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ID Date Author Type Categoryup Subject
  11513   Tue Aug 18 03:56:09 2015 ericqUpdateLSClocking efforts

Now that the updated ALS is stable, and the PRC angular FF is revived, I've been working on relocking PRFPMI. While the RMS arm fluctuations are surely smaller than they used to be, there is no noticible difference to the ears when buzzing around resonance, but this doesn't really mean much. 

Frustratingly, I am not able to stably blend in any RF CARM error signal into the slow length control path (i.e. CARM_B). Bringing AS55 Q into DARM with the 20:0 integrator is working fine, but we really need to supress CARM to get anywhere. I'm not sure why this isn't working; poking around into the settings that were used when we were regularly locking didn't turn up any differences as far as I could tell. Investigations continue... 

Some minor changes to the locking script were made, to account for the increased ALS displacement sensitivity from the longer delay line. 


Since the ALS is now in a fairly stable state, I've updated the calibrated PSD template at /users/Templates/ALS/ALS_outOfLoop_Ref.xml, and added some coherence plots for some commonly coupled quantities (beat signal amplitude, IR error signal, green PDH error signal and green transmission). 

Attachment 1: newALSref.pdf
newALSref.pdf
Attachment 2: xCoh.pdf
xCoh.pdf
Attachment 3: yCoh.pdf
yCoh.pdf
  11515   Wed Aug 19 00:55:35 2015 IgnacioUpdateLSCLSC-YARM-EXC to LSC-YARM-IN1 TF measurement + error analysis

Yesterday, Rana, Jessica and I measured the Transfer function from LSC-YARM-EXC to LSC-YARM-IN1. 

The plot below shows the magnitude and the phase of the measured transfer function. It also shows the normalized standard error in the estimated transfer function magnitude; the same quantity can be applied to the phase, only in this case it is interpreted as its standard deviation (not normalized). It is given by

 \frac{[1-\gamma_{xy}^2(f)]^{1/2}}{|\gamma_{xy}(f)|\sqrt{2n_{d}}}

where \gamma_{xy}^2(f) is the ordinary coherence function and n_{d} is the number of averages used at each point of the estimate, in the case here we used 9 averages. This quantity is of interest to us in order to understand how the accuracy of transfer function measurement affects the ammount of subtraction that can be achieved online.

 

Since this transfer function is flat from 1-10 Hz (out of phase by 180 deg), this means that we can apply our IIR wiener filters direclty into YARM without taking into account the TF by prefiltering our witnesses with it. Of course this is not the case if we care about subtractions at frequencies higher than 10 Hz, but since we are dealing with seismic noise this is not a concern.

The coherence for this transfer function measurement is shown below,

  11518   Thu Aug 20 02:31:09 2015 ericqUpdateLSCPRFPMI is back

PRFPMI locking has been revived.

I've had 6 5min+ locks so far; arm powers usually hit ~125 for a recycling gain of about 7; visibility is about 75%

The locking script takes a little under 4 minutes to take you from POX/POY lock to PRFPMI if you don't have to stop and adjust anything.

At Koji's suggestion, I used digital REFL11 instead of CM_SLOW, which got me to a semistable lock with some RF, at which time I could check the CM_SLOW situtation. It seemed like the whitening Binary IO switch got out of sync with the digital FM status somehow... 

I've been making the neccesary changes to the carm_cm_up script. I also added a small script which uses the magnitude of the I and Q signals to set the phase tracker gain automatically based on some algebra Koji posted in an ELOG some years ago. 

The RF transition seems much smoother now, most likely due to the improved PRC and ALS stability. In fact, it is possible to hold at arm powers of >100 solely on the digital servos; I don't think we were able to do this before until the AO had kicked in. 

Right now I'm losing lock when trying to engage the CARM super boost. I also haven't switched the PRMI over to 1F signals yet. Would be good to hook the SR785 back up for a loop TF, but I'll stop here for tonight since our SURFs are presenting bright and early tomorrow morning. 

Attachment 1: lock.pdf
lock.pdf
  11524   Sat Aug 22 15:48:32 2015 KojiSummaryLSCArm locking recovery

As per Ignacio's request, I restored the arm locking.

- MC WFS relief

- Slow DC restored to ~0V

- Turned off DARM/CARM

- XARM/YARM turned on

- XARM/YARM ASS& Offset offloading

  11528   Tue Aug 25 04:15:51 2015 ericqUpdateLSCPRFPMI is back

More PRFPMI locks tonight. Right now, it's been locked for 22+ minutes, though with the PRMI still on 3F signals. I think the MC2/AO crossover needs some reshaping; there's a whole bunch of noise injected into CARM around 600 Hz, which is where the two paths differ by 180deg. (Addendum: broke lock at ~27 minutes, 4:16AM)

For most of this lock, sensing matrix excitations have been running for daytime analysis. 

The nominal IMC loop gain / EOM crossover were making the AO path very marginal. I've adjusted the nominal settings and autolocker scripts. 

There was some weird behavior of X green PDH earlier... Broadband RIN seen in ALS-TRX, coherent with the DC output of the beat PD, so really on the light. I fiddled with the end setup, and it mostly went away, though I didn't intentionally change anything. Disconcerting. 

  11533   Thu Aug 27 02:09:14 2015 ericqUpdateLSCAUX X Laser Current Changed

I spent some time tonight chasing down the cause of huge RIN in the X green PDH transmitted light, which I had started seeing on Monday. This was preventing robust locking, since the ALS sensing noise was ~10x worse above 50Hz, thus making the AO transition much flakier (though, impressively, not impossible!)

I went down to the X end, and found that turning the laser diode current down by 0.1A (from 2.0 to 1.9) smoothed things out completely. Unfortunately, this causes the power to drop, from GTRX of 0.45 to 0.3, but the ALSX sensitivity is unchanged, as compared with the recenent "out of loop" template. 

