Taking another look at the datasheet, I don't think LM7812 is an appropriate replacement and I think the LM2940CT-12 is supposed to supply 1A, so it's possible the problem actually is on the power board, not on the dewhitening board. The board takes +/- 15V, not +/- 24...

FYI:

D050368 Anti-Imaging Chassis
https://dcc.ligo.org/LIGO-D050368

https://labcit.ligo.caltech.edu/~tetzel/files/equip

D050368 Adl SUS/SEI Anti-Image filter board 
S/N 100-102 Assembled by screaming circuits. Begin testing 4/3/06 
S/N xxx Mohana returned it to the shop. No S/N or traveler. Put in shop inventory 4/24/06 
S/N 103 Rev 01. Returned from Screaming circuits 7/10/06. complete except for C28, C29 
S/N 104-106 Rev 01. Returned from Screaming circuits 7/10/06. complete except for C28, C29 Needs DRV-135’s installed 
S/N 107-111 Rev 02 (32768 Hz) Back from assembly 7/14/06 
S/N 112-113 Rev 03 (65536 Hz) assembled into chassis and waiting for test 1/29/07 
S/N 114 Rev 03 (65536 Hz) assembled and ready for test 020507 

D050512 RBS Interface Chassis Power Supply Board (Just an entry. There is no file)

https://dcc.ligo.org/LIGO-D050512

RBS Interface Chassis Power Board D050512-00

https://labcit.ligo.caltech.edu/~rolf/jayfiles/drawings/D050512-00.pdf
 

Koji gave me some tips on testing this board that I wanted to write down, notes probably a bit intermingled with my thoughts. Thanks Koji, also for the DCC and equipment logging!

• Test the power and AI boards separately with an external supply, ramping the voltage up slowly for each.
• If it seems the AI board is actually drawing too much current, may need to check its TPs for where a problem might be
  • If it's really extensive may use an IR camera to see what elements are getting too hot
  • Testing in segments will prevent breaking more components
• Check the regulator that I've replaced
• The 1 Ohm resistors may have been acting as extra 1A fuses. i need to make sure the resistors I've used to replace them are rated for >1W, if this is the case.
• Can check the resistance between +-12V and Gnd inputs on the AI board, if there is a short drawing too much current it may show up there.
• The 7812 may be an appropriate regulator, but the input voltage may need to be somewhat higher than with the low drop regulator that was used before.
• I want to double check the diagram on the DCC

I completed testing of the AI board mentioned above. In addition to the blown fuse, there were two problems:

• A was a large drop of solder splattered on some of the ch 1 ICs, which is why we couldn't maintain any voltage. I removed the solder.
• The +12V wire from the power board to the AI board was loose, so I removed and replaced that crimp connection

After this, I tested the TF of all channels. For the most part, I found the expected 3rd order ~7500Hz cheby with notches at ~16kHz and 32kHz. However, some of the channels had shallower or deeper notches. By ~32kHz, I was below the resolution on the spectrum analyzer. Perhaps I just have nonideal settings? I'll attach a few representative examples.

I reinstalled the chassis at 1X2, but haven't connected power.

The polarization and alignment of the fiber for the OMC setup were adjusted. The polarization ratio before the PBS was 50:1. Then, the P-pol was sent to the OMC via two steering mirrors.
As a result of the beam alignment, the OMC cavity is flashing with a good amount of occasional TEM00.

Fiber alignment and polarization refinement

- NPRO power ADJ was "-29". The initial fiber output was 6mW.
- The input fiber collimator and an input steering mirror were adjusted to maximize the fiber output. The output power increased to 12mW.

- Adjusted the output fiber mount to minimize the PBS reflection.
- The initial ratio of the P/S was checked. 3mW was reflected by a PBS out of 12W. (i.e. 3:1).
- Went to the PSL table and repeated 1) rotate the fiber coupler 2) maximize the input beam/coupler alignment.
- Again, adjusted the output fiber mount to minimize the PBS reflection.
- Went back to the PSL to repeat the input side adjustment.
- Determined that I could not do it better.

- Increased the NPRO power ADJ to -20, just to have more power.
  Polarization ratio was ~50:1 (Trans 43mW, Refl 0.82mW).

