I think the analytical formula in terms of rho is going to be (1.57/2*pi) * sqrt(E / rho * L^2), since the Roark formula is (1.57/2*pi) * sqrt(A* E * g / w * L^2) and the weight per unit length is w = m * g / L = rho * A * g. With your values for L, A, E, and rho, this gives f1 = 16 kHz. Since A does not appear in the analytical formula, this also explains why changing the area in the Comsol model doesn't change the frequency.

 good catch! Thanks. Then both analytical and FEA results are the same. So our COMSOL results for PMC should be valid, the first body for a stainless steel PMC, see psl:1131,at 16 kHz is reasonable.

I calculated some requirement for the beam jitter at the output of the PMC. A rough estimate shows that we need the angular stability at the PMC about half nano radian so that the frequency noise of the beam locked to the refcav is less than 10^-2 Hz/rtHz.

==Background==

PMC also reduces beam jitters from the laser, so that the beam alignment to the cavity is kept centered. Since the laser is locked to the reference cavity, any misalignment of the input beam will cause the beam to sense the change of the cavity length.

So vibration that shakes the PMC will change the alignment of the output beam. With stiff material, the seismic induced deformation of the PMC will be reduced.

==Calculation==

• calculate the ray tracing matrices from the PMC to the cavity. I assume that only the angle of the output beam changes due to PMC sagging, because of a long distance from the PMC to the refcav, with several mirrors in between. This gives me the position and the angle of the beam going to the cavity.
• find out what is the change of the cavity length (dL), when the input beam is translated by dx, with angle theta.
• convert displacement noise to frequency nosie (dL -> df), as a rough estimate I choose the requirement for df to be less than 10^-2 Hz/rtHz (about the level of the estimated coating noise). This step is not really necessary, but I feel that it is easier to compare the noise in Hz/rtHz unit rather than m/rtHz.
• The required angular stability at the PMC is ~ 0.5 nano rad. This number seems to be too strict. I will double check it.

==next==

Eavn is working on COMSOL to find out the angular tilt of the output beam due to PMC sagging. Optimum support points will be determined to minimize beam jitter due to seismic.

These are plots of the sagging of the front and back mirrors as a function of the longitudinal positions of the mounting holes (these positions are measured from the back of the PMC). The first plot is a coarse search, and the second is more targeted toward a region of lower sagging.

I generated these plots by taking Tara's Comsol model of the PMC body, assigning fixed displacement to the three mounting holes, and assigning a body load to the PMC body equal to the weight of the steel. Then, I extracted the displacements of four points on the front edge and four points on the back edge of the PMC borehole (these edges are where the faces of the mirrors will make contact with the body). I then took some cross-products with these points in order to get the unit normals that would result when the mirrors are placed against the deformed body. I then compute the angle between the deformed unit normals and the undeformed unit normals to get the sag of the mirrors in radians.

I'm a bit uneasy about how precision is handled in the Comsol/Matlab combination used to generate these plots. The Comsol GUI has no problem reporting displacements all the way down to 10^-24 meters, but anything smaller than 10^-15 meters or so gets truncated to exactly 0 when the results are reported in Matlab. When propagated through to the sagging computation, this means any sagging smaller than 10^-8 radians or so also gets rounded to exactly 0. You can see in the second set of plots that there are large swaths of exactly the same light blue and periwinkle, which seems to indicate a low level of precision in the computation. There's probably some obvious Comsol/Matlab setting that I'm missing, but I haven't been able to find it so far.

Regardless, it appears there is an optimum range of hole placements for the PMC body: 10 cm for the front holes and 3 cm for the back holes, give or take a centimeter or so.

[Tara, Evan]

The south PMC can now be controlled on fb2 via C3PSL_PMC.adl.

I measure the OLG TF of the PMC with 3 different RF and gain slider settings. I plot the OLG TF of each setup and identify their UGF.

 I increase the RF as a first step to optimize PMC loop w/o modifying the circuit. This will increase the TF of the optical path.

The setting are

First I  adjust the RF power to reach where I can adjust the stability by changing the gain slider.

