[Suresh / Kiwamu]
The attenuator was removed and now the MC is happily locked with the full power of 1.2 W.
(what we did)
+ replaced the perfect reflector, which was before the MCREFL_PD, by a 10% beam splitter like it used to be.
+ removed the attenuator (combination of HWP and PBS).
+ realigned the beam path on the AP table, including the MCREFL path and WFS path.
+ made the aperture of the MC2F camera narrower in order to avoid a saturation.
+ aligned the MC suspensions so that it resonates with the TEM00 mode.
+ put a ND filter on the AS camera
C1:IOO-MC_RFPD_DCMON = 0.98 (locked)
C1:IOO-MC_TRANS_SUM = 17500 (locekd)
(next things to do)
+ measurement of the spot positions on each MC mirror.
+ centering of the beam spot by steering the input mirrors on the PSL table
Last night I noticed that PZT1 didn't work properly
I am not sure what is going on. Today I will try localizing the cause of the problem.
As far as I remember it was perfectly working at the time just after we readjusted the OSEMs on MC1 and MC3 (Aug 23th)
The symptoms are :
+ No response to both pitch and yaw control from EPICS (i.e. C1:LSC-PZT1_X and C1:LSC-PZT1_Y)
+ When a big value (-3 or so) from EPICS was applied, the PZT1 mirror suddenly jumped.
However it turned out it just corresponded to a state where OOR (Out Of Range) LED lights up.
I did some brief checks :
+ checked the voltage going into the HV amplifiers' "MOD" input. Those are the voltage coming out from DACs and controlled from EPICS.
--> looked healthy. They went from -10 to 10 V as expected (although the HV amp takes up to only +/-5V).
+ swapped the ''MOD" input cables such that C1:LSC-PZT1 controls the PZT2 HV and vice versa.
--> The PZT2 mirror was still controlable, but the PZT1 mirror still didn't move. So the DAC and EPICS are innocent.
+ swapped the D-dub cables, which are directly going into the feedthroughs, such that the PZT1 HV drives the PZT2 mirrors and vice versa.
--> the PZT2 mirror became unable to be controlled. For the PZT1 mirror, only PITCH worked smoothly.
Something happened about 8 years ago.
Old iLog entry by AJW (2003/Sep/8)
Old iLog entry by AJW (2003/Sep/9)
The spot positions on the MC mirrors were measured in the vacuum condition.
The obtained spot positions are quite bad and roughly at 2-3 mm level. We have to realign the beam axis and the MC mirrors.
Aug 23 2011 (in air)
After Steve pointed out the 'deep hoop' issue, we decided to examine putting an RF Amp on the PSL table, between the RF combiner and the triple resonant box.
5) No proper stuff from Teledyne Couger
By looking at what Daniel used in the low noise EOM Driver for aLIGO, we found the A2CP2596 from Cougar.
G = +24 dB, NF = 5 dB, Max Out = +37 dBm. It comes in a 2-stage SMA connector package. I've asked Steve to order 2 of them with the appropriate heatsinks.
The spot positions on the MC mirrors were readjusted.
All the amount of the off-center became smaller than 2 mm, which meet requirements of the beam clearance on the Faraday.
In order to improve the MC1-YAW and MC3-YAW spot positions, the angle of the incident beam has to be shifted by approximately 1/100 rad.
However it turned out to be very difficult to introduce such amount of angle only with the steering mirrors on the PSL table since we have to keep the same translation while changing the angle.
I re-aligned the beam onto the MC TRANS QPD since Kiwamu had centered the spots on the mirrors. However, I then inspected the MC2F camera. After coming back into the control room I noticed that the MC transmission had gone down by 50% and that the MC2 OSEMs showed a large step. My guess is that somehow the opening and closing of the can shifted the suspension. So I adjusted the MC2 alignment biases to recover the transmitted power (its now ~50000 instead of the ~33000 from Friday).
[Mirko / Kiwamu]
The resonant box has been installed together with a 3 dB attenuator.
The demodulation phase of the MC lock was readjusted and the MC is now happily locked.
We needed more modulation depth on each modulation frequency and so for the reason we installed the resonant box to amplify the signal levels.
Since the resonant box isn't impedance matched well, the box creates some amount of the RF reflections (#5339).
In order to reduce somewhat of the RF reflection we decided to put a 3 dB attenuator in between the generation box and the resonant box.
+ attached the resonant box directly to the EOM input with a short SMA connector.
+ put stacked black plates underneath the resonant box to support the wight of the box and to relief the strain on the cable between the EOM and the box.
+ put a 3 dB attenuator just after the RF power combiner to reduce RF reflections.
+ readjusted the demodulation phase of the MC lock.
(Adjustment of MC demodulation phase)
The demodulation phase was readjusted by adding more cable length in the local oscillator line.
