While looking at the DAC anti-imaging filters, Koji noticed an odd feature of the DAC output:

What you see here is 16kHz double data from a model right before the DAC part ('C1:SUS-PRM_ULCOIL_OUT', blue), and the full 64kHz int data sent to the physical DAC as reported by the IOP ('C1:X02-MDAC0_TP_CH0', green).  The balls are the actual sample values (as expected there are four green balls for every blue).  The output data is being ramped continuously between 0 and 1.

As the output data crosses the half-count level, the integer DAC output oscillates continuously at every 64kHz sample between the bounding integer values (in this case 0 and 1).

Here's the data as we hold the output continuously at the half-count level; the integer DAC output just oscillates continuously:

After some probing I found that the oscillation happens between [-0.003 +0.004] of the half-count level.

The result of this is a fairly strong 32 kHz line in the DAC analog output.

We looked in the controller.c and couldn't identify anything that would be doing this.  This is the output procedure as I can see it (controller.c lines): 

1. The double from the model is passed to the IOP
2. The IOP applies a sample-and-hold or zero-pad if the model is running at a slower speed than the IOP (1799)
3. The data is then anti-image filtered (1801)
4. A half-integer is added/subtracted before casting such that the cast is a round instead of a floor (1817)
5. The data double is cast to an int (1819)
6. The data is written to the DAC (1873)

There's nothing there that would indicate this sort of bit flipping.

Let me make a complimentary comment on this effect.

Because of this oscillation feature, we have a 32kHz peak in the DAC spectrum rather than a 64kHz peak.

For advanced LIGO, the universal AI (D070081) was made to have 3rd-order 10kHz LPF with 64kHz notch.
If we have a higher peak at 32kHz (where the rejection is not enough) than at 64kHz, the filter does not provide
enough filtering of the DAC artifacts.

For the 40m, the original filter had the cut off of 7kHz as the sampling rate was 16kHz.
If we want to extend the frequency range by 4times, the correspoding cut off should be 28kHz.
The rejection is again not enough at 32kHz.

If this peak is an avoidable feature by using simple sample&hold the peak freq is pushed up to
64kHz and we can use the AI filters as planned.

After querying CDS folks about this issue, I got some responses that indicated the problems was likely limit-cycle oscillations due to zero-padding of the data when upsampling.  Tobin ran some Matlab tests to confirm this issue.

Starting in RCG 2.5 there is a new "no_zero_pad=1" cdsParameters option turns zero padding OFF.  I tried enabling this option c1scy to see how the behavior changed.  Sure enough, the 32 kHz oscillations mostly went away.  There are no oscillations for outputs held at the half-count value, and the oscillations around the half-count transitions went away as well.

The only thing I could see is a bit of oscillation when converging on a constant half-count value that went away after a couple of milliseconds:

So we might consider adding the no_zero_pad=1 option to all of our coil driver outputs, which might eliminate the need to add notches at the Nyquist in the analog anti-image filters

Is this limit cycle caused by the residual of the digital AI filtering at the half sampling freq and that his the threshold?
Or is this some nonlinear effect? If this is a linear effect associated with the zero-padding, the absolute
value of the DC may affect the amplitude of the oscillation. (Or equivalently the range of the DC where we get this oscillation.)

Anyway, it seems that we should use no-zero-padding.

You pointed out the ringdown of the digital AI filter in the sample-hold case (i.e. no-zero-padding case).
How does it look like in the conventional zero-padding case?

This is a good question.  We may be able to test if it's a linear effect if we have enough DAC range to get the oscillation to be more than a single sample.

 In the zero-pad case the oscillation just continues indefinitely at the half-count value, so it never dies out (at least as far as I can tell).

It seems that the effect is from the (linear) residual fluctuation of the digital AI filter for the zero-padded signal.

Namely, if we give the larger constant number, we get more oscillation.

A few minutes ago, Gautam and I were poking around the IOO rack, looking at where he should power his frequency divider box, and what ADC innputs to use. 

Looking at the mode cleaner signals, it looks like we may have jostled something in a good way. Weird. 

For past few days, a weird sound of decaying gas leakage comes in the 40m control room from the south west corner of ceiling. Attached is an audio capture. This comes about every 10 min or so. 

I also noticed some sound in the control room. (didn't open the MP3 yet)

I'm afraid that the hard disk in the control room iMac is dying.

