I set the MC back to its good alignment (June 21st) using this procedure. The trend of the OSEM values over the last 40 days and 40 nights is attached.

Then I aligned the periscope to that beam. This took some serious periscope knob action. Without WFS, the transmission went to 2.7 V and the reflection down to 0.6V.

Then I re-aligned the MC_REFL path as usual. The beam was far enough off that I had to also re-align onto the MC LSC PD as well as the MC REFL camera (~2 beam radii).

Beams are now close to their historical positions on Faraday and MC2. I then restored the PZT sliders to their April snapshot and the X-arm locked.

Steve - please recenter the iris which is on the periscope. It has been way off for a long time.

So it looks OK now. The main point here is that we can trust the MC OSEMs.

Afterwards I rebooted c1susvme1 and c1susvme2 because they were skewed.

 It is really surprising that we now have again the data from the MC OSEMs since up to two days ago the record looked corrupted (see the attachments in my entry 1774).

The reason I ended up severely misaligning the the MC is exactly that there wasn't anymore a reference position that I could go back to and I had to use the camera looking a the Faraday.

This morning I found the Mode Cleaner unlocked.

I check the sliders for the mirrors bias and they have not changed. Also the OSEMs readbacks show no change in the optics positions.

I don't understand what's wrong because in the previous days, in this state of alignmanet, it could lock.

I tried to tweak a little bit the periscope to check whether it was a problem of beam matching but that didn't help the cavity to lock.

I don't want to change the periscpe alignment to much becasue I believe it is still good and I suspect that there is something else going on.

Friday afternoon the mode cleaner got unlocked. Then some adjustment of the MC1 bias sliders locked it again. The driftmon showed the excursion for pitch and yaw of MC1 becasue it wasn't updated after the change.

Tonight Rana found the MC unlocked and simply touched the sliders to bring the OSEMs back to the driftmon values.

MC1 Yaw remains different from the driftmon. If brught back to htat value, the MC would get unlocked.

More investigation is needed to understand why the MC lock hasn't been stable for the last few days.

 The mode cleaner is still unlocked. I played with the cable at the MC2 satellite to enusre they were all plugged in.

Then I tweaked the the mirrors alignment by the sliders and eventually I could get it locked stably with 1.3 reflection. Then I rebooted C1IOO because the WFS wouldn't engage. After that the cavity wasn't locked anymore. Trying to adjust the mirrors around their position didn't restore the lock.

More work is necessary.

I'll be back on it in a while.

I installed an improvised version of PSL output beam iris at the output periscope last week.

Stephanie has needed the doors to the PSL open all day, and still has them open, so I just turned the HEPAs on high. 

[Alberto, Jenne]

We aligned both the reference cavity and the PMC, each by looking at their Trans PD on Davaviewer, and adjusting the two steering mirrors to maximize the transmission power.  We got a pretty good amount of improvement for the ref cav, but since the PMC hasn't decayed a whole lot, we got a much smaller amount of improvement.

I turned the HEPAs back down to ~50.

After Alberto and I worked on aligning the reference cavity, Rob asked the important and useful question: what is the visibility of the reference cavity.  This helps tell us if we're optimally aligned or not even close.

I did a scan of the ref cav temperature, using /scripts/PSL/FSS/SLOWscan, but there seems to be no real signal is C1:PSL-FSS_RFPDDC.  As shown in Alberto's 200-day plot, it does change sometimes, but if you zoom in on the flat parts, it seems like it's not really reading anything meaningful.  I did a cursory check-out of it, but I'm not 100% sure where to go from here:  There are (as with all of these gold-box PDs) 3 outputs:  a ribbon cable (for ADC purposes I think), an SMA for the RF signal, and a BNC for the DC signal.  The photodiode is clearly working, since if you stick the Lollypop in front of the PD, the cavity unlocks.  I plugged a 'scope into the DC BNC, and it also behaves as expected: block the beam and the signal goes down; unblock the beam and the signal goes up.  Something of note is that this readout gives a positive voltage, which decreases when the beam is blocked.  However, looking at the dataviewer channel, nothing at all seems to happen when the beam is blocked/unblocked.  So the problem lies somewhere in the get-signal-to-DAQ path.  I unplugged and replugged in the ribbon cable, and the value at which the channel has been stuck changed.  Many days ago, the value was -0.5, for the last few days it's been -1.5, and after my unplug/replug, it's now back to ~ -0.5 . The other day Alberto mentioned, and made the point again today that it's a little weird that the PD reads out a negative voltage.  Hmm.

