[Jenne, Sanjit]

It looks like Steve used a GND-12V supply to power the Guralp through the little breakout box (the box is for checking the centering of the mass).  This is BAD.  The Guralps want +/- 12V.

We centered all of the channels on Gur2, and checked the channels on Gur1, so we'll see how they're feeling after a while.

This trend of the last 200 days shows that GUR2 has been bad forever...until now anyways.

I went and double-checked and aligned the styrofoam cooler at ~5:00 UTC. It was fine, but we really need a better huddling box. Where's that granite anyway?

Here's the new Huddle Test output. This time I show the X-axis since there's some coherence now below 0.1 Hz.

You'll also notice that the Wiener filter is now beating the FD subtraction. This happened when I increased the # of taps to 8000. Looks like the noise keeps getting lower as I increase the number of taps, but this is really a kind of cheat if you think about it carefully.

From this morning, now in calibrated units, and with the Güralp self noise spec from the Güralp manual.

Someone adjusted the Guralp2 mass position last night??

NO

1)Power to the seismometers were turned down,

2)Guralp2 was moved to North side of POX table

3)Guralp2 was aligned in N-s Direction and leveled before connecting

4)Power to seismometers was turned on once Guralp2 was connected

 The same thing happening again.  The intermittent offset upstream of the seismometer that never got fixed.

The granite plate and ball bearings are in. I will place seismometers on it.

Short 46" long cables at the base plates were swapped. Their solderings looked horrible.

This cable actually worked at 5-5-2015

Bad cable at ETMY station now.  The new cable should be a little bit longer ~52"

We have one calibration sheet of GUR- B, from 26 June 2008,    model CMG-T40-0008,  sn T4157       at  ETMY  east,  interface box input 1

I'm looking for calibration paper of GUR- A,                                model CMG-T40-0053,  sn T4Q17      at ETMX   south, interface box input 2

Guralps as connected with pictures

I brought the GUR2 seismometer back from Bridge so I can get some more MC/Seismic data during the next week while we're pumped down, before we start doing things to the PSL table.  Both of the Gur Seismometers are connected back up to the breakout box as of ~3:27pm today.  Alastair still has the handheld controller thing (which I use for mass centering, on occasion), since he'll want the seismometer back in a week or two when I'm done with it.

Something is wrong with both X channels of the Guralps.  Alastair claimed that he and Frank didn't do anything bad when they opened up the breakout box, but I am suspicious. 

While I'm at it, a reminder that Jan and his SURF student Greg still have the Ranger, disassembled over in Bridge.  They made a note in their elog, but not in the 40m elog when they took it back again.

Whenever you're done with the Mode Cleaner for the next week, please make sure it is locked, nicely aligned and happy before you leave.  Also please make a note of what you're doing and when, so that I know what is good data and what is data with unusual conditions.

In other, semi-bad news (but already recovered from), when I was finishing putting the Guralp Breakout Box back in the rack, I bumped the power strip that is on the top back side of the rack, near the corner that the door opens on (not the corner the door hinges on).  I turned the power strip back on, and I think everything that is connected to it came back okay.  Anyhow, my bad. Sorry. 

Koji and Steve,

The result: bad Guralp x-arm cable.

I will swap the short cables tomorrow at the base.

I noticed on DataViewer today that GUR2 was outputting only noise (somewhere around 2 counts). Jenne suggested that GUR 2 might not be plugged in. I turned off the ADC, and tried several times to plug GUR 2 back in. I thought something might be wrong with the cable, but when I plugged the GUR1 cable into GUR2, there was still no readout (although the GUR1 cable works fine when I plug it into GUR1). Perhaps I'm just inept at plugging in GUR2, or perhaps there's another issue. Either way, I'll ask Jenne about it tomorrow and try again.

