I found a "vice" in the cleanroom (attachment 1). I used it to push dowel pins into the last suspension block using some alcohol as a lubricant.

I then assembled the 7th and last suspension tower (attachment 2).

Things that need to be done:

1. Push Viton tips into vented screws and assemble the earthquake stops.

2. Glue magnets to dumbells.

Rana came and helped us figure us where to inject the noise. Following are the characteristics of the test we did:

• Inject normal noise at C1:IOO-MC1_PIT_EXC using AWGGUI.
• Excitation amplitude of 54321 in band 12-37Hz with Cheby1 8th order bandpass filter with same limits.
• Look at power spectrum of C1:IOO-MC_F_DQ, C1:IOO-WFS1-PIT_OUT_DQ and the C1:IOO-MC1_PIT_EXC itself.
• Increased the gain of the noise excitation until we see some effect in MC_F.
• Diaggui also showed coherence plot in the bottom, which let's us have an estimate of how much we need to go further.

Attachment 1 shows a screenshot with awggui and diaggui screens displaying the signal in both angular and longitudinal channels.

Attachment 2 shows the analogous screenshot for MC2.

It seemed like the BIO channels were not working, both the inputs and the outputs. The inputs were working on the windows machine though. That is, when we shorted the BIO channel to the return, or put 0V on it, we could see the LED turn on on the I/O testing screen and when we ramped up the voltage above 3 the LED turned off. This is the expected behavior from a sinking digital input. However, the EPICs caget didn't show any change. All the channels were stuck on Disabled.

We checked the digital outputs by connecting the channels to a fluke. Initially, the fluke showed 13V. We tried to toggle the digital output channels with caput and that didn't work. We checked the outputs with the windows software. For that, we needed to stop the Modbus. To our surprise, the windows software was not able to flip the channels either. We realized that this BIO Acromag unit is probably defective. We replaced it with a different unit and put a warning sticker on the defective unit. Now, the digital outputs were working as expected. When we turned them on the voltage output dropped to 0V. We checked the channels with the EPICs software. We realized that these channels were locked with the closed loop definition. We turned on the channels tied to these output channels (watchdog and toggles) and it worked. The output channels can be flipped with the EPICs software. We checked all the digital output channels and fixed some wiring issues along the way.

The digital input channels were still not working. This is a software issue that we will have to deal with later.

(Yehonathan) Rana noticed that the BNC leads on the chassis front panel didn't have isolation on them so I redid them with shrinking tubes.

IOP models created

With all the PCIe issues now resolved, yesterday I proceeded to build an IOP model for each of new FEs. I assigned them names and DCUIDs consist with the 40m convention, listed below. These models currently exist on only the cloned copy of /opt/rtcds running on the test stand. They will be copied to the main network disk later, once the new systems are fully tested.

The models compile and install successfully. The RCG runtime diagnostics indicate that all is working except for the timing synchronization and DAQD data transmission. This is as expected because neither of these have been set up yet.

Timing system set-up

The next step is to provide the 65 kHz clock signals from the timing fanout via LC optical fiber. I overlooked the fact that an SPX optical transceiver is required to interface the fiber to the timing slave board. These were not provided with the timing slaves we received. The timing slaves require a particular type of transceiver, 100base-FX/OC-3, which we did not have on hand. (For future reference, there is a handy list of compatible transceivers in E080541, p. 14.) I placed a Digikey order for two Finisar FTLF1217P2BTL, which should arrive within two days.

We redid the WFS noise injection test and have compiled some results on noise contribution in arm cavity noise and IMC frequency noise due to angular noise of IMC.

Attachment 1: Shows the calibrated noise contribution from MC1 ASCPIT OUT to ARM cavity length noise and IMC frequency noise.