This also seems to have changed the temperatures of the good modes, as no beat was evident at the previously good temperature. Beats were found at +5400 and +10500 counts on the slow servo offset slider; I suspect the third lies around the edge of the DAC range which is why I couldn't uncover it. In any case, I've parked it at 10500 for now, and will continue locking; nailing it down more precisely and offloading the slider offset to the laser controller will happen during daytime work...

  11534   Thu Aug 27 04:23:04 2015 ericqUpdateLSCPRFPMI is back

Got to a 40 minute lock tonight. All other locks broke because of me poking something. 

I redid some sensing excitations, right after carefully measuring the CARM OLG at its excitation frequency, so I can get at the open loop PD response. 

I also used a MCL feedforward filter of Ignacio's which did not inject any observable noise into the CARM error signal during PRFPMI lock. He will make some elog about this. 

  11536   Fri Aug 28 02:20:35 2015 IgnacioUpdateLSCPRFPMI and MCL FF

A day late but here it is.

Eric and I turned on my SISO MCL Wiener filter elog:11535 during his PRFPMI 40min lock. We looked at the CARM_IN and CARM_OUT signals during the lock and with the MCL FF on/off. Here is the spectra:

  11556   Tue Sep 1 17:07:06 2015 ericqUpdateLSCIR beatnote confusion

There has been some discussion here and there of using fiber coupled IR beats for ALS. A few weeks ago, and again today with Eric G, I poked around a bit with the fiber box Manasa set up for the FOL scheme. 

Somehow, the IR beatnote is ~1000 times smaller than expected, both with the Thorlabs fiber coupled PD and a fiber coupled NF 1611.

In essence, after the fiber combiner, there is on the order of hundreds of uW each of PSL and AUX X IR light. The output of the fiber from each source looks nice and gaussian. The DC output of the 1611 indicates that it is seeing the right level of light. The green beatnote exists with good SNR at twice the IR beat frequency, so we know that the IR beat isn't some junky modes beating. 

For the 1611, we would expect an RF signal of ~1mW*0.9A/W*700V/A -> .6V / +8dBm. Instead we see ~2mV / -40dBm.

Incidentally, there is some 20mV / -20dBm signal at ~400kHz, presumably from the green PDH modulation at ~200k. 

(The level out of the thorlabs PD is similarly tiny; it doesn't have a DC output though, so we don't know the DC power that the active surface really sees. Not that I expect it to be much different, but the NF just makes it easier to estimate.)

The only things that should be able to cause the beat to be smaller than expected from the power levels are mode matching and polarization matching. All the fibers are single mode, so mode matching should be effectively 100%. Maybe somthing fishy is happening with the polarizations, but they'd have to be really maliciously close to orthogonal to cause this level of mismatch. 

Maybe we just don't understand the splitter/combiners. Mysterious.

  11557   Tue Sep 1 17:38:58 2015 ericqUpdateLSCIR beatnote confusion
Quote:

Maybe we just don't understand the splitter/combiners.

After an email from Eric G, I think this is the case.

If you read the text at Thorlabs about Fiber-Based Polarization Beam Combiners/Splitters, it suggests that these things take input beams both aligned to their slow axes, and outputs one field along the slow, and one orthogonal to it on the fast axis. Which is exactly what we don't want for a beat. 

  11559   Wed Sep 2 13:44:04 2015 ericqUpdateLSCIR beatnote confusion

From the AFW website about our product, the POBC-64-C-1-7-2-25dB:

port1 slow axis -> port3 slow axis 
port2 slow axis -> port3 fast axis

crying

  11568   Thu Sep 3 17:15:26 2015 ericqUpdateLSCIR beatnote confusion

I was thinking that the "FOSC" product line (which is called a "coupler" instead of a "splitter/combiner") was what we wanted. 

Koji brought to my attention that the 90/10 splitters we already have are of this line. So, I rigged a few up to shine a hopefully beating pair of fields on the fiber coupled thorlabs PD. 

I was able to get ~80uW each of PSL and AUX X light on the PD, which produced a -10dBm beatnoteyes Thus, I think these FOSC splitters are indeed what we want. 

I then threw this IR beatnote at our ALS signal chain. The beatnote was too big to throw through our ~+27dB RF amps, so I just sent the -10dBm over to the LSC rack.

The IR beat spectrum is somwhat noisier from 10-100Hz, but, more interesting, is that the sub-4Hz noise is identical in the two beats, and very coherent. This excludes ALS noise arising from anything happening in the green beat optics on the PSL table.

Obviously, the high frequency noise is largely the same and coherent too, but also coherent with the AUX X PDH control signal, so it is understood. 

Attachment 1: GREENvIRbeats.pdf
GREENvIRbeats.pdf
  11571   Fri Sep 4 04:05:51 2015 ericqUpdateLSCDRMI locked on 1F and 3F

Thanks to some expertly timed coffee from Ignacio, I have been able to achieve indefnite locks of the DRMI, first on a 1F/3F mix (P:REFL11, S: REFL165, M:AS55), and then purely on 3F (P:REFL33, S:REFL165, S:REFL165). MICH is currently actuated on the ITMs. 