I checked the connections specified in the old Gulap Pin Map and found that they do not correspond to the current values. I mapped out the current connections (in this case, the letter refers to the labeled pin on the mil/spec while the number refers to the pin on the 37 pin DSub, labeled consecutively):

A-1, B-2, C-3, D-4, E-5, F-6, G-7, H-Unused, J-8, K-unused, L-9, M-10, N -11, P-12, S-13, T-Unused, U-14, V-15, W-16, X-17, Y-18, Z-Unused, a-Unused, b-19, c-20, UnlabeledPin-Unused.

There are 20 pins in use of 26 total, which is good because that means Jenne and I can use the ~70m long 24 wire cable to make a new Gurlap 1 cable.

ETMY - Guralp (B-MIT) was covered with copper lined can yesterday afternoon. It's long cable is connected to ADC interface box input 1

The vertex Trillium was covered just ~2 days before Ignacio left.

ETMX - Guralp (A-Caltech) is not covered. The long 40m cable is disconnected at the the south end.

I moved Gur A from ETMX to ETMY . Gur B at ETMY was disconnected and its cable  connected to Gur A

It seems that Gur A is alive. I will stop using A and B names after we stop swapping components.

[Jenne, Rana]

We took apart and examined one of the Guralp seismometers this afternoon.  For the most part we think we understand how it works. The horizontal sensors are a little more confusing, since we didn't end up finding the moving masses.  The vertical sensor is a flat rectangle, hinged at one edge.  There are capacitive sensors above and below the rectangle.  The hinged end is connected to a leaf spring. 

The PCBs are packed full of old-school 80's components.  We probably need an actual schematic to figure out where the preamp circuit is, which is what we'd want to think about fitzing with, if we were to try to improve the noise of the seismometer.  For now, we put it all back together, and back out on the granite slab. 

There was a wee bit of confusion when putting the N/S marker-spikes back on as to where they should go.  The solution is that the handle of the seismometer is aligned with the North/South axis, so the spikes should be aligned with the handle.  The lid of the seismometer is uniquely aligned to the stuff inside by the ribbon cable connector, as well as the holes in the lid for accessing the centering potentiometers.  So, align the lid to the pots, and then align the spikes to the handle.

Photos are on Picasa.

I did the recommended modifications on of the boards with serial number S2100028. These included:

• R13, R27: 160 -> 75
• C11, C21: 470 nF -> 68nF
• C19: 4.7 uF -> 470 nF
• R15: 3.23 kOhm -> 1.82 kOhm

I took transfer function measurements with same method as in 40m/15774 and I'm presenting it here to ensure the modifications are correct and if I should proceed to the next board as well. I didn't have the data used to make plots in here but I think the poles and zeros have landed in the right spot. I'll wait for comments until tomorrow to proceed with changes in the other board as well. I'll do noise measurements tomorrow.

Looks fine to me visually but the verdict can only be made once the z:p locations are quantitatively confirmed, and the noise tests pass. It would be interesting to see what kind of time-domain transient (in N of force) switching on the de-whitening introduces, i guess best done interferometrically.

I fitted zeros and poles in the measured transfer function of D1100687 S2100027 and got zeros at 130 Hz and 234 Hz and poles at 10Hz and 2845 Hz. These values are different from the aimed values in this doc, particularly the 234Hz zero which was aimed at 530 Hz in the doc.

I also took the noise measurement using the same method as described in 40m/15780. The noise in Acquisition mode seems to have gone up in 10 Hz - 500 Hz region compared to the measurement in 40m/15780 before the modifications.

All channels are consistent with each other.

Edit Mon Feb 1 12:24:14 2021:
Added zero model prediction after the changes. The measurements match with the predictions.

Edit Wed Feb 3 16:46:59 2021:

Added zero modeled noise in the noise spectrum curves. The acquisition mode curves are in agreement with the model. The noise in Run mode is weirdly lower than predicted by zero.

I have made the modifications on the other board D1100687 S2100028 as well. The measurements were taken as mentioned in 40m/15784. All conclusions remain the same as 40m/15784. The attached zip file contains all measurement data, before and after the modifications.