The beam alignment into the OMC
- Set up the steering mirrors.
- Align the input beam so that I can see the input spot on the center of the second curved mirror (CM2).
- If the alignment is perfect, the input beam should hit the center of the first cavity mirror (FM1)
- The deviation can be adjusted by the mirror/spot position on the last steering mirror.
- So: Adjust CM2 spot by the last steering mirror, Adjust FM1 spot by the penultimate steering mirror.
- This made the cavity flashing. After a bit of alignment, the TEM00 mode was visible.
- A CCD was set at the transmission of CM2

To Do:

• Set up the OMC refl optical path and the refl PD
• Set up a trans monitor PD at CM1
• Set up a platform position marker to ensure the reproducibility
• Moku setup:
  • Temperature sweep
  • Laser PZT sweep
  • Moku RF modulation demodulation setup for PDH locking
     

What we need more to make the work better/easier in/around the HEPA table:

• Proper fiber protection
• Proper stray beam blocks (anodized Al plates)
• Electronics rack or shelves at the north side of the booth
• Parts table at the south side of the booth
• Rotate the table 180 deg and put a storage shelf beneath the table (Wire rack?)

The OMC was locked with Moku Pro.

Attachment 1: Electrical setup. The RF part of the REFL PD signal was fed into Moku pro, while the DC part was monitored on a scope.
Attachment 2: Servo setup. The modulation amplitude is 100mV.
Attachment 3: Image rejection LPF setup
Attachment 4: Laser PZT servo during lock acquisition
Attachment 5: Laser PZT servo for stational operation
Attachment 6: Laser Temp servo setting
Attachment 7: CCD Images during lock. The REFL is still limited by the mode mismatching component.
Attachments 8/9: The REFL locked / unlocked = 340mV/5.4V = 0.06 --> Mode Matching 94%
 

Aaron and I are going to do the checkout of the OMC electronics outside vacuum today. At some point, we will also want to run a c1omc model to integrate with rtcds. Barring objections, I will set up this model on one of the spare cores on the physical machine c1ioo tomorrow.

We found a diagram describing the DC Readout wiring scheme on the wiki page for DC readout (THIS DIAGRAM LIED TO US). The wiring scheme is in D060096 on the old DCC.

Following this scheme for the OMC PZT Driver, we measured the capacitance across pins 1 and 14 on the driver end of the cable nominally going to the PZT (so we measured the capacitance of the cable and PZT) at 0.5nF. Gautam thought this seemed a bit low, and indeed a back of the envelope calculation says that the cable capacitance is enough to explain this entire capacitance.

Gautam has gone in to open up the HV driver box and check that the pinout diagram was correct. We could identify the PZT from Gautam's photos from vent 79, but couldn't tell if the wires were connected, so this may be something to check during the vent.

UPDATE:

Turns out the output was pins 13 and 25, we measured the capacitance again and got 209nF, which makes a lot more sense.

I made a script to scan the OMC length at each setpoint for the two TTs steering into the OMC. It is currently located on nodus at /users/aaron/OMC/scripts/OMC_lockScan.py.

I haven't tested it and used some ez.write syntax that I hadn't used before, so I'll have to double check it.

My other qualm is that I start with all PZTs set at 0, and step around alternative +/- values on each PZT at the same magnitude (for example, at some value of PZT1_PIT, PZT1_YAW, PZT2_PIT, I'll scan PZT2_YAW=1, then PZT2_YAW=-1, then PZT2_YAW=2). If there's strong hysteresis in the PZTs, this might be a problem.

I finished running the cabling for the OMC, which involved running 7x 50ft DB9 cables from the OMC_NORTH rack to the 1X2 rack, laying cables over others on the tray. I tried not to move other cables to the extent I could, and I didn't run the new cables under any old cables. I attach a sketch diagram of where these cables are going, not inclusive of the entire DAC/ADC signal path.

I also had to open up the AA board (D050387, D050374), because it had an IPC connector rather than the DB37 that I needed to connect. The DAC sends signals to a breakout board that is in use (D080302) and had a DB37 output free (though note this carries only 4 DAC channels). I opened up the AA board and it had two IPC 40s connected to an adapter to the final IPC 70 output. I replaced the IPC40 connectors with DB37 breakouts, and made a new slot (I couldn't find a DB37 punch, so this is not great...) on the front panel for one of them, so I can attach it to the breakout board.

I noticed there were many unused wires, so I had to confirm that I had the wiring correct (still haven't confirmed by driving the channels, but will do). There was no DCC for D080302, but I grabbed the diagrams for the whitening boards it was connected to (D020432) and for the AA board I was opening up as well as checked out elog 8814, and I think I got it. I'll confirm this manually and make a diagram if it's not fake news.

I've started testing the OMC channels I'll use.