After some iterations an additional cable length of about 30 cm was inserted to maximize the Q-phase signal.
So for the MC lock we are using the Q signal, which is the same as it had been before.
Before the installation of the resonant box, the amplitude of the MC PDH signal was measured in the demodulation board's monitor pins.
The amplitude was about 500 mV in peak-peak (see the attached pictures of the I-Q projection in an oscilloscope). Then after the installation the amplitude decreased to 400 mV in peak-peak.
Therefore the amplitude of the PDH signal decreased by 20 %, which is not as bad as I expected since the previous measurement indicated 40 % reduction (#2586).
The shift of MC2 which Rana noted caused the beam spots on the MC mirrors to decenter. I used the mcassUp and mcassOn scripts and checked the output of the C1IOO lockins to get the spot positions. I first tried to realign just the MC2 to recenter the spots. But this was not sufficient. I then worked on the pitch of all three optics since it is easier to align. By the time this was done the offset in yaw also reduced, probably due to cross coupling between pitch and yaw in the coils. At the end of the process I obtained all decentering around 1.5mm or less, then I went over to adjust the MC2TransQPD beam path so that we center the spot on the QPD. This action shifted the stack, I had to iterate this two more times before the successive corrections grew sufficiently small. I think it may shift again if we touch the chamber (the image of MC2Face is still inverted).
The new spot positions in mm (MC1,2,3 pit MC1,2,3 yaw):
1.3212 -0.8415 0.6795 -1.4292 -0.3574 -1.5208
- Further improvement of beam centering can be done but first I would like to be sure that the MC is stable. The MC2Trans light is centered on the QPD as a reference.
- We have checked the situation of the broken Piezo Jenna PZT (called PZT1)
- Tested PZT1 by applying a dc voltage on the cables. Found that pitch and yaw reasonably moving and the motions are well separated each other.
The pitch requires +20V to set the IPPOS spot on the QPD center.
- Made a high-voltage (actually middle voltage) amp to convert +/-10V EPICS control signal into -5 to +30V PZTout. It is working on the prototype board and will be put into the actual setup soon.
- The Piezo Jenna driver box has 4 modules. From the left-hand side, the HV module, Yaw controller, Pitch controller, and Ben abbot's connector converter.
- We checked the voltage on Ben's converter board. (Photo1)
It turned out that the red cable is the one have the driving voltage while the others stays zero.
- We hooked a 30V DC power supply between the red cable and the shield which is actually connected to the board ground.
- Applying +/-10V, we confirmed the strain gauge is reacting. If we actuated the pitch cable, we only saw the pitch strain gauge reacted. Same situation for yaw too.
- Kiwamu went to IPPOS QPD to see the spot position, while I change the voltage. We found that applying +20V to the pitch cable aligns the spot on the QPD center.
- I started to make a small amplifier boards which converts +/-10V EPICS signals into -5V to +30V PZT outs.
- The OPAMP is OPA452 which can deal with the supply voltages upto +/-40V. We will supply +/-30V. The noninerting amp has the gain of +2.
- It uses a 15V zener diode to produce -15V reference voltage from -30V. This results the output voltage swing from -5V to +35V.
The actual maximum output is +30V because of the supply voltage.
- On the circut test bench, I have applied +/-5V sinusoidal to the input and successfully obtained +5V to +25V swing.
- The board will be put on Ben's board today.
The PZT driver is now in place. The actual PZTs are not connected yet!
It is accommodated on Ben's connector adapter board.
The panel has additional connectors now: two inputs and a power supply connector.
The supply voltage is +/-30V (actual maximum +/-40V), and the input range is +/-10V
which yields the output range of -5V to 30V. The gain of the amplifier is +2.
It is confirmed that the HV outputs react to the epics sliders although the PZT connector is not connected yet
so as not to disturb the locking activity.
When we engage the PZT connector, we should check the HV outputs with an oscilloscope to confirm they
have no oscillation with the capacitances of the PZTs together with the long cable.
The pzt driver for PZT1 has been installed.
As there was unknown resistive connection in the vacuum chamber as described below,
the PZT out cable at the PJ driver module should always be disconnected.
The sensor cables have no problem to be connected to the controller.
In fact, they are a good monitor for the state of the PZTs.
In this configuration, Pitch and Yaw direction of PZT1 is under the control of the EPICS value as we expected.
- At the beginning, we tested the PZT driver output with low voltage level (~10V). We did not see any oscillation of the opamps.
The pitch output was observed to be OK, while the YAW output exhibited a half of the expected output voltage.
The opamp was holding correct voltage, however the voltage after the 1K output resister was about a half.
This indicated there was a voltage division happening.