Edit Wed Feb 3 16:44:51 2021 :

Added zero modeled noise in the noise spectrum curves. The acquisition mode curves are in agreement with the model. The noise in Run mode is weirdly lower than predicted by zero.

I have taken transfer functions and noise measurements of the two HAM-A coil driver boxes D1100687 #S2100027 and #S2100028. All transfer functions look as expected. I'm not sure about the noise measurements. If anyone sees flaw in my measurement method, please let me know. I'm not sure why in some channels I got 10Hz harmoni peaks in the noise. That was very strange. Also let me know if my current noise estimate is wrong.

Transfer Function Measurement details

• SR785 source out was connected to the differential amplifier input of D1900068.
• The one pair of two BNC outputs of this differential amplifier goes directly to the SR785 Input 1 A and B.
• The DB9 output of the differential amplifier goes to the Coil Input DB9 connector J3.
• Header W2 was shorted to provide ground to the incoming signal.
• Header P4 was shorted to enable all the channels manually.
• Normal operation is the Acquisition mode (Acq) while when pins of header P3 are shorted, we go into the Run mode for respective channel.
• The “To Satellite Box” DB25 port at the read side was conencted to a DB25 breakout circuit and pins 1-9, 3-11, 5-13 and 7-15 were connected to 36 Ohm resistor to simulate Coil load.
• The “Output Monitor” on the rear side is then connected to the test switch DB9 port on D1900068.
• The the pair of BNCs from the test switch is connected to SR785 Input 2 A and B.
• Measurements are taken with file D1100687_TF.yml and D1100687_TF_LF.yml.
• A measurement of just cables without the DUT is taken as well.
• Commands.txt list all the commands used.
• All data is compiled and plotted in Plotting.ipynb
• D1100117_S2100027_TF.pdf and D1100117_S2100028_TF.pdf shows all the transfer functions measured.

Spectrum Measurements

• All channels were kept in disabled mode (Not shorting P4) to ensure their inputs are grounded on the board.
• I ran two BNC cables with their centers connected to output monitors V2+ and V2- and one of their shields connected to board GND.
• in SR785, A-B differential mode always runs with grounded shields mode, so effectively the board GND got grounded to SR785 GND through internal 50 Ohm resistor. But all ground loops have been evaded.
• The two BNC cables were twisted together to minimize the area between the two center cores of the cables as that is the remaining pickoff possible in this measurement.
• Instrument noise with cables was measured first but shorting the clips of the center cores and one of the shields of the two BNC cables together.
• Measurements were taken with file D1100687_SP.yml and D1100687_SP_LF.yml.
• D1100117_S2100027_Voltage_Noise_Spectrum.pdf and D1100117_S2100028_Voltage_Noise_Spectrum.pdf shows the measured voltage noise spectrum at the output monitors when loaded with 36 Ohms.
• D1100117_S2100027_Current_Noise_Spectrum.pdf and D1100117_S2100028_Current_Noise_Spectrum.pdf shows the esitmate current noise through the coil calculated by dividing the measured voltage noise by 2436 Ohms.

I took some steps to reduce the coupling of 60 Hz harmonics in noise measurement. The box was transferred to the floor instead of on top of another instrument. Measurement was immediately converted into single-ended using SR560 in battery mode with a gain of 10. All of the setups was covered in aluminum foil to increase isolation.

Spectrum measurement details

• Boards were powered by sorenson power supplies with +/- 18V DC.
• 36 Ohm load was connected to coil output port.
• Signal was taken out using clips from V2+, V2- and GND.
• Signal was first sent to SR560 in A-B mode with a gain of 10 in battery mode.
• The board along with SR560s were covered in aluminum foil to reduce 60Hz harmonics.
• The output from 50Ohm port was sent to SR785 and read with floating ground.
• Instrument noise was measured by shorting the clips with each other.
• Transfer function of measurement setup was measured and divided by final output.
• Measurements were taken with file D1100687_SP.yml and D1100687_SP_LF.yml.
• D1100117_S2100027_Voltage_Noise_Spectrum.pdf and D1100117_S2100028_Voltage_Noise_Spectrum.pdf shows the measured voltage noise spectrum at the output monitors when loaded with 36 Ohms.
• D1100117_S2100027_Current_Noise_Spectrum.pdf and D1100117_S2100028_Current_Noise_Spectrum.pdf shows the esitmate current noise through the coil calculated by dividing the measured voltage noise by 2436 Ohms.