RF V above (6 or 7) the gain is too large, even with smallest gain slider, the signal is not stable and the PMC_RCTRANSPD drops from maximum.

So RF V ends up around 5.5 V. this makes the gain slider sit around 10 -15 where I obtain maximum stability. 

The gain slider should not to be set too low because of stability problem. The voltage supply for the opamp should be > +10V.

The gain slider setups are chosen to obtain the maximum stability and maximum power out put (PMC_RCTRANSPD.)

\

c and d have the same RF V, I change the gain to see if there would be any significant change in the performance, and

the data will be used for RF V calibration (how much gain we got from RF V adj).

Now we have some room to increase the gain once we lower the power, but

I have to understand why increasing the gain slider makes signal unstable.

The phase margin seems to be ok.  It might be the slope of the TF at UGF that causes instability.

This morning, the PMC couldn't be locked to the laser. The FSS servo was disabled during that time.

When the gain/ RF power were adjusted, PMC was locked to the laser, but the coupling efficiency dropped from 80% to 40%.

I try adjusting the mirror, but it's not the alignment problem because I couldn't increase the efficiency.

So after the noise budget party with Jan and Frank, I check if the EOM works looking at the error signal from mixer out.  The laser frequency is scan at +/- 10V @ 100 Hz.

I'm not sure what is the corresponding freq span, but it must be less than 43 MHz(21.5 MHz x 2) because

three peaks of the signal could not be seen with +/- 10V span, so I use a voltage calibrator to slowly adjust the temperature and see the rest of the signals.

Nevertheless, the signals are there, so I try to lock the PMC again, and now the efficiency back to almost 80% again ( I have to re align again because of the earlier adjustment. The mixer out channel is monitored when I set the PMC gain to make sure there will be no oscillation.

I'm not sure what happen, loosen connectors, mode hopping in the laser, etc. I'll see if I can track this down , otherwise we could not have a stable locking system.

I'm trying to align the PMC.  The transducer is connected to the PMC servo card's HV out.

HV in is driven by a function generator with triangular function. The output signal looks weird. It is not a nice triangular form, it's more like a u shape waveform connecting to each others with a plateau on top.

I'll check if the transducer on the PMC and the HV out from the card are working correctly or not. Right now, there is not a glimpse of signal coming out of the PMC on CCD.

don't the words HV IN ring a bell? look into the schematic. there are only a couple of inputs at the front so it's not too hard to figure out why there was already a BNC cable connected to that input. Did you check the monitor signal? If you would you would have seen that your HV supply is missing now

After checking the PMC servo card,

ramp signal goes to ext DC 

HV in is applied properly,

HV out is fixed.

Now the PMC is scanning and working fine.

The alignment is done. Although optimization is still needed,  I can work on the rest of the setup.

*note on PMC servo card

Ratio between Voltage input (Vin), V monitor (Vmon), and High Voltage output (HVout),

HVout = 24 Vin

Vmon = 1/50 HVout

Vmon = 24/50 Vin

 see the attachment

We try optimizing the PMC transmission in P wave. The maximum we can get for now is ~82%.

The 21.5 EOM is prealigned. We will do fine adjustment again when insulating cables are made.

EOM alignment means to align the polarization of the beam to match the applied electric field in the EOM. This will minimize the amplitude modulating effect.

There are 3 degrees of freedom, 2 for EOM positions, another one is the polarization of the beam.

The 35.5 EOM is also pre aligned, the signal is very small, probably because of its broadband type. I use 4395A spectrum analyzer to see the peak at 35.5 MHz, but it's really hard to tell if I minimize it or not.

I see the thermal effect on EOM crystal clearly when I adjust the EOM. After I minimize the Amplitude Modulation (AM) and left the EOM for awhile, the misalignment gradually increase.

Frank suggests that the calibration of the error signal should be done, so that we can approximate how well the temperature must be controlled to reach our noise budget. I'll think about that measurement.

As I finished my elog, the peak at 35.5 just went up. Case in point.

