Kevin, Gautam and Arijit
Today we performed the in-loop noise measurements of the MCREFL-PD using the SR785 to ascertain the effect of the Noise Eater on the laser. We took the measurements at the demodulated output channel from the MCREFL-PD. We performed a series of 6 measurements with the Noise Eater ''ON'' and ''OFF''. The first data set is an outlier probably, due to some transient effects. The remaining data sets were recorded in succession with a time interval of 5 minutes each between the Noise Eater in the ''ON'' and ''OFF'' state. We used the calibration factor of 13kHz/Vrms from elog 13696 to convert the V_rms to Hz-scale.
The conclusion is that the NOISE EATER does not have any noticeable effect on the noise measurements.
ALS beat spectrum and also the arm control signal look as they did before. coherence between arm control signals (in POX/POY lock) is high between 10-100Hz, so looks like there is still excess frequency noise in the MC transmitted light. Looking at POX as an OOL sensor with the arm under ALS control shows ~10x the noise at 100 Hz compared to the "nominal" level, consistent with what Koji and I observed ~3weeks ago.
We tried swapping out Marconis. Problem persists. So Marconi is not to blame. I wanted to rule this out as in Jan, Steve and I had installed a 10MHz reference to the rear of the Marconi.
the noise eater on/off measurements should be done for 0-100 kHz and from the demod board output monitor
We redid the measurement measuring the voltage noise from the REFL PD demod board output monitor with an SR785 with the noise eater on and off. We used a 100x preamp to amplify the signal above the SR785 noise. The SR785 noise floor was measured with the input to the preamp terminated with 50 ohms. The spectra shown have been corrected for the 100x amplification.
This measurement shows no difference with the noise eater on or off.
We measured the MC coil driver noise at the output monitors of the coil driver board with an SR785 in order to further diagnose the excess IMC frequency noise.
Attachments 1 and 2 show the noise for the UL coils of MC3 and MC2 with various combinations of output filters engaged. When the 28 Hz elliptic filter is on, the analog dewhitening filter is off, and vice versa. The effect of the analog low pass filter is visible in MC3, but the effect of the digital low pass filter is swamped by the DAC noise.
We locked the arms and measured the ALS beatnote in each of these filter combinations, but which filters were on did not effect the excess IMC frequency noise. This suggests that the coil drivers are not responsible for the excess noise.
Attachment 2 shows the noise for all five coils on MC1, MC2, and MC3 as well as for ITMY, which is on a different DAC card from the MCs. All filters were on for these measurements.
Why is MC2 LR so different from the others???
While Kevin is working on the MC2 electronics chain - we disconnected the output to the optic (DB15 connector on coil driver board). I decided to look at the 'free' freeswinging MC2 OSEM shadow sensor data. Attachment #1 suggests that the suspension eigenmodes are showing up in the shadow sensors, but the 0.8Hz peak seems rather small, especially compared to the result presented in this elog.
Maybe I'll kick all 3 MC optics tonight and let them ringdown overnight, may not be a bad idea to checkup on the health of the MC suspensions/satellite boxes... [MC suspensions were kicked @1207113574]. PSL shutter will remain closed overnight...
The previous measurements were made from the coil driver output monitors. To investigate why the MC2 LR coil has less noise than the other coils, I also measured the noise at the output to the coils.
The circuit diagram for the coil driver board is given in D010001 and a picture of the rack is on the 40m wiki here. The coil driver boards are in the upper left quadrant of the rack. The input to the board is the column of LEMOs which are the "Coil Test In" inputs on the schematic. The output monitors are the row of LEMOs to the right of the input LEMOs and are the "FP Coil Volt Mon" outputs on the schematic. The output to the coils "Coil Out" in the schematic are carried through a DB15 connector.
The attachment shows the voltage noise for the MC2 LR coil as well as the UL coil which is similar to all of the other coils measured in the previous measurement. While the LR coil is less noisy than the UL coil as measured at the output monitor, they have the same noise spectrum as measured at the output to the coils themselves. So there must be something wrong with the buffer circuit for the MC2 LR voltage monitor, but the output to the coils themselves is the same as for the other coils.
