ELOG 40m

PMC transfer functions with various brick-on-top configurations

Attached below is a graphical summary of different things that I have tried putting on the PMC to reduce the noise in the loop. The motivation behind these measurements is the current inability here at the 40m to increase the UGF of the PMC. This is part of a broader ISS loop/gain/noise problem that we are having, which is causing Rob's locking efforts to have trouble. (The ISS is next on the to-do list, after we find the best configuration for the PMC, if we are still having problems). Right now, it looks like we are being limited by the gain of the PMC (as mentioned by Rana in elog #968).

Anyhow, Rana and I had noticed that piling heavy things on top of the PMC seemed to reduce the noise. What follows are the transfer functions that I took with the different items on top of the PMC, so that we can compare their effects:

Nothing on the PMC (like it used to be)
New ~14kg lead brick wrapped in copper foil on top of the PMC
A stack of a piece of aluminum, a chunk of steel, and then the lead brick on top of the PMC
The lead brick + Rob pushing on top of the PMC

Unfortunately, I need to retake the power spectra in these configurations, but from eye-balling it, as one might expect, pushing on the PMC with a hand added more noise than the nominal nothing-on-PMC configuration.

Also unfortunately, none of these configurations seems to have significantly helped our noise reduction situation. We need a new plan. Rana is currently trying out some other configurations, including just aluminum+brick.

Attached is an open loop gain TF from 100Hz - 100kHz. Below that is a zoomed-in version from 5kHz - 30kHz. As you can see more clearly in the zoomed in version, the notch that Rana put onto the board at ~14.5kHz is working, but we need to make the notch deeper, to catch more of that 14.5kHz peak. We're going to try removing the resistor or reducing it's value in the RLC filter on the board (see elog #906). Also, we see that there is a giant peak at 18.3kHz. This is probably much more limiting to our stability at this point than the 14.5kHz peak. We need to add another filter to take care of this, or find another way to reduce this peak. Note that it is present even when there is no brick on the PMC, so it is not an artifact of the new brick.

Attachment 1: PMC_OLG_100Hz_to_100kHz.png

Attachment 2: PMC_OLG_5kHz_to_30kHz.png

979

Mon Sep 22 20:00:35 2008

Alberto

ABSL: running measurement

I'm leaving the X arm locked on the TEm01 mode while a measurement is running. Just please wait for 40 minute if you need the interferometer tonight.

981

Mon Sep 22 21:54:05 2008

rana

New Wiener result with x10 gain in ACC

ASS

The 2 attached PDF files show the performance of the Wiener filter code on 2 hours of data
with a 4000 tap filter on 64 Hz data. All 6 accelerometers around the MC and the Ranger seismometer
were used.

I attribute the improved performance in the 3-10 Hz band to the better SNR of the ACC channels. To
do better below 1 Hz we need the Guralps.

Attachment 1: f.pdf

984

Tue Sep 23 11:17:59 2008

The PMC output side has a new madly scattering spot at chamfer 2 o'clock position

Attachment 1: rainbow.png

Attachment 2: pmcclip.png

985

Tue Sep 23 13:25:07 2008

I've been spending time working on the short DOF loops (PRC,MICH,SRC) in an attempt to make the
initial stage of lock acquisition (the DRMI+2ARMs, no spring) better. This seems to have been
largely successful, as last night there were several locks of the DRMI+2ARMs with pretty short
wait times.

The output matrix for the short DOFs is a bit strange, though. The MICH->PRM element is about
3 times too small, which seems to indicate something broken in hardware. The MICH->SRM element
seems normal, though, which suggests the BS is isn't broken--either the PRM has had a sudden
actuation increase or it's a problem with the sensing.

987

Wed Sep 24 17:57:04 2008

Alberto

ABSL: FSS Slow Actuator Control

Rana, Alberto

Today when I started working with the PLL that I use to control the secondary laser on the ABSL experiment, I found that the beat between the two lasers was at a much higher temperature of NPRO than usual (about one Celsius Degrees higher, 49.79 instead of 48.7). It turned out that the main beam frequency had changed, and so had its frequency, because of a too much high value of the slow actuator gain on the FSS. We looked at the trend for the gain and noticed it had changed from 0.3 to 3 at about noon today. We brought it back to the old value and also optimized the single gains in the FSS slow servo to obtain a faster and stabler response to step changes in the laser temperature.

It is very important for the ABSL experiment that the frequency and the NPRO temperature of the main laser do not change.