Ran HDMI to the new tv mounted on the north wall of control room.

I have been trying a couple of HDR algorithms, all of them seem to give very different results. I don't know how suitable these algorithms are for our purpose, because they are more concerned with final display. I'm attaching the HDR image I got by modifying Jigyasa's code a bit (this image has been be modified further to make it suitable for displaying). Here, I'm trying compare the plots of images that look similar. The HDR image has a dynamic ratio of 700:1

PS: 300us_image.png file actually looks very similar to HDR image on my laptop (might be an issue with elog editor?). So I'm attaching its .tiff version also to avoid any confusion.

I captured a few images of the beam spot on ETMX at 5ms, 10ms, 14ms, 50ms, 100ms, 500ms, 1000ms exposure and ran them through my python script for HDR images. Here's what I obtained. 
The resulting image is an improvement over the highly saturated images at say, 500ms and 1 second exposures. 
Additionally, I also included a colormapped version of the image. 

i wonder how 'HDR' these images really are. is there a quantitative way to check that we are really getting more bits? also, how many bits does the PNG format allow for monochrome images? i worry that these elog images are already lossy.

HEPA filter was running at 90% of max. I reduced it to 20%. Acoustic noise moved down

The range of MCL oscillations has also decreased but fluctuations in the frequency range 10-100 are still present.

MCL is much more stable now.

15:30
- PSL HEPA was running at 33% and is now at 100%
- South End HEPA was not on and is now running
- Yarm Portable HEPA was not running and is now running at max speed: the power was taken beneath the ITMY table. It is better to unplug it when one uses the IFO.
- Yend Portable HEPA was not running and is now running (presumably) at max speed

Particle Levels: (Not sure about the unit. The convention here is to multiply x10 of the reading)

Before running the HEPAs at their maximum
9/10/2020 15:30 / 0.3um 292180 / 0.5um 14420
(cf 9/5/2020 / 0.3um 94990 / 0.5um 6210)
==>
After running the HEPAs at their maximum
The number gradually went down and now became constant at about half of the initial values
9/10/2020 19:30 / 0.3um 124400 / 0.5um 7410

The AC cord from the PSL HEPA variac to the junction box was replaced.
Now the HEPA is running at 70%

Showed up at the 40m at 7pm

Preparation

• Closed the PSL shutter.
• Closed the innolight shutter
• Turned off the HEPA mains switch
• Checked the HEPA fan rating: 115V 4.5A.
• Brought the thickest power cord from the wall stock: the rating is 125V 15A. This should sufficiently hold two HEPAs.

Cable Replacing

• Rechecked the wire connection. The new cord has green/black/white wires. And the colors agree with the color of the wires in the junction box.
• Removed the existing cord.
• Attached the new cord.
• Checked the variac AC plug. The terminals in the plug look normal and the AC plug looked sufficiently rigid.
• Checked the connection again. = OK

Testing

• Turned on the HEPA mains switch
• VairAC turned to 70%
• Checked the air flow - The HEPA fans are sucking the air = OK

Closing the work

• Closed the junction box.
• Cleaned up the roof
• Opend the innolight shutter
• Opened the PSL shutter
• Locked the PMC
• Locked the IMC  - found the transmission was ~80% of the pre-work due to misalignment of the PMC
• Aligned the PMC - this recovered the IMC REFL of ~5.2 when the IMC was unlocked

Leaving the 40m at 9:30pm

Memo: 40m wiring/Mask/Camera/Red Pitaya/Particle Counter

I think the PSL HEPA (both 2 units) are not running. The switches were on. And the variac was changed from 60% to 0%~100% a few times but no success.
I have no troubleshooting power anymore today. The main HEPA switch was turned off.