I am working on IMC electronics. IMC is misaligned until further notice.
activities done today - details/plots/data/evidence tomorrow.
I'm working on fixing these (and the associated MEDM scripts) up so that we can get some reliable readback on how well centered the spots are on the MC mirrors. Seems like a bunch of MEDM display paths were broken, and it looks like the optimal demod phases (to put most of the output in I quadrature) are not what the current iteration of the scripts set them to be. It may well be that the gains that convert demodulated counts to mm of spot offset are also not correct anymore. I ran the script ~4times in ~1 hour time span, and got wildly different answers for the spot centering each time, so I wouldn't trust any of those numbers atm...
As you can see in Attachment #1, I stepped the demod phase of one of the servos from -180 to 180 degrees in 5degree increments. The previously used value of 57degrees is actually close to the worst possible point (if you want the signal in the I quadrature, which is what the scripts assume).
I used Attachment #2 to change up the demod phases to maximize the I signal. I chose the demod phase such that it preserved the sign of the demodulated signal (relative to the old demod phases). I also made some StripTool templates for these, and they are in the MC directory. Doing the spot centering measurement with the updated demod phases yields the following output from the script:
spot positions in mm (MC1,2,3 pit MC1,2,3 yaw):
[0.72506586251144134, 7.1956908534034403, 0.54754354165324848, -0.94113388241389784, -3.5325883025464959, -2.4934027726657142]
Seems totally unbelievable still that we are so far off center on MC1 yaw. Perhaps the gains and calibration to convert from counts to mm of spot offset need to be rechecked.
As shown in the Attachments, it seems like IMC DAC and coil driver noise is the dominant noise source above 30Hz. If we assume the region around the bounce peak is real motion of the stack (to be confirmed with accelerometer data soon), this NB is starting to add up. Much checking to be done, and I'd also like to get a cleaner measurement of coil driver and DAC noise for all 3 optics, as there seems to be a factor of ~5 disagreement between the MC3 coil driver noise measurement and my previous foray into this subject. The measurement needs to be refined a little, but I think the conclusion holds.
Since I sunk some time into it already, the motivation behind this work is just to try and make the IMC noise budget add up. It is not directly related to lowering the IR ALS noise, but if it is true that we are dominated by coil driver noise, we may want to consider modifying the MC coil driver electronics along with the ITM and ETMs.
Today, I repeated the coil driver noise measurement. Now, the coil driver noise curve in the noise budget plot (Attachment #1) is the actual measurement of all 12 coils (made with G=100 SR560). I am also attaching the raw voltage noise measurement (input terminated in 50ohms, Attachment #2). Note that POX11 spectrum has now been re-measured with analog de-whitening engaged on all 3 optics such that the DAC noise contribution should be negligible compared to coil driver noise in this configuration. The rows in Attachment #2 correspond to 800 Hz span (top) and full span (bottom) on the FFT analyzer.
The main difference between this measurement, and the one I did middle of last year (which agreed with the expectation from LISO modeling quite well) is that this measurement was done in-situ inside the eurocrate box while last year, I did everything on the electronics benches. So I claim that the whole mess of harmonics seen in the raw measurements are because of some electronics pickup near 1X6. But even disregarding the peaky features, the floor of ~30nV/rtHz is ~6x than what one would expect from LISO modeling (~5nV/rtHz). I confirmed by looking that the series resistance for all 3 MC optics is 430ohms. I also did the measurement with the nominal bias voltages applied to the four channels (these come in via the slow ADCs). But these paths are low-passed by an 8th order low pass with corner @ 1Hz, so at 100 Hz, even 1uV/rtHz should be totally insignificant. I suppose I could measure (with EPICS sine waves) this low-pass filtering, but it's hard to imagine this being the problem. At the very least, I think we should get rid of the x3 gain on the MC2 coil driver de-whitening board (and also on MC1 and MC3 if they also have the x3 factor).
In the IMC actuation chain, it looks like the MC1/MC3 de-whitening boards, and also all three MC optics' coil driver boards, are showing higher noise than expected from LISO modeling. One possible candidate is thick film resistors on the coil driver boards. The plan is to debug these further by pulling the board out of the Eurocrate and investigating on the electronics bench.