After studying Zach's bash autolocker for the ATF PMC, I've written a python autolocker for the CTN PMC. This one is much simpler and just walks the PZT voltage downward until it sees the transmission PD go high. If the PZT hits 0 V, the autolocker puts it up at 300 V and continues walking downward.

The script is in the controls home directory on fb2 and can be invoked via python pmcauto.py

When I showed Frank that the card did not work, I mentioned that I got electric shock when I connected high voltage input to the card.

Frank realized that it happens only when the connector is not grounded, and it was not. The ground connection from HVin to the card

was broken, It's hard to see unless I touched the wire that connected the board to the female BNC on the panel. I replaced that rigid wire by a flexible wire.

Now the PMC card is working fine, and the original PA85 might not be broken at all.

      After adding another 1/2 plate to have P wave into the cavity, I can lock the PMC cavity. It's been 30 minutes so far.

There is only one transmitted beam now (there were two when I used S wave.) 

     When I work or knock on the table, sometime the beam switches to another mode (might be it's side band.)

It's very close to the main TEM00 mode. I need to adjust the DC offset a little bit to get back.

 The incoming power is 9 mW, and the Transmitted beam has ~ 6 mW.

Current setting:

RF Amp: 7V

Phase shift: 2.87 + 180

Gain: 27.91 dB

DC offset: -2.3 V

     I tried to pre align the ref cavity. It's harder than I thought, can't see the beam that well. I'll have to check the manual for the laser controller, so that I can

scan the RefCav when I align the beam into the cavity.

I've pulled the old PMC driver board from the VIM crate architecture and inserted it into a chassis (D1700003). The interface has been reconfigured to insert directly into two Acromag units that are inside the chassis (see attached photo). It still needs a back panel.

So far, the DAC connections (loop gain control and locking point control) are wokring. The binary outputs are not properly switching between 0V and 5V - I'll need to double-check what circuit the Acromag 1541 is expecting to be attached.

Also, I've added a new EPICS database file for these channels (attached).

I added an endcap to Tara's steel PMC Comsol model and looked at the eigenmoedes for a 3-point contact. The lowest mode is a rolling mode at 2.0 kHz, followed by other modes at 3.0 kHz and 3.5 kHz. The first longitudinal stretching mode is at 16 kHz. The rectangular part of the spacer for this steel PMC has dimensions 5" x 2.6 " x 2" and a cavity length of 32 cm (first picture).

I also looked at a beefed up version of the spacer, with dimensions 10" x 4.6" x 2" and a cavity length of 78 cm (second picture). The lowest mode is again a rolling mode at 1.4 kHz, followed by other modes at 2.0 kHz, 2.2 kHz, and so on. The first longitudinal stretching mode is at 9.0 kHz. So it looks like if we want a longer cavity, we can almost double two of the spacer dimensions without shifting the resonances down significantly.

If we use a 10" x 4.6" x 2" spacer but go with a 4-mirror bow-tie design (third picture), we can get something closer to a 1.1 m cavity length. Comsol gives a lowest mode at 1.4 kHz, followed by modes at 2.4 kHz, 2.6 kHz, etc.

OD: 1.63"

Depth: ca. 0.9"

Minimum clearance between cap and mount: ca. 0.5"

the reason why you had this flickering problem was that you had too much power on the RFPD in reflection of the PMC. You already saturated it.
I also reduced the RF power as the error signals were not signals anymore, just spikes.

my new settings are:

RF power : 3.0
Phase : 2.5
PMC Gain: 14dB

reduced laser power to 40mW. Transmitted power is 32mW .You have to exchange the output coupler mirror in front of the RFPD in order to increase the power. I think 32mW is enough, it's something like 13mW per cavity.

 Ok, I'll find another output coupler mirror and replace the current one, and make sure that it will not saturate the RFPD.

 the saturating power seems to be much to low. it saturates at .5V DC, usually you can have something like 2V or so. So we should propably fix the PD even if it is working with lower power levels.

For now it's much more important to connect all the signals to the DAQ and lock the refcav. You still have to make a lot of cables, like the ones going to the laser (fast & slow), RFPD DC, PMC and refcav transmitted light, refcav RFPD DC etc.

