomplish this goal.

Just kidding! Rana's baby is too delicate for our purposes. A layman box of heavy cables was used instead. 

Both accelerometers have been moved in an attempt to optimize their positions. The MC1 accelerometer was moved from one green bar to the other (I don't know what to call them) at the base of the MC1 and MC3 chambers. That area is pretty tight, as there is an optical table right there, and I did my best to be careful, but if you suspect something has been knocked loose, you might check in that area. The MC2 accelerometer was moved from the horizontal bar down to the metal table on which the MC2 chamber rests.

[Sanjit, Jenne]

The set of 6 accelerometers which were semi-randomly placed underneath the MC2 tank are now back into 2 separate sets of 3 - one set at MC2 and one set at MC1.  The channel names once again reflect reality, i.e. MC1_Y is actually under the MC1 tank, and aligned with the y direction.  Also, the Guralp under MC1 was moved a little bit to the left, because Sanjit wanted to put the accelerometers where the seismometer had been. 

Some of these channels are not like the others.

[Steve, Bob, Jamie, Kiwamu, Valera, Jenne]

The access connector is now in place, in preparation for pump-down.  Tomorrow (hopefully) we will do all the other doors.

[Jenne, Koji]

I was trying to lock the Yarm, and saw that I was not getting signals to go between the LSC and SCY models.  I had digital zeros for TRY, and when I overrode the trigger and tried to force signal to ETMY, I had digital zeros at the SUS-ETMY_LSC input. The corresponding filter bank in the rfm model was receiving signals, so the Dolphin connection between LSC and SUS was okay, it was just the RFM connection going to the end station that wasn't succeeding. 

Koji restarted the c1scy model, and then went inside the IFO room, and found that the SUS IO chassis power was off.  We must have accidentally turned it off while we were in there earlier.  Koji turned on the power, and also restarted the rfm model, and we now have real signals going back and forth. 

Yarm is locked, ASS worked nicely, etc, etc, so things seem normal again (with the Yarm....ETMX stuff is still out of order).

We need ADC and DAC channels for a couple of things:

• POP QPD: 3x ADC
• ALS PZTs: 3x 2x 2x DAC (three pairs of PZTs, at ends and vertex, each with two channels for pitch and yaw)
• Fibox: 1x DAC

What's being used:

• c1iscex/c1iscey:
  
  • DAC_0:   7/16 = 9 free
  • ADC_0: 17/32 = 15 free
• c1sus:
  
  • DAC: ?
  • ADC: ?
• c1ioo
  
  • DAC_0:   0/16 = 16 free ?? This one is weird. DAC in IO chassis, half it's channels connected to cross connect (going ???), but no model links to it
  • ADC_0: 23/32 = 9 free
  • ADC_1:  8/32 = 24 free
• c1lsc
  
  • DAC_0: 16/26 = 0 free
  • ADC_0: 32/32 = 0 free

What this means:

• We definitely have enough DACs for the ALS PZTs.  The free channels are also in the right places: at the end stations and in the c1ioo FE, which is close to the PSL and hosts the c1als controller.
• We appear to have enough ADCs for the QPD in c1ioo.
• We don't have any available DAC outputs in c1lsc for the Fibox.  If we can move the Fibox to the IOO racks (1X1, 1X2) then we could send LSC channels to c1ioo and use c1ioo's extra DAC channels.

Of course we'll have to investigate the AA/AI situation as well.  I'll try to asses that in a follow up post.

PS: this helps to identify used ADC channels in models:

grep adc_ sus/c1/models/c1scx.mdl | grep Name | awk '{print $2}' | sort | uniq

1. What are we using 16 DAC channels for in the LSC?
2. What are the functions of those IOO DAC channels which go to cross-connects? If they're not properly sending, then we may have malfunctioning MC or MCWFS.
3. Can we just use the SLOW DAC (4116) for the ALS PZTs? We used this for a long time for the input steering and it was OK (but not perfect).

