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ID Date Author Type Categoryup Subject
  1256   Wed Jan 28 19:08:50 2009 YoichiUpdatePSLLaser is back (sort of)
Yoichi, Peter, Jenne

Summary:
We found that the chiller water is not going to the NPRO base. It was hot whereas it was cold when I touched it a few months ago.
I twisted the needle valve on the water line to the NPRO base. Then we heard gargling noise in the pipe and the water started to flow.
The laser power is now climbing up slowly. The noisiness of the MOPA output is reduced.

I will post more detailed entry explaining my theory of what actually happened later.
Attachment 1: Improving.png
Improving.png
  1257   Thu Jan 29 13:52:34 2009 YoichiUpdatePSLLaser is back (sort of)
Here is what I think has happened to the laser.

After the chiller line to the NPRO base clogged, the FSS slow slider went down to keep the laser frequency constant.
It is evident in the attachment 1 that the behavior of the slow slider and the DTEC (diode temp. stabilization feedback signal) are almost the same except for the direction. This means the slow servo was fighting against the increased heat caused by the lack of the cooling from the bottom.
DTEC was doing the same thing to keep the diode temperature constant.

Even though the slow actuator (a Peltier on the crystal) worked hard to keep the laser frequency constant, one can imagine that there was a large temperature gradient in the crystal and the mode shape may have changed.

Probably this made the coupling of the NPRO beam to the PA worse. It may also have put the NPRO in a mode hopping region, which could be the cause of the noisiness.

Right now, the MOPA power is 2.7W.
The FSS, PMC, MZ are locked. At first, the PMC locked on a sideband. I had to twiddle the phase flip button of the PMC servo to lock the PMC. Probably this is another sticky channel, which needs to be tweaked after a reboot of c1psl. I added a code to do this in /cvs/cds/caltech/scripts/Admin/slider_twiddle.

Currently the ISS is unstable. Kakeru and I are now taking OPLTF of the servo.
Looks like the phase margin at the lower UGF is too small.
Attachment 1: SlowDC.pdf
SlowDC.pdf
  1260   Thu Jan 29 18:10:13 2009 YoichiUpdatePSLISS Bad
Kakeru, Yoichi

As we noted before, the ISS is unstable. You can see the laser power oscillation around 3Hz.
We took the open-loop transfer function of the ISS around the lower UGF.
The phase margin is almost non-existent.
It was measured with the ISS gain slider at 2dB (usually it was set to 7dB).
So if we increase it by 3dB, it is guaranteed to be unstable.

The higher UGF has also a small phase margin (about 12deg.).
With the ISS gain slider at 2dB, the upper UGF is too low, i.e. the UGF is located at the beginning of the 1/f region.
So we if we make the lower UGF stable by lowering the gain, the upper UGF becomes unstable.

We took out the ISS box from the PSL table.
Kakeru and Peter are now trying to modify the filter circuit to give more phase margin at the lower UGF.
Attachment 1: OPLTF1.png
OPLTF1.png
  1262   Fri Jan 30 19:38:57 2009 KakeruUpdatePSLISS Bad
Kakeru, Peter

We try to improve ISS bord, but there isn't circuit diagram with correct parameters.
We are to measure transfar function and guess each parameter before we desogn new circuit parameters.
  1270   Tue Feb 3 23:44:44 2009 Kakeru, Peter, YoichiUpdatePSLISS unstability

We found that one OP-amp used in ISS servo oscillated in 10 MHz, 100mV.

Moreover, we found another OP-amp had big noise.

We guess that these oscilation or noise cause saturation in high frequency, and they effect to lower frequency to cause 

 Attached files are open loop transfar function of ISS.

The blue points are open loop TF, and the green line is product of TF of ISS servo filter and TF of current shunt TF of servo filter.

This two must be same in principle, but They have difference f<2Hz and f>5kHz.

Attachment 1: TFgain.png
TFgain.png
Attachment 2: TFphase.png
TFphase.png
  1276   Thu Feb 5 21:42:28 2009 YoichiUpdatePSLMy thoughts on ISS

Today, I worked with Kakeru on ISS.

The problem is sort of elusive. Some time, the laser power looks fine, but after a while you may see many sharp drops in the power. Some times, the power drops happen so often that they look almost like an oscillation.

We made several measurements today and Kakeru is now putting the data together. Meanwhile, I will put my speculations on the ISS problem here.

The other day, Kakeru took the transfer function of the ISS feedback filter (he is supposed to post it soon). The filter shape itself has a large phase margin ( more than 50deg ?) at the lower UGF (~3Hz) if we assume the response of the current shunt to be flat. However, when we took the whole open loop transfer function of the ISS loop, the phase margin was only 20deg. This leads to the amplification of the intensity noise around the UGF. The attached plot is the spectrum of the ISS monitor PD. You can see a broad peak around 2.7Hz. In time series, this amplified intensity noise looks like semi-oscillation around this frequency.

Since it is very unlikely that the PD has a large phase advance at low frequencies, the additional phase advance has to be in the current shunt. We measured the response of the current shunt (see Kakeru's coming post). It had a slight high-pass shape below 100Hz (a few dB/dec). This high-pass response produces additional phase advance in the loop.

