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ID Date Author Type Category Subjectup
  842   Fri Aug 15 17:38:41 2008 YoichiUpdateSUSOSEM free swinging spectra before the pump down
I ran an overnight measurement of the free swinging OSEM spectra.
The attm1 shows the results. Everything look ok except for the ITMY UL OSEM.
The time series from that OSEM was very noisy and had many spikes.
We suspected the cable from the satellite box to the computer rack because we disconnected the cable
when we tested a spare cable which was used to connect the spare OSEMs to the PRM suspension in the clean room.
Janne remembered when she put the cable back, she trusted the latch on the connector and did not push it in too hard.
However, Rob suggested the latch does not work well. So she pushed the connector again. Then the signal from
the ITMY UL OSEM got back to normal.
The second attachment shows the ITMY spectra after the cable push.
We decided to pump down after confirming this.

There are still a lot of extra peaks especially in the suspensions in the BS chamber.
These may be inter modulations (by the non-linearities of the OSEMs) of the modes of the multiple
suspensions sitting on the same stack.
  12441   Thu Aug 25 15:43:29 2016 ericqUpdateSUSOSEM issues

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...

  PRM Satellite SRM Satellite BS Satellite
PRM OSEMs LR low + small fluctuations LR low + small fluctuations LR low + small fluctuations
SRM OSEMs No signals No Signals No Signals
BS OSEMs LR low, flat OK OK

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

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. 

  12472   Tue Sep 6 18:21:13 2016 ranaUpdateSUSOSEM issues

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.

  7/2011 9/2016
POS 0.993 0.94
PIT 0.612 0.60
YAW 0.833 0.76
SIDE 0.999 0.993

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

  12475   Tue Sep 6 20:52:42 2016 gautamUpdateSUSOSEM issues

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

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.

  12443   Thu Aug 25 20:07:35 2016 gautamUpdateSUSOSEM issues - maybe resolved?

[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?

  6232   Fri Jan 27 09:05:41 2012 steveUpdateSUSOSEM locking plunger


Our existing 300 series SS plungers from McMastercar #8476A43 are silver plated as Atm2 shows.

Problems:  1, they become magnetized after years being close to the magnets

                     2, they oxidize by time so it is hard to turn them


I looked around to replace them.

Titanium body, nose and beryllium copper spring. None magnetic for UHV enviorment.

Can be made in 7 weeks at an UNREASONABLE $169.00 ea at quantity of 50

 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.

  5312   Sat Aug 27 15:47:59 2011 ranaUpdateCDSOSEM noise / nullstream and what does it mean for satellites

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?"

  6048   Wed Nov 30 01:35:49 2011 JenneUpdateCDSOSEM noise / nullstream and what does it mean for satellites

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

  3933   Tue Nov 16 15:32:18 2010 valeraUpdateElectronicsOSEM noise at the output of the satellite box

 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.

  5370   Fri Sep 9 14:55:03 2011 kiwamuUpdateSUSOSEM pictures on ITMs

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


  5132   Sun Aug 7 11:10:54 2011 SureshSummaryGeneralOSEM positioning


This OSEM placement is just the OPPOSITE of what the proper placement is.

Usually, we want to put them in so that the LED beam is vertical. This makes the OSEM immune to the optic's vertical mode.

The orientation with the horizontal LED beam makes the immunity to the side mode better, but may spoil the vertical.

In reality, neither of these assumptions is quite right. The LED beam doesn't come out straight. That's why Osamu and I found that we have to put in some custom orientations.

Also, the magnet gluings relative to the OSEM bracket centers are not perfectly aligned. So...I am saying that the OSEMs have to be oriented empirically to reduce the couplings which we want to reduce.


 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. 

  6258   Tue Feb 7 03:05:08 2012 ZachUpdateSUSOSEM sat amp measurements

I did some more investigation on the OSEM box today.


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.

  11198   Fri Apr 3 10:46:32 2015 SteveUpdateSUSOSEM sensor oscillation

ITMX, ETMY, BS and SRM are oscillating ?

  5269   Fri Aug 19 10:26:53 2011 steveUpdateSUSOSEM sensor spectra

Free swingging OSEM sensors LL at atm

  6255   Fri Feb 3 23:19:22 2012 ZachUpdateSUSOSEM testing begins

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.


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.