** update:

you asked for:   diff 2008/09/25,0:00 2008/09/25,8:50:19 utc 'FSS[-_]SLOW'
LIGO controls: differences, 2008 09/25 00:00:00 utc vs. 2008 09/25 08:50:19 utc
__Epics_Channel_Name______   __Description__________   __value1____     __value2____
C1:PSL-FSS_SLOWKD                                      0.000000         0.001000
C1:PSL-FSS_SLOWKI                                     -0.001000        -0.001700
C1:PSL-FSS_SLOWKP                                     -0.000300        -0.001000

It seemed later that it was not being cool with the derivative gain up at -0.001, so I set it to zero. We really need some documentation on this
loop (e.g. pseudo code and a PID tuning procedure). Note that the PID record as documented in the EPICS Reference Manual
has been deprecated and so we run a perl script that Tobin wrote.

991

Thu Sep 25 10:48:29 2008

FSS calibration again

I did a calibration of the FSS error signal again with a different method.
This time, I swept the laser frequency with the NPRO PZT around a resonance.
The attached figures show the transmitted light power and the PDH error signal vs the applied voltage to the PZT.
From the width of the transmitted light power peak, we can obtain the PZT voltage to the laser frequency coefficient,
i.e. the HWHM (Half Width Half Maximum) equals to the FSR (38kHz).
Once the PZT is calibrated, the PDH error signal can be calibrated by the fitting the central slope with a line.

I repeated the measurement 8 times and fitted the obtained data to get the HWHM and the slope.
The results are the following:
PZT calibration = 6.3 +/-0.1 MHz/V
PDH calibration = 6.5 +/-0.5 kHz/V

Note:
(1) The calibration coefficient (6.5kHz/V) is almost consistent with the previous value (6.83kHz/V elog:958). However, that calibration
used a considerably different value for the PZT calibration (11.172MHz/V elog:791). The discrepancy in the PZT calibration is understandable
because my previous PZT calibration was very rough. The fact that the two calibrations still agree is a mystery.

(2) In the transmitted power curve, there seems to be a slight distortion, probably due to the thermal effect.
We should reduce the power to the reference cavity to remove this effect.

(3) This measurement was done after Peter installed his RF source. The demodulation phase had not yet been optimized. We should
repeat the calibration after he optimizes the phase.

(4) I used the Tektronix oscilloscope for the measurement.
Using the ethernet-wireless converter, you can connect the scope to the network from anywhere in the lab.
No hard wire required anymore.
Then you can download the data from a web browser. It is cool !

Attachment 1: PDTrans.png

Attachment 2: PDHsignal.png

993

Thu Sep 25 15:24:05 2008

I calibrated the VCO driving the AOM for the AO path of the MC feedback.

I injected DC voltage to the VCO and measured the output frequency with the SR620.

The attached plot shows the relation between the input voltage to the VCO and the output frequency.
The coefficient is 1.75MHz/V. Since the AOM is double path, the actual actuation efficiency is 3.5MHz/V.
We can use this value for the calibration of the MC_F. However, the MC_F DAQ channel is sampling the VCO input voltage through a 10Hz high-pass filter.
This filter has to be taken into account to convert the MC_F counts to frequency.
I will measure the transfer function from the VCO input to the MC_F counts tomorrow.

Attachment 1: VCO_Cal.png

995

Fri Sep 26 00:19:54 2008

Filter-action with the PMC

Written, but not posted on 24Sept2008:

PMC adventures for this evening

Today's mission was to make more progress on increasing the bandwidth of the PMC servo.

First order of business was to improve the performance of the 14.6kHz notch that Rana put in the PMC servo board a few weeks ago to remove the 14.6kHz body mode resonance of the PMC. Looking at the zoomed in TF that I posted Monday (elog #978), we see that there is still a remnant of a peak near 14.5kHz. A first gut-reaction is that the notch is not tuned properly, that we have just missed the peak. As previously noted in the elog, the peak that we are trying to notch out is at 14.68kHz (elog #874). By unlocking the PMC and measuring the transfer function between FP2 and OutMon (OutMon is the monitor for the high voltage going to the PMC's PZT), I measure the transfer function of the notch, and find that it is notching at 14.63kHz. So we're a teensy bit off, but the Q of the notch is such that we're still getting improvement at the peak frequency. After checking that we are hitting the correct frequency, I put a short (just some wire) around R21, which is the R in the RLC notch filter, to increase the depth of the notch. At the peak frequency of 14.68kHz, we see a 2.5dB improvement of the notch. At the actual notch frequency of 14.63kHz, we see a 3.2dB increase in the depth of the notch. So, shorting R21 helped a little, but not a lot. Also, it's clear that we don't get that much more improvement by being on the resonant frequency, so there's no need to go in and tune the notch on the board.