• For calibrating the cavity length noise signals, we sent 100 cts 100Hz sine excitation to ITMX/Y_LSC_EXC, used actuator calibration for them as 2.44 nm/cts from 13984, and measured the peak at 100 hz in time series data. We got calibration factors: ETMX-LSC_OUT: 60.93 pm/cts , and ETMY-LSC_OUT: 205.0 pm/cts.
• For converting IMC frequency noise to length noise, we used conversion factor given by where L is 37.79m and lambda is wavelength of light.
• For converting MC1 ASCPIT OUT cts data to frequency noise contributed to IMC, we sent 100,000 amplitude bandlimited noise (see attachment 3 for awggui config) from 25 Hz to 30 Hz at C1:IOO-MC1_PIT_EXC. This noise was seen at both MC_F and ETMX/Y_LSC_OUT channels. We used the noise level at 29 Hz to get a calibration for MC1_ASCPIT_OUT to IMC Frequency in Hz/cts. See Attachment 2 for the diaggui plots.
• Once we got the calibration above, we measured MC1_ASCPIT_OUT power spectrum without any excitaiton and multiplied it with the calibration factor.
• However, something must be wrong because the MC_F noise in length units is coming to be higher than cavity length noise in most of the frequency band.
  • It can be due to the fact that control signal power spectrum is not exactly cavity length noise at all frequencies.  That should be only above the UGF of the control loop (we plan to measure that in afternoon).
  • Our calibration for ETMX/Y_LSC_OUT might be wrong.

After a helpful meeting with Jon, we realized that I have somehow corrupted the sitemap file. So I am going to use the code Chris wrote to regenerate it. 

Also, I am going to connect the controller using the IPC parts. The error that I was having before had to do with the IPC parts not being connected properly. 

I put the box containing the untested OSEMs from KAGRA near the south flow bench on the floor.

We have uploaded the new damping gains on all the suspensions of IMC. This completes changing all the configuration to as mentioned in 16066 and 16072. The old setting can be restored by running python3 /users/anchal/20210505_IMC_Tuned_SUS_with_Gains/restoreOldConfigIMC.py from allegra or donatella.

GPSTIME: 1304265872

Assembled chassis from De Leone placed in the 40 Meter Lab, along the west wall and under the display pedestal table.  The leftover parts are in smaller Really Useful boxes, also on the parts pile along the west wall.

I added the IPC parts back to the plant model so that should be done now. It looks like this again here.

I can't seem to find the control model which should look like this. When I open sus_single_control.mdl, it just shows the C1_SUS_SINGLE_PLANT.mdl model. Which should not be the case.

When using mdl2adl I was getting the error:

to set these in the terminal use the following commands:

On most of the systems, there is a script that automatically runs when a terminal is opened that sets these but that hasn't been added here so you must run these commands every time you open the terminal when you are using mdl2adl.

I copied c1scx.mdl to the docker to attach to the plant using the commands:

We today measured the calibration factors for XARM_OUT and YARM_OUT in nm/cts and replotted our results from 16117 with the correct frequency dependence.

Calibration of XARM_OUT and YARM_OUT

• We took transfer function measurement between ITMX/Y_LSC_OUT and X/YARM_OUT. See attachment 1 and 2
• For ITMX/Y_LSC_OUT we took calibration factor of 3*2.44/f² nm/cts from 13984. Note that we used the factor of 3 here as Gautum has explicitly written that the calibration cts are DAC cts at COIL outputs and there is a digital gain of 3 applied at all coil output gains in ITMX and ITMY that we confirmed.
• This gave us callibration factors of XARM_OUT: 1.724/f² nm/cts , and YARM_OUT: 4.901/f² nm/cts. Note the frrequency dependence here.
• We used the region from 70-80 Hz for calculating the calibration factor as it showed the most coherence in measurement.