  15816   Thu Feb 18 15:15:12 2021 yehonathanUpdateSUSOSEM testing for SOSs

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:

1 PD Cathode
2 LED Anode
3 Coil end
4 PD Anode
5 LED Cathode
6 Coil Start

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.

OSEM # Coil Inductance (mH) Coil resistance (ohm) PD forward voltage (V) LED forward voltage (V)
280 2.87 14.1 0.63 1.1

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



  15832   Mon Feb 22 14:06:49 2021 YehonathanUpdateSUSOSEM testing for SOSs

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.



  15835   Tue Feb 23 20:55:19 2021 KojiUpdateSUSOSEM testing for SOSs

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.

  15837   Wed Feb 24 10:09:16 2021 yehonathanUpdateSUSOSEM testing for SOSs

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

I see you already uploaded the correct pin assignment.


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.


  15838   Wed Feb 24 10:23:03 2021 YehonathanUpdateSUSOSEM testing for SOSs

Continuing with the new rig, I measure the resistance of the cable leading to the coil to be 0.08+(0.52-0.08)+(0.48-0.08)=0.9ohm.


Coil Resistance


Coil Inductance


PD Voltage


LED spot image

(Attachment #)

LED perfectly centered Ready for C&B and install Short/Long Notes
078 13.0 2.8 1.86 1 N Y L Reengraved
280 13.3 2.8 1.92 2


Y L  
117 13.1 2.8 2.12 3 Y Y L Reengraved
140 inf       N N L  
146 12.8 2.8 1.83   Y Y L Reengraved
093 13.1 2.8 2.19   N Y L Reengraved
296 13.1 2.8 2.19   N Y L  
256 13.1 2.8 2.0   N Y L  
060 12.9 2.8 2.0   Y Y L Reengraved
098 13 2.8 1.95   N Y L Reengraved
269 13.2 2.8 1.92   Y Y L  
260 13.2 2.8 2.03   Y Y L  
243 13.1 2.8 1.94   N Y L  
080 12.9 2.8 2.38   Y Y L Reengraved
292 13.3 2.8 2.06   N Y L  
113 13 2.8 2.08   Y Y L Reengraved
251 13.1 2.8 2.04   Y Y L  
231 13.3 2.8 1.89   Y Y L filter not covering the entire PD area
230 13.3 2.8 1.92   Y Y L  
218 13.3 2.8 2.13   Y Y L  
091 13.2 2.8 1.98   Y N L No pigtail. Reengraved
118 13.3 2.8 2.15   Y N L No pigtail. Reengraved
302 13.2 2.8 2.06   Y Y L  
159 13 2.8 2.15   Y N S No pigtail. One cap screw too long. Reengraved.
016 13 2.8 2.54   Y N S No pigtail. Reengraved.


2.8 2.04   N N L No pigtail. Reengraved.
084 13 2.8 1.94   N N L No pigtail. Reengraved.
171 13.1 2.8 2.20   Y N L No pigtail. Reengraved.
052 12.9 2.8 1.75   Y Y S Reengraved.
106 13.1 2.8 1.62   Y Y S Reengraved.
096 13 2.8 2.05   Y Y S Reengraved. The OSEM fell on the floor. I rechecked it. Everything seems fine except the PD voltage has changed. It was previously 1.76
024 13 2.8 1.81   Y Y S Reengraved.
134 12.9 2.8 1.82   N Y S Reengraved.
081 12.9 2.7 1.85   Y Y S Reengraved.
076 12.9 2.8 1.91   N Y S Reengraved.
108 12.9 2.8 1.83   Y Y S Reengraved.
020 12.9 2.8 1.98   N Y S Reengraved.
031 12.9 2.8 1.74   Y Y S Reengraved.
133 13.1 2.8 1.65   Y Y S Reengraved.
007 13 2.8 1.74   Y Y S Reengraved.
088 12.8 2.8 1.77   N Y S Reengraved.
015 12.9 2.7 1.81   Y Y S  
115 13 2.8 1.89   Y Y S Reengraved.
009 12.9 2.8 1.78   Y Y S Reengraved.
099 13.1 2.8 2.00   Y Y S Reengraved.
103 12.9 2.8 1.82   N Y S Reengraved.
143 13.1 2.8 1.80   Y Y S Reengraved.
114 12.8 2.8 2.04   Y Y S  
155 13.1 2.8 1.90   N Y S Reengraved.
121 12.9 2.8 1.86   Y Y S Reengraved.
130 13 2.7 1.78   N Y S Reengraved.
022 13 2.8 1.92   N Y S Reengraved.
150 12.8 2.8 1.90   N Y S Reengraved.
144 12.7 2.7 1.86   N Y S  
040 12.9 2.8 1.70   N Y S Reengraved. way off-center
125 12.8 2.8 1.75   N Y S Reengraved.
097 12.9 2.8 1.81   N Y S Reengraved.
089 12.9 2.8 1.51   Y Y S Reengraved.
095 13 2.8 1.96   Y Y L Reengraved.
054 13.1 2.8 1.86   Y N L Have a long screw going through it. Reengraved.
127 13.1 2.9 1.82   N N L Have a long screw going through it. Reengraved.
135 12.7 2.8 1.75   N N L Have a long screw going through it. Reengraved.
046 13.1 2.8 2.08   Y N L Have a long screw going through it. Reengraved.
000 13.1 3.1 6.6 The LED light looks totally scattered. No clear spot N N S Made out of Teflon? Looks super old. Didn't engrave