Second order of business was to investigate the 18.34kHz peak in the transfer function. (Rana spent some time Monday night measuring this peak, and determined that it was at 18.34kHz) We decided that the best plan was to re-implement the Pomona Box notch filter that had previously existed to remove a higher frequency body mode, but tuned for the 18.34kHz mode. I am still not entirely sure what this mode is, but clearly it's a problem by about 20dB (on the TF, the next highest peak is 20dB below the 18.34kHz peak). Unfortunately, while the components should, by Matlab calculations, give me an 18.3kHz notch, I ended up with something like a 21.7kHz notch. This notch is approximately -30dB at 21.7kHz, and -20dB at 18.3kHz. I still need to take transfer functions and power spectra of the PMC servo with this new filter in place to (a) confirm that it did some good, and (b) to determine how important it is that the notch be right-on. More likely than not, I'll take the filter out and fiddle with the capacitors until I get the correct notch frequency.

Third on the list was to lock everything back up (FSS, PMC) after my tinkering, and see what kind of gain we get. Rob and I fiddled with the PMC gain, and it looks like the servo oscillates just before we get up to the max slider gain of 30dB. Looking at the power spectra in DTT, we do not see any significant peaks that suggest oscillation, so it is likely that there is some investigation to be done at frequencies above the 7kHz that we were able to look at with DTT (which isn't surprising, since all of this work has been at 14kHz and higher).

A final note is that we see a feature around 9kHz in the transfer function, and it is not at all clear where it comes from. At this time, it does not seem to be the dominant feature preventing us from increasing the gain, but at some point if we want the bandwidth of the PMC servo to be 10kHz, we'll have to figure this one out.

Still on the PMC todo list:

Measure the new transfer function, see if 18.34kHz peak is reduced
Tune Pomona Box notch filter to 18.3kHz instead of the current 21.7kHz
Retake power spectra of different items on top of PMC, compare to see if there is any one configuration that it obviously better than the others.
Find out why the PMC still oscillates when we try to take it up to the max slider gain, and fix it.

PS, is anyone else having trouble getting to the elog from laptops on other parts of the Caltech network (but not LIGO network)? My laptop won't go to the elog, but I can get to the rest of the internet using the Caltech wireless. My computer stopped seeing the elog on Tuesday or so. Joe, do you have any inspiration? Thanks.

996

Fri Sep 26 09:05:47 2008

The MC2 sus damping was restored.

998

Fri Sep 26 16:08:39 2008

There's been good progress in locking the last couple of nights. A lot of time was wasted before I found that
all the SUS{POS,PIT,YAW} damping gains on the SRM were set to 0.1 for some reason, which let it get rung up
just a bit during bang locking. After setting these gains to 0.5 (similar to PRM and BS), the initial lock
acquisition of DRMI+2ARMs (nospring) got much quicker. Then more time was wasted by sticky sliders on the
transmon QPD whitening gain, causing the Schmitt triggered HI/LO gain PD switch not to happen. This meant
that the arm power was not reported properly when the CARM offset was reduced, and so loop gain normalizations
were not working properly. After all this, by the end of the night last night, reduced the CARM offset such
that stored power in the arms was about half of the max. Should be able to get to full power with another
good night, and then back to springy locking.

999

Fri Sep 26 16:13:57 2008

rana

IOO

MC_L / MC_F crossover

We were trying to understand why the FAST_F signal had such large excursions (~1V ~ 5 MHz).

Some of this is due to the seismic noise and the resulting MC_F signals. Increasing the MCL
gain reduces it somewhat. But as you can see from the attached loop gain measurement, the
crossover is a healthy 90 Hz with the MCL digital gain = 1. But what's going on in the MC loop
in the 10-20 Hz band? That looks like bad news.

Then I noticed that changing the ISS gain slider puts a large step (~1V) into the FAST. My guess
is that the board has large DC offsets and also much of the switching supply noise. Not sure why
this would be worse than before though.

To prevent large noise in the FAST, I've changed the mcup script to set this gain to -5 dB. Our
intensity noise is now presumably 10-15 dB worse than the nominal good levels we had a year ago.
Needs investigation.

Attachment 1: mcx.png

1000

Fri Sep 26 18:35:17 2008

PMC filter is out for tuning

The PMC's new Pomona Box filter is out for tuning. I'd like to get the notch right on the 18.3kHz, rather than being off in 21.7kHz land.

1002

Fri Sep 26 19:18:39 2008

IOO

MC2 is having a bad day

As Steve mentioned earlier in today's elog, MC2 keeps ringing up for no clear reason. It is definitely only MC2 that is ringing up, since it's sensors will read several hundreds of counts, while all the other optics are at regular 2 counts and below on the Watchdog screen.

Preliminary investigation results: Around the time of these "kick up" events, the Ranger seismometer does not see any motion, nor does the set of accelerometers under the MC1 chamber. The set of accelerometers under the MC2 chamber do see activity that is at the same time as these events. These events are not caused just by someone walking around, since Rana went inside and clunked around near MC2 while I watched the sensor levels. MC2's watchdog did not trip.