Inferring noise contributions to arm cavities:

• For converting IMC frequency noise to length noise, we used conversion factor given by where L is 37.79m and lambda is wavelength of light.
• For converting MC1 ASCPIT OUT cts data to frequency noise contributed to IMC, we sent 100,000 amplitude bandlimited noise  from 25 Hz to 30 Hz at C1:IOO-MC1_PIT_EXC. This noise was seen at both MC_F and ETMX/Y_LSC_OUT channels. We used the noise level at 29 Hz to get a calibration for MC1_ASCPIT_OUT to IMC Frequency in Hz/cts. This measurement was done in 16117.
• Once we got the calibration above, we measured MC1_ASCPIT_OUT power spectrum without any excitaiton and multiplied it with the calibration factor.
• Attachment 3 is our main result.
  • Page 1 shows the calculation of Angle to Length coupling by reading off noise injects in MC1_ASCPIT_OUT in MC_F. This came out to 10.906/f² kHz/cts.
  • Page 2-3 show the injected noise in X arm cavity length units. Page 3 is the zoomed version to show the matching of the 2 different routes of calibration.
  • BUT, we needed to remove that factor of 3 we incorporated earlier to make them match.
  • Page 4 shows the noise contribution of IMC angular noise in XARM cavity.
  • Page 5-6 is similar to 2-3 but for YARM. The red note above applied here too! So the factor of 3 needed to be removed in both places.
  • Page 7 shows the noise contribution of IMC angular noise in XARM cavity.

Conclusions:

• IMC Angular noise contribution to arm cavities is atleast 3 orders of magnitude lower then total armc cavity noise measured.

Edit Mon May 10 18:31:52 2021

See corrections in 16129.

A few corrections to last analysis:

• The first plot was not IMC frequency noise but actually MC_F noise budget.
  • MC_F is frequency noise in the IMC FSS loop just before the error point where IMC length and laser frequency is compared.
  • So, MC_F (in high loop gain frequency region upto 10kHz) is simply the quadrature noise sum of free running laser noise and IMC length noise.
  • Between 1Hz to 100 Hz, normally MC_F is dominated by free running laser noise but when we injected enough angular noise in WFS loops, due to Angle to length coupling, it made IMC length noise large enough in 25-30 Hz band that we started seeing a bump in MC_F.
  • So this bump in MC_F is mostly the noise due to Angle to length coupling and hence can be used to calculate how much Angular noise normally goes into length noise.
• In the remaining plots, MC_F was plotted with conversion into arm length units but this was wrong. MC_F gets suppressed by IMC FSS open loop gain before reaching to arm cavities and hence is hardly present there.
• The IMC length noise however is not suppresed until after the error point in the loop. So the length noise (in units of Hz calculated in the first step above) travels through the arm cavity loop.
• We already measured the transfer function from ITMX length actuation to XARM OUT, so we know how this length noise shows up at XARM OUT.
• So in the remaining plots, we plot contribution of IMC angular noise in the arm cavities. Note that the factor of 3 business still needed to be done to match the appearance of noise in XARM_OUT and YARM_OUT signal from the IMC angular noise injection.
• I'll post a clean loop diagram soon to make this loopology clearer.

Today I brought and installed the new optical transceivers (Finisar FTLF1217P2BTL) for the two timing slaves. The timing slaves appear to phase-lock to the clocking signal from the master fanout. A few seconds after each timing slave is powered on, its status LED begins steadily blinking at 1 Hz, just as in the existing 40m systems.

However, some other timing issue remains unresolved. When the IOP model is started (on either FE), the DACKILL watchdog appears to start in a tripped state. Then after a few minutes of running, the TIM and ADC indicators go down as well. This makes me suspect the sample clocks are not really phase-locked. However, the models do start up with no error messages. Will continue to debug...

Did you match the local PC time with the GPS time?

Attached is the control loop diagram when main laser is locked to IMC and a single arm (XARM) is locked to the transmitted light from IMC.

Working with Chris, we decided that it is probably better to use a simple filter module as a controller before we make the model more complicated. I will use the plant model that I have already made (see attachment 1 of this). then attach a single control filter module to that: as seen in attachment 1. because I only want to work with one degree of freedom (position) I will average the four outputs which should give me the position. Then by feeding the same signal to all four inputs I should isolate one degree of freedom while still using the premade plant model.