Total: 63 OSEMS. Centered working OSEMS: 42. Will upload a more detailed summary to the wiki soon.

Note: The Olympus camera is eating the AA camera very quickly (need to replace every 1.5 days). I'm guessing this is because of the corrosion in the battery housing.


  15856   Wed Mar 3 11:51:07 2021 YehonathanUpdateSUSOSEM testing for SOSs

I finished testing the OSEMs. I put all the OSEMs back in the box. The OSEMS were divided into several bags. I put the OSEM box next to the south flow bench on the floor.

I have uploaded the OSEM catalog to the wiki. I will upload the LED spot images later.

In summary:

Total 64 OSEMS, 31 long, 33 short.

Perfectly centered LED spots, ready for C&B OSEMS: 30, 12 long, 18 short.

Perfectly centered LED spots, need some work (missing pigtails, weird screws) OSEMS: 7, 5 long, 2 short.

Slightly off-centered (subjective) LED spots, ready for C&B OSEMS: 20, 7 long, 13 short.

Slightly off-centered (subjective) LED spots, need some work (missing pigtails, weird screws) OSEMS: 4 long

Defective OSEMS or LED spot way off-center: 3.

  15886   Tue Mar 9 14:30:22 2021 YehonathanUpdateSUSOSEM testing for SOSs

I finished ranking the OSEMS on the OSEM wiki page.

I also moved the OSEM data folder from /home/export/home to /users/public_html and created a soft link instead. I have done the same for the 40m_TIS folder that I uploaded there a while ago.

  15888   Tue Mar 9 15:19:03 2021 KojiUpdateSUSOSEM testing for SOSs

How were the statistics of them? i.e. # of Good OSEMs, # of OK OSEMs, etc...

  15891   Tue Mar 9 18:49:28 2021 YehonathanUpdateSUSOSEM testing for SOSs

29 Good OSEMs, of which 1 is questionable (089) with PD voltage of 1.5V, 5 need some work (pigtailing, replace/remove/add screws). We have 4 pigtails. Schematics.

20 OK OSEMs (Slightly off-centered LED spot), of which 3 need some work (pigtailing, replace/remove/add screws).

13 Bad OSEMS (Way off-centered LED spot)

2 Defunct OSEMs


Ed: KA
Good: 23 complete OSEMs +  5 good ones, which need soldering work (there are 4 pigtails and take one from a defunct OSEM).
OK:  Use good 7 OSEMs for the sides. And keep some functional OSEMs as spares.


  760   Tue Jul 29 21:04:55 2008 SharonUpdate OSEM's Power Spectrum
From 16:30 this afternoon
  11760   Fri Nov 13 15:20:24 2015 SteveUpdateSUSOSEMs

Are they oscillating or not ?


The ITMX OSEMS are oscillating.

ETMX, ETMY and MC2 POS _biases are off. Why ?

The Epics MEDMs screens are going blank in  ~3-5 minutes reluctantly.

  16119   Tue May 4 19:14:43 2021 YehonathanUpdateGeneralOSEMs from KAGRA

I put the box containing the untested OSEMs from KAGRA near the south flow bench on the floor.

  16944   Fri Jun 24 13:29:37 2022 YehonathanUpdateGeneralOSEMs from KAGRA

The box was given to Juan Gamez (SURF)


I put the box containing the untested OSEMs from KAGRA near the south flow bench on the floor.