There seems to be no element to produce such a high-pass response in the current shunt circuit ( http://www.ligo.caltech.edu/docs/D/D040542-A1.pdf )

This Jamie's document shows a similar high-pass response of the current ( http://www.ligo.caltech.edu/docs/G/G030476-00.pdf  page 7 )

Now the question is what causes this high-pass response. Here is my very fishy hypothesis :-)

The PA output depends not only on the pump diode current but also on the mode matching with the NPRO beam, which can be changed by the thermal lensing. If the thermal lensing is in such a condition that an increase in the temperature would reduce the mode matching, then the temperature increase associated with a pump current increase could cancel the power increase. This thermal effect would be bigger at lower frequencies. Therefore, the intensity modulation efficiency decreases at lower frequencies (high-pass behavior). If this model is true, this could explain the elusiveness of the problem, as the cancellation amount depends on the operation point of the PA. 

To test this hypothesis, we can change the pump current level to see if the current shunt response changes. However, the PA current slider on the MEDM screen does not work (Rob told me it's been like this for a while). Also the front panel of the MOPA power supply does not work (Steve told me it's been like this for a while). We tried to connect to the MOPA power supply from a PC through RS-232C port, which did not work neither. We will try to fix the MEDM slider tomorrow.

Attachment 1: INMONPD_Spectrum_1-10Hz.pdf
INMONPD_Spectrum_1-10Hz.pdf
  1277   Fri Feb 6 09:52:35 2009 KakeruUpdatePSLCurrent shunt transfar function

I attach the transfar function of the current shunt.
There is a little gap at 10 Hz for phase, but it is a ploblem of measurement and not real one.
 

Attachment 1: TF_CS_gain.png
TF_CS_gain.png
Attachment 2: TF_CS_phase.png
TF_CS_phase.png
  1278   Fri Feb 6 09:56:11 2009 KakeruUpdatePSLISS servo transfar function

I attache the transfar function of ISS servo.

The 4th stage and variable gain amplifier has alomost same transfar function, so their lines pile up.

Attachment 1: TF_ISSservo_gain.png
TF_ISSservo_gain.png
Attachment 2: TF_ISSservo_phase.png
TF_ISSservo_phase.png
  1279   Fri Feb 6 10:46:40 2009 KakeruUpdatePSLISS servo and noise
I measured the output noise of eache stage of ISS servo, and calcurated the noise ratio between input and 
output of each stage.
Generaly, each noise ratio corresponds to their transfar function. This means servo filter works well, not 
adding extra noise.

I attache example of them.
For 2nd stage, the noise ratio is smaller than transfar function with a few factor. This is because the 
input noise is coverd by analyser's noise and ratio between output and input looks small.
This means the input noise of 2nd stage was enough small and all stage before 2nd stage work well
Attachment 1: ISS_servo_TF_noise.png
ISS_servo_TF_noise.png
  1281   Fri Feb 6 16:20:52 2009 YoichiUpdatePSLMOPA current slider fixed

I fixed the broken slider to change the current of the PA.

The problem was that the EPICS database assigned a wrong channel of the DAC to the slider.

I found that the PA current adjustment signal lines are connected to the CH3 &CH4 of VMIC4116 #1. However in the database file (/cvs/cds/caltech/target/c1psl/psl.db), the slider channel (C1:PSL-126MOPA_DCAMP) was assigned to CH2. I fixed the database file and rebooted c1psl. Then the PA current started to follow the slider value.

I moved the slider back and forth by +/-0.3V while the ISS loop was on. I observed that the amount of the low frequency fluctuation of the MOPA power changed with the slider position. At some current levels, the ISS instability problem went away.

Kakeru is now taking open-loop TFs and current shunt responses at different slider settings.

  1283   Fri Feb 6 23:23:48 2009 Kakeru, YoichiUpdatePSLISS is fixed

Yoichi and me found that the transfar function of the current shunt changed with the current of PA.
We changed PA current and fixed the unstability of ISS.
Now, laser power is stabilized finely, with band of about 1 Hz.
Yoich will post the stabilized noise spectrum.

There looks to be some non-linear relation between PA current and  the TF of current shunt.
It had changed from the TF which we measured yesterday, so it might change again.

I try to write scripts to sweep PA current and measure the laser power and its rms automatically.
It will be apply for auto-adjustment of PA current.


Attached files are the transfar function of the current shunt with changing PA.
They have difference in lower frequency.

Attachment 1: Current_ShuntTF_gain.png
Current_ShuntTF_gain.png
Attachment 2: Current_ShuntTF_phase.png
Current_ShuntTF_phase.png
  1284   Mon Feb 9 16:02:42 2009 YoichiUpdatePSLPSL relative intensity noise
I attached the relative intensity noise of the PSL.
There is no bump around the lower UGF (~1Hz), but at the higher UGF (~30kHz) there is a clear bump.
When the ISS gain slider was moved up to 21dB, the peak got milder, because there is larger phase margin at higher frequencies with the current filter design.
We may want to optimize the filter later.
Attachment 1: RIN-13dB.png
RIN-13dB.png
Attachment 2: RIN-21dB.png
RIN-21dB.png
  1287   Mon Feb 9 19:50:48 2009 YoichiConfigurationPSLISS disconnected
We are doing measurements on ISS.
The ISS feedback connector is disconnected and the beam to the MC is blocked.
  1289   Tue Feb 10 23:36:25 2009 KakeruUpdatePSLPA current and laser output
I changed the PA current and measured laser output power (monitor PD signal).
The gain of ISS is 13dB
Attached figure is the relation of PA current and the average and standard diviation of laser output.
The average of output power decreas as current increase. It looks something is wrong with PA.
When current is -0.125, 0, 0.5, ISS become ocsilating. This looks to be changed from previous measurement.