The PZT of the glass PMC does not seem broken (at least looking at the FSR).

I have implemented the PMC glass again, in order to verify if the PZT has enough range and or if it was functional.

We thought that it may have been broken and we were in the process of removing it from

the glass spacer. It is not the case yet.

Once I have got the 00 mode (South path) I have scanned the PZT of the PMC and I have seen 2 entire FSR. 

However I have noticed that the South laser drifting is very high. I had hard time keeping the

scanning around the desired mode. The other PMCs have beeen tested in the North path

and the laser drift was way less than what I saw in the South path.

I took some hard yellow foam, made it into a U-shape, and wrapped it with a combination of aluminum and duct tape.

This insulation fits snugly over the PMC and its copper shield. In retrospect, the foam is probably a little too thick. I had to temporarily move the beam dump at the input of the Faraday isolator.

Putting 20 V across the 105 Ω heater produces a change of 5 V on the PMC PZT (when locked). So we need better insulation or more heating.

The CTE of fused quartz is something like 0.5×10⁻⁶ K⁻¹, and the CTE of steel is more like 15×10⁻⁶ K⁻¹. So I suspect there's not much point in heating the glass spacer if I'm going to leave the steel end cap open to air.

A possible solution is to put a heater on the end cap, but I worry that the differential expansion of steel vs. glass will cause the end cap to pop off the spacer (it looks like it's only held on by epoxy).

A better solution is to improve the insulation on the back end of the PMC. I'll do that next.

How hot do you need to heat it? if the thermal expansion of aluminum/steel is much higher than that of fused silica, then just heating the end cap might be a better idea. Thermal conductivity is also better.

This is now built, with a few modifications:

• The power supply bypass capacitors are 1 µF tantalum caps.
• The RC low-pass is a  4.8 kΩ resistor and a 3.3 µF capacitor, giving a 10 Hz pole.
• The base of the heating resistor is tied to the negative rail instead of ground, in order to give a greater actuation range.

Both the in-amp stage and the mosfet stage seem to work fine using a 2 kΩ resistor in place of the heater (the actual heater is more like 120 Ω, but the axial resistors in the e-shop are only rated to 0.25 W).

I took a 105 Ω Kapton heater, stuck it to a 15 cm x 25 cm patch of copper foil (thanks Steve), and wrapped the foil around the PMC. This required undoing the top braces on the mount. Currently, the PMC is just sitting on its kinematic contacts. Virtually no tune-up of the pointing was required.

There is currently no insulation, so (perhaps unsurprisingly) the heater doesn't have much of an effect on the PMC's PZT voltage.

I'm building this instead:

Changes:

• The PMC on the south path has been installed with the PMC servo card on the rack.

• I added sliders for setting max, min and step size of autolocker scanning in PMC interface medm windows.

• I used one PLCX-25.4-103.0-UV-1064 and three steering mirrors in front of EOM to mode match with PMC.

• I laid down new cables for PMC reflection RFPD signals and EOM.

• I removed the power supply providing 9V to PMC Servo Cards and made a voltage regulator box with LM7809CT which converts 3-pin 18V to two BNC 9V.

• We are now using external mini-circuits in-line mixers (ZFM-3-S+) and low pass filters (SLP-1.9+) instead of using onboard mixer and filter on PMC servo card and injecting signal through FP1Test input.

• I mounted the inline hanging mixers and splitters on the rack with LO delay lines inside the rack so there are no hanging parts now.

• I changed requirements in ALConfig_NPMC.ini and ALConfig_SPMC.ini so that we can inject the signal from FP1Test and autolocker still functions.

• The HV supply of PMC servo boards was found to be around 180V. We changed it to the designed 160V.

• Attaching few pics for above changes.