Do we have a tester-cable, so that instead of the ribbon cable, I can plug that connector (or pins thereof) into a 'scope?

we have a tester cable, but you don't want it. Instead the problem is probably at the cross-connect. The D-cable goes to a cross-connect and you can probe there with a voltmeter. If the signal is good there, trace it to the ADC. Also trend for several years to see when this happened - Yoichi may know the history better.

Also, we still need to complete the FSS RFPD task list from last year.

For some reason a few minutes ago the FB DAQ crashed and I had to restarted.

 [Jenne, Ben]

I called in the reinforcements today.  Ben came over and we looked all around at all of the cross-connects and cables relating to the FSS.  Everything looks pretty much okey-dokey, except that we still weren't getting signal in the DataViewer channels.  Finally we looked at the psl.db file, which indicates that the C1:PSL-FSS_RFPDDC channel looks at channel 21 of the ADC cross connect thing.  We followed the cable which was plugged into this, and it led to a cable which was disconnected, but laying right next to the Ref Cav refl PD.  We plugged this into the DC out SMA connection of the photodiode (which had not been connected to anything), and suddenly everything was mostly golden again in dataviewer land.  RFPDDC_F now has a signal, but RFPDDC is still flat. 

Even though this seems to be working now, it's still not perfect.  Rob suggested that instead of having this SMA cable going from the photodiode's DC out, we should take the signal from the ribbon cable.  So I'm going to figure out which pin of the D-connector is the DC out, and take that from the cross connect to the ADC cross connect.  This will help avoid some persnickity ground loops. 

I have added/modified SMOO settings to all of the records in psl.db appropriately. Changes checked in to SVN.

As a reminder, you should check in to the SVN all changes you make to any of the .db files or any of the .ini files in chans.

Big thumbs down to whoever put a beam dump on the PSL table in front of the PMC yesterday afternoon without noting it in the elog

The offending beam dump has been removed, and the PMC relocked.

 Maybe it was Russell Crowe

I think the MZ pzt is broken/failing.  I'm not sure how else to explain this behavior.

The first bit of the time series is a triangle wave into the DC offset (output) field, over approximately the whole range (0-250V).   You can see the fringe visbility is quite small.  The triangle wave is stopped, and I then maxed out the offset slider to get to the "high" power point from the triangle wave sweep. Then for a little while with the PZT is held still, and the power still increases.  The MZ is then locked, and you can see the PZT voltage stay about the same but the power continues to rise over the next ~10 minutes or so.

This plot answers the previous question, and raises a new one--what the heck is MZTRANSPD?  I'd guess the pins are unconnected--it's just floating, and somehow picking up the MZ_PZT signal.

I aligned the MZ.  The reflection went from .86 to .374

Alberto, Rana

With the high power meter I measured the reflected power when the PMC was unlocked and used that to obtain the calibration of the PMC-REFL PD: 1.12V/W.

P_in = 1.98W ; P_trans = 1.28W ; P_refl = 0.45W

From that I estimated that the losses account to 13% of the input power.

I checked both the new and the old elogs to see if such a measurement had ever been done but it doesn't seems so. I don't know if such a value for the visibility is "normal". It seems a little low. For instance, as a comparison, the MC visibility, is equal to a few percents.

Also Rana measured the transmitted power after locking the PMC on the TEM20-02: the photodiode on the MEDM screen read 0.325V. That means that a lot of power is going to that mode.