I saved a snapshot of the current settings so I don't lose my settings. I think one thing that prevented earlier recipies from working is that whitening gains may have changed, which we don't typically note down when reporting input matrix settings

My current settings for 3F locking:

REFL33:

+30dB whitening gain, +136 demod phase

PRCL = 9 x I - 200 counts

REFL165:

+24dB whitening gain, +3 demod phase

SRCL = 1 x I, MICH = 5 x Q - 1000counts

MICH: G=-0.03; Acq FM4/5; Trig 2/3/6/9

PRCL: G=-0.003; Acq FM4/5; Trig 1/2/6/9

SRCL: G=0.2; Acq FM4/5; Trig 2/3/6/9

I've injected excitations into the control filter outputs via the LSC-FFC FMS (and notched the frequencies in the control filters themselves), and noted GPS times for offline sensing analysis. (Namely the 10 minutes following 1125398900)

Handing off to pure 3F was a little finicky at first, I needed to use some pretty large offsets in the MICH_B and PRCL_B FMs. (-1000 and -200 counts respectively). Once these offsets were found, the DRMI can acquire on 3F. Alignment is pretty important, too.  Acquiring is much faster when the loop gains are "too high." i.e. I see a fair amount of gain peaking at ~300Hz. Nevertheless, things are stable enough as is that I didn't feel like digging into reducing the gains to quieter values. 

  11575   Fri Sep 4 09:36:48 2015 SteveUpdateLSCIR beatnote confusion.....

 

Quote:

I was thinking that the "FOSC" product line (which is called a "coupler" instead of a "splitter/combiner") was what we wanted. 

Koji brought to my attention that the 90/10 splitters we already have are of this line. So, I rigged a few up to shine a hopefully beating pair of fields on the fiber coupled thorlabs PD. 

I was able to get ~80uW each of PSL and AUX X light on the PD, which produced a -10dBm beatnoteyes Thus, I think these FOSC splitters are indeed what we want. 

I then threw this IR beatnote at our ALS signal chain. The beatnote was too big to throw through our ~+27dB RF amps, so I just sent the -10dBm over to the LSC rack.

The IR beat spectrum is somwhat noisier from 10-100Hz, but, more interesting, is that the sub-4Hz noise is identical in the two beats, and very coherent. This excludes ALS noise arising from anything happening in the green beat optics on the PSL table.

Obviously, the high frequency noise is largely the same and coherent too, but also coherent with the AUX X PDH control signal, so it is understood. 

FOSC-2-64-50-L-1-H64F-2
Single mode coupler, 2x2, 1064nm +/-20nm, 50/50 ratio, 900micron loose tube jacket, Hi1060flex fiber, 1m fiber length, FC/APC connectors

Four of these items ordered yesterday from http://afwtechnologies.com.au/sm_coupler.html

  11577   Fri Sep 4 15:20:31 2015 ericqUpdateLSCVertex Sensing

I've now made a collection of sensing matrix measurements. 

In all of the plots below, the radial scale is logarithmic, each grid line is a factor of 10. The units of the radial direction are calibrated into demod board output Volts per meter. The same radial scale is used on all plots and subplots.

I did two PRMI measurements: with MICH locked and excited with either the ITMS or the BS + PRM compensation. This tells us if our PRM compensation is working; I think it is indeed ok. I though I remembered that we came up with a number for the SRM compensation, but I haven't been able to find it yet. 

The CARM sensing int he PRFPMI measurement has the loop gain at the excitation frequency undone. All excitations were simultaneously notched out of all control filters, via the NotchSensMat filters. 

The angular scale is set to the analog I and Q signals; the dotted lines show the digitial phase rotation angle used at the time of measurement. 

Attachment 1: PRFMI_ITM.pdf
PRFMI_ITM.pdf
Attachment 2: PRFMI_BS.pdf
PRFMI_BS.pdf
Attachment 3: DRMI.pdf
DRMI.pdf
Attachment 4: PRFPMI.pdf
PRFPMI.pdf
  11578   Fri Sep 4 20:06:23 2015 ranaUpdateLSCDRMI locked on 1F and 3F

Nice going. I think the LLO / LHO scheme is to acquire on 1F and then cdsutils avg to get the 3F offsets. The thinking is that that 1F signals have less intrinsic offset than the 3F signals, so we want to be use digital offsets for the 3F locks.

  11588   Thu Sep 10 01:09:20 2015 ranaUpdateLSCMoved LSC sensing matrix notch frequencies

We looked at the DRMI noise spectrum and chose new excitation frequencies such that the lines are lower in frequency than before (~300 Hz instead of 800 Hz) and also not in some noisy region.

New filters is saved and loaded for all LSC DOFs.

Attachment 1: NewLSCnotches.png
NewLSCnotches.png
  11589   Thu Sep 10 04:23:00 2015 ericqUpdateLSCMoved LSC sensing matrix notch frequencies

Frequencies are:

  • CARM: 309.21 Hz
  • DARM: 307.88 Hz
  • MICH: 311.1 Hz
  • PRCL: 313.31 Hz
  • SRCL: 315.17 Hz

POP110 and POP22 demod angles were adjusted for DRMI lock. 

Last week, I never achieved a fully 1F lock, REFL165 was used for SRCL. Tonight, we created input matrix settings for pure 1F locking, and did some signal mixing to reduce the PRCL to SRCL coupling. The PRCL to MICH coupling was already low, since AS55 is fairly insensitive to PRCL. 

Similarly, for the 3F signals, some signal mixing of REFL33I and REFL165Q was used to reduce the PRCL to MICH coupling. The PRCL to SRCL coupling in REFL165 isn't too bad, so no compensation was done. Interestingly, in this setting, the 3F MICH and SRCL signals agree with the 1F signals on their zero crossing, so no offsets are needed. REFL33 I does need an offset, however, to match the REFL11I PRCL zero crossing. 

The DRMI acquires faster with SRCL set to 165I. Once acquired, the 1F/3F can be made smoothly, and both settings are very stable. The sensing matrix in each setting is consistent with each other. (The PRCL and SRCL lines in AS55 change, but really I shouldn't even plot them, since they're not very coherent). 

For some reason, these show a sign flip relative to last week's measurements. The relative angles are consistent, though. 