Today we saw a weird issue with the GPS receiver (EndRun Technologies Tempus LX).  GPS timing on fb1 (which is handled via IRIG-B connection to the receiver with a spectracom card) was off by +18 seconds.  We tried resetting the GPS receiver and it still came up with +18 second offset.  To be clear, the GPS receiver unit itself was showing a time on it's front panel that looked close enough to 24-hour UTC, but was off by +18s.  The time also said "GPS" vertically to the right of the time.

We started exploring the settings on the GPS receiver and found this menu item:

Clock -> "Time Mode" -> "UTC"/"GPS"/"Local"

The setting when we found it was "GPS", which seems logical enough.  However, when we switched it to "UTC" the time as shown on the front panel was correct, now with "UTC" vertically to the right of the time, and fb1 was then showing the correct GPS time.

From the manual:

The fact that moving to "UTC" fixed the problem, even though that is supposed to remove the leap second correction, might indicate that there's another bug in the symmetricom driver...

Welcome to your new abode, Donatella!

This is a kind of summary of what I have worked on this week.

After all the changes made last week, I could not manage to lock the green light to the cavity, but the PDH error signal looks nicer.....at least something.

Alignment of the light to the cavity:

• DC level of green PD when light is non-resonating 100%
• DC level of green PD when light resonates 75%
• --> Not sure if this alignment is good enough
• In comparision to last week the cavity mirrors seem to move more or my alignment is way worse than last week. The bright spot on ETMY could not be observed for more than let's say a second in the unlocked configuration.

Low-pass filter (LPF)

• The PDH error signal was covered with oscillations of 3.3 kHz, 7.1 kHz and 35 kHz.
• Measured cut-off frequency of the LPF used so far is 35 kHz
• Designed and build a new LPF: second order, cut of frequency of 1.1 kHz (this is just the design value, haven't measured that so far)
• With the new LPF the PDH error signal is free of the above mentioned oscillations.
• Impedance should be checked

PDH error signal

• Signal-to-noise ratio (SNR) could be improved to values between 7.8 and 11.1 (old SNR was 5 to 7)
• Looks more like a PDH signal than with the old LPF (now just derivative of the carrier and the first order sidebands show up)
• Amplitude of the first order sidebands are smaller than the zero order, but are still too high (about 80% of the first order), need to work on the proper value of the LO amplitude an the voltage averager

Phase shift between green PD signal and LO

• Phase shift is about 1MHz
• Tried to find a capacity that compensates the phase shift. This was not successful since the PD frequency changed every now and than by +/- 20 kHz

Summary:

I made it to 0 CARM offset, PRMI locked a bunch of times today. However, I could not successfully engage the AO path.

Details:

Much of the procedure is scripted, here is the rough set of steps:

• Transition control of the arms from IR signals to ALS signals.
• DC couple the ITM oplev servos
• Burt-restore the settings for PRMI locking with REFL165I-->PRCL, REFL165Q-->MICH, and then enable the MICH_B / PRCL_B locking servos.
• Add some POPDC to the PRMI triggering (nominally only POP22_I) to let these loops be locked while POP22_I fluctuates wildly when we are near the CARM=0 point.
• Zero the CARM offset.
• Adjust the CARM_A/DARM_A offsets such that CARM_B/DARM_B are fluctuating symmetrically about 0.
• CARM_B gain --> 1.0, to begin the RF blend.
• Prepare to hand the DC control authority to ALS by turning off FM1 in the CARM filter bank, and turning ON an integrator in the CARM_B filter.

As I type this out, I realized that I was incorrectly setting offsets to maximize the arm powers by adjusting CARM/DARM offsets as opposed to CARM_A / DARM_A offsets. Tried another round of locking, but this time, I can't even turn the integrator on to get the arms to click into somewhat stable powers. 

One thing I noticed is that depending on the offsets I put into the 3f locking loops, the mean value of REFL11 and AS55 when the ALS CARM/DARM offsets are zeroed changes quite significantly. What is the correct condition to set these offsets? They are different when locking the PRC without arm cavities, and also seem to change continuously with CARM offset. I am wondering if I have too much offset in one of the vertex locking loops?

Summary:

I want some input about what the short-term (next two weeks) commissioning goals should be.

Details:

Before the vacuum fracas, the locking was pretty robust. With some human servoing of the input beam, I could maintain locks for ~1 hour. My primary goals were:

1. Transition the vertex length DoF control from 3f signals to 1f signals.
2. Turn on some MICH-->DARM feedforward cancellation, because the noise between ~100 Hz and ~1kHz is dominated by this cross-coupling.