  3294   Mon Jul 26 20:12:18 2010 kiwamuUpdateSUSOSEMs on PRM

 [Alberto and Kiwamu]

We installed the OSEMs to the new PRM.

As I wrote down on the elog (see here)  today's mission was to install the OSEMs to the PRM.

After putting them on the tower we adjusted the readout offsets by sliding the OSEMs so that they can stay in the linear sensing ranges. 

Now all of the OSEMs have almost good separation distances from the PRM.

In the attached picture you can see the OSEMs installed on the PRM tower ( middle: PRM tower, left: BS tower)

(what we did)

 1. moved the PRM tower close to the door so that we could easily access the PRM.

 2. leveled the table by putting some weights and confirmed the level by a  bubble level tool.

     - We must level the table every time when we set / adjust any OSEMs,  otherwise the readout voltages of  the OSEMs vary every time due to the tilted table.

 3. released the PRM by loosing the earthquake stops

 4. put the OSEMs with approximately right separation distances from the PRM.

      -  At this phase we can see the readout of the OSEMs, which were oscillating freely because we still didn't enable the damping.

        -  The OSEM positions were checked by looking at useful notes on the wiki (see here).

 5. turned on the damping servo of the OSEMs

       - Without changing any gains, it worked well. 

      - Then we could see stable readouts of the OSEMs which didn't show any oscillations in turn because of the damping.

 6. checked the level of the table again

 7. set each of the OSEM readouts to the half of its maximum value by sliding their positions slightly.

      - The readout offsets were at almost the half value within +/- 100 mV accuracy (this was the best accuracy we could adjust by our hands)

 8. screwed down the earthquake stops to lock the PRM.

      - Now the damping is off.

 9. closed the door


(to be done)

 *  Putting the PRM tower back to the designed place

 *  Installation of the pick off mirror

 *  Arrangement of the PZT mirror

  3688   Mon Oct 11 10:51:36 2010 steveUpdateSUSOSEMs, OSEMs, OSEMs...those lovely little OSEMs
  10480   Tue Sep 9 23:05:01 2014 KojiUpdateCDSOTTAVIA lost network connection

Today the network connection of OTTAVIA was sporadic.

Then in the evening OTTAVIA lost completely it. I tried jiggle the cables to recover it, but in vain.

We wonder if the network card (on-board one) has an issue.

  10483   Wed Sep 10 02:35:55 2014 ranaUpdateCDSOTTAVIA lost network connection


Today the network connection of OTTAVIA was sporadic.

Then in the evening OTTAVIA lost completely it. I tried jiggle the cables to recover it, but in vain.

We wonder if the network card (on-board one) has an issue.

 I would also suspect IP conflicts; I had temporarily put the iMac on the Ottavia IP wire a few weeks ago. Hopefully its not back on there.

  10484   Wed Sep 10 02:52:05 2014 ericqUpdateCDSOTTAVIA lost network connection

I checked chiara's tables, all seemed fine. I switched ethernet cables from the black one labelled "allegra," which seemed maybe fragile, for the teal one that may have been chiara's old ethernet cable. It's back on the network now; hopefully it lasts. 

  10109   Fri Jun 27 20:52:30 2014 KojiUpdateCDSOTTAVIA was not on network

I came in the lab. Found bunch of white EPICS boxes on ottavia.
It turned out that only ottavia was kicked out from the network.

After some struggle, I figured out that ottavia needs the ethernet cable unplugged / plugged
to connect (or reconnect) to the network.

For some unknown reason, ottavia was isolated from the martian network and couldn't come back.
This caused the MC autolocker frozen.

I logged in to megatron from ottavia, and ran at .../scritpt/MC

nohup ./AutoLockMC.csh &

Now the MC is happy.

  17027   Fri Jul 22 17:43:19 2022 KojiUpdateGeneralObtained a functional CRT

[Koji Paco]

Koji went to Downs and found a CRT labeled "for 40m Rana?". So I decided to salvage it to the 40m after getting approval from Rich/Todd.

Paco and I tried this unit with the control room CCD signal and it just worked fine. So we can use this as a spare for any purpose in the lab.

  4298   Tue Feb 15 11:43:53 2011 JenneUpdateComputersOccasional error with NDS2

Just in case anyone has encountered this / knows how to fix it....