I wrote matlab code for this measurement. The code is
/cvs/cds/caltech/users/kakeru/scripts/CS_evaluate.m
This function uses
/cvs/cds/caltech/users/kakeru/scripts/moveCS.m
Attachment 1: PA_current_output.png
PA_current_output.png
  1291   Wed Feb 11 07:28:25 2009 YoichiUpdatePSLPA current and laser output
I think we should also plot the laser power at the MOPA output. The horizontal axis should be the absolute current value read from the PA current monitor channel, not the slider value.

This result is consistent with my hypothesis that the thermal effect is canceling the power change at low frequencies (see elog:1276).
But if it is really caused by thermal effect or not is still unknown.

I'd like to see a larger scan into the lower current region.


Quote:
I changed the PA current and measured laser output power (monitor PD signal).
The gain of ISS is 13dB
Attached figure is the relation of PA current and the average and standard diviation of laser output.
The average of output power decreas as current increase. It looks something is wrong with PA.
When current is -0.125, 0, 0.5, ISS become ocsilating. This looks to be changed from previous measurement.

I wrote matlab code for this measurement. The code is
/cvs/cds/caltech/users/kakeru/scripts/CS_evaluate.m
This function uses
/cvs/cds/caltech/users/kakeru/scripts/moveCS.m
  1295   Wed Feb 11 23:51:53 2009 KakeruUpdatePSLPA current and laser output
I attached a plot of ISS monitor PD and MOPA output to PA current.
The both end of PA current (26.0353[A] and 28.4144[A]) correspond to the slider value of -2.0 and 1.0 .
It looks that we must use MOPA with PA current below 27.5[A].
Attachment 1: PA_current_output.png
PA_current_output.png
  1299   Thu Feb 12 18:35:10 2009 KakeruConfigurationPSLPA current limitter


I added a PA current limiter.
It is only a voltage devider (composed with 3.09k and 1.02k resiste) between DAC and PA current adjustment input.
The output range of DAC is +/- 10[V] and  the conversion factor of PA current adjustment is 0.84[A/V] (measured value), so the PA current adjustment is limited +/- 2.1[A] ( 10[V]*1.02k/(1.02k+3.09k)*0.84[A/V] ).


Actually, the manual of the PA tells that the conversion factor is 0.25[A/V].
There is 3 possibility.
1) There are some mistakes in channels of digital system.
2) The PA manual is wrong.
  2-1) The conversion factor of current adjustment is wrong.
  2-2) The conversion factor of current monitor is wrong.
I measured the signal of current adjustment and current monitor directly, and confirm that they are consistent to the value monitord from MEDM.
Hence the PA manual must be wrong, but I don't know which factor is wrong (or both?).
If the suspect 2-2) is guilty, it means we adjust PA current with very small range.
This is a completly safety way, but a wast of resource.


Now, the slider to control current adjustment indicate the output of DAC.
I will improve this to indicate  current adjustment input, but it takes some time for me to learn about EPICS.

  1357   Wed Mar 4 23:42:45 2009 ranaConfigurationPSLpsl db change

I made the following change to correct the sign of the 126MON channel:

allegra:c1aux>ezcawrite C1:PSL-126MOPA_126MON.EGUF -410
C1:PSL-126MOPA_126MON.EGUF = -410
allegra:c1aux>ezcawrite C1:PSL-126MOPA_126MON.EGUL 410
C1:PSL-126MOPA_126MON.EGUL = 410
allegra:c1aux>

  1395   Thu Mar 12 18:44:02 2009 YoichiUpdatePSLMZ aligned
The MC lost the alignment somehow this afternoon.
So I thought it was good time to touch the MZ because I had to align the MC using the periscope anyway.

I mainly touched the mirror with a PZT. The MZ reflection went down from 0.5 to 0.3.
  1421   Tue Mar 24 13:10:07 2009 AlbertoConfigurationPSLnew mirror installed on the AP table

New flipping mirror installed on the AP table on the beam path to the REFL199 PD.

If you're missing the double demod signal, please check that it is actually down.

  1431   Thu Mar 26 04:01:24 2009 YoichiUpdatePSLFSS Open Loop Gain
Yoichi, Peter, Jenne

Attached is the open loop transfer function of the FSS as of today with the common gain = 12dB and the fast gain = 16dB.
The UGF is only 250kHz. If we increase the common gain, the PC goes crazy. Exactly the same symptom as before I fixed the oscillating op-amp.

I wanted to check the cross over frequency but there is no excitation point in the fast path nor PC path. Therefore, it is not easy.
Attachment 1: OpenLoopTF.png
OpenLoopTF.png
  1470   Fri Apr 10 18:11:18 2009 JenneUpdatePSLISS has a bad cable?

[Rob, Jenne]

I noticed that the ISS Mean Value and CS Saturation were both RED and unhappy. (The alarms were going off, and they were both red on the MEDM screen).  None of the MEDM settings seemed off kilter, so we went out to take a look at the PSL table. 