Next up is finding the right coefficient for the SRM in the MICH output matrix, when actuating on the BS. 

Attachment 1: DRMI_1F.pdf
DRMI_1F.pdf
Attachment 2: DRMI_3F.pdf
DRMI_3F.pdf
  11594   Mon Sep 14 16:50:12 2015 ericqUpdateLSCQuick note

Just a heads up while I'm out for a bit: the delay line is currently installed in the 55MHz modulation path. 

I'll be back later, and will revert the setup.

  11596   Mon Sep 14 23:12:49 2015 ericqUpdateLSC55MHz modulation phase effect on PRMI

With the adjustable delay line box installed in the 55MHz modulation path, I've measured the PRMI sensing matrix as a function of delay / relative phase between the 11MHz and 55MHz modulations. The relative frequency difference of 44MHz tells us that this should be cyclical after ~23nsec of delay, but losses in the delay cable change this; see Koji's elogs about the modulation cancellation setup for details. 

TL;DR: Nothing really changes, other than REFL33 optical gain. MICH/PRCL angles remain degenerate.


The results aren't so surprising. The demod angles for the 55MHz diodes don't even change, since the same 55MHz signal is used for the modulator and demodulators, so delaying it before the split should go unnoticed. Most of these measurements were made during the same lock stretch, PRCL on REFL11 I and MICH on AS55Q.

The only signals we would expect to change much are ones that have significant contriubtions from field products influenced by both modulations. None of the 1F PDs are like this, nor is REFL165. REFL33 is the odd man out, where the +44MHz field produced as a -11MHz sideband on the +55MHz sideband beats with the +11MHz sideband (and the same with the signs flipped). I made a simulation for the 40m poster at the March 2015 LVC meeting, but I don't think it ever made it to the ELOG. 

So:

Here are the results for the 0ns and 4ns cases, as an illustration of what changes (REFL33), and what doesn't (everything else). Again, these are calibrated to Volts out of the analog demod boards per meter of DoF motion. 

 

So, since REFL33 is the only one really changing, let's just look at it by itself:

Qualitatively, the change in magnitude looks similar to the simulation result. The demod angles fall by some roughly linear amount. The angle difference is even more stationary than predicted there, though. 

Attachment 1: PRMI_CAR_0ns.pdf
PRMI_CAR_0ns.pdf
Attachment 2: PRMI_CAR_4ns.pdf
PRMI_CAR_4ns.pdf
Attachment 3: delaySweep_nominal.pdf
delaySweep_nominal.pdf
Attachment 4: 55delay_PRMI_REFL33.pdf
55delay_PRMI_REFL33.pdf
  11597   Tue Sep 15 01:14:10 2015 ranaSummaryLSCneed to check LSC Whitening switch logic ... again

Tonight we noticed that the REFL_DC signal has gone bipolar, even though the whitening gain is 0 dB and the whitening filter is requested to be OFF.

We should check out the switch operation of several ofthe LSC channels in the daytime - where is the procedure for this diagnostic posted?

  11598   Tue Sep 15 15:01:23 2015 ranaSummaryLSCdisabling the LSC AA filters + mod to whitening

While investigating the BIO situation with the LSC machine and the iscaux2 processor last night, we wondered if maybe the Anti-Aliasing filters were mistakenly disabled. But why do we need these anyway?

Our ADCs digitize at 64 kHz and there is a digital lowpass in the IOP at 5 kHz before we downsample to 16 kHz. So mainly we're trying to prevent some aliasing at the 64 kHz IOP rate. But our analog AA filter is a 8th order ELP at 7570 Hz, so its overkill.

So, I propose that we bypas the AA via hardwiring the board and implement a 10 kHz pole in the whitening board (D990694) before the whitening by turning R127, etc. into a 0.1 uF cap. Along with the 100 Ohm series resistor, this will make a pole at ~15 kHz. Probably ought to check that the input resistor is metal film. Also, if we replace C158/C159, etc. with a 0.47 nF cap, we'll get 2 poles at 35 kHz to limit the higher frequencies from saturating.

  11599   Tue Sep 15 15:10:48 2015 gautam, ericq, ranaSummaryLSCPRFPMI lock & various to-do's
I was observing Eric while he was attempting to lock the PRFPMI last night. The handoff from ALS to LSC was not very smooth, and Rana suggested looking at some control signals while parked close to the PRFPMI resonance to get an idea of what frequency bands the noise dominated in. The attached power spectrum was taken while CARM and DARM were under ALS control, and the PRMI was locked using REFL_165. The arm power was fluctuating between 15 and 50. Most of the power seems to be in the 1-5Hz band and the 10-30Hz band.

Rana made a number of suggestions, which I'm listing here. Some of these may directly help the above situation, while the others are with regards to the general state of affairs.

  • Reroute both (MC and arm) FF signals to the SUS model
  • For MC, bypass LSC
  • Rethink the MC FF -
  • Leave the arm FF on all the time?
  • The positioning of the accelerometer used for MC FF has to be bettered - it should be directly below the tank
  • The IOO model is over-clocking - needs to be re-examined
  • Fix up the DC F2P - Rana mentioned an old (~10 yr) script called F2P ratio, we should look to integrate the Python scripts used for lock-in/demod at the sites with this
  • Look to calibrate MC_F
  • Implement a high BW CARM servo using ALS
  • Gray code implementation for EPICS gain-stepping

Attachment 1: powerSpec0915.pdf
powerSpec0915.pdf
  11601   Tue Sep 15 18:35:21 2015 ericqSummaryLSCsome further notes

About the analog CARM control with ALS:

We're looking at using a Sigg designed remotely switchable delay line box on the currently undelayed side of the ALS DFD beat. For a beat frequency of 50MHz, one cycle is 20ns, this thing has 24ns total delay capability, so we should be able to get pretty close to a zero crossing of the analog I or Q outputs of the demod board. This can be used as IN2 for the common mode board. 