Why bother? Mainly because I want to see how good the IR ALS noise is, and currently, the PSL frequency noise is causing the measurement to be worse than references taken from previous known good times.
Sometime ago, rana suggested to me that I should do this measurement more systematically.
I've now restored all the wiring at 1X6 to their state before this work.
I have pulled out MC1 coil driver board from its Eurocrate, so IMC is unavailable until further notice. Plans:
If there are no objections, I will execute Step #5 in the next couple of hours. I'm going to start with Steps 1-4.
This work is now complete. MC1 coil driver board has been reinstalled, local damping of MC1 restored, and IMC has been locked. Detailed report + photos to follow, but measurement of the noise (for one channel) on the electronics workbench shows a broadband noise level of 5nV/rtHz () around 100Hz, which is lower than what was measured here and consistent with what we expect from LISO modeling (with fast input terminated with 50ohm, slow input grounded).
I have pulled out MC1 coil driver board from its Eurocrate, so IMC is unavailable until further notice.
In any case, if it is indeed true that the optic sees this current noise, the place to make the measurement is probably the Sat. Box. Who knows what the pickup is over the ~15m of cable from 1X6 to the optic.
Detailed report + photos to follow
Last night, Rana fact-checked my story about the coil driver noise measurement. Conclusions:
Note: All measurements were made with the fast input of the coil driver board terminated with 50ohms and bias input shorted to ground with a crocodile clip cable.
The first goal is to figure out where this pickup is happening, and if it is actually going to the optic. To this end, I will put a passive 100 kHz filter between the coil driver output and the preamp (Busby Box instead of SR560). By getting a clean measurement of the noise floor with the coil driver board in the Eurocrate (with the bias input driven), we can confirm that the optic isn't being buffeted by the excess coil driver noise. If we confirm that the excess noise is not a measurement artefact, we need to think about were the pickup is actually happening and come up with mitigation strategies.
RXA: good section EMI/RFI in Op Amp Applications handbook (2006) by Walt Jung. Also this page: http://www.electronicdesign.com/analog/what-was-noise
I was checking on the slow machine channels and found something I could not understand.
On the IOO WFS HEAD screen, there are two sets of 4 switches (magenta rectangles in Attachment 1) labeled 2/4/8/16dB.
But as far as I could confirm with the WFS demod (D980233) and WFS head (D980012) drawings, they are the gain (attenuation) switches for the individual segments.
Their epics variable names are "C1:IOO-WFS1_SEG1_ATTEN", "C1:IOO-WFS1_SEG2_ATTEN", etc...
"C1:IOO-WFS1_SEG1_ATTEN", "C1:IOO-WFS1_SEG2_ATTEN", etc...
I confirmed the switches are alive (effective), and they are not all ON or OFF. I wonder what is the real situation there...
The unfortunate discovery today was that the attenuator switches on the IMC WFS heads are actually assigned to individual segments, and they are active. That means that we have been running the WFS with an uneven gain setting. The attached PDFs show that the signals with the attenuators on and off all at the same time, while the WFS servo output was frozen. A more annoying feature is that when some of the attenuators are on, this does not lower the gain completely. I mean that the attenuated channels show some reduction of the gain, but that is not the level of reduction we see when all attenuators are turned on. This RF could come from some internal RF coupling or some similar effect.
Moreover, the demodulation phases are quite off for most of the segments.
So far, the WFS is running with this uneven attenuation. We take time to characterize the gain and retune the demod phases and input matrices.
its painful, but you and I should probably take these out, bypass the switches and use them with fixed gain; the 'Reed Relay' attenuators are not a good part for this app.
The historical problem is that they tend to self oscillate with full gain because they had 2 MAX4106 in series which couple to each other in the bad way --- need to remove one of them and set the gain of the other one to 10.
The unfortunate discovery today was that the attenuator switches on the IMC WFS heads are actually assigned to individual segments, and they are active. That means that we have been running the WFS with an uneven gain setting.