For the new input and output tip-tilts.  Two input, two output, each requires four channels.

I have no idea.  I don't know what the hardware is, or is supposed to be, connected to.  DAC for WFS??  Was there at some point supposed to be fast output channels in the PSL?

 Probably. I'm not as familiar with that system.  I don't know what the availability of hardware channels is there.  I'll investigate tomorrow.

Looking back at elog 12528, the uncertainty in the armloss number from the individual quantities in the equation for can be written as:

Making some generous assumption about the individual uncertainties and filling in typical values we get in our measurements, results in the following uncertainty budget:

In my recent round of measurements I had a 2.5% uncertainty in the ASDC reading, which completely dominates the armloss assessment.

The most recent numbers are 57 ppm for the YARM and 21 ppm for the XARM, but both with an uncertainty of near 150 ppm, so while these numbers fit well with Gautam's estimate of the average armloss via PRG, it's not really a confirmation.

I set the whitening gain in ASDC to 24 dB and ran LSC offsets, and now I'm getting a relative uncertainty in measured reflected power of .22%, which would be sufficient for ~25ppm accuracy according to the above formula. I'm going to start a series of measurements tonight when I leave, should be done in ~2 hours (10 pm) the latest.

If anybody wants to do some night work: I misaligned ITMY by a lot to get its reflection off ASDC. Approximate values are saved as a restore point. Also the whitening gain on ASDC will have to be rolled back (was at 0dB) and LSC offsets adjusted.

I had a mistake in my script that reported the wrong error after averaging several datapoints, and because I hadn't looked at the individual numbers I didn't catch it so far. Thanks to Gautam it is no more.

The updated numbers are (with fresh, more trustworthy data):

XARM: 21 +/ 35 ppm
YARM: 69 +/- 45 ppm

This looks much better. I'm planning to take more data with the AS110 PD rather than AS55 when I get the chance, increase the averaging time, and also sigma filter the datapoints. That should get us to a good spot and cut down the uncertainty even further.

I don't like AS110 or AS55. Neither of them are designed for DC and so the DC readout chain is hokey. How about use an actual transimpedance PD with a 100-1000 Ohm resistor and a 3 mm diode? This would eliminate the alignment sensitivity and the drifts due to electronics and room lights.

This is an update for 17794.

The UMIK 1 + REW combination gave satisfactory results for creating the acoustic noise spectrum for various spaces. This combination was corroborated using the NIOSH app on iOS (by OSHA) and the real time readings were usually in the +-2dB range of each other. dBA scale (reference values)  and NC scale (reference values) were used for measurement. Since the microphone is omnidirectional, the data was collected in the upright position. About 300 averages were taken for each reading and for open spaces, the data was collected with minimal activity (a few people walked by while collecting the stairwell data but they tried to be discreet). For closed spaces, readings were taken at 2/3 positions depending on the size of the room.

HIGHLY SUGGEST GETTING A CALIBRATION DEVICE IN THE FUTURE TO MAKE FAITHFUL MEASUREMENTS.

This is the Noise Floor of the UMIK-1 for reference (it was taken by covering it in a multiple layers of a bedsheet). The remaining readings can be found in ANS_Script_Data_Images.zip

The zip file contains the following:
Acoustic Noise Spectrum.pdf - This contains the keywords and spectrums consolidated in one pdf document
ANS_Positions.pdf - This contains images of the mic position while collecting the data
NC_Data_points.txt - This contains the data points used to generate the NC curves (Spline fit)
Spectrum Data - This folder contains the text files with the raw data to create the spectrum as well as some additional information about the recordings (source, date, etc)
Spectrum Images - This folder contains individual images for all the spaces
Final_Analyze_Signal.ipynb - Notebook used to create the spectrum from the text data

Update: Added spectrums for Downs-Lauritsen Rooms (226, 314, Sub Basement Corridor)
Update: Superimposed noise floor on each spectrum

dB(A) (A-weighted) scale and the Noise Criterion (NC) scale are popularly used in the United States for creating the spectrum. 