For further investigation: Why is it that only the MC2 accelerometers are seeing the motion? Similarly, why is MC2 the only optic being kicked? Has anyone done anything lately to the MC2 stack?

1004

Mon Sep 29 11:17:14 2008

steve

horizontal viewports are protected with lexan

SAFETY

The four horizontal viewports of arms are protected
by 3/8" thick, 8.5" OD Lexan disk of MR10 Polycarbonate.

ITMX, ETMX, ITMY and ETMY ccd cameras are not focused now.

1007

Mon Sep 29 15:09:36 2008

steve

almost 4 yrs plot of power & temps

The water chiller is normally running 1.5 C warmer than the laser head temp.
When control room temp is stable and PEM-count_temp is stable we can expect the head temp to be stable 20.0 C

PSL-126MOPA_HTEMP is running warmer in the last ~40 days

The ifo arm thermostate temp settings were raised by 2 F on 8-11-08

Attachment 1: 3.5y.jpg

1008

Mon Sep 29 17:53:33 2008

ISS has been saturating easily.
Today I opened the PSL enclosure to inspect the ISS box. Then I found that the sensor PD was disconnected from the box.
I don't know for how long it has been like this, but it is clearly bad.
I connected the PD and I was able to increase the ISS gain to 0dB (from -5dB).
When I turned off the FSS, I was able to increase the gain further up to 8dB. So the FSS must have been doing something bad to the laser intensity.
The FSS fast path did not get huge kicks when ISS was turned on as observed before. But still the FSS fast signal is wondering around about +/-0.3V.
It does not stop wondering even when the ISS is turned off (even if the CS drive cable is physically disconnected).
I will try to optimize the slow servo.

After Peter tried to optimize the demodulation phase of the FSS (see his entry), I was able to increase the ISS gain to 8dB even with the FSS running.
I haven't fully understood what is behind this behavior.

To investigate what is going on in the ISS, I opened the box and inspected the circuit.
I found many innovative implementations of electric circuit components. See the attached photo. It is a three dimensional mounting of
a surface mount AD602 !
Anyway, the board is somewhat different from the schematic found in the DCC. But I roughly followed the circuit.
I will measure open loop TFs and various signals to see how we can improve the ISS.

Attachment 1: IMG_1671.JPG

1009

Tue Sep 30 13:43:43 2008

Steady progress again in locking again last night. Initial acquisition of DRMI+2ARMs was working well.
Short DOF handoff, CARM->MCL, AO on PO_DC, and power ramping all worked repeatedly, in the cm_step script.
This takes us to the point where the common mode servo is handed off to an RF signal and the CARM offset
is reduced to zero. This last step didn't work, but it should just require some tweaking of the gains
during the handoff.

1010

Tue Sep 30 19:50:27 2008

Quicky Summary - more details later

Quicky summary for now, more details later tonight / tomorrow morning:

PMC notch: It's tuned up, but it is out, and it is staying out. It looks like the 18.3kHz junk isn't being helped by the brick, in fact the brick makes it worse. And the notch isn't enough to make the peak go away. Rana's and my conclusions about the PMC: the 18.3kHz resonance is associated with the way the PMC touches its mount. Depending on where we push (very gently, not much pressure) on the PMC, we can make the peak come and go. Also, if the PMC happens to be set nicely on its ball bearings, the peak doesn't appear. More notes on this later.

PMC's RF modulation depth: Since with the PMC's brick off, and the PMC sitting nicely on its ball bearings, we don't see any crazy oscillations, we were able to take the gain slider on the PMC screen all the way up to 30dB. To give us more range, we changed the modulation depth of the RF to 2V, from its previous value of 1V.

Phase of PMC servo: Since the phase of the PMC servo hasn't been set in a while, I eyeballed it, and set the phase to: Phase Flip = 180, Phase Slider = 4.8000 . I measured many points, and will plot a calibration curve later.

I also measured the actual value of the RF out of the PMC's LO board, when changing the RF output adjust slider. Again, will post the calibration later.

The attached PNG shows the PMC spectra from now and from Aug. 30 (ref). As you can see there's been some good reduction in the acoustic noise (red v. orange). The large change in the error signal is because of the much higher gain in the servo now. We'll have to redo this plot once Jenne measures the new UGF.

Attachment 1: mcf.png

1011

Wed Oct 1 00:24:54 2008

I had mistakenly left the MC boost off during my FAST investigations. The script is now restored.

The ISS is still saturating with gains higher than -5 dB. We need to request a PeterK / Stefan consult in the morning.

Also found the MZ gain down at -10 dB around midnight - need an alarm on that value.

1012

Wed Oct 1 02:10:03 2008

Here's a 2 day trend of the MZ. You can see that there is something bad with ERR - it should really be going to zero.

Also LODET is dead. We need to rejuvinate LODET somehow.