That makes us think that we're dealing with a mode matching problem with the PMC.

Rana, Alberto

This afternoon we tried to improve the mode matching of the beam to the PMC. To do that we tuned the positions of the two lenses on the PSL table that come before the PMC.

We moved the first lens back an forth the without noticing any improvement on the PMC transmitted and reflected power. Then we moved the first backwards by about one cm (the order is set according to how the beam propagates). That made the things worse so we moved also the second lens in the same direction so that the distance in between the two didn't change significantly. After that, and some more adjustments on the steering mirrors all we could gain was about 0.2V on the PMC transmission.

We suspect that after the problems with the laser chiller of two months ago, the beam size changed and so the mode matching optics is not adequate anymore.

We have to replace the mode matching lenses with other ones.

the servo needs some work. 

2 day trend

Koji, Yoichi

The Mach Zehnder and I got to know each other today.  The reason for redoing the alignment was to improve pointing from the PSL table into the MC/IFO in hopes that this would solve the MC unlocking problems that we've been having lately.  Since Rana had aligned the IOO QPDs a few weeks ago when all of the alignments and things were good, I used them as a reference for my Mach Zehnder alignment activities. 

 
The order of operations were approximately as follows:

1. Block the secondary (west) arm of the Mach Zehnder using either an aluminum or razor dump.

2. Use SM1 in the MZ to align the beam to the IOO_QPDs (Pos and Ang).  I unfortunately also touched BS2 at this juncture, which made the refl path no longer a reference.

3.  Make sure that the QPD Sum on both Pos and Ang was sensible.  Since there are 2 beamsplitters in a Mach Zehnder, the power on the QPDs should be a quarter when only one beam is on them.  Be careful not to allow the beam no clip on anything.  The biggest problem was the bottom periscope mirror - if you hit it too high or too low, since it is a very thick optic, you end up coming out its side!  This is the frosty part on the edges, totally inappropriate for beams to go through!  Since the side of the periscope mirror isn't HR coated, when going through it like this, I was able to saturate the QPDs.  Not so good. 

4. Also, make sure that this first beam is on the MZ Refl PD.  Do this using the steering optics after the beam has left the MZ.  Use a viewer to look at the PD, and see the small spot of the beam on the diode.  We closed the iris which is present and was standing fully open to remove a spurious beam which was a parallel split-off of the main beam.  Since it was very weak, it is fine.

5.  Unblock the west arm, and block the east arm of the MZ.

6. Align this arm to both the IOO QPDs and the MZ refl diode using the adjustments on BS1, the PZT mirror and if necessary, BS2.  Note that the adjust knobs on the PZT mirror have lock screws.  Make sure to unlock them before adjusting, and relock afterward, to avoid slipping while the PZT is moving.

7.  Unblock all the beams, and make sure there is only one spot both on the transmission side and the reflection side, i.e. the 2 spots from the 2 arms are completely overlapping.  For the Trans side, make sure to look both in the near field and the far field (even after the periscope) to ensure that you really have one spot, instead of just the 2 spots crossing at a single location.

8.  Look at the MZ refl DC out and the PD out from the ISS box (which is essentially MZ trans, looking at Morag and Siobhan) on a 'scope.

9.  Touch / gently wiggle BS1 or another optic, and watch the 'scope.  At the same time, adjust BS1, the PZT mirror and BS2 to maximize the contrast between light and dark fringes.  Ideally, the refl PD should go almost to zero at the dark fringes.

10.  Check that you still have only one overlapping beam everywhere, and that you're actually hitting the MZ refl PD.

11. Because I was concerned about clipping while still figuring out the status of the lower periscope mirror, I removed the beam pipe holders between the last optic before the periscope, and the lower periscope mirror.  The beam pipe had already been removed, this was just the pedestals and the snap-in clamps.