I needed to update the model, because I was getting "Unable to setup testpoint" errors for the DAC channels that I had created earlier, and didn't have any ADC channels yet defined. I attach a screenshot of the new model. I ran

An interesting thing was happened in the OMC-LSC timing clock.

Right now the clock of the OMC and the LSC are completely synchronized.

 The trend data is shown below. At the first two measurements (Oct.27 and Nov.1),  LSC had constant retarded time of 3Ts (~92usec.).

The last measurement, on Nov.15, number of shifts goes to zero, this means there are no retarded time.

Also the variance between the two signal gets zero, so I conclude the OMC and the LSC are now completely synchronized.

The measurement on Nov.8 is somehow meaningless, I guess the measurement did not run correctly by an influence from megatron(?)

According to my measurements I conclude that LSC-signal is retarded from OMC-signal with the constant retarded time of 92usec.
It means there are no timing jitter between them. Only a constant time-delay exists.

(Timing jitter)
Let's begin with basics.
If you measure the same signal at OMC-side and LSC-side, they can have some time delay between them. It can be described as followers.

where tau_0 is the time delay. If the tau_0 is not constant, it causes a noise of the timing jitter.

(method)
I have injected the sine-wave with 200.03Hz into the OMC-LSC_DRIVE_EXC. Then by using get_data, I measured the signal at 'OMC-LSC_DRIVE_OUT' and 'LSC-DARM_ERR' where the exciting signal comes out.
In the ideal case the two signals are completely identical.
In order to find the delay, I calculated the difference in these signals based on the method described by Waldman. The method uses the following expression.

Here the tau_s is the artificial delay, which can be adjusted in the off line data.
By shifting tau_s we can easily find the minimal point of the RMS, and at this point we can get tau_0=tau_s.
This is the principle of the method to measure the delay.  In my measurement I put T=1sec. and make the calculation every 1sec. in 1 min.

(results)
Attachment is the obtained results. The above shows the minimum RMS sampled every 1sec. and the below shows the delay in terms of number of shifts.
1 shift corresponds to Ts (=1/32kHz).  All of the data are matched with 3 times shift, and all of the minimum RMS are completely zero.
Therefore I can conclude that LSC-signal is retarded from OMC-signal with constant retarded times of 3*Ts exactly, and no timing jitter has been found.
 

[Murtaza, Paco, Radhika]

We got some LT1128s from downs (Dean) to get this board up and running again. We first did a test replacement on Ch2 (since Ch1 was working) and got the desired transfer function (z=1, p=[10, 1000]) measured up to the test point. We ended up replacing a total of 5 ICs, all 1128s, and the board seems fine now. See Attachments #1-2 showing which ICs we replaced and a snap of the TF measured using 100 mV of source amplitude to avoid saturation.

Wed Oct 18 15:26:38 2023 Updated the dcc entry reflecting these changes

Installation

Attachment 3 shows the original state, plus the unconnected whitening board installed to the right of the oplev board. Here the oplev board output ribbon cable was sent directly to the AA chassis input 21-24. We then routed the oplev monitors to the whitening board (via 1-->2 pin LEMO cables) and send the whitening board output to the AA chassis input 21-24 [Attachment 4]. We verified the board was drawing current; this concluded the install.

[Yuta, Paco, Murtaza]

[WIP]

Chasing the excess noise in TRX, Yuta suspected the whitening-dewhitening situation for the ETMX.
We compared the OPLEV spectrum for the IFO optics to gauge the situation. The spectrum with dewhitening filters (p = 1Hz, z = 10Hz) (FM3, FM4) 
-Active for all optics (Attachment 1)
-Deactive for ETMX (Atachment 2)

Attachment 1: ETMX >1Hz shows the extra dewhitening filter applied which concludes a misisng analog whitening filter (which it is supposed compensate for)

We compared the X-end with the Y-end rack and found the whitening board for ETMX OPLEVs missing (Pentek Generic Input Board).
We found the board but could not determine the reason for the missing board in previous elogs.

We proceeded to check the board for potential damage. To do this, we we evaluated the transfer functions the filters.