The model I made that is shown in attachment 2 is the model I made from the plan. And it complies! yay! I think there is a better way to do the average than the way I showed. And since the model is feeding back on itself I think I need to add a delay which Rana noted a while ago. I think it was a UnitDelay (see page 41 of RTS Developer’s Guide). So I will add that if we run into problems but I think there is enough going on that it might already be delayed.

Since our model (x1sup_isolated.mdl) has compiled we can open the medm screens for it. I provide a procedure below which is based on Jon's post. 

To see a list of all medm screens use:

Some of the other useful ones are:

The first one of these screens that are of interest to us (shown in attachment 3) is the X1SUP_ISOLATED_GDS_TP.adl screen, which is the CDS runtime diagnostics screen. This screen tells us "the success/fail state of the model and all its dependencies." I am still figuring out these screens and the best guide is T1100625.

The next step is taking some data and seeing if I can see the position damp over time. To do this I need to:

1. Edit the plant filter for the model and add the correct filter.
2. Figure out a filter for the control system and add it to that. (I can leave it as is to see what the plant is doing) 
3. Take some position data to show that the plant is a harmonic oscillator and is damping away.

No, this is the property of the suspension assembly. The mass says 10kg

Could you do the same for the testmass assembly (only the suspended part)? The units are good, but I expect that the values will be small. I want to keep at least three significant digits.

Here are the mass properties for the only the test mass assembly (optic, 3" ring, and wire block). (Updated with g*mm^2)

We came in the morning with the following scene on the zita monitor:

The MC1 watchdog was tripped and seemed like IMC struggled all night with misconfigured WFS offsets. After restoring the MC1 WD, clearing the WFS offsets, and seeing the suspension damp, the MC caught lock. It wasn't long before the MC unlocked, and the MC1 WD tripped again.

We tried few things, not sure what order we tried them in:

• Letting suspension loops damp without the WFS switched on.
• Letting suspension loops damp with PSL shutter closed.
• Restoring old settings of MC suspension.
• Doing burt restore with command:
  burtwb -f /opt/rtcds/caltech/c1/burt/autoburt/snapshots/2021/May/12/08:19/c1mcsepics.snap -l /tmp/controls_1210513_083437_0.write.log -o /tmp/controls_1210513_083437_0.nowrite.snap -v <

Nothing worked. We kept seeing that ULPD var on MC1 keeps showing kicks every few minutes which jolts the suspension loops. So we decided to record some data with PSL shutter closed and just suspension loops on. Then we switched off the loops and recorded some data with freely swinging optic. Even when optic was freely swinging, we could see impulses in the MC1 OSEM UL PD var which were completely uncorrelated with any seismic activity. Infact, last night was one fo teh calmer nights seismically speaking. See attachment 2 for the time series of OSEM PD variance. Red region is when the coil outputs were disabled.

Inference:

• We think something is wrong with the UL OSEM of MC1.
• It seems to show false spikes of motion when there is no such spike present in any other OSEM PD or the seismic data itself.
• Currently, this is still the case. We sometimes get 10-20 min of "Good behavior" when everything works.
• But then the impulses start occuring again and overwhelmes the suspension loops and WFS loops.
• Note, that other optic in IMC behaved perfectly normally throughout this time.
• In the past, it seems like satellite box has been the culprit for such glitches.
• We should look into debugging this as ifo is at standstill because of this issue.
• Earlier, Gautum would post Vmon signals of coil outputs only to show the glitches. We wanted to see if switching off the loops help, so we recorded OSEM PD this time.
• In hindsight, we should probably look at the OSEM sensor outputs directly too rather than looking at the variance data only. I can do this if people are interested in looking at that too.
• We've disabled the coil ouputs in MC1 and PSL shutter is off.

Edit Thu May 13 14:47:25 2021 :

Added OSEM Sensor timeseries data on the plots as well. The UL OSEM sensor data is the only channel which is jumping hapazardly (even during free swinging time) and varying by +/- 30. Other sensors only show some noise around a stable position as should be the case for a freely suspended optic.