From the last failure, I had ordered 2 extra capacitors (they are placed on top of the PSL enclosure above where the capacitors would normally be installed). If the new capacitors lasted < 6months, may be symptomatic of some deeper problem though, e.g. the HEPA fans themselves need replacing. We don't really have a good diagnostic of when the failure happened I guess as we don't have any channel recording the state of the fans.

Gautam reported that the PSL HEPA stopped running (ELOG 15592). So I came in today and started troubleshooting.

It looks like that the AC power reaches the motors. However, both motors do not run. It looks like the problem exists in the capacitors, the motors, or both.
Parts specs can be found in the next ELOG.

Attachment 1 is the connection diagram of the HEPA. The AC power is distributed by the breaker panel. The PSL HEPA is assigned to use M22 breaker (Attachment 2). I checked the breaker switch and it was (and is) ON. The power goes to the junction box above the enclosure (Attachment 3). A couple of wires goes to the HEPA switch (right above the enclosure light switch) and the output goes to the variac. The inside of the junction box looked like this (Attachment 4).

By the way, the wires were just twisted and screwed into a metal threaded (but isolated) caps (Attachment 5). Is this legit? Shouldn't we use stronger crimping? Anyway, there was nothing wrong with the caps w.r.t the connection for now.

I could easily trace the power up to the variac. The variac output was just fine (Attachment 6). The cord goes from the variac to the junction box (and then HEPAs) looked scorched. The connection from the plug to HEPAs was still OK, but this should be eventually replaced. Right now the cable was unplugged after the following tests for the safety reason.

The junction box for each HEPA unit was opened to check the voltage. The supply voltage came to the junction boxes and it was just fine. In Attachments 8 & 9, the voltages look low but this is because I just turned the variac only a little.

At the (main) junction box, the resistances of the HEPAs were checked with the Fluke. As the HEPA units are connected to the AC in parallel, the resistances were individually checked as follows.

The coils were not disconnected (... I wonder if the wiring of South HEPA was flipped? But this is not the main issue right now.)
 

By removing the pre-filters, the motors were inspected Attachments 10 & 11. At least the north HEPA motor was warm, indicating there was some current before. A capacitor was connected per motor. When the variac was tuned up a bit, one side of the capacitor could see the voltage. I could not judge which has the issue between the capacitor and the motor.

Dimensions / Specs

- HEPA unit dimentions
- HEPA unit manufacturer
- Motor
- Capacitor

I implemented the BLRMS on WFS1/2_I_PIT/YAW outputs and using there value, a HEPA state can be defined. I've currently set it up to use average of 10-30 Hz noise on WFS signals low passed at 0.3 Hz. For ON threshold of 100 and OFF threshold of 50, it is working for my limited testing time. To read HEPA state, one can do caget C1:IOO_HEPA_STATE. I've turned OFF HEPA for tonight's shimmer test. This is bare bones quick attempt, people can make the screen more beautiful and add more complexity if required in future.

this is very exciting! Its the beginning of the task of reducing vast amounts of PEM data into human-useful (bite sized) info. Imagine if we had 60 Hz BLRMS on various channels - we would know exactly when ground loops were happening or disappearing.

Turned HEPA OFF / Lab Lights OFF / WFS Input Gain switched off for the IMC WFS signal tests.
The IMC is still well aligned.

Clean data from the following time:
2022/10/26 5:24:00 UTC (10/25 22:24 PDT)
GPS 1350797056

Turned HEPA ON this morning at 10:28 local (pacific time) or gpstime = 1350802758. WFS ON right after that. IMC was locked and nominally aligned at this time.