Gautam is testing the functionality of the delay and switching, and should post a link to the DCC page of the schematic. Rana and Koji have been discussing the implementation of the remote switching (RCG vs. VME). 

I spent some time this afternoon trying to lock the X arm in this way, but instead of at IR resonance, just wherever the I output of the DFD had a zero crossing. However, I didn't give enough thought to the loop shapes; Koji helped me think it through. Tomorrow, I'll make a little pomona box to go before the CM IN2 that will give the ALS loop shape a pole where we expect the CARM coupled cavity pole to be (~120Hz), so that the REFL11 and ALS signals have a similar shape when we're trying to transition. 

The common mode board does have a filter for this kind of thing for single arm tests, but puts in a zero as well, as it expects the single arm pole, which isn't present in the ALS sensing, so maybe I'll whip up something appropriate for this, too. 

  11603   Tue Sep 15 20:44:13 2015 gautamSummaryLSCChecking the delay line phase shifter DS050339
I checked out the delay line phase shifter D050339, (theory of operation here) this afternoon. I first checked that the power connection was functional, which it was, though the power connector is is not the usual chassis one (see image attached, do we need to change this?).

The box has two modes of operation - you can either change the delay by flipping switches on the front panel or via a 25pin D-sub connector on the back (the pin numberings for this connector on the datasheet are a little misleading, but I determined that pins 1-9 on the D-sub connector correspond to the 9 delays on the front panel in ascending order, pin 10 is the mode selector switch, should be high for remote operation, pins 11 and 13 are NC, pin 12 is VCC of 5V, and pins 14-25 are grounded). I first checked the front-panel mode of operation, using an oscilloscope to measure the delay between the direct signal from the Fluke 6061 and the output from the D050339. This corresponds to the first set of datapoints in the plot attached (signal was 100MHz sine wave).

I then used a 25 pin D sub breakout boards to check the remote operation mode as well, which corresponds to the second set of datapoints in the plot attached. For this measurement, I used the Agilent network analyzer to measure the phase lag between the direct signal (for all delays, I measured the phase lag at 100MHz, having first calibrated the "thru" path by connecting the R and A inputs of the network analyzer using a barrel BNC) and the delayed output from the box, and then converted it to a time delay.

Both sets of data are linear, with a slope nearly equal to 1 as expected. I conclude that the box is functioning as expected. Right now, Koji is checking a board which will be used to remotely control this box. On the hardware side it remains to make a cable going from the DS050339 Dsub input to the driver board output (also 25 pin Dsub).
Attachment 1: IMG_20150915_193100.jpg
IMG_20150915_193100.jpg
Attachment 2: Calibration.pdf
Calibration.pdf
  11605   Wed Sep 16 03:44:18 2015 KojiUpdateLSCRF micky mouse

1. POP110 RF amps are powered from the cross connect. But that +15V block has GND connections that are not connected to the ground.
    i.e. The ground potential is given by the signal ground. (Attachment 1)

    This is caused by the misuse of the DIN connector  blocks. The hod side uses an isolated block assuming a fuse is inserted.
    However, the ground sides also have the isolated blocks

2. One of the POP110 RF cable has a suspicious shiled. The rigidity of the cable is low, suggesting the broken shield. (Attachment 2)

Attachment 1: IMG_20150915_231038191.jpg
IMG_20150915_231038191.jpg
Attachment 2: IMG_20150915_234257144.jpg
IMG_20150915_234257144.jpg
  11606   Wed Sep 16 15:04:33 2015 ericqSummaryLSCDC PD Whitening Board Fixed
Quote:

Tonight we noticed that the REFL_DC signal has gone bipolar, even though the whitening gain is 0 dB and the whitening filter is requested to be OFF.

Fixed! I noticed that whitening gain changes weren't having any effect on CM_SLOW. I then checked REFL_DC, where this also seemed to be the case. Since the gain is controlled via VME machine, and whitening filter switching is controlled via RCG, I figured there must be something wrong with the board. I checked all of the DC PD signals, which share a whitening filter board, and they all had the same symptoms. 

I went and peeked at the board, and it turns out the backplane cable had fallen off. frown

I plugged it in, things look ok. 

  11609   Thu Sep 17 03:48:10 2015 ericqSummaryLSCsome further notes

Something odd is happening with the CM board. Measuring from either input to OUT1 (the "slow output") shows a nice flat response up until many 10s of kHz. 

However, when I connect my idependently confirmed 120Hz LPF to either input, the pole frequency gets moved up to ~360Hz and the DC gain falls some 10dB. This happens regardless if the input is used or not, I saw this shape at a tee on the output of the LPF when the other leg of the tee was connected to a CM board input. 

This has sabotaged my high bandwidth ALS efforts. I will investigate the board's input situation tomorrow.

  11611   Thu Sep 17 13:06:05 2015 ericqSummaryLSCLow input impedance on CM board

As it turns out, our version of the common mode board does not have high input impedence. I think this is what is messing with the lowpass. 

I added photos of the PCB to our 40m DCC page about this board: D1500308, wherein you can see that we have Revision B. 

On the aLIGO wiki's CommonModeServo page, one finds that high input impedence was added in Revision E. At LIGO-D040180, one finds this was implemented via an additional dual AD829 instrumentation amplifier stage before the input amplification stage that exists on our board.

Also, I find that the boosts installed are the default 40:4k, 1k:20k, 1k:20k, 500:10k pole zero pairs. Given our 30-40kHz UGF for CARM thus far, maybe we would like to lower some of these boost corner frequencies, to actually be able to use them; so far we only use the first two.