- The cause of the voltage division was tracked. We found that the yaw red (=hot) line is connected to pitch black
in the vacuum chamber with a resistance of 1.4kOhm. The black cables are shorted to the ground level in the PJ driver.
- We decided to unplug the PJ's cable so that we can isolate the black cables while hoping the PZTs were drived only
by the red and white cables. And they did.
- This means that we should not connect the PZT driving cable to the PJ's driver. The sensors have no problem to be connected.
|. o| 5
|o | 17
| o| 4
|o | 16 Yaw Black
| o| 3 Pitch Black
|o | 15 Yaw White
| o| 2 Yaw Red
|o | 14 Pitch White
\ o| 1 Pitch Red
* Pitch White and Yaw White are connected to the ground at the amplifier side.
* Yaw Red and Pitch Black is connected with 1.4kOhm and isolated from the others.
IPPOS is back. A cable had been disconnected at the 1Y2 rack. So I put it back to place.
The cartoon below shows the current wiring diagram. I think this configuration is exactly the same as it it used to be.
+ Fixing IPPOS (volunteers)
We started to investigate the AM modulation mistery again. Checking just after the EOM, there are AM modulation about -45dBm. Even if we adjust the HWP just before the EOM, AM components grow up in 5 mins. This is the same situation as before. Only the difference from before is that we don't have PBS and HWP between the EOM and the monitor PD. So we have a simpler setup this time.
We will try to align the pockells cell alignment tomorrow daytime, as it may be a problem when the crystal and the beam are not well parallel. This adjustment has been done before and it didn't improve AM level at that time.
Since the MC wasn't able to capture the 00 mode in this morning I aligned the incident beam going to MC.
As a result C1:IOO-RFPD_DCMON went down to 0.6. However the beam on IPPOS is almost falling off from the QPD.
Modulation resonator box is removed and the modulation depth is small right now.
I have broke the BNC connector on the modulation resonator box. The connector was attached by the screw inside very loosely and when we connect and disconnect the BNC cables from outside, extra force was applied to the cable inside and it was broke. It is being fix by Kiwamu and will be back in a bit.
Resonator box and the modulations are back now. But the modulation depth seems to be a bit smaller than yesterday, looking at the optical spectrum analyser.
I have broke the BNC connector on the modulation resonator box. The connector was attached by the screw inside very loosely and when we connect and disconnect the BNC cables from outside, extra force was applied to the cable inside and it was broke. It is being fix by Kiwamu and will be back in a bit
This morning after Kiwamu maximised the PSL beam coupling into the MC we noticed that the MC2 face camera showed the spot position had moved away from the center by about a diameter. So I checked the beam spot positions with MCASS and indeed found that the spot on MC2 had moved to about 6mm away from the center in yaw and about 3mm in pitch. I adjusted the MC2 (and only MC2) to recenter the spots on all the three mirrors. The new spot positions are given below
spot positions in mm (MC1,2,3 pit MC1,2,3 yaw):
1.3337 -0.2660 0.6641 -1.0973 0.0468 -1.7130
The PSL beam into MC has been readjusted for maximal coupling into MC.
AM modulations are still there ... the mechanical design for the stages, RF cables, and connections are not good and affecting the alignment.
I write the activity in the time series this time - Because we suspect the slight EOM misalignment to the beam produces the unwanted AM sidebands, we tried to align the EOM as much as possible. First I aligned the EOM tilt aligner so that the maximum power goes through. I found that about 5% power was dumped by EOM. After adjusting the alignment, the AM modulation seemed be much better and stable, however, it came up after about 20 mins. They grew up up to about -40dBm, while the noise floor is -60 dBm (when AM is minimised, with DC power of 8V by PDA225 photodetector).
We changed the EOM stage (below the tilt aligner) from a small plate to a large plate, so that the EOM base can be more stable. The EOM stands on the pile of several black plate. There was a gap below the tilt aligner because of a small plate. So we swapped the small plate to large plate to eliminate the springly gap. However it didn't make any difference - it is the current status and there is still AM modulations right now.
During above activities, we leaned that the main cause of the EOM misalignment may be the RF cables and the resonator box connected to the EOM. They are connected to the EOM by an SMA adaptor, not any soft cables. It is very likely applying some torc force to the EOM box. The resonator box is almost hunging from the EOM case and just your slight touch changes EOM alinment quite a bit and AM mod becomes large.
I will replace the SMA connector between the resonator box and EOM to be a soft cable, so that the box doesn't hung from EOM tomorrow. Also, I will measure the AM mod depth so that we compare with the PM mod depth.
AM modulation depths are found to be 50 times smaller than PM modulation depths.
m(AM,f1) ~ m(AM, f2) = 0.003 while m(PM, f1)=0.17 and m(PM, f2)=0.19.