The next plot is a 90 day hour-trend of the same signals. You can see that LODET came back to us between
September 10 and 19 ??? I looked at a 4 year trend and it seems that this signal has always been zero
(nice use of disk space) except for a few days in Nov of 06 and then whatever happend on Sep 10.

Attachment 1: Untitled.png

Attachment 2: Untitled.png

1013

Wed Oct 1 02:47:53 2008

rana

PSL ERR & LODET: Too much offset

Looks like there is an anomolous mixer offset correlated with the increase in the LO level. This may be leading to crazy offset locking in the FSS and too much coupling from ISS to FSS.

Attachment 1: Untitled.png

1014

Wed Oct 1 02:54:03 2008

Tried the spring-y side tonight with a discouraging lack of progress. There were several locks of DRMI+2ARMs with
the +f2 (springy) sideband resonating in the DRM, but they weren't very stable. Moving to just the DRMI and resonating
the +f2, in order to tune up the acquisition and the handoff to the double demod signals, revealed the problem that the
DRM just won't stay locked on the +f2 sideband. It locks quickly, but only for a few seconds. This is different from the
behaviour with the -f2 sideband, which locks quickly and stably. In theory, the two sidebands should behave similarly.
It could be problems with HOMs in the recycling cavities, and so we may try changing the modulation frequency slightly.

1017

Wed Oct 1 23:05:14 2008

Stefan, Yoichi

We took relative intensity noise (RIN) spectra of the ISS error point and the monitor PD (attm1).
In-loop RIN is the sensor PD and "Out of the loop RIN" is the monitor PD.
The ISS gain slider was at 8dB in this measurement.
It looks normal.
An open loop transfer function of the ISS loop was measured (attm2). The UGF was 22kHz with the phase margin of ~22deg.
We should increase the UGF up to ~60kHz

When we increase the gain up to 14dB, the CS saturation warning comes up in the EPICS screen.
We confirmed this by monitoring the CS drive signal with an oscilloscope.
It is the output of an AD602J, which has +/-3V output range.
By increasing the gain of AD602J, we saw that the output signal hits the rail.
There seems to be a lot of high frequency (100kHz - a few MHz) noise, out of the control band.
We also observed that AD602J itself oscillates at about 10MHz (don't remember the exact number) when the gain is increased.
(We saw this even when the loop is off. There is no such an oscillation in the input to the AD602J).
When we took wide band spectra of the CS drive signal, we saw many large harmonics of ~180kHz. We believe these peaks are limiting
our ISS gain now (causing the CS saturation). The harmonics persisted even when we disconnected the PDs. So it is not coming from the light.
We saw the same harmonics in the power lines. They may be the switching noise of the Sorensens.
We took spectra of those harmonics, but the netgpibdata.py somehow did not save the data from AG4395A correctly. I have to debug this.

Stefan removed DC offsets from the AD829s (many of them are used in the ISS board) by turning the pots for offset adjustment.
This eliminated the problem of getting a large DC CS feedback (observable in C1:PSL-ISS_CSDRIVE_MEAN) when the gain is increased.

During the investigation, I noticed that increasing the PMC gain too much (~22dB) caused an oscillation of the PMC loop and consequently made
the ISS saturate. When the ISS is behaving bad, we should check the PMC gain.

Currently, the ISS is running OK with the gain = 8dB. I modified the mcup script to set the ISS gain to 8dB when the MC is locked.

TO DO:
Wait for Peter's answer about spare ISS boards.
Power line filtering.
Find the cause of AD602J oscillation (Well this is the one mounted upright. So just mounting it normally might solve the problem :-).

Attachment 1: RIN.png

Attachment 2: OPLTF.png

1019

Thu Oct 2 02:45:50 2008

Locking the DRMI with the +f2 sideband was marginally better tonight. I was able to get it lock stably enough to take transfer
functions and handoff MICH & PRC to double demod signals. After re-alignment, however, behaviour was similar to last night
(locks quickly but only for a few seconds), so that lends some credence to HOM-as-bad-guy theories.

1023

Fri Oct 3 15:09:58 2008

Last night during locking, for no apparent reason (no common mode), the PSL FAST/SLOW loop starting going just a little
nutz. Attached is a two day plot. The noisy period started around 11-ish last night.

Attachment 1: FASTSLOW.png

1024

Fri Oct 3 15:57:05 2008

Last night was basically a repeat of the night before--marginally better locking with the DRMI resonating the +f2
sideband. Several stable locks were achieved, and several control handoffs to DDM signals worked, but never from
lock to lock--that is, a given DD handoff strategy would only work once. This really needs to work smoothly before
more progress can be made.

Also, a 24Hz mode got rung up in one/several of the suspensions--this can also impede the stability of locks.