Few numbers:

South PMC Mode matching ~ 70%
Modulation frequency = 14.75 MHz
Modulation Index  rad
 

Few notes:

• When aligning to PMC, it is a good idea to keep a white screen infront of transmission and work in dark with IR viewer to get an idea of what is happening.
• A camera on the back side of PMC also helps when sufficient light starts building up in the cavity.
• While finding optimum LO delay using the SRS delay box DB64, use the rated 2.5 ns extra lag written in the datasheet.
• Once maximum swing in PDH error signal is found, check locking once and see if the transmission is good or not. You might be locking to the sideband as the servo locks to one kind of slope only. If you find feeble transmission, just add T/2 delay in the delay box where T is the time period of modulation frequency. This lands you to near right spot.
• While soldering an SMA connector to the cable, put the heat shrink in first and past it to the cable before proceeding. I made this mistake few times.

 We still need two SMA cables. One connects between 21.5Mhz EOM and PMC servo card, another one connects between PMC PD and the servo card.

The 21.5 and 35.5 local oscillator were in the wrong slots, we fixed them.

The 21.5 MHz  photo diode that detects the reflected beam from PMC saturates at 15 mW.

Now I'm trying to optimize the PMC setup so that we have maximum transmittedd power.

You should make sure not to blow up the PMC PD: i.e. the total power on the PD out of lock should be less than 100 mW. The beam size on the PD should also be ~0.5 mm diameter with the actual beam waist being more like 0.3 mm dia.

PD should also be tilted by ~30 deg from normal incidence and the reflection dumped. Its OK if the RF output saturates somewhat at the peak of the PDH signal, but the in-lock RF level should be below ~50 mVrms into 50 Ohms.

 The power is small, our laser is 100 mW. The power on the PD is not saturated. Right now it's receiving ~10mW. It's tilted a bit and the reflected beam is blocked appropriately.

Following the previous elog entry today we succeeded in locking the PMC.

As a reminder this is only a temporary setup. The optical path need to be re-design in order to allow

the implementation of the PMC together with mode matching lenses.  

This is the list of things we did today:

• Setup RFPD on the table for the PMC
• Added the EOM on the path (may be temporary, as the mount is not ready)
• Connected the LO to EOM and the PMC card
• Checked Error signal
• Locked the cavity

reached the end of the actuator after 4h, so the mode jumped and the measurement didn't fully finish, but still very interesting. One can see the bunch of bond pads for the bond wires around the 3mm EG&G PD with a resolution of 10um (left picture). It's not that nice with 25um resolution i did before (picture on the right). One can also see the shadow of the bond wires on the left. Started a new measurement over night (15um resolution)

Today we have tested the second PMC that we have assembled.

We have obtained the 00 mode;

We measured the finesse (~300);

We have scanned the PMC PZT and we see 3 FSR;

We also noted again the presence of a second 00 mode and we confirmed that it was due to laser mode hopping. This has been checked

by injecting a voltage (0.2V) in the temperature input of the laser. Once the voltage was applied the second mode disappeard.

We think that it is enough PMC testing for now. I am tempted to assemble a third PMC, while we should try to fix the glass PMC.

We need to work on the lab organization too.

Today I measured open loop transfer function of PMC loop.

The measurement has two parts.

First the swept sine signal is sent to FP2 test point, TP4 is connected to A, TP3 is connected to B,

the magnitude, B/A, gives us [C][D][E] .

For the second part, the swept sine is sent to ext DC channel,

TP3 is connected to A, and TP4 is connected to B.

this is the TF of [F][A][B]

======================================================================

 [A]--<FP2>-----[B]-----{TP4} ------[C]-----[D]---<Ext DC> ----[E] ---- {TP3}----[F]-----> back to [A]

======================================================================

The magnitudes and phase from both measurements are added up

to get the whole open loop TF of PMC loop [A][B][C][D][E][F].

UGF is ~1k Hz.

PMC setup

Gain 30dB (mzx)

LO PWR 0.585

Power input 30.9 mW

PMC_PHCON 2.5 + 180 flip

PMC_RFADJ 4.0

I'll verify that the schematic matches up with the real circuit we are using.

 I checked the PSL setup today, and the PMC gain setup has to be changed from 30 dB (maximum on gain slider) to 22.5 for best transmission signal.