- The board schematic does nott exist on D020432 anymore and is moved to D1500270 (The label on the board says D020432)
- The schematic does not record the modified values for the resistors and capcacitors to place the pole-zero pair at 1, 10Hz
[INSERT NEW VALUES]
- The transfer functions were evaluated using a swept sine measurement from the {input}-> {1st header, 2nd header, tie point} (for example, {J3} -> {J1, J2, T1}) for the first 4 filters (which had existing connections) (Attachemnt 6)
- A good transfer function ( Attachment 3)  is expected with the filter design was obtained on a few ports ✓; others looked garbage (Attachment 4) ❌
- Attachment 5 shows the good/bad outputs

Summary of QPD filter whitening situations:
 - ETMX and ETMY oplevs have whitening (not now for ETMX) of two 10:1 (D020432, which is actually D1500270)
 - TRX and TRY QPDs have whitening of two 40:4 (D1400415, D1400414)
 - ITMX and ITMY oplevs have whitening of two 10:1 (D020432, which is actually D1500270)
 - BS, PRM, SRM oplevs and MC2 TRANS QPD do not have whitening
 - They are always on and compensated with digital anti-whitening filters (not now for ETMX; for now, ETMX digital anti-whitening filters are turned off to have better oplev damping).

There is a new machine on the martian network: 32 cores and 128GB of RAM. Probably this is more useful for intensive number crunching in MATLAB or whatever as opposed to IFO control. I've set up some of the LIGO analysis tools on it as well. 

A successor to Megatron, I dub it: OPTIMUS

 I swap an OSA at PSL and OSA at REFL. It was because the PSL-OSA had a better resolution, so we place this better one at REFL. The ND filter (ND3) which was on the way to REFL OSA was replaced by two BSs, because it was producing dirty multiple spots after transmitting.

Optical spectrum analyzers like the Attachment made by Coherent , Meles Griot- CVI and Spectral Product are all discontinued.

The 40m have Coherent models C240 analyzer with controller C251 Their Finesse measured in 2004: sn205408  F302,  sn205409  F396,

Jenne borrowed Jan's Meles Griot model 13SAE006, Peter King has the same model. FSR 300 MHZ, finnees 200 minimum

[John / Valera / Kiwamu]

 We installed a new weapon, an optical spectrum analyzer in the AS port.

Like we used to do in the old days, two BNC cables were newly laid down and they bring the output of the OSA to the control room to monitor the spectrum with an oscilloscope.

(Some notes)

The photo diode of the OSA was replaced by a Thorlab PDA100A to amplify the signals.

The carrier peak is at about 6.9 V and the f1 and f2 sidebands peaks are at about 40 mV when the beam is in straight shot (everything is misaligned except ITMY and BS).

According to a rough calculation, those numbers correspond to a modulation depth of about 0.16 or so.

The depth agree with what Mirko measured before (#5519)

It wasn't a dream or illusion -- I was locking the DRMI to the right condition last Wednesday (#6489).

Here is a snap shot of the AS-OSA signal taken today when the DRMI was locked with the same control settings (#6489).

The blue curve is data taken when the PRMI was locked for comparison.

You can see that both the upper and lower 55 MHz sideband are amplified by the SRC.

(Some notes)

Currently SRM is slightly misaligned such that the MICH optical gain at AS55Q doesn't increase so much with the presence of SRM.

With this condition I was able to acquire the lock more frequently than how it used to be on the Wednesday.

The next step is to gradually align SRM, to optimize the controls and to repeat this process several times until SRM is fully aligned.

Frank pointed out to me that I had dumbly forgotten to include the voltage reference's noise. The LT1031 has an output noise level of ~125 nV/rHz above 10 Hz or so, and this at least makes the estimate much closer. I had also not included an extra LT1125 stage between the reference and the other stages. I guess I was tired.

The estimate is now within a factor of a few of the measured level, and it has roughly the right shape. Around 1 Hz, it looks like the measured data begin to roll up away from the model, though it's tough to say due to the effect of the AC coupling on the analyzer less than a decade below. If there is indeed extra noise here, Frank thinks it could be due to resistor current noise.

I'll switch one or two out for nicer ones and see if things change.

I worked on the OSEM box a little more today, with the hopes of reducing the measured output current noise. I succeeded, at least modestly. It turns out that most of the noise was indeed caused by the crappy resistors.

Below is the circuit for one of the 5 LEDs. The output of the op-amp structure directly after the LT1031 reference is split between 5 stages identical to the structure on the right. I have shown just one (UR) for clarity. The various measurement points are explained below.

I started from the beginning of the circuit, directly after the LT1031, to make sure that the excess noise seen the other day wasn't just from a noisy reference. Below is the measured output voltage noise along with the LISO estimate. Clearly, the LT1031 is performing to spec (as it should, since it's a new part that I just put in). Note that the apparent better-than-spec performance at low frequencies is just from the AC coupling, which I needed due to the high DC level.