IMC WFS tuning
- IMC was aligned manually to have maximum output and also spot at the center of the end QPD.
- The IMC WFS spots were aligned to be the center of the WFS QPDs.
- With the good alignment, WFS RF offset and MC2 QPD offsets were tuned via the scripts.
The PMC and IMC were unlocked. Both were re-locked, and alignment of both cavities were adjusted so as to maximize MC2 trans (by hand, input alignment to PMC tweaked on PSL table, IMC alignment tweaked using slow bias voltages). I disabled the inputs to the WFS loops, as it looks like they are not able to deal with the glitching IMC suspensions. c1lsc models have crashed again but I am not worrying about that for now.
9pm: The alignment is wandering all over the place so I'm just closing the PSL shutter for now.
I restarted the LSC models in the usual way via the c1lsc reboot script. After doing this I was able to lock the YARM configuration for more noise coupling scripting.
The IMC has been misbehaving for the last 5 hours. Why? I turned the WFS servos off. afaik, aaron was the last person to work on the IFO, so i'm not taking any further debugging steps so as to not disturb his setup.
That was likely me. I had recentered the beam on the PD I'm using for the armloss measurements, and I probably moved the wrong steering mirror. The transmission from MC2 is sent to a steering mirror that directs it to the MC2 transmission QPD; the transmission from this steering mirror I direct to the armloss MC QPD (the second is what I was trying to adjust).
Note: The MC2 trans QPD goes out to a cable that is labelled MC2 op lev. This confusion should be fixed.
I realigned the MC and recentered the beam on the QPD. Indeed the beam on MC2 QPD was up and left, and the lock was lost pretty quickly, possibly because the beam wasn't centered. Lock was unstable for a while, and I rebooted C1PSL once during this process because the slow machine was unresponsive.
When tweaking the alignment near MC2, take care not to bump the table, as this also chang es the MC2 alignment.
Once the MC was stably locked, I was able to maximize MC transmission at ~15,400 counts. I then centered the spot on the MC2 trans QPD, and transmission dropped to ~14800 counts. After tweaking the alignment again, it was recovered to ~15,000 counts. Gautam then engaged the WFS servo and the beam was centered on MC2 trans QPD, transmission level dropped to ~14,900.
This problem resurfaced. I'm doing the debugging.
6:30pm - "Solved" using the same procedure of stepping through the whitening gains with a small (10 DAC cts pk) signal applied. Simply stepping through the gains with input grounded doesn't seem to do the trick.
Gautam was doing some DRMI locking, so I replaced the photodiode at the AS port to begin loss measurements again.
I increased the resolution on the scope by selecting Average (512) mode. I was a bit confused by this, since Yuki was correct that I had only 4 digits recorded over ethernet, which made me think this was an i/o setting. However the sample acquisition setting was the only thing I could find on the tektronix scope or in its manual about improving vertical resolution. This didn't change the saved file, but I found the more extensive programming manual for the scope, which confirms that using average mode does increase the resolution... from 9 to 14 bits! I'm not even getting that many.
There's another setting for DATa:WIDth, that is the number of bytes per data point transferred from the scope.
I tried using the *.25 scope instead, no better results. Changing the vertical resolution directly doesn't change this either. I've also tried changing most of the ethernet settings. I don't think it's something on the scripts side, because I'm using the same scripts that apparently generated the most recent of Johannes' and Yuki's files; I did look through for eg tds3014b.py, and didn't see the resolution explicitly set. Indeed, I get 7 bits of resolution as that function specifies, but most of them aren't filled by the scope. This makes me think the problem is on the scope settings.
sstop using the ssscope, and just put the ssssignal into the DAQ with sssssome whitening. You'll get 16 bitsśšß.
I ran a BNC from the PD on the AS table along the cable rack to a free ADC channel on the LSC whitening board. I lay the BNC on top of the other cables in the rack, so as not to disturb anything. I also was careful not to touch the other cables on the LSC whitening board when I plugged in my BNC. The PD now reads out to... a mystery channel. The mystery channel goes then to c1lsc ADC0 channels 9-16 (since the BNC goes to input 8, it should be #16). To find the channel, I opened the c1lsc model and found that adc0 channel 15 (0-indexed in the model) goes to a terminator.