I didn't succeed in either so far.

1. I find that there is poor separation of the length DoFs in the 1f sensors, which makes this transition hopeless.
   • Why should this be? I can't get any sensing matrix in Finesse to line up with what I measure in-lock.
   • One hypothesis I came up with (but haven't yet tested) is that the offsets from the 3f photodiodes are changing from time to time, which somehow changes the projection of the various DoFs onto the photodiode quadratures. 
   • The attached GIF shows the variation in the measured sensing matrix on two days - while the sensing of MICH/PRCL in the 3f photodiodes have hardly changed, they are significantly different in the 1f photodiodes. Note that the I and Q have changed for REFL11 and REFL55 between the two days because I changed the demod phase.
   • I also thought that maybe the CARM suppression isn't sufficient for REFL11 to be used as a PRCL sensor - but even after engaging a CM board SuperBoost, I was unable to realize the PRCL 3f-->1f transition, even though the CARM-->REFL11 coupling did get smaller in the measured sensing matrix (red line in the GIF). I don't think we can juice up the CARM gain much more without modifying the CM board boosts, see Attachment #1.
2. I was able to measure the MICH CTRL --> DARM ERR transfer function with somewhat high coherence (~0.98).
   • I then used the infrastructure available in the LSC model to try and implement some cancellation, but didn't really see any effect.
   • Perhaps the TF needs to be measured with higher coherence.
   • It may also be that if I am able to successfully execute the 3f-->1f transition, the coupling gets smaller because the 1f sensing noise is lower?

I guess apart from this, we want to run the ALS scan to try and infer something about the absorption-induced thermal lens. I guess at this point, the costs outweigh the benefits in trying to bring in the SRC as well, since we will be changing the SRC config?

Per the discussion at the meeting today, the plan of action is:

1. Lock the PRMI on carrier and measure the sensing matrix, see if the MICH and PRCL signals look sensible in 1f and 3f photodiodes.
2. Try locking CARM on POP55 (since there is currently no POP55 photodiode, can we use POX/POY as an intermediary?).
3. For the ASC, can we hijack one of the IMC WFS heads to study what the AS port WFS signals would look like, and maybe close a feedback loop on the ETMs?
   • My guess is no, because currently, the L2A is so poorly tuned on MC2 that the CARM length control messes with the alignment of the IMC significantly.
   • So we need the IMC WFS loops to maintain the pointing.
   • Of course, the MC2 L2A can be tuned to mitigate this problem. 
   • I also believe there is something funky going on with the WFS heads. More to follow on that in a later elog.
   • Apart from these issues, for this scheme to be tested, some mods to the c1ioo model will have to be made so that we can route the servo output to the ETMs (as opposed to the IMC mirrors as is the usual case).

If I missed something, please add here.

I'm not sure I understand what F2A is? I couldn't find a description of this filter anywhere and don't remember if you have already explained it. Can you describe what is needed to be done again, please? We would keep SUS state space model and seismic transfer functions calculation ready meanwhile.

Force to Angle. It just means the filters that are in the POS OUTPUT matrix. I think in the past sometimes they are called F2P or F2A.

These filters account for the frequency dependent coupling of the DOFs around the suspension resonance. Take a look at what Bhavini is doing for the plots.

Today image capture did not work again, though it had worked 3 days before. I also found that red indicator light on the front pannel of SENSORAY was not turned on, which had been turned on 3 days before (you can find SENSORAY on the floor near Pianosa). Possible reason that it did not work again was I restarted Pianosa last night. Anyway, it works now. Here I report what I did to make it work.

I ran thes commands in shell, following the instruction of the manual of SENSORAY 2253 (Page 5; link or you can find the manual in /users/sensoray; I put it there). 

> cd /users/sensoray/sdk_2253_1.2.2_linux

> make all

> sudo make install

> modprobe s2253

Then the red light got turned on, and image capture worked.

If you recieve an error like "No such file or directory: /dev/video0" at the beginning of the error message when you run image capture scripts from the medm screen, or if you notice that the red indicator light of SENSORAY is not on, this procedure could help you. 

Do we need "make" everytime? Do you mean just running "modprobe" didn't work?

I don't know if just running "modprobe" will work or not, because I didn't try it...  When the same problem happens again, we can try just running "modprobe" first.

I can't find the DELL laptop anywhere in the lab. Does anyone know where it is?