All done for now!  Still to be done:  Optimize the position of the EOMs.  There is a waveplate out front and the EOMs are mounted in such a way that they can be moved in several directions, so that we can optimize the alignment into them.  They ideally only should see a single polarization, in order to apply solely a phase modulation on the beam.  If the input polarization isn't correct, then we'll get a bit of amplitude modulation as well, which on PDs looks like a cavity length change.  Also, the little blue pomona-type box which has the RF signals for the EOMs needs to be clamped to the table with a dog clamp, or better yet needs to be moved underneath the PSL table, with just the cables coming up to the EOMs.  The SMA connections and the SMA cable kept interfering with the MZ refl beam...it's a wonder anyone ever made the beam snake around those cables the way they were in the first place. Right now, the box is sitting just off the side of the table, just inside the doors.

 
Something else that Rana and I did while on the table:  We moved the PMC trans optics just a teensy bit toward the PSL door (to the east) to avoid coming so unbelievably close to the MZ refl optics.  The PMC trans beam shown in the lowest part of my sketch was very nearly clipping on the MZ refl steering optic just near it.  This situation isn't totally ideal, since (as it has been in the past), the first optic which is dedicated to the PMC trans isn't fully sitting on the PSL table.  The pedestal needs to hang off the edge of the table a bit to keep this beam from clipping.  Unfortunately there really isn't space to make a better beam path.  Since we're planning on getting rid of the MZ when the upgrade happens, and this isn't causing us noticeable trouble right now, we're going to let it stay the way it is.

Also, we dumped the reflection from the PMC RFPD onto a razor blade dump. And we noticed that the PZT mirror and BS2 in the MZ are badly vibrationally sensitive. BS2 has a ~400 Hz resonance (which is OK) but a ~150 ms ringdown time!! PZT mirror is similar.

Q = pi * f * tau = 200!  Needs some damping.

In the future, mirrors shouldn't be so close together that you can't get at their knobs to adjust them No good.  I ended up blocking the beam coming out of the PMC to prevent sticking my hand in some beam, making the adjustment, then removing the dump.  It worked in a safe way, but it was obnoxious. 

- we finished the MZ alignment; the contrast is good.

- we did the RFAM tuning using a new technique: a bubble balanced analyzer cube and the StochMon RFPD. This techniques worked well and there's basically no 33 or 166 RFAM. The 133 and 199 are as expected.

- the MC locked right up and then we used the periscope to align to it; the transmission was ~75% of max before periscope tuning. So the beam pointing after the MC should be fine now.

- the Xarm locked up with TRX = 0.97 (no xarm alignment).

If Rob/Yoichi say the alignment is now good, the we absolutely must center the IOO QPDs and IP POS and IP ANG and MC TRANS  today so that we have good references.

-----------------------------------

The first photo is of our nifty new setup to get the beam to the StochMon PD.  The MZ transmitted beam enters the photo from the bottom right corner, and hits the PBS (which we leveled using a bubble level).  The P-polarization light is transmitted through the cube, and the S-polarization is reflected to the left.  The pure S-polarized light hits a Beam Splitter, which we are using as a pickoff to reduce the amount of light which gets to the PD.  Most of the light is dumped on an aluminum dump.  The remaining light hits a steering mirror (Y1 45-S), goes through a lens, and then hits the StochMon PD.  While aligning the MZ to maximize visibility, we look at the small amount of P-polarized light which passes through the PBS on an IR card, and minimize it (since we want to be sending purely S-polarized light through the EOMs and into the MC).

The second photo is of a spectrum analyzer which is directly connected to the RF out of the StochMon PD.  To minimize the 33MHz and 166MHz peaks, we adjust the waveplates before each of the EOMs, and also adjusted the tilt of the EOM holders.

The final photo is of the EOMs themselves with the Olympus camera.

Once we finished all of our MZ aligning, we noticed that the beam input to the MC wasn't perfect, so Rana adjusted the lower periscope mirror to get the pointing a little better.  

The MZ refl is now at 0.300 when locked.  When Rana reduced the modulation depth, the MZ refl was about 0.050 .  Awesome!