* DC power = 5.2V which is assumed to be 0.74mW according to the PDA255 manual.
*AM_f1 and AM_f2 power = -55.9 dBm = 2.5 * 10^(-9) W.
AM f2 power is assumed to be the similar value of f1. I can't measure f2 (55MHz) level properly because the PD (PDA255) is 50MHz bandwidth. From the (P_SB/P_CR) = (m/2) ^2 relation where P_SB and P_CR are the sideband and carrier power, respectively, I estimated the rough the AM modulation depths. Although DC power include the AM SB powers, I assumed that SB powers are enough small and the DC power can be considered as the carrier power, P_CR. The resulting modulation depth is about 0.003.
On the other hand, from the OSA, today's PM mod depths are 0.17 and 0.19 for f1 and f2, respectively. Please note that these numbers contains (small) AM sidebands components too. Comparing with the PM and AM sideband depths, AM sidebands seems to be enough small.
AM modulations are still there ... the mechanical design for the stages, RF cables, and connections are not good and affecting the alignment.
I'd like to see some details about how to determine that the ratio of 1:50 is small enough for AM:PM.
* What have people achieved in past according to the elogs© of the measurements?
* What do we expect the effect of 1:50 to be? How much offset does this make in the MICH/PRC/SRC loops? How much offset is too much?
Recall that we are using frontal modulation with a rather small Schnupp Asymmetry...
The signal offset due to the AM modulation is estimated by a simulation for PRCL for now. Please see the result below.
Too see how bad or good the AM modulation with 1/50 modulation depths of PM, I ran a simulation. For example I looked at PRCL sweep signal for each channel. I tried the three AM modulation depths, (1) m_AM=0 & m_PM = 0.17 (2) m_AM = 0.003 & m_PM = 0.17 which is the current modulation situation (3) m_AM = 0.17 & m_PM = 0.17 in which AM is the same modulation depth as PM. For the current status of (2), there are offsets on signals up to 0.002 while the maximum signal amplitude is 0.15. I can't tell how bad it is.... Any suggestions?
(1) m_AM=0 & m_PM = 0.17. There is no offset in the signals.
(2) m_AM = 0.003 & m_PM = 0.17. There are offsets on signals up to 0.002 while the maximum signal amplitude is 0.15.
(3) m_AM = 0.17 & m_PM = 0.17. There are offsets on signals up to 0.1 while the maximum signal amplitude is 0.2.
I will look at MICH and SRCL in the same way.
I found the PSL beam into the MC off in pitch by large amount. I readusted the PSL beam for optimal coupling.
The beam had shifted on the WFS as well. So I recentered the DC signal on the WFS with the MC unlocked. However both the DC and RF signals on the WFS shift when we lock the MC. This ought to indicate sub-optimal coupling of PSL into MC. But instead, if we were to reduce these offsets on the WFS by adjusting the MC axis it leads to higher reflected power from the MC.
The current plan is to retain these RF offsets and lock the WFS with a DC offset in the servo filters.
How about changing the x-axis of all these plots into meters or picometers and tell us how wide the PRC resonance is? (something similar to the arm cavity linewidth expression)
Also, there's the question of the relative AM/PM phase. I think you have to try out both I & Q in the sim. I think we expect Q to be the most effected by AM.
AM modulation will add offset on SRCL signal as well as PRCL signal. About 2% of the signal amplitude with the current AM level. MICH will not be affected very much.
From #5504, as for the AM modulation I checked the MICH and SRCL signals in addition to the last post for PRCL, to see the AM modulation effect on those signals. On the last post, PRCL (REFL11I) was found to have 0.002 while the maximum signal amplitude is 0.15 we use . Here, I did the same simulation for MICH and SRCL.
As a result, MICH signals are not affected very much. The AM modulation slightly changes signal slopes, but doesn't add offsets apparently. SRCL is affected more, for REFL signals. All the REFL channels get about 0.0015 offsets while the signal ampliture varies up to 0.002. AS55I (currently used for SRCL) has 1e-7 offset for 6e-6 amplitude signal (in the last figure) - which is the same offset ratio comparing with the amplitude in the PRCL case -
(1) MICH signals at AS port with AM m=0
(2) MICH signals at AS port with AM m=0.003
(3) SRCL signals at AS/REFL port with AM m=0
(3) SRCL signals at AS/REFL port with AM m=0.003
Rana noticed that the sum on WFS2 was about 10 times smaller than that on WFS1. Though the beam appeared centered on the DC QPD screens it was not really true. When I went and checked the actual beam position it was landing on the metal enclosure of the WFS2 sensor and scattering back on to the diode.