Rob checked that light is indeed going to both of the ISS photodiodes (Morag and Siobhan).  Next we checked that all the cables were good, and that the power to the ISS box was plugged in. In this process, Rob wiggled all the cables to check that they were plugged in.  Just after doing this, the Mean Value and CS Sat were happy again.  Rob thinks the current shunt connection might be bad, but we don't really know which one it was since all of the cables were jiggled between our checking the screens. 

Right now, everything is happy again, but as with all bad-cabling-problems, we'll probably see this one again.

 

 

I don't know why in particular the connection decided to spaz out this afternoon...I don't think anyone opened the PSL table before Rob and I went to investigate.  I was working on the PMC servo (checking the LO levels...to be posted in a couple minutes), but didn't have anything to do with the ISS. After I was done, I put everything back, and locked the PMC and the MC, and everything was good, until some time later when the ISS started flipping out.

  1471   Fri Apr 10 19:09:48 2009 JenneUpdatePSLPMC LO Calibration
I measured the RF LO output level from the PMC's LO board which goes directly into the LO input on the PMC Servo board. This goes hand-in-hand with Rana's thoughts
that we might be giving the PMC mixer a too-low LO value, and we might need to switch out the mixer. Steve ordered some new mixers today to try out.

The RF Output Adjust slider (on the C1:PSL_PMC_PS screen) goes from 0-10V; The nominal value (or at least the value I found it at today) is 2.014V.

To measure the RF level: I unlocked the Mode Cleaner and turned off the ISS servo per Yoichi's suggestion. I then unplugged the input to the PMC servo board's LO input,
and put that cable into a 300MHz 'scope, with 12dB attenuation. The 'scope was AC coupled, with the input set to 50Ohms.

I then changed the RF Output Adjust slider in increments of 0.5, and measured the peak-to-peak values on the scope. In the table and on the plots, I've taken into account
the 12dB attenuation. i.e I actually measured 964mV, so 964mV*10^.6 = 3838mV.


RF Output AdjustOutput measured on scopeOscillator Output Monitor
[V]
[Vpp]
[no units given on MEDM screen]
All \pm 0.0159 all of this column is NEGATIVE
0.00003.8380.007
0.50003.8540.007
1.00003.8380.006
1.50003.8380.007
2.00003.8380.006
2.50003.8380.007
3.00003.8380.007
3.50003.8380.007
4.00003.8380.007
4.50003.8220.007
5.00003.8220.012
5.50003.7900.076
6.00003.7580.257
6.50003.6940.555
7.00003.6150.931
7.50003.5351.277
8.00003.4561.532
8.50003.3921.709
9.00003.3441.829
9.50003.3121.908
10.00003.2961.966


I think it's kind of funky that it's so flat for ~half the slider. Also, the third column includes the Oscillator Output Monitor value from the MEDM screen at various RF Adjust slider values. All of these should be negative (i.e. -0.007), but the TABLE function doesn't like "-" signs. I don't know if this information is degenerate with the 'scope measurements, or if it's an indicator of what (might be) wrong.

After finishing, I plugged the cable back into the PMC servo board as it was, turned back on the ISS and relocked the PMC and the MC.
Attachment 1: RFSliderAdjustCalib.png
RFSliderAdjustCalib.png
Attachment 2: RFSliderAdjustCalibWithOsc.png
RFSliderAdjustCalibWithOsc.png
  1473   Sat Apr 11 00:45:41 2009 YoichiUpdatePSLPMC LO Calibration

Quote:

I then changed the RF Output Adjust slider in increments of 0.5, and measured the peak-to-peak values on the scope. In the table and on the plots, I've taken into account the 12dB attenuation. i.e I actually measured 964mV, so 964mV*10^.6 = 3838mV.


3.8Vpp is about 16dBm.
The mixer for the PMC demodulator is level 23. So 16dBm is insufficient.
What is the level of the new mixer Steve ordered ? 13 ?
  1475   Sun Apr 12 19:27:20 2009 ranaUpdatePSLPMC LO Calibration

Quote:

3.8Vpp is about 16dBm.
The mixer for the PMC demodulator is level 23. So 16dBm is insufficient.
What is the level of the new mixer Steve ordered ? 13 ?


Since Steve and Jenne were on it, I'm sure they ordered the optimum values...

From the table, it looks like the drive level adjuster is busted. Its not supposed to just give a
1-2 dB change over the full range. We'll have to think about what exactly to do, but we should
probably install the level 13 mixer and put in the right attenuation to make the LO be ~13.5 dBm
including the filter. Also need to calibrate the LO readback on the board like what Peter did for
the FSS.
  1477   Mon Apr 13 08:59:57 2009 steveUpdatePSLmixers on order

Quote:

Quote:

I then changed the RF Output Adjust slider in increments of 0.5, and measured the peak-to-peak values on the scope. In the table and on the plots, I've taken into account the 12dB attenuation. i.e I actually measured 964mV, so 964mV*10^.6 = 3838mV.


3.8Vpp is about 16dBm.
The mixer for the PMC demodulator is level 23. So 16dBm is insufficient.
What is the level of the new mixer Steve ordered ? 13 ?