Rather than mess with the LSC model, Gautam freed up C1:ALS-BEATY_FINE_I, and I'm reading out the AS signal there.
I misaligned the x-arm then re-installed the AS PO PD, using the scope to center the beam then connecting it to the BNC to (first the mystery channel, then BEATY). I turned off all the lights.
I went to misalign the x-arms, but the some of the control channels are white boxed. The only working screen is on pianosa.
The noise on the AS signal is much larger than that on the MC trans signal, and the DC difference for misaligned vs locked states is much less than the RMS (spectrum attached); the coherence between MC trans and AS is low. However, after estimating that for ~30ppm the locked vs misaligned states should only be ~0.3-0.4% different, and double checking that we are well above ADC and dark noise (blocked the beam, took another spectrum) and not saturating the PD, these observations started to make more sense.
To make the measurement in cds, I also made the following changes to a copy opf Johannes' assess_armloss_refl.py that I placed in /opt/rtcds/caltech/c1/scripts/lossmap_scripts/armloss_cds/ :
I started taking a measurement, but quickly realized that the mode cleaner has been locked to a higher order mode for about an hour, so I spend some time moving the MC. It would repeatedly lock on the 00 mode, but the alignment must be bad because the transmission fluctuates between 300 and 1400, and the lock only lasts about 5 minutes.
Back to loss measurements.
I replaced the PD I've been using for the AS beam.
I misaligned the x arm.
I tried to lock the y arm, but PRC was locked so I could was unable. Gautam reminded me where the config scripts are.
The armloss measurement script needed two additional modifications:
I ran successfully the loss measurement script for the x and y arms. I'm getting losses of ~100ppm from the first estimates.
I made the following changes to the lossmap script:
When the optic aligns itself not at the ideal position, I'm noticing that it often locks on a 01. When the cavity is then misaligned and restored, it can no longer obtain lock. To fix this, I've moved my 'save' commands to just before the loop begins. This means the script may take longer to run, but as long as the cavity is initially locked and well aligned, this should make it more robust against wandering off and never reacquiring lock.
I left the lossmap script running for the x-arm. Next would be to run it for the y arm, but I see that after stepping to a few positions the lock is again lost. It's still trying to run, but if you want to stop it no data already taken will be lost. To stop it, go to the remaining terminal open on rossa and ctrl+c
the analysis needs:
I made additional measurements on the x and y arms, at 5 offset positions for each arm (along with 6 measurements at the "zeroed" position).
need to vary start/stop times in fit to test for systematics
Both were measured using the FieldMate power meter. I was hesitant to use the Ophir power meter as there is a label on it that warns against exceeding 100 mW. I can't find anything in the elog/wiki about the measured inesrtion loss / isolation of the input faraday, but this seems like a pretty low amount of light to get back from PRM. The IMC visibility using the MC_REFL DC values is ~87%. Assuming perfect transmission of the 87% of the 97mW that's coupled into the IMC, and assuming a further 5% loss between the Faraday rejected port and the AP table, the Faraday insertion loss would be ~30%. Realistically, the IMC transmission is lower. There is also some part of the light picked off for IPPOS. Judging by the shape of the REFL spot on the camera, it doesn't look clipped to me.
Either way, seems like we are only getting ~half of the 1W we send in on the back of PRM. So maybe it's worth it to investigate the situation in the IOO chamber during this vent.
c1psl, c1susaux,c1iool0,caux crates were keyed. Also, the physical shutter on the PSL NPRO, which was closed last Monday for the Sundance crew filming, was opened and the PMC was locked. PMC remains locked, but there is no light going into the IMC.
In order to see the AS beam a bit more clearly in our low-power config, I swapped out the ND=1.0 filter on the AS camera for ND=0.5.
I'm running a script that moves TT1 and TT2 randomly in some restricted P/Y space to try and find an alignment that gets some light onto the TRY PD. Test started at gpstime 1228967990, should be done in a few hours. The IMC has to remain locked for the duration of this test. I will close the PSL shutter once the test is done. Not sure if the light level transmitted through the ITM, which I estimate to be ~30uW, will be enough to show up on the TRY PD, but worth a shot I figure.