I also checked the power levels of light landing on the sensors It was about 0.25mW in both cases. This needs further investigation since the power split at the beam spitter is like 0.25mW onto WFS1 and 0.45 towards WFS2. The lost 0,20 mW has to be traced and we have to be sure that it is not scattered around on the table.
Rana advised that we put in a lockin-output matrix which will allow us to excite any combination of MC mirrors so that we can excite pure translations or rotations of the MC beam axis. This would require us to direct a lockin output into all the three mirrors simultaneously with a +1 or -1 as needed in the matrix..
I noticed that the beam centering on the WFS had changed over night and the MC_TRANS_SUM was about 40k counts. When well aligned this SUM is around 50-55k counts. So PSL coupling into MC was suboptimal. It was not clear whether the MC shifted or the PSL beam shifted. So I looked at the PSL ANG and POS QPDs.
The plots above show the gradual drift of the PSL beam in vertical direction during the last 8hrs or so. But the last bit shows the adjustments I had to make to reobtain optimal alignment. And these adjustments are not undoing the drift! This would indicate that the MC axis has also shifted during the same time period.
From the night day before yesterday (Sep 22nd, Thursday night. Sorry for my late update), there are more AM modulations than I measured in the previous post. It is changing a lot, indeed! Looking at the REFL11 I and Q signals on the dataviewer, the signal offset were huge, even after "LSCoffset" script. Probably the modulation index of AM was same order of PM at that time. The level of AM mod index is changing a lot depending on the EOM alingment which is not very stable, and also on the environment such as temperature .
To reduce AM modulations, here I note some suggestions you may want to try :
* Change the SAM connectors between RF resonator and EOM to be a soft but short connector, so that the resonator box doesn't hung from the EOM.
* Change the RF resonator base to be stable posts. Now several black plates are piled to make one base.
* Install a temperature shield
* Also probably you want to change the BNC connector on the RF resonator to be SMA.
* Be careful of the EOM yaw alignment. Pitch seemed to be less sensitive in producing AM than yaw alignment.
We have reviewed the AM issue and confirmed the ratio of AM vs. PM had been about 6 x103.
The ratio sounds reasonably big, but in reality we still have some amount of offsets in the LSC demod signals.
Next week, Mirko will estimate the effect from a mismatch in the MC absolute length and the modulation frequency.
Please correct us if something is wrong in the calculations.
According to the measurement done by Keiko (#5502):
DC = 5.2 V
AM @ 11 and 55 MHz = - 56 dBm = 0.35 mV (in 50 Ohm system)
Therefore the intensity modulation is 0.35 mV / 5.2 V = 6.7 x 10-5
Since the AM index is half of the intensity modulation index, our AM index is now about 3.4 x 10-5
According to Mirko's OSA measurement, the PM index have been about 0.2.
As a result, PM/AM = 6 x 103
I relocked the PMC (why is it unlocking so much lately??), and then noticed that even though the MC is locked, MC Trans Sum, P, Y, are all seeing digital zero. I'm putting Suresh, as IOO guy, in charge of figuring it out.
The shutter before the MC was closed at 3:30 as I started working on the RFAM.
MC REFL (INLOCK): 0.6~0.7
MC REFL (UNLOCK): 6.9
MC TRANS: 50000~52000
I thought this problem might be arising because the MC2_TRANS QPD signals are not being passed from the c1mcs to c1ioo models over the rfm. But there was no way to check if there is any data being picked up in c1mcs model. So I copied the MCTRANS block from the c1ioo model into the c1mcs. This block takes the four segments of the MC2_TRANS QPD and computes the pitch, yaw and sum signals from that. It also exports these into epics channels. I then recompiled and started the c1ioo c1mcs and c1rfm models.
Restared fb at
Tue Oct 4 15:19:10 PDT 2011
Koji then noted that the MC2_TRANS filter banks in c1rfm and in c1ioo were showing nonzero values. So the signals were infact reaching the c1ioo model. They were being blocked by the INMATRIX (which the autoburt had not restored) of the MC_TRANS block, because all its elements were zero. We burtrestored the c1iooepics to about 30hrs ago and then MC_TRANS signals were back in the LOCK_MC screen.
Finished the work at 6:30
MC REFL (INLOCK): 0.50-0.52
MC REFL (UNLOCK): 6.9
MC TRANS: 54400~547000
Before the work: -48.5dBm for 1.07VDC (both 50Ohm terminated)
Right after the work: -80dBm for 0.896VDC (both 50Ohm terminated)
10min after: -70dBm
1hour after: -65dBm
3hours after: -62dBm
1day after (Oct 5, 20:00): -62.5dBm
2days after (Oct 6, 23:20): -72.5dBm
3 days after (Oct 7, 21:00): -57.8dBm
MC REFL (INLOCK): 0.6~0.7
MC REFL (UNLOCK): 6.9
MC TRANS: 50000~52000
Koji and Kiwamu had adjusted the MC beam axis slightly such that we can couple the MC output into the Y-arm without exceeding the current range of adjustability on PZT1. This changed the centering of beam spots on MC mirrors. I checked the mc-decentering make sure we have not made too big a compromise. And since we can move MC2 spot position while maintaining the current positions on MC1 and MC3 decentering, we can atleast eliminate the A2L coupling on that mirror. I used the scripts in $scripts$/MC/moveMC2/ to adjust the MC2 spot position.