I ordered mixers level 13, 17 on Friday and level 23 now.
They should be here Tuesday

NOTE: level 23 power is illegal to use in the 40m lab
They get hot
  1478   Mon Apr 13 17:55:37 2009 JenneUpdatePSLPMC LO Mon Calibration

I have calibrated the PMC LO Mon (C1:PSL-PMC_LODET) on the PMC's EPICS screen, by inputting different RF LO levels into the LO input of the PMC servo board.

 

Since the RF output adjust slider on the PMC's Phase Shifter screen doesn't do a whole lot (see elog 1471), I used a combination of attenuators and the slider to achieve different LO levels. I measured the level of the attenuated RF out of the LO board using the 4395A in spectrum analyzer mode, with the units in dBm, with 50dB attenuation to make it stop complaining about being overloaded.  For each row in the table I measured the RF level using the 4395, then plugged the cable back into the PMC servo board to get the EPICS screen's reading.

The last 2 columns of the table below are the 'settings' I used to get the given RF LO level. 

RF LO Input to PMC Servo Board [dBm] LO Mon on EPICS Screen [no units] RF Output Adjust Slider [V] Attenuators used [dB]
16.004 +- 0.008 0.1200 +- 0.0003 0 0
15.001 +- 0.004 0.0708 +- 0.0008 0 1
14.079 +- 0.008 0.0318 +- 0.0001 8 1
13.002 +- 0.006 0.0126 +- 0.0004 0 3
11.992 +- 0.010 0.0024 +- 0.0008 0 4
10.994 +- 0.010 -0.0024 +- 0.0003 0 4+1=5
9.993 +- 0.008 -0.0047 +- 0.0007 0 3+3=6

 

When the new mixers that Steve ordered come in (tomorrow hopefully), I'll put in a Level 13 mixer in place of the current Level 23 mixer that we have.  Also, Rana suggested increasing the gain on the op-amp which is read out as the LO Mon so that 13dBm looks like 1V.  To do this, it looks like I'll need to increase the gain by ~80.  

Attachment 1: LOmonCalibration.png
LOmonCalibration.png
  1487   Wed Apr 15 17:11:37 2009 JenneUpdatePSLEdited c1psl.db to calibrate PMC's LO mon


Following the method in Peter's Elog, 

I edited c1psl.db to include the following: 


grecord(calc, "C1:PSL-PMC_LOCALC")
{
        field(INPB,"C1:PSL-PMC_LODET")
        field(SCAN,".1 second")
        field(PREC,"4")
        field(CALC,".955*LOGE(B)-17.11")
}

 

I restarted c1psl (had to go hit the physical reset button since it didn't come back after telnet-ing and "reboot"ing) to make this take effect.

Next step is to tell the PMC screen to look at this _LOCALC rather than _LODET, and the screen will be calibrated into dBm. 

Right now, the screen is as it always has been, because after relooking at the calibration, I no longer believe it.  This calibration claimes -19dBm for an LOmon value of 0.1200, when I actually measured +16dBm for this LOmon value.  So I've screwed something up in doing my MatLAB calibration.  I'll fix it tomorrow, and put in the correct calibration before I change the PMC screen.

 

RefCav, PMC, MC are all back and locked after my shenanigans. 

  1488   Thu Apr 16 11:17:56 2009 JenneUpdatePSLEdited c1psl.db to calibrate PMC's LO mon

Quote:

I edited c1psl.db to include the following: 


grecord(calc, "C1:PSL-PMC_LOCALC")
{
        field(INPB,"C1:PSL-PMC_LODET")
        field(SCAN,".1 second")
        field(PREC,"4")
        field(CALC,".955*LOGE(B)-17.11")
}

 

 As it turns out, I apparently can't tell X from Y when fitting a function in a rush.  The real calibration stuff which is now in c1psl.db is:

 

 

grecord(calc, "C1:PSL-PMC_LOCALC")
{
        field(INPB,"C1:PSL-PMC_LODET")
        field(SCAN,".1 second")
        field(PREC,"4")
        field(CALC,"1.004*LOGE(B)+17.76")
}

I restarted c1psl (again, had to go hit the physical reset button since it didn't come back after a telnet-reboot) to have it take in the changes.  The psl.db file that was in place before yesterday (before I touched it) is saved as psl.db.15Apr2009 just in case.

I edited the PMC EPICS screen to have the LO mon look at C1:PSL-PMC_LOCALC, which is the calibrated channel in dBm.  I also stuck a little label on the screen saying what units it's in, because everyone likes to know what units they're looking at.
  1502   Mon Apr 20 19:51:51 2009 JenneConfigurationPSLPMC has new Level 13 Mixer installed

The new Level 13 mixer on the PMC servo board is installed (minicircuits SRA-3MH).   Since the RF output of the LO board was ~16dBm, I put a 3dB attenuator between the LO board and the LO input on the servo board.  Since the previous cable was *just* the right length, this required adding a tiny bit of cable.  I found a very short cable, which worked out nicely, and didin't leave bunches of extra cable between the two boards.  One of these days if I have time (i.e. if it is necessary), I'll make a new cable for this purpose, so that we don't have 2 cables daisy-chained. 