The PSL Temperature Box (D980400-B-C, what kind of numbering scheme is that?) modified at LHO/LLO ~8 years ago to have better resolution on the in-loop temperature sensors.

I haven't been able to find a DCN / ECN on this, but there's an elog entry from Hugh Radkins here.  I'm also attaching the PDF of the latest drawing (circa 2000) from the DCC.

The schematic doesn't show it, but I am guessing that the T_SENSE inputs are connected to the AD590 chips, and that 4 of these are attached somehow to the RefCav can. IF this is true, I don't understand why there are input resistors on the LT1125 of U1; the AD590 is supposed to be a current source ?

Peter King is supposed to be coming over to work on this today so whoever spots him should force/cajole/entice him to elog what he's done. Film him if necessary.

I also think R1-8 should be swapped into metal film resistors for stability. The datasheet says that it puts out 1 uA/K, so the opamps put out 10 mV/K.

J8 and JP1 should be shorted to disable both the tidal and VME control input. Both are unused and a potential source of drift.

 Peter King is updating our temp box as Hugh did at Hanford Oct.22 of 2001 I still have not seen an updated drawing of this.

The LT 1021-7 reference chip will arrive tomorrow morning. This modification should be completed by noon.

 ** The link to the DCN from Hugh is here in the DCC.

 Is that the reason of the PSL craziness tonight? See attachment.

There's no elog entry about what work has gone on today, but it looks like Peter took apart the reference cavity temperature control around 2PM.

I touched the reference cavity by putting my finger up underneath its sweater and it was nearly too hot to keep my finger in there. I looked at the heater power supply front panel and it seems that it was railed at 30 V and 3 A. The nominal value according to the sticker on the front is 11.5 V and 1 A.

So I turned down the current on the front panel and then switched it off. Otherwise, it would take it a couple of days to cool down once we get the temperature box back in. So for tonight there will definitely be no locking. The original settings are in the attached photo. We should turn this back on with its 1A setting in the morning before Peter starts so that the RC is at a stable temp by the evening. Its important NOT to turn it back on and let it just rail. Use the current limit to set it to 1 A. After the temperature box is back in the current limit can be turned back up to 2A or so. We never need the range for 3A, don't know why anyone set it so high.

The reference cavity vacuum chamber temp is plotted starting Feb 22 of 2005

This plot suggest that the MINCO temp controller is not working properly.

While Peter King is still working on the reference cavity temperature box, I turned the power supply for the reference cavity's heater back on. Rana turned it off last night since the ref cav temperature box had been removed.

I just switched it on and turned the current knob in the front panel until current and voltage got back to their values as in Rana's picture.

I plan to leave it like that for half an hour so that the the cavity starts warming up. After that, I'll turn the current back to the nominal value as indicated in the front panel.

The 40m Lab reference cavity temperature box S/N BDL3002 was modified as per DCN D010238-00-C.

These were:

    R1, R2, R5, R6 was 10k now are 25.5k metal film

    R11, R14 was 10k now are 24.9k metal film

    R10, R15 was 10k now are 127k thick film - no metal film resistors available

    R22 was 2.00k now is 2.21k

    R27 was 10k now is 33.2k

    U5, the LM-336/2.5 was removed

    An LT1021-7, 7 V voltage reference was added.  Pin 2 to +15V, pin 4 to ground, pin 6 to U6 pin 3.

    Added an 8.87k metal film resistor between U6 pin 1 and U4 pin 6.

    Added an 8.87k metal film resistor between U6 pin 1 and U4 pin 15.

    The 10k resistor between J8 pin 1 and ground was already added in a previous modification.

In addition R3, R4, R7, R8, R12 and R13 were swapped out for metal film resistors of the same value

(1.00k).

    The jumper connection to the VME setpoint was removed, as per Rana's verbal instructions.

This disables the ability to set the reference cavity vacuum chamber temperature by computer.