Spot positions in mm (MC1,2,3 pit MC1,2,3 yaw) before adjustment:
1.4674 -0.3548 1.0199 -1.5519 1.9834 -1.5971
After correcting MC2:
1.4528 0.1431 0.9958 -1.2147 0.3823 -2.0163
After correcting MC1:
1.3745 0.0669 0.8899 -1.5269 0.0296 -1.7314
The spot positions on MC1 and MC3 are very nearly (+/- 0.06 mm) same as before, while the MC2 decentering has been reduced close to zero.
A slight adjustment of the PZTs may be required to reset the beam pointing.
After centering the spot on the MC2, I started to adjust the spot position on MC_TRANS_QPD to center the beam on it. I noticed that the spot size was about 3 to 4mm dia. because the 200mm lens was too close to the QPD. I moved it back and decreased the spot size to about 1mm and the sensitivity to spot position increased. However, Koji noted that the QPD sectors were near saturation, so I put in a ND=0.3 filter to reduce the incident power on the QPD.
At optimal alignment the current QPD_SUM is around 25k to 26k counts (factor of 2 down). Eventually the gain of the QPD ckts have to be reduced to prevent saturation, for the moment this is temporary fix.
The MC_TRANS_SUM trigger for MC autolocker is working fine no further change was required.
[Kiwamu, Koji, Suresh]
After correcting several errors in the WFS loops, we turned them on today and saw them working!
A while back (last week actually) I noticed that the WFS1 and WFS2 QPD segments were numbered in a different order but that their input matrices did not reflect this change. As result the WFS pitch and yaw definitions were pretty much mixed up. However even after clearing this up the signals still showed significant amount of cross couplings.
This problem was finally traced to the relative phase between I and Q channels of the WFS segments. Koji suggested that I check the relative phase between all the segments to be sure. I then repeated the procedure that Valera and I followed in our earlier elog # 5321 , and found that the phases indeed required to be adjusted. The excitation of MCL was at 6Hz, 100mVpp, as before. The WFS response after this was much improved i.e. the pitch yaw cross couplings were not visible when we misalign the MC with sliders in MC_ALIGN. And the magnitude of the response also increased since the signal was transferred from the Q to I channels. The the phases were tweaked by hand till Q< 1% of I. However when I repeated this measurement an hour later (I wanted to save the plots) I found that the phases had changed by a few percent!
Koji noticed that the MC_REFL camera image showed significant intensity fluctuations and advised that we try a higher frequency and lower amplitude to avoid nonlinear effects in the WFS and in the MCL to PSL lock. So we repeated the process at 20Hz and 20mVpp, introduced at the IN2 of the MC_Servo. The fig below shows the level to which we reduced the signal in Q.
We then checked the relative phase between various quadrants by looking at the time series in dataviewer. WFS2 Seg4 phase had to be flipped to bring it into phase with all the rest.
After this I tried to see the WFS response to moving the MC1 and MC3 with the sliders and determined the following relations:
Disregarding the MC2 for now and assuming arbitrary gains of 1 for all elements we inverted these matrices inserted them into the WFS_servo_outmatrix. We then found that the with a sign flip on all elements the loops were stable. In the servo filters we had turned on only the filter modules 3 and 4. There was no low frequency boost. We gradually increased gain till we saw a significant suppression of the error signal at low frequencies as shown below. There was also an associated suppression of Intensity noise at REFL_DC after a single bounce from PRM.
To see if the locks can actually realign the MC if it were manually misaligned, we turned the loops off and misaligned MC by moving MC3 pitch by 0.05 (slider position), and then turned on the loops. The locks were reengaged successfully and the MC regained alignment as seen on the StripTool below:
We can now proceed with the fine tuning the servo filters and understand the system better:
Q1: Does the WFS (I to Q) phase drift rapidly? How can we prevent it?
Q2: How is that we do not see any bounce or roll resonances on the WFS error signals?
Q3: How do we include the MC2 QPD into the WFS Servo?
I will proceed with determination of the actual transfer coefs between the MC DoF and the WFS sensors.