A note on the Mixer-replacement:  The mixer on the PMC servo board is soldered in a set of 8 through-holes, not stuck in a socket.  So I had to desolder the old Level 23 Mixer (minicircuits RAY-3) which was a total pain.  Unfortunately, in this process, I lifted one of the pads off the back side of the board.  Once the old mixer was removed, it became clear that the pin for the pad I had lifted was shorted via a trace on the front side of the board to the pin directly across from it.  So when installing the new mixer, I did my best to get some solder into the through-hole for the lifted-pad-pin, and then tied it using a jumper wire to the pin that it's shorted to on the front of the board.  You can't see the trace that shorts the two pins because it's underneath the mixer, when the mixer is installed.  (Sidenote: after talking with Rana, this should be okie-dokie, especially if these are ground pins).

The PMC and MC locked nice and happily after I replaced the board and turned all the HV supplies back on, so I call this a success!

I also measured the OLG of the PMC servo after today's adventures in mixer-land.  I get a UGF of 1.4kHz, with 66 degrees of phase margin.  The method for this is in elog 924.

I checked the phase slider setting of the PMC phase screen by putting 30kHz at 100mV into the Ext DC input of the servo board, and looking at the 30kHz peak output of the Mixer Out.  I fiddled with the phase slider, and chose the value for which the 30kHz peak was maximized.  The phase slider is now set to 5.0V. 

Attachment 1: PMColg20Apr2009.png
PMColg20Apr2009.png
  1568   Sat May 9 00:15:21 2009 YoichiUpdatePSLLaser head temperature oscillation
After the laser cooling pipe was unclogged, the laser head temperature has been oscillating in 24h period.
The laser power shows the same oscillation.
Moreover, there is a trend that the temperature is slowly creeping up.
We have to do something to stop this.
Or Rob has to finish his measurements before the laser dies.
Attachment 1: laser.png
laser.png
  1569   Sat May 9 02:20:11 2009 JenneUpdatePSLLaser head temperature oscillation

Quote:
After the laser cooling pipe was unclogged, the laser head temperature has been oscillating in 24h period.
The laser power shows the same oscillation.
Moreover, there is a trend that the temperature is slowly creeping up.
We have to do something to stop this.
Or Rob has to finish his measurements before the laser dies.


How's DTEC doing? I thought DTEC was kind of in charge of dealing with these kinds of things, but after our laser-cooling-"fixing", DTEC has been railed at 0, aka no range.

After glancing at DTEC with Dataviewer along with HTEMP and AMPMON (my internet is too slow to want to post the pic while ssh-ed into nodus), it looks like DTEC is oscillating along with HTEMP in terms of frequency, but perhaps DTEC is running out of range because it is so close to zero? Maybe?
  1570   Sat May 9 15:19:10 2009 ranaUpdatePSLLaser head temperature oscillation
This is 8 days of 10-minute trend.

DTEC is just the feedback control signal required to keep the NPRO's pump diode at a constant temperature.
Its not the amplifier or the actual NPRO crystal's temperature readout.

There is no TEC for the amplifier. It looks like to me that by opening up the flow to the NPRO some more
we have reduced the flow to the amplifier (which is the one that needs it) and created these temperature
fluctuations.

What we need to do is choke down the needle valve and ream out the NPRO block.
Attachment 1: Picture_2.png
Picture_2.png
  1573   Mon May 11 11:49:20 2009 steveUpdatePSLMOPA cooling water lines are backwards

Quote:
This is 8 days of 10-minute trend.

DTEC is just the feedback control signal required to keep the NPRO's pump diode at a constant temperature.
Its not the amplifier or the actual NPRO crystal's temperature readout.

There is no TEC for the amplifier. It looks like to me that by opening up the flow to the NPRO some more
we have reduced the flow to the amplifier (which is the one that needs it) and created these temperature
fluctuations.

What we need to do is choke down the needle valve and ream out the NPRO block.




I have measured the "input" line temp at the MOPA box 10 C and the "out" line 8 C

This must be corrected.

However look at the 80 days plot of operation where the head temp variation is nothing new
Attachment 1: htempvar80d.jpg
htempvar80d.jpg
  1617   Thu May 21 18:07:32 2009 ranaUpdatePSLScrew on Needle valve loosened
Alberto and I went in to loosen up the needle valve yesterday around 4:30 PM. The idea was to cut down on
the flow to the NPRO so that the cooling power of the chiller would be used almost entirely on the
amplifier instead of the NPRO block.

The need valve was basically all the way open. The lock nut was screwed in all the way and stuck. By using
pliers and a wrench for the nut, we freed the lock nut. Even so, the screw for the needle valve seemed to
be bad: I think the thread is stripped; it doesn't go down even after several turns. I even tried to squirt
alchohol on it and really press down in the hopes of catching a thread. It may have closed slightly but its
impossible to be sure.

I also increased the NPRO diode current to the max (+0.1 A). This got us a little bit of NPRO power and
I hope some more AMPMON stability. The attached plot shows 4 days of minute trend. If you squint you
might believe that we got some suppression in the HTEMP fluctuations over the last two days.
Attachment 1: Untitled.png
Untitled.png
  1621   Fri May 22 17:03:14 2009 rob, steveUpdatePSLMOPA takes a holiday

The MOPA is taking the long weekend off.