[Anchal Koji]

Koji and I did a few tests with an OSEM emulator on the satellite amplifier box used for MC1 which is housed on 1X4. This sat box unit is S2100029 D1002812 that was recently characterized by me 15803. We found that the differential output driver chip AD8672ARZ U2A section for the UL PD was not working properly and had a fluctuating offset at no input current from the PD. This was the cause of the ordeal of the morning. The chip was replaced with a new one from our stock. The preliminary test with the OSEM emulator showed that the channel has the correct DC value.

In further testing of the board, we found that the channel 8 LED driver was not working properly. Although this channel is never used in our current cable convention, it might be used later in the future. In the quest of debugging the issue there, we replaced AD8672ARZ at U1 on channel 8. This did not solve the issue. So we opened the front panel and as we flipped the board, we found that the solder blob shorted the legs of the transistor Q1 2N3904. This was replaced and the test with the LED out and GND shorted indicated that the channel is now properly providing a constant current of 35mA (5V at the monitor out).

After the debugging, the UL channel became the least noisy among the OSEM channels! Mode cleaner was able to lock and maintain it.

We should redo the MC1 input matrix optimization and the coil balancing afterward as we did everything based on the noisy UL OSEM values.

I believe I did the identical test with the one in [40m ELOG 15786]. The + input of PA95 was shorted to the ground to exclude the noise from the bias input. The voltage noise at TP6 was measured with +/-300V supply by two HP6209 and two Matsusada R4G360.

With R4G360, the floor level was identical and 60Hz line peaks were less. It looks like R4G360 is cheap, easier and precise to handle, and sufficiently low noise.

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

The NPRO has been off since ~1AM this morning it looks like. Is this intentional? Can I turn it back on (or at least try to)? The interlock signal we are recording doesn't report getting tripped but I think this has been the case in the past too.

After getting the go ahead from Koji, I turned the NPRO back on, following the usual procedure of diode current ramping. PMC and IMC locked. Let's see if this was a one-off or something chronic.

I want to work on the IFO this weekend, so I reverted the IMC suspension settings just now to what I know work (until the new settings are shown quantitatively to be superior). There isn't any instruction here on how to upload the new settings, so after my work, I will just restore from a burt-snapshot from before I changed settings.

In the process, I found something odd in the MC2 coil output filter banks. Attachment #1 shows what it it is today. This weird undetermined state of FM9 isn't great - I guess this flew under the radar because there isn't really any POS actuation on MC2. Where did the gain1 filter I installed go? Some foton filter file corruption? Eventually, we should migrate FM7,FM8-->FM9,FM10 but this isn't on my scope of things to do for today so I am just putting the gain1 filter back so as to have a clean FM9 switched on.

I wrote the values from the c1mcs burt snapshot from ~1400 Saturday May 15, at ~1600 Sunday May 16. I believe this undoes all my changes to the IMC suspension settings.

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.

Fluke. Temp fluctuations are as usual, but the overall temperature is still lower. We ought to put some temperature sensors at the X & Y ends to see what's happening there too.

Calculation for the SOS POS/PIT/YAW resonant frequencies

- Nominal height gap between the CoM and the wire clamping point is 0.9mm (cf T970135)

- To have the similar res freq for the optic with the 3" metal sleeve is 1.0~1.1mm.
As the previous elog does not specify this number for the current configuration, we need to asses this value and the make the adjustment of the CoM height.

For future reference, the new settings can be upoaded from a script in the same directory. Run python /users/anchal/20210505_IMC_Tuned_SUS_with_Gains/uploadNewConfigIMC.py from allegra.

HP HV power supply ( HP6209 ) were returned to Downs

11 new Satellite Amps were picked up from Downs. 7 more are coming from there. I have one spare unit I made. 1 sat amp has already been used at MC1.