From the previous  setup, see quote below, the maximum gain of 30 dB on the PMC gain slider was not high enough,

This means that even though the gain is set to maximum, the signal from the transmitted light does not oscillate.

But today it did oscillate, and I had to reduce the gain to 22.5 dB. When I checked the PMC gain, I turned off the FSS loop

to make sure that the FSS loop won't actuate on the NPRO, and the signal are purely from PMC loop.


There are no other changes of parameters. The power input is 30.7 mW, RF power, phase shift are the same

as before.


After adjusting the PMC's gain, I also roughly adjust FSS's loop gain. I haven't optimized it yet, just determined it by looking

at C3:PSL-RCAV_RCTRANSPD signal on the oscilloscope.

common gain is changed from 5 to 8 dB

Fast gain is changed from 8.5 to 13 dB.


I saved change the values for PMC gain, common gain and fast gain in STARTUP.CMD file.

I don't know what causes the gain changes here, I will check the TF of PMC loop again. If it is real, it means

we might not have to modify the PDH servo card.

NOTE: the slowDC for locking both cavities is ~ -0.103 V

This morning I sent an email to Evan in order to obtain PMC documentation. 

For now the only documents found is a mechanical drawing E1400332. I am aware of additional 2 documents that he wrote for this design. I also asked for the electronic/servo

instructions as I am not aware if he built/bought parts for the PMC servo.

This morning I have also poked Rich, in order to have advices on what type of epoxy we need to buy for pzt gluing. Not sure about that. I am going to investigate

on what to buy and especially what should be the best procedure for gluing.

We have been collected the materials bought from Evan:

1. Spacers;

2.  Mirrors;

3. PZTs;

Things to buy:

1. O rings;

2. Epoxy for PZT;

3. Screws;

I am considering to use the table in the TCN lab, once we have a functionally lab. All the information about the PMC will be collected in a section on the PSL wiki page.

O rings and screws have been ordered!!!

I re-aligned the PMC, same for the electro-optic amplitude modulator (EOAM). I also adjusted the power levels everywhere up to the PMC for maximum performance.

I also had to re-adjust the PMC phase. Startup-setting was 2.29V but had to be 3.29V! Error signal is 2.46Vpp at mixer mon.

Power is set to 20mW transmitted through the PMC when modulation is off. Power can be adjusted behind the PMC as it was setup before.
Power modulation is +/-1.5mW around 20mW with max on function generator (~15%).

The DC path of the north PMC resonant reflection photodetector was not showing any signal.

Some work on the North PMC resonant reflection phododetector:

• Drop in voltage accross R4 is 0.9 V, its 22 Ω so that would be a current of 40 mA: way too much current when dark.
• I looked inside and there was a lot of blobbed solder joints R4 and C8, C33 was also not fully contacted on the ground side. I wicked all the excess solder off and retouched all the joints that didn't look great. These modifications didn't fix the problem
• Checked voltage supplies and DC levels in the DC path.  The first OP27 (U5) is showing 1 V on the input but 2 V on the output.  This should be a buffering stage: the op amp is busted. I removed U5 and replaced with new.  Pulled of the pin5 pad but this is not used anyway.  The dark PD doesn't show any voltage drop accross R4 anymore, this is good.
• Modified the gain of the final DC output stage OP27 (U6).  It is now R16=1 kΩ, R11=10 Ω so gain of that stage is x101 and the total DC transimpedance gain is 2222 Ω.  

PMC scanned using slow actuator (NPRO temp)

   The weird TF result from PMC seems to be the result of the insufficient voltage input. When I increased the swept sine voltage from 2mV to 500 mV, the result of the TF becomes as expected. See fig 1.

    Before the signal is fed back to PMC, there is a PMC notch box. It is a low pass filter. It's TF looks fine (fig.2.)

However, when the TF of the servo and the notch is measured together, they look shaky.

I just read Frank's comment. I'll check the schematic of the PMC servo again.

that's not the TF of the PMC servo, it's something else. look at the gain level: -100dB. that's not more than some crosscoupling. Never trust a flat response, always think if the measured form and values make sense at all !