Steve went out to wipe off the condensation inside the MOPA and found beads of water inside the NPRO box, perilously close to the PCB board.  He then measured the water temperature at the chiller head, which is 6C.  We decided to "reboot" the MOPA/chiller combo, on the off chance that would get things synced up.  Upon turning off the MOPA, the neslab chiller display immediately started displaying the correct temperature--about 6C.  The 22C number must come from the MOPA controller.  We thus tentatively narrowed down the possible space of problems to: broken MOPA controller and/or clog in the cooling line going to the power amplifier.  We decided to leave the MOPA off for the weekend, and start plumbing on Tuesday.  It is of course possible that the controller is the problem, but we think leaving the laser off over the weekend is the best course of action.

 

 

  1625   Tue May 26 17:05:44 2009 robUpdatePSLMOPA re-activated

steve, rob, alberto

 

Steve installed two rotary flow meters into the MOPA chiller system--one at the chiller flow output and one in the NPRO cooling line.  After some hijinks, we discovered that the long, insulated chiller lines have the same labels at each end.  This means that if you match up the labels at the chiller end, at the MOPA end you need switch labels: out goes to in and vice-versa.  This means that, indubitably, we have at some point had the flow going backwards through the MOPA, though I'm not sure if that would make much of a difference. 

Steve also installed a new needle valve in the NPRO cooling line, which works as expected as confirmed by the flow meter. 

We also re-discovered that the 40m procedures manual contains an error.  To turn on the chiller in the MOPA start-up process, you have to press ON, then RS-232, then ENTER.  The proc man says ON, RS-232, RUN/STOP.

The laser power is at 1.5W and climbing.

Attachment 1: DSC_0513.JPG
DSC_0513.JPG
Attachment 2: DSC_0517.JPG
DSC_0517.JPG
  1626   Tue May 26 17:34:14 2009 robUpdatePSLMOPA re-deactivated

Quote:

steve, rob, alberto

 

Steve installed two rotary flow meters into the MOPA chiller system--one at the chiller flow output and one in the NPRO cooling line.  After some hijinks, we discovered that the long, insulated chiller lines have the same labels at each end.  This means that if you match up the labels at the chiller end, at the MOPA end you need switch labels: out goes to in and vice-versa.  This means that, indubitably, we have at some point had the flow going backwards through the MOPA, though I'm not sure if that would make much of a difference. 

Steve also installed a new needle valve in the NPRO cooling line, which works as expected as confirmed by the flow meter. 

We also re-discovered that the 40m procedures manual contains an error.  To turn on the chiller in the MOPA start-up process, you have to press ON, then RS-232, then ENTER.  The proc man says ON, RS-232, RUN/STOP.

The laser power is at 1.5W and climbing.

 Rob, Alberto

The chiller HT alarm started blinking, as the water temperature had reached 40 degrees C, and was still rising.  We turned off the MOPA and the chiller.  Maybe we need to open the needle valve a bit more?  Or maybe the flow needs to be reversed?  The labels on the MOPA are backwards?

Attachment 1: laser_temp.jpg
laser_temp.jpg
  1627   Wed May 27 10:54:09 2009 robUpdatePSLwe don't understand the chiller (broken)

Quote:

Quote:

steve, rob, alberto

 

Steve installed two rotary flow meters into the MOPA chiller system--one at the chiller flow output and one in the NPRO cooling line.  After some hijinks, we discovered that the long, insulated chiller lines have the same labels at each end.  This means that if you match up the labels at the chiller end, at the MOPA end you need switch labels: out goes to in and vice-versa.  This means that, indubitably, we have at some point had the flow going backwards through the MOPA, though I'm not sure if that would make much of a difference. 

Steve also installed a new needle valve in the NPRO cooling line, which works as expected as confirmed by the flow meter. 

We also re-discovered that the 40m procedures manual contains an error.  To turn on the chiller in the MOPA start-up process, you have to press ON, then RS-232, then ENTER.  The proc man says ON, RS-232, RUN/STOP.

The laser power is at 1.5W and climbing.

 Rob, Alberto

The chiller HT alarm started blinking, as the water temperature had reached 40 degrees C, and was still rising.  We turned off the MOPA and the chiller.  Maybe we need to open the needle valve a bit more?  Or maybe the flow needs to be reversed?  The labels on the MOPA are backwards?

 The chiller appears to be broken.  We currently have it on, with both the SENSOR and RS-232 unplugged.  It's running, circulating water, and the COOL led is illuminated.  But the temperature is not going down.  The exhaust out the back is not particularly warm.  We think this means the refrigeration unit has broken, or the chiller computer is not communicating with the refrigerator/heat exchanger.  Regardless, we may need a new chiller and a new laser.

  1628   Wed May 27 15:59:44 2009 robUpdatePSLwe don't understand the chiller (broken)

steve, alberto, rob

After some futzing around with the chiller, we have come to the tentative conclusion that the refrigeration unit is not working.  Steve called facilities to try to get them to recharge the refrigerant (R-404a) tomorrow, and we're also calling around for a spare chiller somewhere in the project (without luck so far).

  1629   Thu May 28 14:34:25 2009 robUpdatePSLchiller diagnosis

Quote:

steve, alberto, rob

After some futzing around with the chiller, we have come to the tentative conclusion that the refrigeration unit is not working.  Steve called facilities to try to get them to recharge the refrigerant (R-404a) tomorrow, and we're also calling around for a spare chiller somewhere in the project (without luck so far).