I'm running NDS2 on Rossa, trying to get a bunch of raw data from S5.  I get 10min of data at a time, and it goes through ~200 iterations successfully, and then throws the following error:

Getting new data
Connecting.... authenticate ... done
daq_recv_id: Wrong length read (0)
Error reading writerID in daq_recv_block
Warning: daq_request_data failed
??? Error using ==> NDS2_GetData
Fatal Error getting channel data.

Error in ==> getDARMdataTS at 37
oot = NDS2_GetData({...

Error in ==> SaveRawData_H1_DARM at 40
    oot = getDARMdataTS(t0s(ii), strideDuration, srate);

  12132   Wed May 25 02:54:09 2016 ericqUpdateGeneralOdds and ends

WFS locking point seemed degraded; I hand aligned and reset the WFS offsets as usual.

ITMX oplev recentered. While doing so, I noticed an ETMX excursion rear its head for the first time in a long while :crying

There was no active length control on ETMX, only OSEM damping + oplevs. Afterwards, its still moving around with only local damping on. I'm leaving the oplevs off for now.

  743   Sun Jul 27 20:25:49 2008 ranaConfigurationEnvironmentOffice Temperature increased to 75 F
Since we have the chiller for the PSL chiller now, I've just increased the office area
temperature set point by 2 F
to 75 F to see if the laser will still behave.
  3571   Tue Sep 14 00:21:51 2010 ranaOmnistructureEnvironmentOffice area temperature change

I changed the setpoint for the HVAC control (next to Steve) from 73F to 72F. This is to handle the temperature increase in the control room with the AC unit there turned off.

We know that the control setpoint is not linear, but I hope that it settles down after several hours. Lets wait until Tuesday evening before making another change.

  6078   Wed Dec 7 00:11:58 2011 DenUpdateAdaptive FilteringOfflineAF

 I did offline adaptive filtering with yesterday's 3 hours of MC-F and GUR1X data. It turns out that normalized-lms can strongly outperform static Wiener filtering!


This is interesting. It might be something inside MC_F that Wiener static does not see. I think the problem is either with seismometer noise or tilt.

  11846   Fri Dec 4 10:18:33 2015 yutaroUpdateASSOffset in the dither loop of XARM vs beam spot shift on ETMX

As I did for YARM (elog 11779), I measured the relation between offsets added just after the demodulation of the dithering loop of XARM and beam spot shift on ETMX. Defferent from YARM, the beam spot on ITMX DOES change because only BS is used as a steering mirror (TT1&2 are used for the dithering of YARM). Instead, the beam spot on BS DOES NOT change.

This time, I measured by oplevs the angles of both ETMX and ITMX for each value of offset, and using these angles I calculated the shift of the beam spot on ETMX so that I got two independent estimations (one from ETMX oplev, and the other from ITMX oplev) as shown below. The calibration of the oplevs reported in elog 11831 is taken into account. 

The difference of two estimations comes from the error of calibration of oplevs and/or imperfect alignment, I think. 

  5747   Thu Oct 27 18:00:38 2011 kiwamuSummaryLSCOffsets in LSC signals due to the RFAMs : Optickle simulation

The amount of offsets in the LSC signals due to the RFAMs have been estimated by an Optickle simulation.

The next step is to think about what kind of effects we get from the RFAMs and estimate how much they will degrade the performance.


  We have been having relatively big RFAM sidebands (#5616), which generally introduce unwanted offsets in any of the LSC demodulated signals.
The motivation was that we wanted to estimate how much offsets we've been having due to the RFAMs.
The extreme goal is to answer the question : 'How big RFAMs do we allow for operation of the interferometer?'.
Depending on the answer we may need to actively control the RFAMs as already planed (#5686).
Since the response of the interferometer is too complicated for analytic works, so a numerical simulation is used.

(Results : Offsets in LSC error signals)





  Figure: Offsets in unit of meter in all the LSC demodulated signals.  Y-axis is the amount of the offsets and the X-axis represents each signal port.
In each signal port, the signals are classified by color.
(1) Offsets in the PRCL signal. (2) Offsets in the MICH signal. (3) Offsets in the SRCL signal.
Roughly the signals showed offsets at a 0.1 nm level.
The numerical error was found to be about 10-10 nm by running the same simulation without the AM sidebands.
Here is a summary of the amount of the offsets:
    offsets [nm] (1f signal port)  offsets [nm] (3f signal port)  biggest offsets [nm] (signal port)
PRCL       0.3 (REFL11)       0.2 (REFL33)     1 (REFL55)
MICH      0.00009 (AS55)       0.8 (REFL33)     7 (POP11)
SRCL      0.1 (REFL55)       0.1 (REFL165)     40 (POX11)
In the SRCL simulation  REFL11I, REFL11Q, POP11I, POP11Q and POX11I didn't show any zero crossing points within 100 nm range around the resonance.
It is because that the SRCL doesn't do anything for the 11MHz sidebands. So it is the right behavior.
However POX11 was somewhat sensitive to the SRCL motion and showed a funny signal with a big offset.