Take a minute and think about the form and values of the TF you expect from a servo like this. Have a look into the schematic and draw the TF shape of the individual gain stages and add them to an overall TF or use LISO to simulate it.  Then measure parts of the servo step by step in order to verify that the individual parts are working as expected.

I fitted the TF of PMC servo card simulated from LISO, and found poles at 2.01 Hz, 59.7 Hz, 13.4 MHz, and zero at 479.4 Hz.

 From last week, I used LISO to model the TF but it did not provide the values of poles and zeroes.

Thanks Koji who taught me how to use LISO fitting feature. Now I can find poles and zeroes of the simulation.

The frequency range spans from 1 Hz -  1 MHz, covering out region of interest (~1 Hz up to a few hundred kHz).

  For higher frequency, I couldn't make it work yet.

pole 2.0139158941  ### fitted (name = pole0)
zero 479.4339553158  ### fitted (name = zero0)
pole 59.7091341574k  ### fitted (name = pole1)

factor 9.5703858437

pole 13.4116105660M 99.7575256877m  

The plot shows simulated data and fit data, we have a nice fit that we can hardly see red and green plots.

 The code for simulating TF is pmc.fil, which can be found on previous entry, the code for fitting, tffit.fil, is attached below.

Hoo! So beautiful fit!

I'm working on Simulink model to calculate PMC's open loop gain. For now, all the parameters for frequency discriminator are copied from linfss6.m.

I'll work on correcting those parameters later.

The simulink model will allow us to learn how external noise will look like in our system.

The bode plot for PMC's TF is plotted in fig1.

I'm not sure why the measurement on both magnitude and phase looks bad at low frequency (f<10 Hz).

I think the model (fig2) is not correct because of the wrong units ( angular frequency,w, to frequency, f.) I'll check  this again.

The phase part seem to be completely wrong.

The parameters, (for example, cavitiy pole, frequency discriminator) for  the TF are not confirmed yet. I'll elog them once I verify them.

 *******************************

Yesterday, I had a chance to test U6(OPA 27) in the schematic.The measurement agrees very well with the computed result, see fig 3.

The signal from source out was sent through FP2 test. TP2 and TP4 were connected to channel A and B on SR785 respectively.

SR785 was set to swept sine mode, frequency span from 1Hz to 10^5 Hz.

So we know that at least one part of the servo works properly.

 I was going to check the TF on each stage of PMC's servo.

Unfortunately, I couldn't find the floppy disc drive, so I slide the sliders (gain, RF power) around. When I add more RF power (from 1V to 7V) to 21.5 MHz EOM, the oscilaltion subsides*.

(*5 mins later I came back to turn down the RF power to 1 V again, and the beam was perfectly locked for a few minutes before fluctuated again)

It's not a long term solution, but I note this for further debugging.

One thing about the gain, I see the TF of the whole PMC servo, when I increase the common gain from 0 to ~8 dB, the magnitude of the TF gets higher. If I increase more gain to ~ 10dB or something, the magnitude goes down . So there might be sth wrong about the opamp that controls the gain.

 How sad. Stop using the floppies and get one of the GPIB-Ethernet converters from Dmass. You can download the python scripts from the 40m wiki.

 we already have one but i was waiting for one the wireless bridge devices someone wanted to buy to make it wireless.

But why do you need a floppy to measure a TF?

found the problem why the PMC servo card wasn't working: the medm screens on the sun workstation didn't have a toggle button for the disable signal for the variable gain amplifier (AD602). this signal was set to "disabled" by default and because there was no button to enable it Tara couldn't get the servo to work. added a toggle button on the screen, PMC is now locked stable

the PMC seems to be very dirty. If we lock it in s-pol the transmitted power is only 7%, even if 60% are going into it (didn't try to optimize it). the rest is dumped in the pmc. switched back to p-pol but should think about cleaning the mirrors. we also have first contact. i think it's worth a try and we can't loose much. peter has also spare mirrors (and a spare spacer)