Also one of the two netbooks is missing.

One dell is in the clean room for the suspension work.

While trying to implement the regular yellow shell script button in MEDM for my new OAF screen, I noticed that the update snapshot stuff in all of the buttons that I checked (including IFO Align and LSC Overview) are pointing to folders in the old /cvs/cds/caltech/ area.  Also, I think some of the folders that it's looking for don't exist anymore, even in the old system.  So.  Has anyone thought about where the snapshots should live in the new world order?  Previously they were in ...../medm/c1/subsystem/ .  Maybe we should make a snapshots folder in each subsystem's medm folder, at the same level as the 'master' folder for the custom screens?  This is my current proposal.

Unless someone objects / has a better plan / knows why they're still pointing to the old place, I'll do this in the morning, and work on changing all the buttons to point to the new place.

The following directory exists. We can apply this convention to all of the models.

/cvs/cds/rtcds/caltech/c1/medm/c1lsc/snap

Alex checked out the old rts (which he is no longer sure how to compile) from CVS to megatron, to the directory:

/home/controls/cds/rts/

In /home/controls/cds/rts/src/include you can find the various h files used.  Similarly, /fe has the c files.

In the h files, you can work out the memory offset by noting the primary offset in iscNetDsc40m.h

A line like suscomms.pCoilDriver.extData[0] determines an offset to look for.

0x108000 (from suscomms )

Then pCoilDriver.extData[#] determines a further offset.

sizeof(extData[0]) = 8240  (for the 40m - you need to watch the ifdefs, we were looking at the wrong structure for awhile, which was much smaller).

DSC_CD_PPY is the structure you need to look in to find the final offset to add to get any particular channel you want to look at.

The number for ETMX is 8, ETMY 9 (this is in extData), so the extData offset from 0x108000 for ETMY should be 9 * 82400.  These numbers (i.e. 8 =ETMX, 9=ETMY) can be found in losLinux.c in /home/controls/cds/rts/src/fe/40m/.  There's a bunch of #ifdef and #endif which define ETMX, ETMY, RMBS, ITM, etc.  You're looking for the offset in those.

So for ETMY LSC channel (which is a double) you add 0x108000 (a hex number) + (9 * 82400 + 24) (not in hex, need to convert) to get the final value of 0x11a160 (in hex).

-----------

A useful program to interact with the RFM network can be found on fb40m.  If you log in and go to:

/usr/install/rfm2g_solaris/vmipci/sw-rfm2g-abc-005/util/diag

you can then run rfm2g_util, give it a 3, then type help.

You can use this to read data.  Just type help read.  We had played around with some offsets and various channels until we were sure we had the offsets right.  For example, we fixed an offset into the ETMY LSC input, and saw the corresponding memory location change to that value.  This utility may also be useful for when we do the RFM test to check the integrity of the ring, as there are some diagnostic options available inside it.

I have a simulated version of the differences that we expect to see between the 2 different sides of the CARM resonance.  The point is that we can try to compare these results with Q's measured results (elog 10594) to see if we know if we are on the spring or antispring side.

I calculated the same transfer functions vs CARM offset again, although tonight I do it in steps of 20pm because I was getting bored of waiting forever.  Anyhow, this is important because my previous post (elog 10591) didn't have spring side calculations all the way down to 1pm.

This is similarly true for that elog 10591, but here are some notes on how I am currently getting the W/N units out of Optickle.  First of all, I am still using old Optickle1.  I don't know if there are significant units ramifications for that, but just in case I'll write it down.  Nic tells me that to get [W/N] out of Optickle1, I need to multiply sigAC (units of [W/m]) by my simple pendulum (units of [m/N]).  Both of these "meters" in the last sentence are "mevans meters", which are the meters you would get per actuation if radiation pressure didn't exist.  So, I guess they're supposed to cancel out?  I need to camp out in Nic's office until I figure this out and get it untangled in my head.

Plots of transfer functions for both sides of CARM resonance (same as prev. elog), as well as the ratio between the spring and antispring transfer functions at each CARM offset:

The take-away message from the 3rd column is that other than a sign flip, we don't expect to see very much difference between the 2 sides of the CARM resonance, particularly above a few hundred Hz.  (Note that we do not see the sign flip in Q's measurements because he is looking at CARM_IN1, which is after the input matrix, and the input matrix elements have opposite signs between the signs of the CARM offsets.  So, the sign flip between spring and antispring around the UGF is implied in the measurements, just not explicit).