Test was completed and PSL shutter was closed at 1228977122.
I removed the ND filter from the ETMYT camera to facilitate searching for a TRY beam. This should be replaced before we go back to high power.
I've suspected that the TTs are drifting significantly over the course of the last couple of days, because despite repeated alignment efforts, the AS beam spot has drifted off the center of the camera view. I tried looking at IPPOS, but found that there was no data. Looking at the table, the QPD was turned backwards, and the DAQ cable wasn't connected (neither at the PD end, nor at 1Y2, where instead, a cable labelled "Spare QPD" was plugged in). Fortunately, the beam was making it out of the vacuum. So as to have a quantitative diagnostic, I reconnected the QPD, turned it the right way round, and adjusted the steering onto it such that with the AS spot on the center of the CCD monitor, the beam is also centered on the QPD. The calibration is uncertain, but at least we will be able to see how much the spot drifts on the QPD over some days. Also, we only have 16 Hz readback of this stuff.
I leave it to Chub to take the high-res photo and update the wiki, which was last done in 2012.
Already, in the last ~1 hour, there has been considerable drift - see Attachment #2. The spot, which started at the center of the CCD monitor, has now nearly drifted off the top end. The ITMX and BS Oplev spots have been pretty constant over the same timescale, so it has to be the TTs?
To debug the issue of the suspected drifting TTs further, I temporarily hijacked CH0-CH8 of ADC1 in the c1lsc expansion chassis, and connected the "MON" outputs of the coil drivers (D010001) to them via some DB9 breakouts. The idea is to see if the problem is electrical. We should see some slow drift in the voltage to the TTs correlated with the spot walking off the IPPOS QPD. From the wiring diagram, it doesn't look like there is any monitoring (slow or fast) of the control voltages to the TT coils, this should be factored into the Acromag upgrade of c1iscaux/c1iscaux2. EPICS monitoring should be sufficient for this purpose so I didn't setup any new DQ channels, I'll just look at the EPICS from the IOP model.
IMC was not locked for the past several hours. Turned out MC autolocker was stuck, and I could not ssh into megatron because it was in some unresponsive state. I had to hard-reboot megatron, and once it came back up, I restarted the MCautolocker, FSS slow servo and nds2 processes. IMC re-locked immediately.
I was pulling long stretches of OSEM data from the NDS2 server (megatron) last night, I wonder if this flakiness is connected. Megatron is still running Ubuntu12.
Can we get some panel mount FC/APC connectors and put them on a box? Then we could have the whole setup inside of a box that is filled with foam and sits outside the PSL hut.
Steve had showed me some stock of long fibers a while back - they are from Oz Optics, and are 50m long, and are already spooled - so barring objections, we will try the MZ setup with the spooled fiber and see if there is any improvement in the fringing rate of the MZ. Then we can evaluate what additional stabilization of the fiber length is required. Anjali will upload a photo of the spooled fiber.
At ~4pm, the main volume pressure (CC1) was reported to be ~5e-5 torr. So I replaced the HR mirror in the MC REFL path with the usual 10% beamsplitter, and aligned the beam onto MCREFL photodiode. I also replaced the ND filter on the AS port camera, and in front of the IPPOS QPD.
Then I turned up the power by HWP rotation - at the input to the IMC, I now measured 960 mW with the Coherent power meter, so the NPRO power has certainly decayed by ~10% from 2018 July. Normal high-power IMC autolocker script was re-enabled on megatron (and the slow servo enable threshold raised from 1000 cts to 8000cts). IMC was readily locked, after some hand alignment, I got a maximum of 14500 cts transmission. I was then able to lock the Y-arm. The dither alignment servo did not work with the nominal settings, but by hand alignment, I was able to get TRY up to 0.6 (I didn't try too hard to optimize this in any systematic way). X arm was also locked.