It turned out that half an hour was too long. In less than that the reference cavity temperature passed the critical point when the temperature controller (located just below the ref cav power supply in the same rack) disables the input power to the reference cavity power supply.

The controller's display in the front shows two numbers. The first goes with the temperature of the reference cavity; the second is a threshold set for the first number. The power supply gets enabled only when the first number comes under the threshold value.

Now the cavity is cooling down and it will take about another hour for its temperature to be low enough and for the heater power supply to be powered.

 The cavity temp cooled below SP2 set point 0.1  The Minco SP1 (present temp in Volts) now reading -0.037 so DC power supply was turned on and set to 12V 1A  

Basically, in addition to the replacement of the resistors with metal film ones, Peter replaced the chip that provides a voltage reference.

The old one provided about 2.5 V, whereas the new one gets to about 7V. Such reference voltage somehow depends on the room temperature and it is used to generate an error signal for the temperature of the reference cavity.

Peter said that the new higher reference should work better.

Summary: This afternoon we managed to get the temperature control of the reference cavity working again.

We bypassed the MINCO PID by connecting the temperature box error signal directly into EPICS.

We couldn't configure the PID so that it worked with the modified temperature box so we decided to just avoid using it.

Now the temperature control is done by a software servo by using the channel C1:PSL-FSS_MINCOMEAS as error signal and driving C1:PSL-FSS_TIDALSET (which we have clip-doodle wired directly to the heater input).

We 'successfully' used ezcaservo to stabilize the temperature:

ezcaservo -r C1:PSL-FSS_MINCOMEAS -s 26.6 -g -0.00003 C1:PSL-FSS_TIDALSET

We also recalibrated the channels:

C1:PSL-FSS_RMTEMP

C1:PSL-FSS_RCTEMP

C1:PSL-FSS_MINCOMEAS

with Peter King on the phone by using ezcawrite (EGUF and EGUL) but we didn't change the database yet. So please do not reboot the PSL computer until we update the database.

More details will follow.

I made the changes to the psl.db to handle the new Temperature box hardware. The calibrations (EGUF/EGUL) are just copied directly from the LHO .db file (I have rsync'd their entire target area to here).

allegra:c1psl>diff psl.db~ psl.db
341,353d340
< grecord(ai,"C1:PSL-FSS_TIDALOUT")
< {
<       field(DESC,"TIDALOUT- drive to the reference cavity heater")
<       field(DISV,"1")
<         field(SCAN,".5 second")
<       field(DTYP,"VMIVME-3113")
<       field(INP,"#C0 S28 @")
<       field(EGUF,"10")
<       field(EGUL,"-10")
<       field(EGU,"volts")
<       field(LOPR,"-10")
<       field(AOFF,"0")
< }
493,494c480,481
<         field(EGUF,"285.675")
<         field(EGUL,"-214.325")
---
>         field(EGUF,"67.02")
>         field(EGUL,"7.96")
508,509c495,496
<         field(EGUF,"726.85")
<         field(EGUL,"-1273.15")
---
>         field(EGUF,"75.57")
>         field(EGUL,"12.31")
531,532c518,519
<         field(EGUF,"726.85")
<         field(EGUL,"-1273.15")
---
>         field(EGUF,"75.57")
>         field(EGUL,"12.31")
605,617d591
< grecord(ai,"C1:PSL-FSS_TIDALINPUT")
< {
<       field(DESC,"TIDALINPUT- tidal actuator input")
<       field(DISV,"1")
<         field(SCAN,".5 second")
<       field(DTYP,"VMIVME-3123")
<       field(INP,"#C0 S3 @")
<       field(EGUF,"10")
<       field(EGUL,"-10")
<       field(EGU,"volts")
<       field(LOPR,"-10")
<       field(AOFF,"0")
< }
1130a1105,1130
> grecord(ai,"C1:PSL-FSS_TIDALINPUT")
> {
>       field(DESC,"TIDALINPUT- tidal actuator input")
>       field(DISV,"1")
>         field(SCAN,".5 second")
>       field(DTYP,"VMIVME-3123")
>       field(INP,"#C0 S3 @")
>       field(EGUF,"10")
>       field(EGUL,"-10")
>       field(EGU,"volts")
>       field(LOPR,"-10")
>       field(AOFF,"0")
> }
> grecord(ai,"C1:PSL-FSS_TIDALOUT")
> {
>       field(DESC,"TIDALOUT- drive to the reference cavity heater")
>       field(DISV,"1")
>         field(SCAN,".5 second")
>       field(DTYP,"VMIVME-3113")
>       field(INP,"#C0 S28 @")
>       field(EGUF,"10")
>       field(EGUL,"-10")
>       field(EGU,"volts")
>       field(LOPR,"-10")
>       field(AOFF,"0")
> }
1143,1144c1143,1144
<         field(HOPR,"0.010")
<         field(LOPR,"-0.010")
---
>         field(HOPR,"2")
>         field(LOPR,"0")