Since the reference was in order, the next step was to switch out some of the crappy old resistors for nicer thin-film ones. In case anyone is interested, Frank has done some detailed investigation of excess 1/f current noise in resistors. I measured the voltage noise level at the point labeled "inter-stage measurement" above, first without any modifications and then after swapping the old 10k resistors (R1 & R2) out for nice Vishay thin-film ones. There is clearly a big improvement, and the modified circuit essentially agrees with LISO now down to 1 Hz. Below this, it looks like there could still be an issue.

I wanted to see what the improvement was in the overall output current noise of the system, so I went about measuring the current noise as I had the other day (by measuring the voltage noise across R55 and dividing by the resistance). The performance was already better than the old measurement, but not at the LISO level. So, I replaced the current-setting resistors (R54 & R55)---which were actually 3 parallel resistors on a single pad in each case---by nice Vishay ones, as well. I didn't have any that were close to the original resistance of ~287 ohms, so I put three 1k ones in parallel. This of course shifts the resistance up to 333 ohms, but that only causes a ~16% change in current. I was sure to convert voltage noise into current noise with this new resistance, though.

With this change, the total output current noise is now very close to the LISO estimate as well down to ~1 Hz.

Some notes:

• First, I apologize for the noise margin at higher frequencies. I redid the higher frequency measurements with an SR560 as a preamp, but I must have screwed up the calibration because the data don't match up quite right with the LF measurements. It was clear while I was taking them that they followed the LISO trace.
• There still seems some excess noise below 1 Hz. It could be that the noisy resistors in the parallel stages were somehow still contaminating the cleaned-up channel. I'll look into this more soon.

On the bounce roll balancing:

Recall that back in 2006, the main issue was not with the bounce mode coupling into the OSEMs but instead with too much cross-coupling between the damping loops themselves:

Old elogs from Osamu (reader / readonly). Osamu will be here in a couple weeks and can try to explain what he was doing back then.

The problem was that without a good input matrix, the low frequency motion of the suspension point was dominated by the damping noise rather than the seismic noise. The bounce mode is a nice indicator of whether the OSEM is oriented up/down but its not the most important thing. More important is that the magnet is in the actual LED beam, not just the apparent center of the OSEM.

Then we should be able to fix things by running the diagonalization script and correcting the input matrix (which depends somewhat on the DC alignment).

Hi 40m people,

As Rana is saying, the bounce mode does not matter, or we cannot do anything. Generally speaking, the bounce mode cannot be damped by the setting of 40m SUS. Some tweak techniques may damp a bounce mode by res-gain or something, but it is not a proper way, I think.

This is also that Rana is already saying that the important thing is to find a good direction of OSEM to hit the LED beam to the magnet. Even if the magnet is not located at the center of OSEM hole, still you can find the optimal orientation of OSEM to hit the LED beam to the center of magnet by rotating the OSEM.

I know only an old document of T040054 that Shihori summarized how to adjust the matrix at the 40m. Too bad input/output matrix may introduce some troubles, but even roughly adjusted matrix should be still fine.

I will be at Caltech on 12-14 of September. If I can help something, I am willing to work with you!

Below is angular spectra of every suspended core optics.
As you can see, there's a peak at 3.3 Hz for BS and PRM angular motion. Compared with other optics, they look large.

I briefly checked suspension filters and found that BounceRoll filters and f2a filters are not turned on for BS.
I checked elog and there was no reason for them to be off, so I turned them on. It didn't change angular spectra very much, though.

I'm going to check BS suspension damping and see where 3.3 Hz peak comes from.

Note that oplev quadrant sums are different for every optics, so we can't simply compare angular motion between optics from OLPIT/OLYAW. But for OSEMs, there are "cnt2um" which calibrate sensor outputs into um. and input matrix should be normalized, so we can compare SUSPIT/SUSYAW with other optics.

I centered all oplevs to do this measurement.
Quadrant sum (C1:SUS-XXX_OLSUM) for each optic now is

ITMX   ITMY   ETMX   ETMY     BS    PRM    SRM
2456  14630   1476  14885   3650   4302   2937   (counts)


  

We have 50 pieces in the clean cabinet.

We've seen for some time now that one of the PRM OSEM signals has been gone, and all of the SRM signals seem dark. We had tried squishing various cables to no avail.

Today I played some "musical satellite boxes," in an attempt to see if the problems are in the chambers or in the signal chains. That is, I swapped the OSEM cables from the vacuum feedthroughs between the satellite boxes, and observed what happened.

It seems clear that something is up with SRM inside the chamber. For PRM, it's not so clear...

Somehow, issues with the LR channel follow both the PRM OSEMs and the PRM satellite box. 