Also, something that Rana pointed out to me, and I still don't know why it's true:  The antispring transfer functions (at least for the transmission) don't have all the phase features that we expect to see based on their magnitudes.  If you look at the TRX antispring plot, blue trace (which is about 500pm from resonance), you'll see that the magnitude starts flat at DC, has some slope in an intermediate region, and then at high frequencies has 1/f^2.  However, the phase seems to not know about this intermediate region, and magically waits until the 1kHz resonance to flip the full 180 degrees. 

 I made some measurements to try and see if any difference could be seen with different CARM offset signs. 

Specifically, at various offsets, I used a spare DAC channel to drive IN1 of the CM board, as an "AO Exciter." I used CM_SLOW to monitor the signal that was actually on the board. I used the CARM_IN1 error signal to see how the optical plant responded to the AO excitation. Rather than a swept sine, I used a noise injection kind of TF measurement. 

Here are plots of CARM_IN1 / CM_SLOW at different CARM FM offsets; I chose to plot this in an attempt to divide out some of the common things like AA and delays and make the detuned CARM pole more evident). The offsets chosen correspond roughly to powers of 2, 2.5, and 3. I tried to go higher than that, but didn't remain locked for long enough to measure the TF. 

By eye, I don't see much of a difference. We can zpk fit the data, and see what happens. 

 I went back into the DQ channels to look at the TF from AO injection to REFLDC (which is easy to do with this kind of noise injection TF).  

I fear that REFL does not seem to have as much phase under the resonance as we have modeled, lacking about 10-20 degrees. This could result from the zero in the REFL DC response that we've modeled at ~200ish Hz is actually higher. I'll look into what affects the frequency of that feature. 

It is, of course, possible, that this measurement doesn't properly cancel out the various digital effects, but the REFLDC phase curves do seem to settle to (+/-) 90 after the pole as expected. 

DTT XML file is attached. 

Some measurements.  Unclear meaning.  

We tried both positive and negative numbers in the CARM offset, and then looked at transfer functions at various arm powers. The hope is to be able to compare these with some simulation to figure out which side of the CARM resonance we are on.

The biggest empirical take-away is that we repeatedly (3 times in a row) lost lock when holding at arm powers of about 5 with negative CARM offsets.  However, we were repeatedly (2+ times tonight) able to sit and hold at arm powers of 10+ with positive CARM offsets.

I am not sure that we get enough information out of these plots to tell us which side of the CARM resonance we are really on.  Q is working on taking some open loop CARM measurements (actuating and measuring at SUS-MC2_LSC) to see if we can compare those more directly to Rana's plots.

Positive number in the digital CARM offset:

Negative numbers in digital CARM offset:

[Jenne, Diego]

In order to distinguish between the spring and antispring sides of the CARM resonance, we need to have transfer function measurements down to at least 100 Hz (although lower is better). 

We tried to get some transfer functions the same way Q did, but noticed that (a) we couldn't get any low frequency coherence, and (b) that when we increased the amplitude of the white (well, lowpass at 5kHz) noise, the coherence between the AO injection and REFL DC went down.  Not clear why this is.

Anyhow, we tried taking good ol' fashioned swept sine transfer functions, although eventually the lightbulb came on that the AO path has a highpass in it.  Duh, Jenne.  So, we started trying to actuate on MC2 position rather than the AO path laser frequency.  We didn't get too far though before El Salvadore decided to have a few 7.4 earthquakes.  We're bored of aftershocks knocking us out of lock, so we're going to come back to this tomorrow.

 Since no one was here, I started the Ubuntu 10 - 12 upgrade on Rossa. It didn't run at first because it wanted to remove 'update-manager-kde' even though it was on the blacklist. I removed it from the command line and now its running. Allegra, OTOH, refuses to upgrade. Someone please ask Diego to wipe it and then install Ubuntu 12 LTS on there in the morning...its a good way to learn the Martian CDS setup.

 I have plotted measured data from last night (elog 10607) with a version of the result from Rana's simulink CARM loop model (elog 10593).

The measured data that was taken last night (open circles in plots) is with an injection into MC2 position, and I'm reading out TRX.  This is for the negative side of the digital CARM offset, which is the one that we can only get to arm powers of 5ish.