1027

Mon Oct 6 10:00:49 2008

Monday morning conditions:

The laser head temp is up to 20.5 C
The laser shut down on Friday without any good reason.
I was expecting the temp to come down slowly. It did not.
The control room temp is 73-74 F, Matt Evans air deflector in perfect position.
The laser chiller temp is 22.2 C

ISS is saturating. Alarm is on. Turning gain down from 7 to 2 pleases alarm handler.

c1LSC computer is down

Attachment 1: htup.jpg

1030

Tue Oct 7 10:49:29 2008

This morning I found that the photodidode of the PLL in the PSL table was not aligned to the beam anymore. The PD support was not tight to the pedestal so that the PD was rotated and completely off of the beam.

It is possible that the BNC cable connected to the PD was pulled very strongly, or the PD was hit so that the support got unscrewed by its pedestal. Anyways, it did not happen spontaneously.

I re-aligned the PD and observed again the beat between the two laser beams. Here are the values from the measurement of the signal from the PD:
I measured the DC values of the hitting power, alternatively occluding one of the two laser beams, and I measured the beat amplitude letting them interfere and reading the peak-to-peak amplitude of the oscillating signal:

main beam DC: 200mV
secondary beam DC: 490
beat: 990mV
beat at the spectrum analyzer (after the two-way splitter of the PLL): -8.40dBm on a noise floor of the photodiode of -75dBm

the frequency of the beast is 8.55MHz and the temperature of the NPRO of the secondary beam, as read from the laser driver display, is 48.7357C.

Alberto

1032

Tue Oct 7 21:19:40 2008

IOO

MC_F calibrated spectrum

I updated the plots because I did not take into account the double path AOM effect, which doubles the frequency actuation efficiency. (2008/10/8)

I determined the MC_F counts to the PSL frequency change calibration.
The attachment 1 is the calibrated MC_F spectrum, which is, above the cross over frequency, equivalent to the frequency noise seen by the MC.

The calibration method is the following:

1) I picked spare AD and DA channels (C1:IOO-MC_TMP1 and C1:OMC-SPARE_DAC_CH_16_EXC). C1:OMC-SPARE_DAC_CH_16_EXC is labeled C1:OMC-OSC_FM on the cable.

2) C1:IOO-MC_TMP1 was calibrated by injecting a sine wave of known amplitude and measuring the amplitude in counts in dataviewer.
It was 63uV/cnt.

3) C1:IOO-MC_TMP1 was connected to the feedback BNC connector of the MC board, that is the direct monitor of the feedback voltage to the VCO.

4) C1:OMC-SPARE_DAC_CH_16_EXC was connected to the channel B excitation input of the MC board, which adds the signal to the fast feedback path.

5) Using DTT a swept sine signal was injected to the MC board through C1:OMC-SPARE_DAC_CH_16_EXC, and the transfer function from C1:IOO-MC_TMP1 to the
C1:IOO-MC_F was measured.

6) Using the calibration of C1:IOO-MC_TMP1, the transfer function from the MC_F count to the actual voltage applied to the VCO input was obtained.
(attm2)

7) Using the DC calibration of the VCO input voltage to the VCO frequency change (1.75MHz/V elog:993) and the fact that there is a 1.6Hz pole and a 40.8Hz zero between the VCO input connector and the actual input of the VCO chip, the final calibration transfer function from the MC_F count to the frequency change of the PSL (that is twice the frequency change of the VCO within the bandwidth of the FSS) can be obtained (attm3).

8) The analytic form of the calibration TF is, poles at [1.6Hz, 11.42Hz, 11.42Hz] and zeros at [40.8Hz, 113Hz, 113Hz] with the DC gain of 110Hz/cnt.

Attachment 1: MC_F-spectrum.png

Attachment 2: VCO_VoverMC_F.png

Attachment 3: PSL_FoverMC_F.png

1035

Wed Oct 8 21:26:20 2008

Attempt to replace the DC-DC converter (aborted)

Rich, Steve, Yoichi

We opened the MOPA box and inspected our NPRO.
We concluded that this NPRO is different from the ones at the sites.
At the sites, the NPROs have a connector on the board which accepts the output of the DC-DC converter.
Rich's replacement DC-DC converter has a matching connector to it. So replacement of the DC-DC converter is easy.
In our NPRO, there is no such a connector found. The cables coming from the external power supply are directly soldered
on to the PCB (see attm1).

We have to take out the PCB in order to work on it.
As shown in the second picture, there is a D-SUB connector sticking out of the box through the rear panel.
In addition, the PCB is connected to the metal box containing the crystal with an IDE style connector.
This means the PCB is tightly constrained.
To take out the PCB without applying too much stress on it, we have to take off the rear panel.
To do so, we have to remove the screws on the bottom of the NPRO box. That means we have to move the NPRO.
We did not want to do so, because it will screw up the alignment to the amplifier.