We had 8 HAM-A coil drivers delivered from the assembling company. We also have two coil drivers delivered from Downs (Anchal tested)

DC Power Strip Assemblies delivered and stored behind the Y arm tube (Attachment 1)

• 7x 18V Power Strip (Attachment 2)
• 7x 24V Power Strip (Attachment 2)
• 7x 18V/24V Sequencer / 14x Mounting Panel (Attachment 3)
• DC Power Cables 3ft, 6ft, 10ft (Attachments 4/5)
• DC Power Cables AWG12 Orange / Yellow (Attachments 6/7)

I also moved the spare 1U Chassis to the same place.

• 5+7+9 = 21x 1U Chassis (Attachments 8/9)

The transfer function given in the previous post was slightly incorrect the units did not make sense the new function is:

I have attached a quick derivation below in attachment 1

[Anchal, Paco]

We went into 40m to identify where XARM PDH loop control elements are. We didn't touch anything, but this is to note we went in there twice at 10 AM and 11:10 AM.

The plant transfer function of the pendulum in the s domain is:

Using Foton to make a plot of the TF needed and using m=40kg, w₀=3Hz, and Q=50 (See attachment 1). It is easiest to enter the above filter using RPoly and saved it as Plant_V1

The new HAM-A coil drivers have a single DB9 connector for all the binary inputs. This requires that the dewhitening switching signals from the fast system be spliced with the coil enable signals from c1auxey. There is a common return for all the binary inputs. To avoid directly connecting the grounds of the two systems, I have looked for a suitable opto-isolator for the c1auxey signals.

I best option I found is the Ocean Controls KTD-258, a 4-channel, DIN-rail-mounted opto-isolator supporting input/output voltages of up to 30 V DC. It is an active device and can be powered using the same 15 V supply as is currently powering both the Acromags and excitation. I ordered one unit to be trialed in c1auxey. If this is found to be good solution, we will order more for the upgrades of c1auxex and c1susaux, as required for compatibility with the new suspension electronics.

- High priority units: 2x 18AI / 1x 16AI / 3x 16AA

All six are reworked and on the electronics workbench. The rest should be ready by the end of the week.

Chub

Updated IOO.strip on Zita to show WFS2 pitch and yaw trends (C1:IOO-WFS2_PIY_OUT16 and C1:IOO-WFS2_YAW_OUT16) and changed the colors slightly to have all pitch trends in the yellow/brown band and all yaw trends in the pink/purple band.

No one says, "Here I am attaching a cool screenshot, becuz else where's the proof? Am I right or am I right?"

Mon May 24 18:10:07 2021 [Update]

After waiting for some traces to fill the screen, here is a cool screenshot (Attachment 1). At around 2:30 PM the MC unlocked, and the BS_Z (vertical) seismometer readout jumped. It has stayed like this for the whole afternoon... The MC eventually caught its lock and we even locked XARM without any issue, but something happened in the 10-30 Hz band. We will keep an eye on it during the evening...

Tue May 25 08:45:33 2021 [Update]

At approximately 02:30 UTC (so 07:30 PM yesterday) the 10-30 Hz seismic step dropped back... It lasted 5 hours, mostly causing BS motion along Z (vertical) as seen by the minute trend data in Attachment 2. Could the MM library have been shaking? Was the IFO snoring during its afternoon nap?

All remaining chasses have been reworked and placed on the floor along the west wall in Room 104. 

I was preparing a short write-up / test procedure for the custom HV coil driver, when I thought of something I can't resolve. I'm probably missing some really basic physics here - but why do we not account for the shot noise from DC current flowing through the series resistor? For a 4kohm resistor, the Johnson current noise is ~2pA/rtHz. This is the target we were trying to beat with our custom designed HV bias circuit. But if there is a 1 mA DC current flowing through this resistor, the shot noise of this current is 18pA/rtHz, which is ~9 times larger than the Johnson noise of the same resistor. One could question the applicability of this formula to calculate the shot noise of a DC current through a wire-wound resistor - e.g. maybe the electron transport is not really "ballistic", and so the assumption that the electrons transported through it are independent and non-interacting isn't valid. There are some modified formulae for the shot noise through a metal resistor, which evaluates to 10pA/rtHz for the same 4kohm resistor, which is still ~5x the Johnson noise. 