 The repair man thinks it's a bad start capacitor, which is 240uF at 120V.  Steve has ordered a new one which should be here tomorrow, and with luck we'll have lasing by tomorrow afternoon.

  1630   Thu May 28 18:41:26 2009 steveUpdatePSLthe saga of the chiller is ending

I drained the water and removed side covers from the Neslab RTE 140 refrigerated water cooler unit this morning. The hoses to the laser were disconnected.

This abled you to see the little window of refregerant  R404A was free of bubles, meaning: no recharge was needed.

The circulator bath was refilled with 7 liters of Arrowhead distilled water and the unit was turned on.

The water temp was kept 20.00+- .05C without any load. Finally the AC-repair man Paul showed up.

He measured the R404A level to be as specified: 23-24 PSI on the suction side and 310 PSI on the discharge side.

The unit was working fine. Paul found an intermittently functioning starting capacitor on the compressor  that was removed.

The 240 micro Farad 120VAC cap will arrive tomorrow

  1631   Fri May 29 18:57:09 2009 steveUpdatePSLthe laser is back

Steve, Rob and Alberto

 

Starting capacitor 216 miroFarad was installed on the compressor. Water lines were connected to the MOPA as corrected, so the flow meter readings are logical.

Now IN means flowing water in the direction of black arrow on the hose.

We struggled with the Neslab presetting:  temp, bauds rate  and other  unknowns  till Rob found the M6000 manual on Peter king's website.

Alberto realized that the chiller temp had to be reset to 20C on water chiller.

I put 1mg of Chloramin T into the water to restrict the growth of algae in the bath.

The NPRO heat sink  was around ~20C without flow meter wheel rotation  and the PA body ~25C by touch of a finger

I just opened up the needle valve a litle bit so the flow meter wheel would started rotating slowly.

That small glitch at the end of this 3 hrs plot shows this adjustment.

Attachment 1: laserisback.jpg
laserisback.jpg
  1632   Sat May 30 11:24:56 2009 robConfigurationPSLNPRO slow scan

I'm setting SLOWDC to about -5.

I had to edit FSSSlowServo because it had hard limits on SLOWDC at (-5 and 5).  It now goes from -10 to 10.

 

 

Attachment 1: slowSCAN.png
slowSCAN.png
  1633   Sat May 30 12:03:34 2009 robUpdatePSLMC locked

I locked to PSL loops, then tweaked the alignment of the MC to get it to lock. 

I first steering MC1 until all the McWFS quads were saturated.  This got the MC locking in a 01 mode.  So I steered MC1 a little more till it was 00.  Then I steered MC2 to increase the power a little bit.  After that, I just enabled the MC autolocker.

  1636   Mon Jun 1 13:56:52 2009 AlbertoUpdatePSLLaser Power after fixing the laser chiller

The laser power seems to have become more stable after fixing the laser chiller. The power is lower than it used to be (MOPA amplitude 2.5 versus 2.7) but, as shown in the attchement, it became more steady.

Attachment 1: MOPAtrend.jpg
MOPAtrend.jpg
  1638   Mon Jun 1 14:49:07 2009 robSummaryPSLpsl thoughts

Some thoughts on what happened with the MOPA cooling. 

Some unknown thing happened to precipitate the initial needle valve jiggle, which unleashed a torrent of flow through the NPRO.  This flow was made possible by the fact that the cooling lines are labeled confusingly, and so flow was going backwards through the needle valve, which was thus powerless to restrict it.  The NPRO got extremely cold, and most of the chiller's cooling power was being used to unnecessarily cool the NPRO.  So, the PA was not getting cooled enough.  At this, point, reversing the flow probably would have solved everything.  Instead, we turned off the chiller and thus discovered the flaky start-motor capacitor. 

Now we have much more information, flow meters in the NPRO and main cooling lines, a brand-new, functioning needle valve, a better understanding of the chiller/MOPA settings necessary for operation, and the knowledge of what happens when you install a needle valve backwards.

 

  1639   Mon Jun 1 15:01:31 2009 ranaUpdatePSLLaser Power after fixing the laser chiller: more traces
If you look at the correlation between RMTEMP and HTEMP, you see what we knew: namely that there
was a 1:1 correlation before. After the chiller fix, I can see no correlation between the room and
amplifier temperature at the resolution of 10:1. So the chiller loop has a gain > 10 at 24 hour time
scales.

I don't understand why the PMC looks more stable.
Attachment 1: Picture_7.png
Picture_7.png
  1640   Mon Jun 1 19:19:26 2009 ranaUpdatePSL1000 days of hour-trend
Attachment 1: u.png
u.png
  1651   Thu Jun 4 15:53:15 2009 steveUpdatePSLNPRO cooling flowrate adjusted

The Neslab chiller is working well. It's temp display shows 20.0 C rock solid. Flow meter rotating at 13.5Hz at the out put of the chiller.

The MOPA temp was measured with a hand held thermocouple . The  PA was  34 C and 29 C at NPRO heat sink.

The NPRO flow meter was not rotating at this time. There was just trickeling water flow though the meter.

I closed the needle valve this point. It needed 8 turns clockwise. This drives head temp to 19.9 C

Than I opened the needle valve 9 turns and the flow meter wheel was  rotaing at ~ 1 Hz

We gained a little power. Can you explain this?

 

Attachment 1: needlevalve.jpg
needlevalve.jpg
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