PRM LR first went dark on Jul 2nd, after the IFO was vented, but before we took any doors off (which happened on the 5th). I'm not sure what may have caused this.

SRM OSEMS first went dark on the evening of Jul 18, the day before ELOG 12310, when ITMY was moved in the same chamber. Maybe this ELOG was written about work the day before, but the sensors show disturbances over the course of hours. I think we need to double check the connections in chamber. 

I looked at the PRM free swing spectra. The modes look like they're at the right frequencies, so pointing more and more towards a LED or satellite box issue.

Some of the frequencies have changed between the 2011 in-vac measurement and our 2016 in-air measurement, but that seems within usual parameters.

We peeked into the BS-PRM chamber via the ITMX chamber to see if we could shed any light on this situation. It's hard to get a picture that is in focus, but it looks quite clear that the LR LED (in the lower left when viewed from the HR side) isn't anywhere near as bright as the rest (see Attachment #1). Various hypothesis include failed LED / piece of Al foil blocking the LED / teflon aperture slipped over the LED. But looks like we can't solve this without opening up the BS-PRM chamber. The plan tomorrow is to open up the chamber, pull out the problematic coil. Once we have a better idea of what is going wrong, we can decide what the appropriate course of action is - replace the OSEM or something else. 

As part of the diagnosis, I switched the PRM and SRM satellite boxes earlier today evening around 6pm. They remain in this switched state for now.

Steve, we plan to take the BS-PRM heavy door off tomorrow morning.

[lydia, johannes, gautam]

While struggling to minimize the bounce mode coupling into the sensor signals, we briefly poked into the ITMY chamber, and think that we understand the origin of the problem, at least for the SRM.

Essentially, we believe that moving the ITM from its nominal position to the edge of the table has shifted the table leveling such that the optic (SRM) is tilted backwards (hence the magnets are completely occluding the LEDs) and that perhaps the optic is in contact with one or more of the bottom EQ stops (hence the signal is stationary, no oscillations visible. The timing of the signals going dark as Eric mentioned supports this hypothesis. The reason why we believe this to be the case is that when I was trying to loosen the screw on the clamp holding the ITMY cage to the table, we saw ~1Hz signals from all 5 SRM OSEM sensors, though they were well away from the nominal equilibrium values. The arrangement of towers in the chamber right now did not permit me to get a good look at the SRM magnets, but I believe they are all still attached to the optic, and that they are NOT stuck to the OSEM coils. If this is indeed the case, putting ITMY back in will solve the issue completely.

It is not clear what has happened to the LR coil on the PRM - could it be that during the venting process, somehow the LR magnet got stuck to the OSEM? If so, can we free it by the usual bias jiggling?

 In order to get a better price from Vlier's Tom Chen I changed Ti body back to SS304L-siver plated and music wire spring. The price is still ~$120 ea. at quantity 50

I will talk to Mike G about modifying the  McMaster plunger with a hex nut.

In the previous elog of mine, I looked at the nullstream (aka butterfly mode) to find out if the intrinsic OSEM noise is limiting the displacement noise of the interferometer or possibly the Wiener FF performance.

The conclusion was that its not above ~0.2 Hz. Due to the fortuitous breaking of the ITMX magnet, we also have a chance to check the 'bright noise': what the noise is with no magnet to occlude the LED beam.

As expected, the noise spectra with no magnets is less than the calculated nullstream. The attached plot shows the comparison of the LL OSEM (all the bright spectra look basically alike) with the damped

optic spectra from 1 month week ago.

From 0.1 - 10 Hz, the motion is cleanly larger than the noise. Below ~0.2 Hz, its possible that the common mode rejection of the short cavity lengths are ruined by this. We should try to see if the low frequency

noise in the PRC/SRC is explainable with our current knowledge of seismicity and the 2-dimensional 2-poiint correllation functions of the ground.

So, the question is, "Should we try to upgrade the satellite boxes to improve the OSEM sensing noise?"

I'm picking points off of this no-magnet OSEM plot, and I thought I'd write them down somewhere so I don't have to do it again when I lose my sticky note...

1e-2 Hz        1.05e-2 um/rtHz

1e-1 Hz        3.4e-3 um/rtHz

1 Hz            1.3e-3 um/rtHz

10 Hz          2.5e-4 um/rtHz

60 Hz          7.5e-5 um/rtHz

100 Hz        7e-5 um/rtHz

400 Hz        7e-5 um/rtHz

 I measured the SRM OSEM (no magnets at the moment) noise out of the satellite box with a SRS785 spectrum analyzer. I inserted a break out board into the cable going from the satellite box to the whitening board. The transimpedances of the SRM OSEMs are still 29.2 kOhm. The DC voltages out of the SRM satellite box are about 1.7 V. The signal was AC coupled using SR560 with two poles at 0.03 Hz and a gain of 10.