  11613   Thu Sep 17 17:27:01 2015 gautamUpdateLSCRF micky mouse - dodgy DIN connector blocks fixed

[Steve, gautam]

We fixed the problematic DIN connectors on 1Y2, by swapping out the 3 DIN connector blocks that were of the wrong type (see attached image for the difference between the types appropriate for "Live" and "Ground").

Before doing anything, Eric turned the Wenzel multiplier off. We have not turned this back on.

Then we turned off the power supply unit at the base of 1Y2, removed the connectors from the rail, swapped out the connectors, reinstalled them on the rail, and turned the power supply back on. After swapping these out, we verified with a multimeter that between each pair of "Live" and "Ground" blocks, there was ~15V. We could now use the third unused pair of blocks to power the delay line phase shifter box, though for the moment, it remains powered by the bench power supply. 

Quote:

1. POP110 RF amps are powered from the cross connect. But that +15V block has GND connections that are not connected to the ground.
    i.e. The ground potential is given by the signal ground. (Attachment 1)

    This is caused by the misuse of the DIN connector  blocks. The hod side uses an isolated block assuming a fuse is inserted.
    However, the ground sides also have the isolated blocks

2. One of the POP110 RF cable has a suspicious shiled. The rigidity of the cable is low, suggesting the broken shield. (Attachment 2)

 

Attachment 1: DIN_rail_terminal.jpg
DIN_rail_terminal.jpg
  11614   Thu Sep 17 19:42:43 2015 KojiUpdateLSCRF micky mouse - dodgy DIN connector blocks fixed

1. The delay-line box is now hooked up to the cross connect +15V supply.

2. The broken RF cable was fixed.

It is actually the POP22 cable.
Therefore, we might see significant change of the signal size for POP22.
Be aware.

RG405 + SMA connector rule

- Don't bend the cable at the connector.

- Always use a cap on the connector. It is a part of the impedance matching.

- Use transparent shrink tube for strain relieving and isolation. This allow us to check the condition of the shield without removing the cover.

Attachment 1: IMG_20150917_190635033.jpg
IMG_20150917_190635033.jpg
Attachment 2: IMG_20150917_192551919.jpg
IMG_20150917_192551919.jpg
  11616   Fri Sep 18 08:03:53 2015 ranaUpdateLSCRF micky mouse - dodgy DIN connector blocks fixed

Steve and I turned on the box this morning so that the IMC would lock again.

For future reference, remember that one should turn off the Marconi output before turning off the RF distribution box. Don't drive the input of unpowered RF amps.

 

  11617   Fri Sep 18 08:04:09 2015 ranaUpdateLSCRF micky mouse - dodgy DIN connector blocks fixed

Steve and I turned on the box this morning so that the IMC would lock again.

For future reference, remember that one should turn off the Marconi output before turning off the RF distribution box. Don't drive the input of unpowered RF amps.

 

  11619   Fri Sep 18 11:59:08 2015 ericqUpdateLSCAUX X Laser Current Reverted

Once again, the transmitted X green beam was showing enormous intensity fluctuations (50x higher than normal). Last month, I reduced the AUX X laser current from 2.0A to 1.9A, which I thought had fixed it somehow.

However, when I sent to the end to check it out today, I found the SR560 which is there to amplify the green PDH error signal before being sent to the AA board was overloading. Not so surprising, since the error signal was similarly noisy as the transmitted light. 

I turned the SR560 gain down, and, after relocking, the transmitted light was stable. I've turned the AUX X laser current back up to 2.0A, it's previous nominal value, and the green transmitted light is still stable. 

I'm a little mystified that the 560 could intefere with the loop, since it is not in the feedback path. Could it be that when it is overloading, it sends garbage backwards out of the inputs? But even then, its input is not connected to the real error point, but the buffered monitor port. Could it be interfering via the power line?

Before, I had hesitated adding gain to the PDH board's monitor point for DAQ purposes, because the motivation of the port is to provide a 1:1 version of the real error signal, and I didn't want to add gain to the AA board, because we normally don't have gain in those boards, and I didn't want to surprise future people. The SR560 was meant to be temporary, but as often happens, it was forgotten. Now, I think I will add gain to the error monitor buffer stage of the PDH boards. 

  11620   Fri Sep 18 13:33:17 2015 ericqUpdateLSCFast ALS troubles - Noise at 36kHz

To get around the problems between the pomona LPF and low CM board input impedance, I've placed the LPF at the CM board fast output. This won't work as a permanent solution, since we only want to lowpass the ALS signal, but it should be fine for a single arm test. 

However, I kept getting blown out of lock when turning up the AO gain, but well before I really expect any real action from the fast path. Looking at the OLTF, I was seeing some large spike at ~36kHz nearing 0dB loop gain with unstable phase. This prompted me to look at the ALS error signal out to higher bandwidth with the SR785; before I only ever looked at it through the digital system. 

So, with the X arm locked via POX11 I, and ITMY misaligned to use AS55 as an out of loop sensor, I measured the spectrum of the I ouput of the ALS X demod board (which was set to be near a zero crossing via the delay line), and the Q Mon of the AS55 demod board. 

Both ALS and AS55 show a sharp line at around 36.5kHz, so something is really happening in the IFO at this frequency. Koji might have seen an indication of this back in March.

What's going on here? And what would be different about PRFPMI that wouldn't have made this a problem for locking?

Attachment 1: IRlock_noises.pdf
IRlock_noises.pdf
  11621   Fri Sep 18 16:08:41 2015 ericqUpdateLSCFast ALS troubles - Noise at 36kHz

 I looked at REFL11 and REFL55 during PRMI lock - the line is there.

In fact, it is even visible in REFL11 I from a single bounce off of the PRM (ITMs misaligned).

This led me to look at the IMC error point (via the OUT2 on the servo board, no compensation for the input gain). Also there!