AUX drypump valved off and shutdown at ~610pm. I also switched both TP2 and TP3 to their lower rotation "standby" mode. So overall no major mishaps this time around. I am leaving the PSL shutter open over the long weekend. For in-air vs vacuum suspension spectra comparison, I kicked the ETMY optic at Fri May 24 18:26:10 PDT 2019.
Since ~ 2 hours ago, the IMC autolocker has not been able to keep the IMC locked. I don't see any obvious trends in the wall StripTool that may point to what's going on. For the brief periods in which a TEM00 mode is locked, the PC Drive RMS level is ~5x what the nominal level is, and while the autolocker is trying to lock the IMC, the PC drive RMS level is hovering around 4V DC, which is high. The PMC Error and Control signal spectra show huge 60 Hz (and harmonics) peaks, and indeed this is visible in the time domain signals as well (on ndscope or on the oscilloscope on the PSL table), but this is not a new feature in the last two hours. Usually, this kind of problem signals that either/both the c1psl or c1iool0 slow machines need to be power-cycled, but I confirmed that both machines are online and telnet-able. Possibilities: (i) some card in the c1psl / c1ioo crates have failed or (ii) something in the MC/FSS electronics chain has failed or (iii) there is a huge amount of excess high-frequency noise from the NPRO.
I am leaving the PSL shutter closed.
I briefly managed to lock the IMC today - it stayed locked for ~10 minutes. Attachment #1 shows spectra of a few error and control signals for today's lock, and from a stretch yesterday before the problems surfaced*. The 60 Hz lines are much bigger, and MC_F signals broadband excess noise above a few Hz. I suspect a problem somewhere in the electronics.
*I confess the comparison isn't entirely valid because I had to tweak the FSS FAST gain from its nominal value of 22 to 25 in order to get the PC drive RMS down to the ~1.5V level. At the nominal gain setting, with the laser frequency locked to the cavity length, the PC Drive RMS was ~4 V. Still, indicative of something being off in the electronics.
As per Gautam's request, I looked at the IMC situation.
I'll complete the entry later.
Continuing this investigation of the IMC, today I am getting familiar with the PMC and FSS. I'd like to measure the frequency noise of the PSL referenced to the PMC.
I checked that the PSL shutter is off, so no light reaches the IMC.
I'm not really sure what I'm looking for on the FSS boxes. I found a few documents to guide:
I ran the FSS autolock script from C1PSL_FSS, nothing obvious changes when I do so. The FSS error signal (which I think is PSL-FSS_MIXERM) is flatlined, and the RC-RF_PD has no LO (PSL-FSS_LOCALC is nan).
SURFS want some locking of IMC for camera adjustment.
So I left the IMC with intermediate gains so that it keeps locking and unlocking.
VCO (overall) iMC gain of -32, FSS common gain 3, and the FAST gain 20. I believe MC2tickle is ON too.
The circuit diagram for the PMC servo card is D980352. From this diagram, I see that I can send an excitation from the network analyzer to FP2TEST (9.09 kOhm input impedance) where it is added to the PMC error signal before going to the loop filters.
I hook up the following
I 'Enable' Test 2 on the PSL screen, so FP2TEST gets added to the error signal.
I was able to see the carrier and both sidebands.
I tried to grab this data from the scope via ethernet, but was unsuccessful (timeout errors, I'm using the scripts from scripts/tektronix/tek-dump, and the GPIB box that Kruthi had been using for the GigE cam; I also tried plugging in directly scope->ethernet. Never got anything but timeout errors, so maybe I'm not specifying the port correctly. Anyway the trace is frozen on the scope for later use, or I can easily repeat this now that I know how).
Next, I locked the PMC (Test1 is off, tune DC output adjust until I get some transmission, turn on the loop at Test1, increase the gain to before the loop goes unstable). I'm sending the following channels to SR560 (gain = 2, no filtering, high dynamic reserve, 50 Ohm outputs), and reading spectra from the Agilent 4395A:
The HV mon was always saturating the preamp, so I disconnected it; I added a 50 Hz (6db) high pass to the Trans PD signal, since it has a DC component.
I got to take a look at the traces on the spectrum analyzer front panel, but too tired to do the GPIB for now. There are peaks, things look reasonable.