In the case of the HV coil driver circuit, the passive filtering stage I added at the output to filter out the excess PA95 noise unwittingly helps us - the pole at ~0.7 Hz filters the shot noise (but not the Johnson noise) such that at ~10 Hz, the Johnson noise does indeed dominate the total contribution. So, for this circuit, I think we don't have to worry about some un-budgeted noise. However, I am concerned about the fast actuation path - we were all along assuming that this path would be dominated by the Johnson noise of the 4kohm series resistor. But if we need even 1mA of current to null some DC DARM drift, then we'd have the shot noise contribution become comparable, or even dominant?

I looked through the iLIGO literature, where single-stage suspensions were being used, e.g. Rana's manifesto, but I cannot find any mention of shot noise due to DC current, so probably there is a simple explanation why - but it eludes me, at least for the moment. The iLIGO coil drivers did not have a passive filter at the output of the coil driver circuit (at least, not till this work), and there isn't any feedback gain for the DARM loop at >100 Hz (where we hope to measure squeezing) to significantly squash this noise.

Attachment #1 shows schematic topologies of the iLIGO and proposed 40m configs. It may be that I have completely misunderstood the iLIGO config and what I've drawn there is wrong. Since we are mainly interested in the noise from the resistor, I've assumed everything upstream of the final op-amp is noiseless (equivalently, we assume we can sufficiently pre-filter these noises).
Attachment #2 shows the relative magnitudes of shot noise due to a DC current, and thermal noise of the series resistor, as a function of frequency, for a few representative currents, for the slow bias path assuming a 0.7Hz corner from the 4kohm/3uF RC filter at the output of the PA95.

Some lit review suggests that it's actually pretty hard to measure shot noise in a resistor - so I'm guessing that's what it is, the mean free path of electrons is short compared to the length of the resistor such that the assumption that electrons arrive independently and randomly isn't valid. So Ohm's law dictates  and that's what sets the current noise. See, for example, pg 432 of Horowitz and Hill.

The current vertical distance between the CoM and the wire clamping point on the 3" Ring assembly is 0.33mm. That is the CoM is .33 mm below the clamping point of the wire. I took the clamping point to be the top edge of the wire clamp piece. see the below attachments.

I am now modifying the dumbell mechanism at the bottom of the ring to move the CoM to the target distance of 1.1mm.

I have received the opto-isolator needed to complete the new c1auxey system. I left it sitting on the electronics bench next to the Acromag chassis.

Here is the manufacturer's wiring manual. It should be wired to the +15V chassis power and to the common return from the coil driver, following the instructions herein for NPN-style signals. Note that there are two sets of DIP switches (one on the input side and one on the output side) for selecting the mode of operation. These should all be set to "NPN" mode.

An update on recent progress in the lab towards building and testing the new FEs.

1. Timing problems resolved / FE BIOS changes

The previously reported problem with the IOPs losing sync after a few minutes (16130) was resolved through a change in BIOS settings. However, there are many required settings and it is not trivial to get these right, so I document the procedure here for future reference.

The CDS group has a document (T1300430) listing the correct settings for each type of motherboard used in aLIGO. All of the machines received from LLO contain the oldest motherboards: the Supermicro X8DTU. Quoting from the document, the BIOS must be configured to enforce the following:

• Remove hyper-threading so the CPU doesn’t try to run stuff on the idle core, as hyperthreading simulate two cores for every physical core.
• Minimize any system interrupts from hardware, such as USB and Serial Ports, that might get through to the ‘idled’ core. This is needed on the older machines.
• Prevent the computer from reducing the clock speed on any cores to ‘save power’, etc. We need to have a constant clock speed on every ‘idled’ CPU core.