Attachment 1: PRMIlock_REFLspectra.pdf
PRMIlock_REFLspectra.pdf
Attachment 2: IMCspectrum.pdf
IMCspectrum.pdf
  11622   Fri Sep 18 19:15:35 2015 ranaUpdateLSCFast ALS troubles - Noise at 36kHz

One the Wiki (https://wiki-40m.ligo.caltech.edu/40mHomePage), we have a Mech Resonance page for mechanical frequencies and a PEM page where we want to list the sources of all of our environmental lines. So please put in an entry when you find out what's at this frequency. This reminds me that I need to upload my MC2 COMSOL eigenmode analysis.

  11632   Tue Sep 22 03:48:18 2015 ericqUpdateLSCDRMI tweaked, briefly held with ALS arms

Given the RF component power supply grounding, POP110, POP22 and REFL165 all changed somewhat. They have all been rephased for the DRMI, as they were before. 

I tweaked the 3F DRMI settings, and chose to phase REFL165I to PRCL, instead of SRCL as before, to try and minimize the PRCL->MICH coupling instead of the SRCL->MICH coupling. 

With these settings, I once locked the DRMI for ~5 seconds with the arms held off on ALS, during which I could see some indications of neccesary demod angle changes. Haven't yet gotten longer, but we're getting there...

  11637   Wed Sep 23 03:08:50 2015 ericqUpdateLSCDRMI + ALS Arms

[ericq, Gautam]

We can reliably lock the DRMI with the arms held off on ALS. yes

I have not been able to hold it at zero CARM offset; but this is probably just a matter of setting up the right loop shapes with enough phase margin to handle the CARM fluctuations ( or figuring out high bandwidth ALS...)

Right now, it's the most stable at CARM offsets larger (in magnitude) than -1. Positive CARM offsets don't work well for some reason. 


The key to getting this to work was to futz around, starting from the misaligned arms DRMI settings, until brief locks were seen (triggering all 3 DRMI DoFs on POP22, since the correct AS110 sign was amiguous). I could tell from how the control signals responded to gain changes that REFL165Q, which was being used as the MICH error signal, was seeing significant cross coupling from both PRCL and SRCL, suggesting the demod angle of REFL165 had to be adjusted. I randomly tweaked the REFL165 demod angle until a 20 second lock was achieved, with excitations running. Then, I downloaded that data and analyzed the sensing matrix. This showed me that the REFL33 demod angle was ok, and the PRCL-from-SRCL subtraction factor determined with the arms misaligned was still valid. The main difference was indeed the SRCL angle in REFL165.

With the REFL165 demod angle properly adjusted, the DRMI would briefly lock, but the DRMI had become somewhat misaligned at this point, and the SRC could be seen to mode hop. Interestingly, the higer order modes had an opposite sign in AS110, with respect to the TM00. At that point, I went back to PRMI on carrier to dither-align the BS and PRM. 

With alignment set, the DRMI would lock on TM00 readily, still only triggering on POP22. I set the AS110 angle, and moved SRCL triggering over to that, which sped up acquisition even more. The input matrix and FM gains from no-arms DRMI still work for acquistion; UGF servos were used to adjust overall gains a bit. 

At CARM offsets larger in magnitude than -1, the DRMI lock seems indefinite. I just broke it to see how fast it would acquire; 3 seconds. cool

Lastly, here is the sensing matrix at CARM offset of -4, measured over five minutes. REFL11 is the only degenerate looking PD. Thus, I feel like controlling the DRMI of the DRFPMI should be more managable than I had feared.

(I didn't include/excite CARM or DARM, because I'm not sure it would really mean anything at such a large CARM offset)

Attachment 1: DRMIarms.pdf
DRMIarms.pdf
  11638   Wed Sep 23 10:31:49 2015 ericqUpdateLSCDRMI + ALS Arms

Looking good. How many meters of CARM is '-1 counts'?

  11639   Wed Sep 23 12:51:03 2015 JenneUpdateLSCDRMI + ALS Arms

Nice!!

  11648   Tue Sep 29 16:52:49 2015 ericqUpdateLSCFast ALS troubles - unknown zero

Fast ALS control continues to elude me. 

I fixed my LPF to take the input impedance of the CM board input into account; this unfortunately results in about -12dB DC gain of the ALS signal due to voltage-divider-y things, but by my estimation, this still puts the DFD noise above the input-referred voltage noise of the input AD829 on the CM board, so it'll do for now. The 120Hz pole shows up as expected when comparing the usual digital channels and the CM_SLOW output, and is digitally compensated with a zero at 120Hz (with a digital pole at 5k so nothing blows up). 

However, there seems to be some zero in the analog path somewhere that spoils the loop shape for the AO path. Here's a measurement of the X arm OLG from 10-100kHz, when the digital control is happening with ~100Hz UGF via ALS X I -> CM IN2 -> CM_SLOW -> LSC_CARM -> ETMX, and there is some AO action via ALS X I -> CM IN2 -> IMC IN2

The peak is recognizable as the gain peaking in the IMC servo (and changes predictably with changes to the IMC crossover and loop gains), which is expected. However, one can see that the magnitude is roughly flat before the peak, and the phase is around 0. With the 1/f LPF, we should see some downward slope and phase starting around -90. 

Thus, there must be some zero in the fast or common path, maybe at a few kHz where the digital loop wouldn't really see its effect. I'm not sure what it could be at this point in time.

One thought I had is that I never really checked the TF of DFD response to frequency modulation of the RF beat. I used an SR785 to drive the external FM input of a Fluke 1061A synthesizer, and saw it to be totally flat from 1-100kHz with carriers from 30-100MHz, so that should be fine. (For a little while I was confused by what seemed to be some heavy high-passing going on, but it turns out that the Fluke just can't push much low frequency FM; the manual says -3dB at 20Hz.)