dB(A) Explanation: https://www.engineeringtoolbox.com/decibel-d_59.html

NC Explanation: https://www.engineeringtoolbox.com/nc-noise-criterion-d_725.html

(tldr: dBA applies an A-weighted filter to the dB scale to account for relative loudness that humans perceive at different frequencies. NC scale assigns a number, eg NC-55 such that at no frequency does the noise go beyond 55dB)

To capture this coherently, engineers usually use a SPL (Sound Pressure Level) Meter which is in essence, just another microphone. It is calibrated using a SPL Calibration Device which plays sound at a given loudness (usually 94dB, 114dB) and at a set frequency (usually 1kHz). You latch it on your SPL meter and make sure it is reading the output. 

The good thing about an SPL meter is, you don’t need to worry about the internal gains and so forth, it does all of that under the hood and gives you the measurement straight in decibels (A/B/C weighted if required).

The alternative to this suggested was using a UMIK 1 (a microphone that has a low noise floor - needs to be measured, online blogs mention it as ~30dbA). The suggested softwares are REW and Dirac Live (this one is paid).

UMIK 1 can be used in a couple of ways:

1. UMIK 1 + REW has a fair amount of documentation online for setting up. You can calibrate the microphone by pressing some keys which brings you in the green zone which the software likes (hopefully). This video explains it well.
   https://www.youtube.com/watch?v=3mOn6_3j5DU.
   UMIK-1 also comes with a calibration file, however one of the blogs mentions that it does not make a huge difference. This calibration file can be used directly in the REW software. This old graph does not show a huge difference in the bandwidth of interest between the factory settings and the calibrated settings. Additionally, it has a Sens Factor which I don't fully understand. (explained in this blog).
   The two REW features that may get the job done are the SPL Meter and the RTA (Real Time Analyzer). However, the issues with both are as described in this question I posted on their forum. https://www.avnirvana.com/threads/rew-umik-1-measurements-dba-nc.12420/#post-94154 (Update: There was a reply on the post needs to be checked out).

2. The signal can be read directly into something like Audacity and the time series can then be analyzed manually. However, the specification sheet for UMIK 1 does not provide it’s sensitivity so it’s difficult to know what it’s actually reading (have contacted the tech support, they said they’ll get back on Monday posted on a forum as well). A couple of recordings that were done on Audacity were of extremely low level using the UMIK 1 which probably means there’s some gain configurations that need to be figured out to get a good signal.

(Another microphone, the YETI Nano Blue may be used with Audacity, have requested for the specifications sheet. Update: 4.5mV/Pa at 1kHz).

My box has been suspended in the PSL using surgical tubing, and it has been connected to C1:PEM-MIC_1 (C17) with a BNC. I made a braided power cable as well but it turned out to be slightly too short... Once this is fixed, everything should be ready and we can see if it's working correctly. I also set up a new tab on the summary pages for this channel:

https://ldas-jobs.ligo.caltech.edu/~praful.vasireddy/1154941217-1154942117/pem/acoustic/

This data is back from when I had my solderless breadboard running near MC2. I'll add this tab to the real pages once the box is working (which could be a while since I'm gone for a month). Let me know if you see any issues with either the tab or the box/cables.

1. add photo of installation
2. no more secret personal pages! put channels into the actual pages that we look at
3. make it ASD instead of PSD, same as the other channels
4. add specgram (whitened and not)

I'll add a picture of the installation when I get back to campus and finish hooking up the power cable. I haven't added this channel to the actual pages yet because there's not any data right now- the box is still unpowered because my braided power cable wasn't long enough. I just changed the format of the spectrum to ASD and added spectrograms. Here's how the tab looks now: https://ldas-jobs.ligo.caltech.edu/~praful.vasireddy/1155014117-1155015017/pem/acoustic/

Let me know if there's anything else to change.