The modeled data (solid lines in plots) is derived from what Rana has been plotting the last few days, but it's not quite identical.  I added another excitation point to the simulink model at the same place as the "CARM OUT" measurement point.  This is to match the fact that the measured transfer functions were taken by driving MC2.  I then asked matlab to give me the transfer function between this new excitation point (CARM CTRL point) and the IN1 point of the loop, which should be equivalent to our TRX_OUT.  So, I believe that what I'm plotting is equivalent to TRX/MC2.  The difference between the 2 plots is just that one uses the modeled spring-side optical response, and the other uses the modeled antispring-side response.

I have zoomed the X-axis of these plots to be between 30 Hz - 3 kHz, which is the range that we had coherence of better than 0.8ish last night in the measurements.  The modeled data is all given the same scale factor (even between plots), and is set so that the lowest arm power traces (pink) line up around 150 Hz. 

I conclude from these plots that we still don't know what side of the CARM resonance we are on. 

 I have not plotted the measurements from the positive side of the digital CARM offset, because those transfer functions were to sqrtInvTRX, not plain TRX, whereas the model only is for plain TRX. There should only be an overall gain difference between them though, no phase difference.  If you look at last night's data, you'll see that the positive side of the CARM offset measured phase has similar characteristics to the negative offset, i.e. the phase is not flat, but it is roughly flat in both modeled cases, so even with that data, I still say that we don't know what side of the CARM resonance we are on.

I made some rough measurements, using the setup I had used for CCD calibration, to get an idea of how good of a Lambertian scatterer the white paper is. Following are the values I got:

Note: All the measurements are just rough ones and are prone to larger errors than estimated.

I also measured the transmittance of the white paper sample being used (it consists of 2 white papers wrapped together). It was around 0.002

{Mayank, Yehonathan}

We measured today the TFs of the whitening boards. We measured in particular REFL11 I/Q and AS55 I/Q channels using SR785.

There seems to be an issue with turning on whitening gain bigger than 18dB. In all our measurements, when the whitening filter was off the TF was flat and had the right gain. However, when we turned the whitening on, the measured TFs for gains higher than 18 dB would like exactly like as if the whitening gain was 18 dB. This happened in all channels that were measured and across two separate whitening filter boards.

Also, it was hard to measure both low and high-frequency parts of the TFs when the gain was high. The gain difference should be normally 40 dB but for higher gains it seems smaller. We verified that at higher gain level the high-frequency response was dependant on the ecxitation level meaning we had some saturation there.

We forgot to take a reference TF measurement by looping the SR785 on itself using the same BNC cables used for the actual measurement. I took this measurement today (attachment 1). As can be seen, there is a significant delay in the SR785 + cables themselves.

I also retook some measurements on the AS5_I whitening channel for various gains. Being careful with the excitation level and the channel range on the SR785 to avoid saturation I was also able to see low-frequency gains higher than 18dB so that problem is gone too. The results are shown in attachment 2 with the reference phase subtracted from the measurements.

I finally managed to install a differential-receiving whitening board in 1Y2 - 4 channels are available at the moment. As I claimed, one stage of 15:150 Hz z:p whitening does improve the ALS noise a little, see Attachment #1. While the RMS (from 1kHz-0.5 Hz) does go down by ~10 Hz, this isn't really going to make any dramatic improvement to the 40m lock acquisiton. Now we're really sitting on the unsuppressed EX laser noise above ~30 Hz. This measurement was taken with the arm cavities locked with POX/POY, and end lasers locked to the arm cavities with uPDH boxes as usual. This was just a test to confirm my suspicion, the whitening board is to be used for the air BHD channels, but when we get a few more stuffed, we can install it for the ALS channels too.

No, there should be no unscheduled visits from any inspector, marshal, tech, or vendor. They all have to be escorted or they don't get in. If they have a problem with that, please give them my cell #.

For the ALS, in addition to the beat note spectrum, I think we need to know the loop gain use to feedback to the ETM to determine the true cavity length fluctuation. w/o ALS, the noise would be only due to the seismic noise, OSEM damping noise, and the IR-PDH residual. Those are all suppressed by the ALS loop, but then the ALS loop puts its sensing noise onto the cavity. So, if I'm thinking about this right, the ALS beat noise > 200 Hz doesn't matter so much to the CARM RMS. So the whitening seems to be doing good in the right spot, but we would like to have another boost in the green PDH to up the gain below ~300 Hz?

Summary:

With the chosen transimpedance of 300 ohms, in order to be able to see the shot noise of 10 mW of light in the digitized data streams, we'd need all 3 stages of whitening. If we want to be shot noise limited with 1 mW of LO light, we'd need to increase said transimpedance I think.