(Simulation setup)

I applied the current PM/AM ratio according to the measurement (#5616, #5519)
The modulation indices used in the simulation are :
    + PM index in 11MHz = 0.17
    + PM index in 55MHz = 0.14
    + AM index in 11MHz = 0.17 / 200 = 8.5x10-4
    + AM index in 55MHz = 0.14 / 200 = 7.0x10-4
Note that the phases of the AM and PM sidebands are the same.

For clarity, I also note the definition of PM/AM ratio as well as how the first order upper sideband looks like.



The optical parameters are all at ideal length although we may want to check the results with more realistic parameters:
    + No arm cavities
    + PRCL length = 6.75380
    + SRCL length = 5.39915
    + Schnupp asymmetry = 3.42 cm
    + loss in each optic = 50 ppm
    + PRCL = resonant for 11 and 55MHz
    + MICH = dark fringe
    + SRCL = resonant for 55 MHz
The matlab script will be uploaded to the cvs server.

Quote from #5686
  8. In parallel to those actions, figure out how much offsets each LSC error signal will have due to the current amount of the RFAMs.
    => Optickle simulations.

  10815   Thu Dec 18 15:41:30 2014 ericqUpdateComputer Scripts / ProgramsOffsite backups of /cvs/cds going again

Since the Nodus switch, the offsite backup scripts (scripts/backup/rsync.backup) had not been running successfully. I tracked it down to the weird NFS file ownership issues we've been seeing since making Chiara the fileserver. Since the backup script uses rsync's "archive" mode, which preserves ownership, permissions, modification dates, etc, not seeing the proper ownership made everything wacky. 

Despite 99% of the searches you do about this problem saying you just need to match your user's uid and gid on the NFS client and server, it turns out NFSv4 doesn't use this mechanism at all, opting instead for some ID mapping service (idmapd), which I have no inclination of figuring out at this time. 

Thus, I've configured /etc/fstab on Nodus (and the control room machines) to use NFSv3 when mounting /cvs/cds. Now, all the file ownerships show up correctly, and the offsite backup of /cvs/cds is churning along happily. 

  10519   Thu Sep 18 17:44:55 2014 JenneUpdateLSCOld AO cable pulled

[Q, Jenne]

We pulled the old 2-pin lemo cable after I had a look at the connectors.  When I unscrewed the connector on the MC side, one of the wires came off.  I suspect that it was still hanging on a bit, but my torquing it finally killed it. 

We pulled the cable with the idea of resoldering the connectors, but there are at least 2 places where the cable has been squished enough that the shielding or the inner wires are exposed.  These places aren't near enough the ends to just cut the cable short.

Downs doesn't have a spool of shielded twisted single-pair cable, so Todd is going to get me the part number for the cable they use, and I've asked Steve to order it tomorrow. 

For now, we will continue using the BNC cable that we installed last night - I don't think it's worth resoldering and putting in a crappy 2-pin lemo cable that we'll just throw out in a week.

  7851   Tue Dec 18 15:51:33 2012 JenneUpdateIOOOld G&H TT mirrors' phase maps measured

I took the 2 G&H mirrors that we de-installed from PR3 and SR3 over to GariLynn to measure their phase maps. Data is in the same place as before, http://www.ligo.caltech.edu/~coreopt/40MCOC/Oct24-2012/ .  Optic "A" is SN 0864, and optic "B" is SN 0884, however I'm not sure which one came from which tip tilt.  It's hard to tell from what photos we have on picasa.

Both are astigmatic, although not lined up with the axes defined by where the arrow marks the HR side.  Both have RoCs of -600 or -700m. RMS of ~10nm.

  3826   Fri Oct 29 16:39:01 2010 JenneUpdateTreasureOld Green suspension towers disassembled

[Jenne, Joonho]

At Koji's request, we disassembled 2 of the old Green suspension towers that have been sitting along the X-arm forever (read that last word in a 'Sandlot' voice.  Then you'll know how long the suspensions have been sitting there).