The noise is consistent with the one measured by the ADC except for the 3 Hz peak which does not show up in the ADC spectrum from Sunday. The peak appears in several channels I looked at. The instrument noise floor was measured by terminating the SR560 with 50 Ohm.

I recommend to change all OSEM transimpedance gains from 29 to 161 kV/A. Beyond this gain one will rail the AA filter module when the magnet is fully out of the OSEM.

The OSEM noise at 1 Hz is about factor of 10 above the shot noise. The damping loops impress this noise on the optics around the pendulum resonance frequency. Also the total contribution to the MC cavity length is sqrt(12) time the single sensor as there are 12 OSEMs contributing to MC length. The ADC noise is currently close but never the less not limiting the OSEM noise below 100 Hz. It can be further reduced by getting an extra factor of 2-3 in whitening gain above ~0.3 Hz. The rms of the ADC input of the modified PRM SD (R64 = 161 kOhm) channel is 10-20 cts during the day with damping loop off and whitening on.

The transimpedance amplifier LT1125CS is also not supposed to be limiting the noise. At 1 Hz the 1/f part of the noise: In<1pA/rtHz and Vn<20nV/rtHz.

The OSEM pictures taken in Sep/6 have been uploaded to Picasa.

https://picasaweb.google.com/foteee

 Kiwamu suggested that since the side resonance is at a lower frequency than the bounce (~17Hz)  we ought to worry about the side more than the bounce.  If this is okay we can reposition the OSEMs to minimise this coupling. 

More over, in the current position, the OSEM s will not sense the side motion!!  So we definitely need to reposition them.  Sorry! I was being a spatz. 

I did some more investigation on the OSEM box today.

Troubleshooting:

After removing some capacitors and still finding that the +15V rail was at over +20V, I decided to see if the TO-3 7815 that I removed behaved properly all by itself. It did. After some more poking around, I discovered that whoever assembled the board isolated the case of the regulator from the board. It is through the case that this package gets its grounding, so I removed the mica insulator, remounted the regulator, and all worked fine.

Since I had gotten a spare from Downs, I also replaced the LT1031 (precision 10-V reference), for fear that it had been damaged by the floating voltage regulator.

Noise measurements:

LED Driver

With the above out of the way, I was finally able to take some measurements. The first thing I did was to look at the LED drivers. I fixed the one stage that I mentioned in my last post by adding two 820-ohm resistors in parallel with the 1k, such that it was very close to all the others (which are 806 || 806 || 1k). With that, using a red LED, I measured a current of 34.5 mA (+/- 0.1) out of each of the 5 stages (UL, UR, LL, LR, S).

I then measured the current noise of each one by monitoring the voltage across the 287-ohm resistor in series with the LED. The driver works by putting the LED in the feedback path of an inverting amp. There is a 10-V input from the LT1031, and the values of the input and feedback resistors determine the current drawn through the LED. There is a buffer (LM6321) in the path to provide the necessary current.

The LISO model I made according to that description seems to make sense. I simply modeled the LED as a small resistor and asked LISO for the current through it. The transfer function shows the proper DC response of -49.15 dB(A/V) -->  34.8 mA @ 10 V, but, the estimated current noise doesn't add up with the measured levels:

I have to get to the bottom of this. Two possibilities are: 1) The buffer adds noise, and/or 2) I am modeling this invalidly.

PD Amp

I also began measuring the PD amplifier noise levels, though I only measured two of them for lack of time. I find it odd that there is a 100-ohm input series resistor on what I thought would be just a transimpedance amplifier. For that reason, I want to look into how the OSEMs are connected to this guy.

In any case, I measured the output noise of two of the PD amps by shorting the input side of the 100-ohm resistors to ground, and then I divided by their TF to get the input noise level. Here it is compared with the LISO estimate. I have plotted them in units of voltage noise at the input side of the resistors for lack of a way to infer the equivalent photocurrent noise level.

Above 2 Hz or so, the measured level agrees with the prediction. Below this, the measured noise level increases as 1/f, while it should go as the standard 1/sqrt(f) (the manufacturer-quoted 1/f corner is at 2 Hz). Another thing to get to the bottom of.

ITMX, ETMY, BS and SRM are oscillating ?