After we had a rough idea of what the output matrix looks like (see this elog),I tried to measure the transfer function coefs (TFCs) between mirror degrees of freedom and the WFS sensors (WFS1, WFS2 and MC_Trans QPD)I found that the TFCs that I obtained at 10.15 Hz did not have any resemblance to the previously identified output matrix.The problem, I realised, arises because the various lockins usedin the C1IOO model do not have the same relative phase; So if we try to excite a mirror with one of themand demodulate a sensor signal on any of the other lockins the resulting output would not have the correct phase(relative to the 1st lockin output). As a result unless we can reset the phase of all the lockinssimultaneously, we cannot demodulate multiple signals at the same time. (Joe/Jamie, Is it possible toreset/reinitialise the phase of the CLK signals of the lockings? )To get around this problem Koji suggested that I use just one lockin and determine all the 36 elements of the transfer matrix with it one at atime rather than six at a time. When I did that, I got results consistent with the previoulsly determined outmatrix. It, of course, takes six times longer.
After we had a rough idea of what the output matrix looks like (see this elog),I tried to measure the transfer function coefs (TFCs) between mirror degrees of freedom and the WFS sensors (WFS1, WFS2 and MC_Trans QPD)I found that the TFCs that I obtained at 10.15 Hz did not have any resemblance to the previously identified output matrix.
The problem, I realised, arises because the various lockins usedin the C1IOO model do not have the same relative phase; So if we try to excite a mirror with one of themand demodulate a sensor signal on any of the other lockins the resulting output would not have the correct phase(relative to the 1st lockin output). As a result unless we can reset the phase of all the lockinssimultaneously, we cannot demodulate multiple signals at the same time. (Joe/Jamie, Is it possible toreset/reinitialise the phase of the CLK signals of the lockings? )
To get around this problem Koji suggested that I use just one lockin and determine all the 36 elements of the transfer matrix with it one at atime rather than six at a time. When I did that, I got results consistent with the previoulsly determined outmatrix. It, of course, takes six times longer.
The matrix I first got is this one
Note that when MC2 is excited all the sensors showed a response about 75 deg out of phase with the reference (MC1 --> WFS1_PIT ) This was traced to the fact that while there is a 28Hz Elliptic LP filter on
both MC1 and MC3, while it is absent on MC2. The Transfer functions below show the difference in the phase of their response
Since the MC2 POS is used in servos involving MCL we cannot afford to install a 28 Hz LP filter into the MC2 coil drivers. However a module with the 28 Hz ELP was switched on, in each of the
MC2 PIT and YAW filter banks. I then checked to see if this has affected the relative phase of variour sensors. The Phase angle between I and Q on each sensor channel was checked and corrected.
Below are the spectra with the "before" and "after" correction of phases.
Obviously this needed adjustment to reduce Q phase.
After twealkng the angle "R":
And again determined the transfer matrix (below).
This time the signals are all nearly in the same phase and in agreement with the outmatrix estimate made earlier.
I plugged these TFCs into the matrix inversion code: wfsmatrix2.m. And get the following inverse:
I have ignored the MC2_Trans_P and Y sensors for now.
In order to save time and sanity, you should not measure the pitch ->yaw and yaw-> pitch. It makes things too complicated and so far is just not significant. In the past we do not use these for the matrix work.
i.e. there should just be a 3x3 pitch matrix and a 3x3 yaw matrix. Once the loops are working we could investigate these things, but its really a very fine tweak at the end. There are quite a few other, more significant effects to handle before then.
To make things faster, I think we can just make a LOCKIN which has 3 inputs: it would have one oscillator, but 6 mixers. Should be simple to make.
I think the idea of having multiple inputs in a LOCKIN module is also good for the LSC sensing matrix measurement.
Because right now I am measuring the responses of multiple sensors one by one while exciting a particular DOF by one oscillator.
Moreover in the LSC case the number of sensors, which we have to measure, is enormous (e.g. REFL11I/Q, REFL33I/Q, REFL55I/Q, ... POY11I/Q,...) and indeed it has been a long-time measurement.
To see if the loops will stay locked when the Integrators in the servo are switched on, we stayed with the same simple output matrix (just 1 or -1 elements) and switched on the FM1 on all WFS servo filter banks. We monitored the time domain error signals to see if engaging the locks made the error signals go to zero. Most of the error signals did go to zero even when an intentional offset was introduced into the MC pitch of the suspension.
We need to include TestPoints just before the Input Servo Matrix so that we can monitor the error signals without being affected by the gain changes in the WFS_GAIN slider. These are currently not present in the C1IOO model and the position of the WFS_GAIN also has to be shifted to the other side of the Input matrix.
The C1IOO_WFS_MASTER screen has been changed to the new one. This incorporates filter banks for the MC_TRANS_P and _Y channels. The screen is not yet fully functional but I am working on it and I it will continue to improve it.