They are now hanging out in plastic trays, covered with foil.  They will now be much easier to store.

We should remember that we have these, particularly because the tables at the top are really nice, and have lots of degrees of freedom of fine adjustment.



Atm1, there is one more of these old suspension towers

Atm2, disassembled

  1455   Mon Apr 6 19:09:15 2009 JenneUpdatePEMOld Guralp is hooked back up to the ADC

Old Guralp is hooked back up, the new one is sitting next to it, disconnected for now.

  3736   Mon Oct 18 17:16:30 2010 JenneUpdateSUSOld PRM, SRM stored, new PRM drag wiped

[Jenne, Suresh]

We've put the old PRM and SRM (which were living in a foil house on the cleanroom optical table) into Steve's nifty storage containers.  Also, we removed the SRM which was suspended, and stored it in a nifty container.  All 3 of these optics are currently sitting on one of the cleanroom optical tables.  This is fine for temporary storage, but we will need to find another place for them to live permanently.  The etched names of the 3 optics are facing out, so that you can read them without picking them up.  I forgot to note the serial numbers of the optics we've got stored, but the old optics are labeled XRM ###, whereas the new optics are labeled XRMU ###. 

Koji chose for us PRMU 002, out of the set which we recently received from ATF, to be the new PRM.  Suresh and I drag wiped both sides with Acetone and Iso, and it is currently sitting on one of the rings, in the foil house on the cleanroom optical table.

We are now ready to begin the guiderod gluing process (later tonight or tomorrow).

  3737   Mon Oct 18 18:00:36 2010 KojiUpdateSUSOld PRM, SRM stored, new PRM drag wiped

- Steve is working on the storage shelf for those optics.

- PRMU002 was chosen as it has the best RoC among the three.


[Jenne, Suresh]

We've put the old PRM and SRM (which were living in a foil house on the cleanroom optical table) into Steve's nifty storage containers.  Also, we removed the SRM which was suspended, and stored it in a nifty container.  All 3 of these optics are currently sitting on one of the cleanroom optical tables.  This is fine for temporary storage, but we will need to find another place for them to live permanently.  The etched names of the 3 optics are facing out, so that you can read them without picking them up.  I forgot to note the serial numbers of the optics we've got stored, but the old optics are labeled XRM ###, whereas the new optics are labeled XRMU ###. 

Koji chose for us PRMU 002, out of the set which we recently received from ATF, to be the new PRM.  Suresh and I drag wiped both sides with Acetone and Iso, and it is currently sitting on one of the rings, in the foil house on the cleanroom optical table.

We are now ready to begin the guiderod gluing process (later tonight or tomorrow).


  11419   Thu Jul 16 03:01:57 2015 ericqUpdateLSCOld beatbox hooked back up

I was having issues trying to get reasonable noise performance out of the aLIGO demod board as an ALS DFD. Terminating the inputs to the LSC whitening inputs did not show much 60Hz noise, and an RMS in the single Hz range. 

A 60Hz line of hundreds of uV was visible in the power spectrum of the single ended BNC and double-ended DB25 outputs of the board no matter how I drove or terminated.

So, I tried out hooking up the ALS beatbox. It turns out to work better for the time being; not only is the 60Hz line in the analog outputs about ten times smaller, the broadband noise floor in the resultant beat spectrum when driven by a 55MHz LO on the LSC rack is a fair bit lower too. I wonder if this is due to not driving the aLIGO board LO at the +10dBm it expects. With the amplifiers and beat note amplitudes we have, we'd only be able to supply around 0 dBm anyways. 

Here's a comparison of the aLIGO board (black) and ALS beatbox (dark green) driven with the 55MHz LO, both going through the LSC whitening filters for a resultant magnitude of 3kCounts in the I-Q plane. The RMS sensing noise is about 30 times lower for the beatbox. (Note, this is with the old delay cables. When we switch to the 50m cables, we'll win further frequency noise sensitivity through the better degrees->Hz calibration.) I'm very interested to see what the green beat spectrum looks like with this setup. 

Not only is the 60Hz line smaller, there is simply less junk in the beatbox signal. I did not expect this to be the case. 

There were some indications of funky status of the aLIGO board: channels 3 and 4 are totally nonfunctioning, so who knows what's going on in there. I've pulled it out, to take a gander if I can figure out how to make it suitiable for our purposes. 

ELOG V3.1.3-