[Koji, Suresh]

    We investigated the effect of airflow from the HEPA filters on the PSL beam fluctuation and the resultant noise injected into the WFS loops.   The hint that the WFS are injecting PSL beam jitter into MC mirror motion lies in the MC2_TRANS_PIT and YAW signal's power spectrum shown here.  First, in the blue trace, which shows the spectrum when the WFS loops are off, we see that the WFS1 and WFS2 error signals have a different shape from that of MC2_TRANS.  Since WFS are affected by the PSL beam jitter while the MC2_TRANS_QPD is not, the WFS spectrum contain excess noise, while the MC2_TRANS signals show only the mirror motion.  Next, upon switching on the WFS1 and WFS2 loops, we notice that the MC2_TRANS  spectra acquire the same shape as the WFS spectra.  This shows that the excess noise from the beam jitter has been injected into the MC2 motion, and shows up in the MC2_TRANS spectra.

   To confirm these conclusions we repeated the above measurement with the HEPA fans at 0% (Blue trace), 20% (Red), 30% (Brown) and  100% (Green).   The plots are shown below.  We can see that there is no difference between 0 and 20% levels but beam jitter is visible at 30% HEPA level.  The WFS loops were ON during this time and we can can see the PSL noise injected in to MC2 motion (Green).

The HEPA filter fans are now at 20%.  How can we be sure that they are really working at 20%, since we cannot see any difference between 0 and 20%?

Now that we have this quiet situation, we also investigated the effect (or lack thereof) of switching on the MC2_TRANS loops.  The figure below shows the spectra with all the loops turned off (Blue), with the WFS1 and WFS2  loops turned on (Green)  and with everything turned on (Red).   With the current output matrix, which is the same simple one as the one in this elog, we see some low frequency suppression.  But it also seems to add some noise into the other WFS loops.  I am not sure of this result, due the long duration of this measurement, the seimic noise level may have changed over the course of this measurement.

As they are not doing any good just now.  I have turned them off by setting the gain in MC2_TRANS PIT and YAW to zero.

[JV, GV]

The HEPAs work again. After running the HEPAs for ~1 hour, I checked the particle count on the PSL table - the meter registered 0 for both 0.3 um and 0.5 um. So I decided to turn the NPRO back on, at ~1730 local time. The PMC and IMC were readily locke, so the basic interferometer functionality is returned, and we can now go ahead with (i) vent prep (ii) air BHD tests and (iii) IMC debuggin as was discussed on the call today. The earth is shaking, but nothing serious so far, I will resume alignment of the interferometer later in the evening when hopefully things have calmed down a bit more...

Procedure:

1. Turned off mains switch on the NW corner of the PSL enclosure. Then, disconnected the power cables from mains to Variac and from Variac to HEPAs. Made sure both HEPAs were set to "OFF".
2. With confidence that no AC power was reaching the motors, I removed the pre-filters, and removed the old startup capacitors. These don't have a polarity, but I marked the cable that was connected to the left terminal of the capacitor when the cap is viewed with the label facing you, in the interest of changing as few things as possible.
3. The two new capacitors were measured with the LCR meter - the meter registered ~7.5 uF, as expected. Unsurprisingly, the old capacitors that were removed didn't register any reading on the LCR meter. The terminals weren't shorted, but I don't know what the failure mode for this kind of capacitor is.
4. The two new capacitors were installed. Then, I tested the system by undoing all the changes in bullet #1. We found that the Variac needs to be set to 100% for the motors to startup.
5. The motor speed was found to vary as the Variac dial was turned. FWIW, at the "nominal" setting of 33% on the Variac (when we run the interferometer), I could see both fan blades were turning, but the flow was low enough that you couldn't hear any wind (at least, neither Jordan nor I could).
6. Turned off the mains agian, and cleaned up - restored the insulating rubber sleeve on the capacitor leads, and re-installed the pre-filters on the HEPA blowers. Then we turned both blowers back on. 