[Suresh / Koji / Rana / Kiwamu]
Last night we had a discussion about what we do for the RFAM issue. Here is the plan.
1. Build and install an RFAM monitor (a.k.a StochMon ) with a combination of a power splitter, band-pass-filters and Wenzel RMS detectors.
=> Some ordering has started (#5682). The Wenzel RMS detectors are already in hands.
2. Install a temperature sensor on the EOM. And if possible install it with a new EOM resonant box.
=> make a wheatstone bridge circuit, whose voltage is modulated with a local oscillator at 100 Hz or so.
3. Install a broadband RFPD to monitor the RFAMs and connect it to the StochMon network.
=> Koji's broadband PD or a commercial RFPD (e.g. Newfocus 1811 or similar)
4. Measure the response of the amount of the RFAM versus the temperature of the EO crystal.
=> to see whether if stabilizing the temperature stabilizes the RFAM or not.
5. Measure the long-term behavior of the RFAM.
=> to estimate the worst amount of the RFAM and the time scale of its variation
6. Decide which physical quantity we will stabilize, the temperature or the amount of the RFAM.
7. Implement a digital servo to stabilize the RFAMs by feeding signals back to a heater
=> we need to install a heater on the EOM.
8. In parallel to those actions, figure out how much offsets each LSC error signal will have due to the current amount of the RFAMs.
=> Optickle simulations.
9. Set some criteria on the allowed amount of the RFAMs
=> With some given offsets in the LSC error signal, we investigate what kind of (bad) effects we will have.
In keeping with the current protocol, I have started to move all the user-built medm screens associated with C1IOO into the $screens$/c1ioo/master/ directory.
I then edited the menu button in the sitemap.adl to point to the screens in the ..c1ioo/master/ directory. All the screens in $screens$/c1ioo/ directory have been backed up into bak/. I plan to edit the c1ioo model soon and at that time I will delete all the screens in the $screens$/c1ioo directory and let only the automatically regenerated screens stay there. If there are broken links to user-built screens associated with c1ioo, please copy the relevant screen to the master/ directory and edit the path in the menus.
I found that the MC WFS had large offset control signals going to the MC SUS. Even though the input switch was off, the integrators were holding the offset.
I have disabled the ASCPIT outputs in the MC SUS. Suresh is going to fix the MC autolocker script to gracefully handle the OFF and ON and then test the script before resuming the WFS testing.
MCL data for OAF may be suspect from this morning.
I have edited (uncommented existing commands) the following scripts to enable WFS locking to come on when the MC is locked.
I have checked that the autolocker script switches off the mcwfs when mc loses lock and then switches it on after re-obtaining lock.
The image on the PMCR camera was quite assymetric and PMC output was at 80% .... upon improving the alignment I managed to push it up to 87%
A while back we faced the problem that when we use several lockins to excite the MC degrees of freedom, their relative phase was not known. The solution suggested was to use one oscillator and several demodulators.
I have now modified the C1IOO.mdl so that this can be implemented. Previously we were using the MC_ASS lockins for WFS work. I have now separated the WFS and MC_ASS structures.
Other jobs to be done in this context are:
1) The medm screens associated with WFS lockins need to be updated with new channel names.
2) The scripts associated with both MC_ASS decentering and WFS ouput matrix determination have to be updated with the new channel names.
3) I also deleted all medm screens in the $screens$/c1ioo/ directory after copying them to $screens$/c1ioo/bak/. After installing the new c1ioo model $screens$/c1ioo directory now contains just the automatically created screens. All other user made screens should go into $screens$/c1ioo/master/ directory
This is a pic of the new c1ioo model:
I forgot to mention another change I made to the C1IOO model.
The location of the WFS global switch and the WFS_GAIN have been shifted. The switch now cuts off signals just before the WFS servo filters.
I have also added some test points just before the switch and the so that we can monitor the WFS error signals which would be unaffected even if the WFS_GAIN is changed..
I have now modified the C1IOO.mdl so that this can be implemented. Previously we were using the MC_ASS lockins for WFS work. I have not separated the WFS and MC_ASS structures.
3) I also deleted all mdem screens in the $screens$/c1ioo/ directory after copying them to $screens$/c1ioo/bak/. After installing the new c1ioo model $screens$/c1ioo model now contains just the automatically created screens. All other user made screens should to into $screens$/c1ioo/master/ directory
Some small fixes to the c1ioo model.
1) I edited the WFS lockin modules to make use of new library part called demod.
2) c1ioo model has been compiled and restarted.
3) fb was restarted at Tue Oct 25 18:43:55 PDT 2011
The location of the WFS global switch has been shifted. It now cuts off signals just before the WFS servo filters.
I have also added some test points just before the switch so that we can monitor the WFS sensor signals even if the switch is off.