I stepped the TIDALSET and looked at what happened. Loop was closed with the very low gain.

The RED guy tells us the step/impulse response of the RC can to a step in the heater voltage.

The GREY SLOWDC tells us how much the actual glass spacer of the reference cavity lags the outside can temperature.

Since MINCOMEAS is our error signal, I have upped his SCAN period from 0.5 to 0.1 seconds in the database and reduced its SMOO from 0.9 to 0.0. I've also copied over the Fricke SLOW code and started making a perl PID loop for the reference cavity.

Since ~Aug. 27, the reference cavity has been running with no thermal control. This is not really a problem at the 40m; a 1 deg change of the glass cavity

will produce a 5 x 10^-7 strain in the arm cavity. That's around 20 microns of length change.

This open loop time gave us the opportunity to see how good our cavity's vacuum can insulation is.

The first plot below shows the RCTEMP sensors and the RMTEMP sensor. RMTEMP is screwed down to the table close to the can and RCTEMP is on the can, underneath the insulation. I have added a 15 deg offset to RMTEMP so that it would line up with RCTEMP and allow us to see, by eye, what's happening.

There's not enough data here to get a good TF estimate, but if we treat the room temperature as a single frequency (1 / 24 hours) sine wave source, then we can measure the delay and treat it as a phase shift. There's a ~3 hour delay between the RMTEMP and RCTEMP. If the foam acts like a single pole low pass filter, then the phase delay of (3/24)*360 = 45 deg implies a pole at a ~3 hour period. I am not so sure that this is a good foam model, however.

The colorful plot is a scatter plot of RCTEMP v. RMTEMP. The color denotes the time axis - it starts out blue and then becomes red after ten days.

I have added the records for the RC thermal PID servo into the psl/slowpid.db file which also holds the records for the SLOW servo that uses the NPRO-SLOW to minimize the NPRO-FAST. This new database will take effect upon the next PSL boot.

The perl script which runs the servo is scripts/PSL/FSS/RCthermalPID.pl. Right now it is using hard-coded PID parameters - I will modify it to use the on-screen values after we reboot c1psl.

The new screen C1PSL_FSS_RCPID.adl, the script, and the .db have been added to the SVN.

I have got some preliminary PID parameters which seem to be pretty good: The RCTEMP recovers in ~10 minutes from a 1 deg temperature step and the closed loop system is underdamped with a Q of ~1-2.

I'm leaving it running on op340m for now - if it goes crazy feel free to do a 'pkill RCthermalPID.pl'.

I have replaced the temporary clamps that were connecting the RC heater to its power supply with a new permanent connection.

In the IY1 rack, I connected the control signal of the RC PID temperature servo - C1:PSL-FSS_TIDALSET - to the input of the RC heater's power supply.

The signal comes from a DAC in the same rack, through a pair of wires connected to the J9-4116*3-P3 cross-connector (FLKM). I joined the pair to the wires of the BNC cable coming from the power supply, by twisting and screwing them into two available clamps of the breakout FKLM in the IY1 rack - the same connected to the ribbon cable from RC Tmeperature box.