Free swingging OSEM sensors LL at atm

I took one of the spare OSEM satellite amps (schematic) from the cabinet down the Y arm this afternoon to begin testing. I spent most of the day amassing the melange of adapters and connectors I needed to talk to the relic. The most elusive was the über-rare 64-pin IDE connector, for which neither the 40m nor Downs or Bridge had a breakout (despite there being several Phoenix boxes on each electronics rack at the 40m---hmm...). The solution I came up with was to make a breakout cable myself, only there was no 64-pin ribbon. So, I carefully fed a 50-pin and most of a 16-pin ribbon side by side into one push-down connector, and that was that:

I also finally found a 25-pin D-sub breakout just after figuring out the proper pinout for a 25-to-9 adapter, which I thought I was going to have to use. OH WELL.

Science

The first thing I figured I'd do is measure the LED drivers' current noise and see how it compared with LISO. I powered the box up and found that the TO-3 7815 regulator was putting out +20V---bad. I assumed it was broken, so I got another one from Downs and replaced it. Powered it up again and the output was still at +20V (WTF?). My suspicion is that one of the shielding capacitors has failed in some bizarre way, but I didn't have time to check this before I was beckoned to another task. This is where I'll start again next.

Another thing Frank and I noticed as we were figuring out how the driver worked was that the current-specifying resistor of one of the driver stages had not been properly modified along with the others, so it was forcing the feedback loop to rail. This mod was done precariously by adding two perpendicular sandwiched "Radd" resistors on top of the main one, so it's also possible that the ones for this stage had just been knocked off somehow (perhaps by the massive gender-switching ribbon chain hanging down on it). Steve and I noticed that there was a label on the box complaining that some part of the amp for one of the OSEMs wasn't working, but we peeled it off and threw it away because he figured it was outdated.

Anyway, in short, the plan going forward is as follows:

• For this box
  • Measure the LED driver and PD transZ amp noises with dummy components
    
  • Compare with LISO to make sure they make sense
  • Measure the noise again with an OSEM connected
  • Based on the above and more LISO modeling, decide if it's a good idea to replace the LT1125's with OP497's
  • Increase the dynamic range by allowing +/-10V output, rather than +/-2V as was needed for old ADCs
• After
  • Systematically mirror the changes in all other boxes by switching one out at a time

Comments welcome.

I am setting up a testing rig for the OSEMs we recently obtained. I found the schematic for the OSEM assembly from which the pin assignment can be read.

I connected the OSEM's pin plate to a female DB15 on a breakout board. I find the pin assignment (attachment 1, sorry for the image quality) to be:

There are several things that need to be done for each OSEM.

1. Measuring inductance of the coils. I checked that the measurement wires don't add any measurable inductance.

2. Check that the PDs and LEDs are alive (e.g. check forward voltage drop with fluke)

3. Energize the LED and PD.

4. Check PD DC level. For this, I might need the satellite box amplifier.

5. Check LED spot position on the PD.

6. Re-engrave OSEM S/N if needed.

I still need to figure a sensible scheme for points 3-5.

Continuing with the OSEM testing. I measure the resistance of the wires from the RLC meter to the coil to be ~ 0.9ohm. I will subtract this number from the subsequent coil resistance measurements.

I took the old MC1 satellite box for powering the PD and LED in the OSEM assemblies. I connected an idc breakout board to J4 and powered the box with a DC supply according to the box's schematics.

After getting a bit confused about some voltage reading from one of the PD readouts Gautam came and basically redid the whole rig. Instead of using breakout boards, he powered the amplifier circuit directly from the DC supply. Then, to connect the OSEM pinboard directly to the J1 connector he made a DB25 ribbon cable where the two connectors are opposite to one another to mimic the situation with the vacuum feedthru. He also connected a DB25 to BNCs breakout cable, specific to the satellite box, to the J3 port to read the individual PDs through a BNC connector. We managed to confirm the normal operation of one OSEM (Normal PD voltage and LED light spot hitting the PD using a camera with no IR filter).

It was getting a bit late. Going to start checking the OSEMs tomorrow.

I can't obtain a consistent view between the existing drawings/photographs and your pin assignment. Please review the pin assignment again to check if yours is correct.

Looking from the back side and the wires are going down, the left bottom pin is "Coil Start" and the upper right adjacent pin is "Coil End". (See attachment)
So in your picture 1 should be the coil start and 4 should be the coil end, but they are not according to your table.

Yes, my phone camera mirrored the image. Sorry for the confusion.

I see you already uploaded the correct pin assignment.