Note that the many other issues Koji noted in the preceeding elog (e.g. flaky wiring) have not been addressed.

Flow measurements:

Chub kindly provided us with an electronic anemometer. With the meter held directly against the HEPA filter inside the enclosure, we measured ~700 cfm of airflow on each of the two HEPAs, with the Variac set to 100% and the HEPAs themselves set to "High". With the Variac at 50%, the flow drops to ~160 cfm. At the nominal setting of 33%, the meter didn't register any flow. I don't know what the spec'd flow rate is for this combination of blower + filter, but Jordan says similar units in Downs register ~1500 cfm at the "High" setting. The two protable (similarly sized) HEPA units in the 40m, one at ITMY and one at ETMY, register ~900 cfm and ~1100 cfm respectively, when set to high. So we may want to revisit what the "nominal" HEPA setting should be, in case the filters have become clogged over time. 

Some photos of the HEPA blowers with the pre-filters off and the capacitors switched out may be found here.

it would be a good idea for us to have an auto-reminder to have us check the flow of all the HEPAs in the lab and elog it once a year so that we can replace filters and pre-filters appropriately.

I set up a simple HEPA filter dryer to dry your clean room garment before  you can put it away into your storage box.

Our lab is dusty ! This is  specially important when we are vented. Please wipe things daily and cover item with foils .... etc.

[Koji, Suresh]

8:50PM HEPA@100% for the test

8:55PM HEPA@0%

9:20-35PM HEPA level varies from 0%-50%

9:35PM HEPA@40% and left it running at this level

Nov18 1:40 AM HEPA@80% for a work around the PSL table (by KI)

Nov18 4:35 AM HEPA@40% (by KI)

I will upload some plots later - but in summary, I set the HEPA speed to ~40%. I used (i)IMC transmission RIN, (ii) Arm cavity transmission RIN and (iii) ALS beat noise as 3 diagnostics, to see how noise in various frequency bands for these signals change as a function of the HEPA speed. The MC2T RIN shows elevated noise between 1-10Hz at even the lowest speed I tried, ~20% of the max on each blower. The elevated noise extended to ~50-70 Hz for HEPA speeds >40% of the maximum, and the arm cavity RIN and ALS signals also start to become noisy for speeds >60% of the maximum. So I think 40% is a fine speed to run at - for squeezing measurement we may have to turn off the HEPA for 10mins but for the usual single arm / PRMI / DRMI locking, this should be just fine. For the elevated ALS noise - I'm not sure if the coupling is happening over the top of the enclosure where the fiber bringing light from EX comes close to the HEPA filters, or if it is happening inside the PSL enclosure itself, near the beat mouth - but anyways, at the 40% speed, I don't see any effect on the ALS noise.

I checked with a particle counter at the SW corner of the PSL table (which is the furthest away we can be on the table from the HEPA blowers) after leaving the blowers on for ~30mins and it registered 0 for both 0.3um and 0.5um sized particles (if the blowers are off, the respective numbers are 43 and 9 but I forgot what the units were, and I believe they have to be multiplied by 10). 

I have not yet marked the speed control units yet in case there is some other HEPA science that needs to be done before deciding what is the correct setting. But I think I can get the PRFPMI lock without much issue with this lower speed, which is what I will try later today evening.

I believe that there is an internal setting for the minimum flow, so the flow is not linear ("0%" is not zero), but we should mark this flow speed once you find this is sufficiently low for the locking too.

The PSL was too hot, so I turned on the south HEPA on the PSL. The north one was on and the south one was off (or so slow as to be inaudible and no vibration, unlike the north one). Lets watch the trend over the weekend and see if the temperature comes down and if the PMC / WFS variations get less. Fri May 14 17:46:26 2021

Looks like the fan lowered the temperature as expected. Need to get a few more days of data to see if its stabilized, or if that's just a fluke.

The vertical line at 00:00 UTC May 18 is about when I turned the fans up/on.