I generally followed the T1300430 instructions but found a few adjustments were necessary for diskless and deterministic operation, as noted below. The procedure for configuring the FE BIOS is as follows:

1. At boot-up, hit the delete key to enter the BIOS setup screen.
2. Before changing anything, I recommend photographing or otherwise documenting the current working settings on all the subscreens, in case for some reason it is necessary to revert.
3. T1300430 assumes the process is started from a known state and lists only the non-default settings that must be changed. To put the BIOS into this known state, first navigate to Exit > Load Failsafe Defaults > Enter.
4. Configure the non-default settings following T1300430 (Sec. 5 for the X8DTU motherboard). On the IPMI screen, set the static IP address and netmask to their specific assigned values, but do set the gateway address to all zeros as the document indicates. This is to prevent the IPMI from trying to initiate outgoing connections.
5. For diskless booting to continue to work, it is also necessary to set Advanced > PCI/PnP Configuration > Load Onboard LAN 1 Option Rom > Enabled.
6. I also found it was necessary to re-enable IDE direct memory access and WHEA (Windows Hardware Error Architecture) support. Since these machines have neither hard disks nor Windows, I have no idea why these are needed, but I found that without them, one of the FEs would hang during boot about 50% of the time.
   • Advanced > PCI/PnP configuration > PCI IDE BusMaster  > Enabled.
   • Advanced > ACPI Configuration > WHEA Support > Enabled.

After completing the BIOS setup, I rebooted the new FEs about six times each to make sure the configuration was stable (i.e., would never hang during boot).

2. User models created for FE testing

With the timing issue resolved, I proceeded to build basic user models for c1bhd and c1sus2 for testing purposes. Each one has a simple structure where M ADC inputs are routed through IIR filters to an M x N output matrix, which forms linear signal combinations that are routed to N DAC outputs. This is shown in Attachment 1 for the c1bhd case, where the signals from a single ADC are conditioned and routed to a single 18-bit DAC. The c1sus2 case is similar; however the Contec BO modules still needed to be added to this model.

The FEs are now running two models each: the IOP model and one user model. The assigned parameters of each model are documented below.

The user models were compiled and installed following the previously documented procedure (15979). As shown in Attachment 2, all the RTS processes are now working, with the exception of the DAQ server (for which we're still awaiting hardware). Note that these models currently exist only on the cloned copy of the /opt/rtcds disk running on the test stand. The plan is to copy these models to the main 40m disk later, once the new FEs are ready to be installed.

3. AA and AI chassis installed

I installed several new AA and AI chassis in the test stand to interface with the ADC and DAC cards. This includes three 16-bit AA chassis, one 16-bit AI chassis, and one 18-bit AI chassis, as pictured in Attachment 3. All of the AA/AI chassis are powered by one of the new 15V DC power strips connected to a bench supply, which is housed underneath the computers as pictured in Attachment 4.

These chassis have not yet been tested, beyond verifying that the LEDs all illuminate to indicate that power is present.

After changing the material of the Balance Mass from 6061 Al to 304 Steel, and changing the thickness to 0.21" from 0.25". The CoM is now 1.11mm below the clamping point.

Koji expected a mass change of ~ 4g to move the mass to 1.1mm. The 6061 mass weighed ~1.31g and the 304 mass weighs 4.1g.

A potential issue with this is the screw used the adjust the position of these balance masses, threads through both the aluminum ring and this now 304 steel mass. A non silver plated screw could cold weld at the mass, but a silver plated screw will gall in the aluminum threads.

I tried to push the clean Viton tips into the vented screws just to find out that the vented holes are too small. We need to drill 0.1" diameter holes about 0.1" deep into these screws and clean them again.

Can you just cut the viton tips smaller? If you cut it to have some wedge (or say, taper), it can get stuck with the vent hole.

How about to use the non-Ag coated threaded shaft + the end SS masses with helicoils inserted? Does this save the masses to get stuck?

I borrowed the little red cart 🛒 to help clear the path for new optical tables in B252 West Bridge. Will return once I am done with it.