Instead of opening the BNC cable coming from the power supply, I thought it was a cleaner and more robust solution to use a BNC-to-crocodile clamp from which I had cut the clamps off.

During the transition process, I connected the power supply BNC input to a a voltage source that I set at the same voltage of the control signal before I disconnected it (~1.145V).

I monitored the temperature signals and it looked like the RC Temperature wasn't significantly affected by the operation.

The RC thermal PID is now controllable from its own MEDM screen which is reachable from the FSS screen. The slowpid.db and psl.db have been modified to add these records and all seems to be working fine.

Also, I've attached the c1psl startup output that we got on the terminal. This is just for posterity.

I'm also done tuning the PID for now. Using Kp = -1.0, Ki = -0.01, and Kd = 0, the can servo now has a time constant of ~10 minutes and good damping as can be seen in the StripTool snap below. These values are also now in the saverestore.req so hopefully its fully commissioned.

I bet that its much better now than the MINCO at holding against the 24 hour cycle and can nicely handle impulses (like when Steve scans the table). Lets revisit this in a week to see if it requires more tuning.

We measured the voltage noise of the heater used to control the RC can temperature. It is large.

The above scope trace shows the voltage directly on the monitor outputs of the heater power supply. The steps are from the voltage resolution of the 4116 DAC.

We also measured the voltage noise on the monitor plugs on the front panel. If these are a true representation of the voltage noise which supplies the heater jacket, then we can use it to estimate the temperature fluctuations of the can. Using the spectrum of temperature fluctuations, we can estimate the actual length changes of the reference cavity.

I used the new fax/scanner/toaster that Steve and Bob both love to scan this HP spectrum analyzer image directly to a USB stick! It can automatically make PDF from a piece of paper.

The pink trace is the analyzer noise with a 50 Ohm term. The blue trace is the heater supply with the servo turned off. With the servo on (as in the scope trace above) the noise is much much larger because of the DAC steps.

I added a new database record (C1:PSL-FSS_RCPID_SETPOINT) to allow for changing of the RC setpoint while the loop is on. This will enable us to step the can's temperature and see the result in the NRPO's SLOWDC.

I stepped the RC can temperature to see the response in the laser frequency. This gives a true measure of the thermal time constant of the RC. Its ~4 hours.

Since the RCPID screen now has a setpoint field, I can remotely type in 1 deg steps. The NPRO SLOW actuator locks the NPRO to the RC at long time scales and so we can use C1:PSL-FSS_SLOWDC to measure the RC length. By knowing what the step response time constant is, we can estimate the transfer function from can temperature to frequency noise and thereby make a better heater circuit.

 Does the observed temperature shift make any sense? Well, John Miller and I measured the SLOW calibration to be 1054 +/- 30 MHz / V.

We know that the thermal expansion coefficient of fused silica, alpha = 5.5 x 10^-7 (dL/L)/deg. So the frequency shift ought to be alpha * c / lambda = 155 MHz / deg.

Instead we see something like 110 MHz / deg. We have to take more data to see if the frequency shift will actually asymptote to the right value or not. If it doesn't, one possibility is that we are seeing the effect of temperature on the reflection phase of the mirror coatings through the dn/dT and the thermal expansion of the dielectric layers. I don't know what these parameters are for the Ta2O5 layers.

A more useful measure of the frequency noise can be gotten by just looking at the derivative in the first 30 minutes of the step, since that short time scale is much more relevant for us. Its 0.04 V / hour / (2 deg) =>  860 (Hz/s)/deg.

In the frequency domain this comes out to be dnu/dT = 860 Hz/deg @ 0.16 Hz or dnu/dT = 137 *(1/f) Hz / deg.

Our goal for the reference cavity frequency noise is 0.01 * (1/f) Hz/rHz. So the temperature noise of the can needs to be < 0.1 mdeg / rHz.