The model number of the DC-DC converter looks like NMH0512-something.
According to the datasheet of NMH0512S, the switching frequency is typically 95kHz. We saw 77kHz harmonics in the FSS error signal.
I'm not sure if this is the culprit. I will try to measure the EMI from this guy later.

Attachment 1: DCDC.JPG

Attachment 2: NPRO.JPG

1037

Wed Oct 8 23:18:23 2008

Correlation between the Sorensen switching noise and the FSS error signal

I took some spectra and coherence function of the FSS error signal and the +24V Sorensen power line.
The first plot shows spectra of the two signals. Looks like Sorensen is not responsible for most of the lines
in the FSS error signal.
The coherence function between the two signals supports it (second plot).
Slight coherence can be seen at 23kHz and 98.4kHz but not significant.

I will check the coherence of the power line with the ISS signal next.

Attachment 1: PowerLineSpe.png

Attachment 2: Coherence.png

1042

Mon Oct 13 11:32:50 2008

Yoixhi

MOPA is in trouble now

Steve, Alberto, Yoichi

A quick update.
The MOPA output went down to zero on Sunday early morning (00:28 AM).
We found that the NPRO beam is mis-aligned on the power monitoring PD (126MON).
We don't know yet if it is also mis-aligned to the power amplifier (PA) because the mechanical shutter is not working (always closed).
Most likely the beam is not aligned to the PA.
A mystery is that although the beam is terribly (more than a half inch) missing the monitor PD, the beam still goes through two faradays.
Another mystery is that the NPRO output power is now increased to 600mW.

The power drop was a very fast phenomenon (less than 1/16 sec).
We are trying to figure out what happened.
The first step is to fix the mechanical shutter. We have a spare in our hand.

Attachment 1: powerdrop.png

1044

Mon Oct 13 13:56:03 2008

MOPA is not that much in trouble now

The problem was found to be all to do with the shutter.
The shutter started to work again, after a while, apparently for no clear reason.
The alignment to the PA was actually not screwed, and the MOPA output is now slowly increasing.
We figured that the 126MON PD has been mis-aligned for a long time. It was just picking the
scattered light from the output of the PA. So when the shutter is closed, it is natural that 126MON also goes down to zero.
It is a bit difficult to center the beam on the PD because there is not much room for moving the PD.
However, Alberto came up with a configuration (flip the PD and reflect back the beam with a mirror to the PD), which seems to
be feasible. We will do this modification when the MOPA is confirmed to be ok.

Here is more detail about the shutter problem:
The shutter is controlled by the MOPA power supply. There are three ways to command the power supply.
The switch on the front panel of the power supply, the EPICS switch (through a XYCOM XY220), and the interlock.
The ribbon cable from the power supply's back is connected to J1 of the cross connect. The pin 59 of the cable is the one
controlling the shutter. It is then routed to J12 pin 36. The interlock and a XYCOM switch are both connected to this
pin.
Now what happened was, on the way tracking down those cables, I pushed some connectors, especially the ones on the XYCOM.
After that, I was able to open the shutter from the EPICS button.
Steve and Alberto tried the EPICS button many times in the morning without success.
My guess is that it was some malfunctioning of the XY220 accidentally fixed by my pushing of the cables.
But I cannot exclude the possibility of the interlock malfunctioning.

Quote:

1045

Mon Oct 13 18:59:39 2008

NPRO EMI and FSS error signal correlation

I made a simple loop antenna to measure the electro-magnetic inteference (EMI) around the master oscillator NPRO.

The first plot shows the comparison of the FSS error signal with the EMI measured when the antenna was put next to the NPRO (the MOPA box was opened).
There are harmonics of 78.1kHz which are present in both spectra. It is probably coming from the DC-DC converter in the NPRO board.

The second plot is the same spectra when the antenna was put far from the NPRO (just outside of the PSL enclosure).
The 78.1kHz harmonics are gone. So these are very likely to be coming from the NPRO.

The third plot shows the coherence functions between the signal from the antenna and the FSS error signal.
When the antenna was put near the NPRO, there is a strong coherence seen around 78.2kHz, whereas there is no strong coherence
when the antenna is far away from the NPRO.
This is a strong evidence that the 78.2(or 78.1)kHz harmonics is coming from the NPRO itself.

There are many peaks other than 78.1kHz harmonics in the FSS error signal spectrum. For most of them you can also find corresponding peaks in the EMI spectrum.
We have to hunt down those peaks to avoid the slew-rate saturation of the FSS.