Details:

The measurements were taken with

1. No light incident on the DCPDs.
2. The flat whitening gain was set to 0 dB.
3. Whitening engaged sequentially, stage by stage, shown as (Blue, Red, Orange and Green) curves corresponding to (0, 1, 2, 3) stages of whitening.

Of course, it's unlikely we're going to be shot noise limited for any configuration in the short run. But this was also a test of 

1. My soldering.
2. Change of whitening corner frequencies.
3. Test of the overall whitening board assembly.

All 3 tests passed.

For whitening electronics noise for WFS1, I get (attachment). This doesn't seem right, right?

We use D990694 in various places. Today, Rana alerted me to an important consideration to be kept in mind when we use this board, which I found quite interesting. I still don't understand the problem at the BJT level, but I think one can appreciate the problem without going to the transistor design of the LT1125. I'm attaching an annotated schematic of the whitening section in question. If the following assumptions are valid, then I think my picture is valid.

1. The switch used to bypass the various whitening gain stages, namely the ADG333ABR, has infinite impedance in the "OFF" state, such that when the 24dB gain stage is bypassed, U28A (or in general one of the 4 quad op-amps) is forced to drive it's output voltage across 1.0665 kohms of resistance.
2. The individual LT1125 Op Amps can drive a maximum of 30mA of current.

Then, as one can see in the attached schematic, when we set the gain of any input to <24dB, we must ensure that the input voltage is less than approximately 2V. Otherwise, by asking too much of the first stage op-amp in the quad IC LT1125, we may be messign around with all the 4 op amps in the quad! Even the 0dB setting is not immune to this problem, as it uses one of the 4 op amps.

I don't think the usual rules of calculating the gain of a non-inverting amplifier (G = 1 + Rf/Ri) remain valid even when the op-amp is forced to drive more output current than it can, and I don't have a way to quantify the possible interference between the 4 op amps in the quad - but does this seem like a valid conclusion? If so, we must check signal levels of various LSC signals. AS55 signals currently have the 0dB gain setting - I had turned this down from 6dB some months ago, because it seemed like the ADC was saturating at the 6dB gain setting, which suggests that the input voltage is ceratinly > 2V, and AS55_Q is what is used for MICH control in the DRMI. All of my noise budgeting work over the last few months used this setting, I wonder if they are all invalid 

Now that I think about this a bit more - this problem shouldn't be significant for the usual LSC degrees of freedom when in lock, as the huge DC gain of the loop should squish large DC values of the error signals, and so there shouldn't be any danger of overloading the LT1125. But I don't know if we are being hurt by this effect when flashing through resonances, when the PDH horn-to-horn voltage can be quite high (which is in principle a good thing?). I don't know if there is any "hysterisis" effect where the overloaded quad IC has some relaxation time before it returns to normal operation, and if we are being limited in our ability to catch lock because if this effect. 

The concerns remain valid for th ALS demodulated error signals though, for which the signals will remain large throughout.

this is the note from Hartmut Grote on this topic from 2004

After discussing with Koji, we looked at the aLIGO incarnation of this board. Interestingly, it too has a similar topology of 4 switchable gain stages with gains of 24, 12, 6 and 3dB. The main differences are that they use single Op27 ICs instead of the quad LT1125s, and also, they use a different combination of feedback resistors to realize the various gains. 

We considered upping the feedback resistance (R15, R143) on the 24dB gain stage of our boards from (1k, 66.5ohms) to (3k, 200ohms) as on the aLIGO boards - but this doesn't really help? Because KCL demands that the same current flow in R15 and R143, and so the output Vsat of the op amp and its max current driving capabilities in combination determine if the inverting input can follow the non inverting input?

As Hartmut points out in his note, he was able to access the full range of ADC voltages when the gain was set to 3dB, despite the fact that the LT1125 was still getting internally saturated. Operating with minimum 24dB whitening gain doesn't really solve the problem either because the problem just gets shifted to the next gain stage in the chain, and we still have saturation. I also don't have a feeling for how much differential voltage these LT1125s can sustain before they are damaged - I guess the planned THD check will reveal if they are okay or not.

It seems to me like the only way to truly fix this problem of one stage saturating and screwing up the others is to use single Op27s (or equivalent) in place of the quad LT1125s. The aLIGO design also has a series resistance to the non-inverting input - this can help prevent current overdraw from the previous stage (due to a lowered input impedance of the OpAmp - but I wonder how low this can go?).