Attachment 1: OLG_fastALS.pdf
OLG_fastALS.pdf
  11649   Tue Sep 29 18:03:11 2015 ranaUpdateLSCuse LISO

Use LISO - see what it tells you. I would think that you should make a differential RC filter to get the right behavior. (e.g. 1K on each leg and 1 uF between them)

Each leg of the diff input of the board has a 4k input impedance.

But surely the AO input to the MC servo should also make sense independently.

Attachment 1: Screen_Shot_2015-09-29_at_5.55.34_PM.png
Screen_Shot_2015-09-29_at_5.55.34_PM.png
  11651   Wed Sep 30 10:00:02 2015 ericqUpdateLSCused LISO

LISO confirms that I did my algebra right in picking the component values, and shows no extra zeros. 

I also took some TFs with the SR785 and confirmed that both CM board inputs behave the same, and that including the LPF on the input gives the expected 1/f shape at the slow and fast outputs.

  11658   Fri Oct 2 03:29:16 2015 ericqUpdateLSCFast ALS progress - AO path crossed over, but no high BW

I've been using an SR560 to experiment with differnent pole frequencies, to try and cancel the mystery zero. It's after the ALS demod board, before the pomona LPF with a gain of five. 

A pole frequency of 3kHz seems to recover sensible loop shapes. I've been able to crossover the AO path to make a nice long phase bubble which isn't the prettiest, but seems workable.

Getting to this point is now almost entirely scripted and repeatable; one just has to make sure that the ALS beat has the correct sign and adjust the delay line length. Most frustratingly, due to the dependence of the ALS gain on beat frequency / magnitude / delay, which can all vary on the order of a few dB, the AO gain settings to get to the crossed over point are not always the same, so at the end it's a lot of small steps and frequent loop measurements. 

The FSS crossover and overall IMC loop gain have to be pretty actively managed too. It's all too easy to drive the pockel's cell crazy. And if it's going crazy on its own anyways, there's no hope in trying to pile ALS sensing noise on top of it... It would really help in this effort to fix the whole PC situation up. 

Unfortunately, lock is lost when increasing the overall gain on the common mode board even by 1dB.angry We've seen in the single arm tests, that the gain settings have an appreciable difference in offset between them. Maybe this step is more than what the loop can handle? Or maybe it's the voltage glitches... Maybe some gain reallocation can put me on a region of the slider that glitches less.

In terms of the mystery plant features, I figure I'd like to take the analog TF of AO control signal to, say, AS55, and see what may or may not be there. I just haven't done this tonight since it would involve recabling the analyzer, and I still need frequent loop measurements to get to the crossed over state. Having ITMY misaligned and using the digital AS55Q spectrum as an out of loop monitor has been very helpful. 

Attachment 1: crossedover.pdf
crossedover.pdf
  11662   Sun Oct 4 13:53:30 2015 jamieUpdateLSCSENSMAT oscillator used for EPICS tests

I've taken over one of the SENSMAT oscillators for a test of the EPICS system.

These are the channels I've modified, with their original and current settings:

controls@donatella|~ > caget C1:LSC-OUTPUT_MTRX_7_13 C1:CAL-SENSMAT_CARM_OSC_FREQ C1:CAL-SENSMAT_CARM_OSC_CLKGAIN
C1:LSC-OUTPUT_MTRX_7_13          -1
C1:CAL-SENSMAT_CARM_OSC_FREQ    309.21
C1:CAL-SENSMAT_CARM_OSC_CLKGAIN   0
controls@donatella|~ > caget C1:LSC-OUTPUT_MTRX_7_13 C1:CAL-SENSMAT_CARM_OSC_FREQ C1:CAL-SENSMAT_CARM_OSC_CLKGAIN
C1:LSC-OUTPUT_MTRX_7_13           0
C1:CAL-SENSMAT_CARM_OSC_FREQ      0.1
C1:CAL-SENSMAT_CARM_OSC_CLKGAIN   3
controls@donatella|~ >

 

 

  11669   Tue Oct 6 03:30:17 2015 ericqUpdateLSCDRFPMI Progress

[ericq, Gautam]

Highlight of the night: the DRFPMI was held at arm powers > 110 for 20 seconds. ALS feedback was still running though, but so was some nonzero REFL11 AO path action.

In short, time was spent finding the right FM trigger settings to keep the DRMI locked while CARM is fluctuating through resonance, what CARM offset to acquire DRMI lock at, order of operations of turning on AO / turning up overall CARM gain, etc. 

Sadly, for the past hour or so, the DRMI has refused to stay locked for more than ~20 seconds, so I haven't been able to push things much further. This is a shame, since I'm very nearly at the equivalent point in the PRFPMI locking script where the ALS control is turned off completely. 

  11671   Thu Oct 8 04:48:50 2015 ericqUpdateLSCDRFPMI Progress

Progress was made. CARM was stably locked on RF only. DARM was RF only for a few moments before I typed in a wrong number...

A change was made to the LSC model's triggering section to make the DRMI hold more reliably at zero CARM offset. Namely, the POPDC signal now has its absolute value taken before the trigger matrix. Even unwhitened, it occaisionally would somehow go negative enough to break the DRMI trigger.

AUX X laser was acting up again. As before, tweaking laser current is the temporary fix.

  11672   Thu Oct 8 13:13:20 2015 KojiUpdateLSCDRFPMI Progress

Please clarify: I wonder if you were at the zero offset for CARM and DARM or not. I am 25% excited right now.

  11673   Thu Oct 8 14:14:50 2015 ericqUpdateLSCDRFPMI Progress
Quote:

Please clarify: I wonder if you were at the zero offset for CARM and DARM or not. 

Yes, this was at the full DRFPMI resonance.

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