Attachment 1: IMG_1692.JPG

Attachment 2: Spectrum.png

Attachment 3: SpectrumFar.png

Attachment 4: Coherence.png

1047

Tue Oct 14 19:18:18 2008

Rana, Yoichi

Most of the FE computers failed around the lunch time.
We power cycled those machines and now all of them are up and running.
I confirmed that the both arms lock.
Now the IFO is in "Restore last auto-alignment" status.

1049

Wed Oct 15 17:40:50 2008

I set the PMC servo input offset: closed the MOPA shutter, zeroed the mixer output with the offset slider,
relocked everything, and set the nominal to the new value of -6 V.

1051

Thu Oct 16 09:44:49 2008

Yesterday arount 1:30PM, we lost the LO signal for the FSS.
I found it was caused by a bad cable connecting from the peter's RF oscillator box to the LO of the FSS.
I temporarily replaced it with a BNC cable of comparable length.

1056

Fri Oct 17 21:41:09 2008

Computer Scripts / Programs

burtwb missing on Solaris but installed on linux64

c1lsc stalled this evening, so I powercycled it.
After that, I tried to lock arms to confirm the computer is working.
Then I realized that the restore alignment buttons do not work from any control room computer.
I found that it was because burtwb command was missing. For Solaris, looks like there used to be /cvs/cds/epics/extensions/burtwb but now
there is no /cvs/cds/epics directory. I thought there were directories other than "caltech" in /cvs/cds/, weren't there ?
Right now, there is only /cvs/cds/caltech.
Anyway, I installed burt for 64bit linux computer (under /cvs/cds/caltech/apps/linux64/epics/extensions/).
At this moment the alignment save/restore works on allegra (and probably on rosalba), but not on op440m yet.

1057

Mon Oct 20 09:45:56 2008

The PSL HEPA filter was turned on.
It should be running all times.
The 0.5 micron particle count is up to 20,000 this morning.

1058

Mon Oct 20 12:18:38 2008

Alan

Computer Scripts / Programs

burtwb missing on Solaris but installed on linux64

Quote:

The automatic backup of /cvs/cds (and /frames/minute-trends ) to the LIGO archive in Powell-Booth,
which runs from fb40m using the scripts in /cvs/cds/caltech/scripts/backup ,
stopped when fb40m was rebooted on June 28, 2008,
and the check_backup script I run to send an email when this happens also failed due to a scripting error.

But we still have a backup of /cvs/cds from June 27.

The backup of /cvs/cds (excluding /cvs/cds/caltech and /cvs/cds/tmp)
circa June 27, 2008
has been restored to
/cvs/cds/recover_20081020 .

Please check to see that it has what we need.

Before moving it over to where it belongs,
it would be really nice to figure out what happened...

Meanwhile, I have fixed the check_backup script and restarted the backup, which will run this evening...
but maybe I should wait till the dust settles?

Now is also a good time to think about whether there is anything else besides for
/cvs/cds and /frames/minute-trends that should be backed up regularly.

- Alan

1062

Tue Oct 21 16:14:42 2008

steve

divergence of He Ne 1035P

The ITM oplevs laser diodes are noisy.
They will be replaced by JDS 1035P
SN T8093307 was measured with the beamscanner.
This will able us to calculate the right lenses to get a small beam on the qpd.

**

The first column is distance from the front face of the laser in cm.
The second column is beam diameter in the horizontal direction in microns.
The third column is the beam diameter in the vertical direction in microns.

(edit by Rana)

Attachment 1: 1035p_divergence.png

1063

Tue Oct 21 16:17:45 2008

AD797 Oscillation in the FSS board

I checked each op-amp's output in the FSS board to see if any indication of slew-rate saturation can be found.
PA85, which was the most suspicious one, actually has a very large slew rate limit (1000V/usec).
Its output swing was about 5V/usec. So PA85 was ok in terms of slew rate.
However, I found that an AD797 used at the first stage of the PC path was oscillating by itself, i.e. even without the loop closed.
The frequency was about 50MHz and the amplitude was large enough to reach the slew rate limit of this chip (the steepest slope was 30V/usec whereas the slew
rate limit of AD797 is 20V/usec).

I replaced it and another AD797 right after the oscillating one with AD829s. Just replacing the chips caused oscillation of AD829.
It was because there were no phase compensation capacitors connected to the pin 5 of AD829s.
Since the PCB was designed for AD797, there is no pattern for compensation caps. So I ended up putting Mica capacitors (47pF) across the pin 5 and the nearest ground point.
It worked and the oscillation stopped.

As I reported in an earlier elog, stopping the oscillation did not solve the problem of low FSS bandwidth.

1067

Wed Oct 22 12:37:47 2008

Attached in open office format as well as excel format is spreadsheet containing all the devices with IP addresses at the 40m. Please contact me with any corrections.

Attachment 1: 40m_network_10-15-08.ods

Attachment 2: 40m_network_10-15-08.xls

1069

Wed Oct 22 17:48:58 2008