I plan to do some characterization of this problem. The plan is to use THD as a metric for whether we are having hidden saturations. Pg 9 of the LT1125 datasheet tells us what fraction of THD to expect. I will use one of the several unused DAC channels available at the LSC rack to drive a 100Hz sine wave into one of the inputs of the whitening chassis, and measure the THD up to a reasonable harmonic number (will probably be set by the ADC noise) for (i) various whitening gain settings and (ii) various input signal amplitudes.

The motivation is to attempt to quantify the problem better:

1. How bad is it to have one or more of the OpAmps in the quad IC either saturated to its voltage rails, or max output current?
2. Can we reproduce Hartmut's observations?
3. Are the OpAmps already irreversibly damaged because of extended abuse?

Then we can decide what, if anything, to do about this issue.

{Mayank, Yehonathan}

We measured the noise at the WF1 (REFL11) and WF2 (AS55) boards at the LSC rack with and without whitening filter. We switch the filter on and off by switching off and on the unwhitening in the PDs filter bank.

Attachment 1 shows the measurements.

Attachment 2 shows the ratio between the noise with and without whitening filter. I also plot the inverse of the unwhitening MEDM filter (all the unWhite filters were the same). I tune the gain of that filter to match the ratio of the AS55 whitening noises.

This is because I couldn't match the ratio of the REFL11 noises.

Moreover, the overall gain doesn't make sense to me. AS55 whitening has a gain of 24db and REFL11 has a gain of 18db. I'm not entirely sure where these values should show up. Also seems like REFL11 whitening has more gain than AS55 whitening. Will have to investigate more tomorrow.

DTT has only SUS and "X02" channels under C1 in the drop down channel selection menu.  Basically, we can't measure any fast channels with DTT.  I keep getting the error: "Unable to select testpoints."  Sadface.

Similar things are true for DataViewer.  The same limited number of fast channels, and no data found:

Server error 13: no data found
datasrv: DataWriteRealtime failed: daq_send: Illegal seek

Is this a framebuilder problem?  Is this something that the CDS team has on the to-do list?

Test points for the SUS channels should be there.  They have been working previously this week.  Possibly break down points include awgtpman, mx_streams, and the fb itself.  I'll look into that.

As far as other fast channels, there are no other fast front ends running than the suspensions ones we have.  Until additional channels get connected to the front ends and the models updated, those are the channels we have available.  However I am working on getting c1ioo up and running, and we can try connecting in some PEM channels today to the c1sus front end's 4th ADC.

Edit:

I tried starting a fresh instance of the frame builder, but when I brought the old copy down, it left a pair of zombie or dead mx_stream processes running on c1sus . Basically c1mcs and c1rms were still running, while c1x02 and c1sus came down.  I tried to kill the processes but this caused the c1sus machine to crash.  In the past I've killed left over mx_stream processes running after the frame builder has gone down, but I've never seen them crash the computer.  I'm unsure why this happened since we haven't done any updates of the code, just updated models and daq configuration files.

When adding the ETMX DAQ channels using the daqconfig gui (located in /opt/rtcds/caltech/c1/scripts/) on C1SCX.ini, we forgot to set the acquire flag to 1 from 0.

So the frame builder was receiving the data, but not recording it.

We have since then added ETMX and the C1SCX.ini file to Yuta's useful "activateDAQ.py" script in /opt/rtcds/caltech/c1/chans/daq/, so that it now sets the sensor and SUSPOS like channels to be acquired at 2k when run.  You still need to restart the frame builder (telnet fb 8087 and then shutdown) for these changes to take effect.

The script now also properly handles files which already have had channels activated, but not acquired.

The VEA laptop asia was configured to be able to connect to too many WiFi networks - it was getting conflicted in its default position at the vertex and trying to hop between networks, for some reason trying to connect to networks that had poor signal strength. I deleted all options from the known networks except 40MARS. Now the network connection seems much more stable and reliable.

The model of our martian wifi router (NETGEAR R6400) was found in the FBI router list to be rebooted asociated with the malware "VPNFilter" issue.

I checked the attached devices and found bunch of (legit) devices blocked to access the wifi router. This is not an immediate problem as most of the packets do not go through the wifi router. But potentially a problem in some cases like Wifi enables GPIB adapters. So I marked them to be "allowed".

In this opprtunity, I have updated the firmware of the wifi router and this naturally involved rebooting of the device.