Attached are plots of dust counts > .3 microns and > .5 microns in particles per cubic foot from approximately 5 PM Jan. 22 to 5 PM Jan. 23. Also attached are plots of the modes to show when they were running/acquiring data. Dust monitor 10 in the H1 PSL enclosure is still indicating a calibration failure.

We checked the grounding of WFS and LSC cables to the table.

Disconnected the cable from the DC interface and checked if the ground pin on the cable was connected to the ground pin of the DC interface, and they were not.

Then we went to the table, disconnected the WFS cable from the feedthrough panel of the table, connected a DB15 cable to the feedthrough and locally supplied +-18V from a power supply.

No oscillation was observed, but none of the channels in WFSA was responding to the light. For WFSB, segment 1 and 2 (pin4-12 and pin3-11)  were good, positive output of the segment 3 (pin2) was dead but the negative output (pin 10) was fine, and the segment4 (pin1-9) was dead.

We removed the heads from the table and opened them to find that:

For WFSA, in 3 segments AD8599 (U1 in D1101614, that's the dual opamp for the differential output stage) was blown up, and the remaining one segment had a fried AD8597 (U2, that's the trans impedance amp before the differential stage).

For WFSB, only one segment had what seems to be a fried AD8597.

Pictures will be posted by Lisa or Giacomo.

We don't know how these things were broken.

Keita K., Giacomo C., Richard M., Filiberto C., Kiwamu I.

The resonant RF PD [1][2] that has been used for the length sensing of the IMC, was found to have two broken amps on the circuit board. This PD is the one which showed a sudden big offset in the DC signal as reported in [3]. We further investigated and fixed it. After fixing we tested the DC path and no big offset was observed, which is good.


Symptom
 The differential output was insane. The positive pin showed -2.2 V and the negative one showed -0.8 V with respect to the ground when no light is on the diode, resulting in an offset of -1.4 V in total. Though this number is not really what we got yesterday [3], the symptom remains the same --- a big offset and somehow magically the PD responds to light.

The repair
 We removed the PD from the IOT2L table and brought it to the EE shop to have a close look. It seemed that
 (1) one of two amplifiers for the differential output (U3 : at the very last stage of the DC path) seemed blown, resulting in such unbalance at the outputs.
 (2) the trans-impedance amplifier (U2) was not closing the feedback loop at all. In the same trans-impedance loop there was a current buffer (U5) and this was also suspicious initially.

 Filiberto replaced U3 and U2 with a new AD8672 and OP27 respectively. After the repair, it started working OK. We have tested the DC path by illuminating the diode with a visible laser pointer. It responded to the light, which tells us not only the DC path is OK but also the diode is still alive. Note that U2 was an AD8675 before the repair and interestingly it looked it had been replaced once as the foot prints were clearly dirtier than everyone else.


[1] D1101124-v6 
[2] SN:1203396
[3] LHO alog #5219
 

Apparatus-
Each HAM6 support tube bellows bagged (hermetically sealed) to encompass the large conflat joint and bellow's convolutions but not the small conflat joint -> 3/8" i.d. x 5' long exhaust tube (penetrating bottom of bag) -> Supply of helium to the top of the bag -> Applied 90 seconds of helium pressurization/flow per bag such that each bag remained inflated (like a balloon) and with confirmed/noticeable flow out of the exhaust tube -> Leak detector backing HAM6 turbo via series combo of (4) each 1.5" x 3' flex hoses

HAM6 volume = ~7,500L  
Net pump speed for helium > 500 L/sec  
Indicated helium baseline at start of testing < 1 x 10-10 torr*L/sec

Results-
SW bellows and big CF joint -> OK 
NW bellows and big CF joint -> OK 
SE bellows and big CF joint -> OK 
NE bellows and big CF joint -> inconclusive -> large signal response -> need to reverse order of testing and pressurize this bag with air while applying low flow of helium the corresponding small conflat to rule it out then test bellows convolutions separate from the big conflat joint

Will continue tomorrow

Kyle, Gerardo

~1055 hrs. local -> Connected and restarted HAM3 turbo backing pump and resumed pumping HAM2-HAM3 volume.  

~1630 hrs. local -> 3.0 x 10-6 torr @ turbo inlet

After SUS made sure everything was clear and not biasing the measurements, IAS gave us direction.  We moved the ITMy HEPI down 1.3mm, & 0.8mm North and tried to do no Yaw.  After this we locked the ISI and looked at the level of the Optical Table.  We saw a runout of 0.019" on the Optical Table.  We did a tilt correction, down on the SE corner and up on the NW of ~0.2mm each.  This put our runout on the Optical Table measurements at 0.12mm.
Then, wouldn't ya know it, IAS says we have to Yaw 577urad CW.  So we turned the HEPI Springs 1/2turn each for CW yaw and that got us under 100urad.  Have to say after doing that I do want to confirm the Optical Table is still level.

On the 15th I started a purge on one of the oldest, and least purged ISIs we have. The LN2 boil-off straight from the dewar was measuring ~ -40 td°C, while ambient air was ~ -5 td°C. This unit was taking longer than usual to dry out and wasn't reaching as low of levels as other containers had in the past. I think revisiting Assy. 1 soon would be helpful.

Installed four vertical actuators and four horizontal actuators with the help of Apollo today.  

There is a fault with the file server for /ligo this morning, the file system that contains user account home directories and applications for control room tools.  The file system will be unavailable for use until further notice.

Jeff B reported that the triple test stand watchdogs were being tripped when turning damping loops ON for the SR3 (HLTS) suspension.

This morning I've remotely logged-on to verify that the medm environment is correctly configured for a HLTS suspension (matrices & signs etc) i.e. the correct model is running and the correct environment has been BURT restored.

I also observed watchdogs tripping when enabling damping loops, specifically for the Pitch DOF.

Initially, I suspected some damping loop gain re-tuning maybe required, however the gain factor is consistent with other L1 & H1 HLTSs (-0.002).

Offsets were injected into each OSEM channel, T1, T2, T3, LF, RT, and SD, whilst monitoring the corresponding OSEM sensor readout in dataviewer. This indicated that there was a sign issues with T2 and T3 OSEMs. Temporarily changing the sign in the COIL OUTPUT FILTERS allowed damping loops to close, without tripping watchdogs. Therefore, I would recommend the assembly team double check T2 and T3 magnet polarity.

The IMC locked at undisturbed since 8:00 pm local time (2013/01/22)

[Kiwamu, Lisa, Keita, Matt, Giacomo]

At about UTC 2013-01-22 21:17:40, the IMC_REFL_DC channel suddenly showed and offset of about -8000 counts. In the past week it has been consistently reading between about 50 (IMC locked) and 450 counts (IMC unlocked). The attached plot IMC_REFL_DC_trend shows the trend in the last 12 days, witht he "jump" visible at the extreme right.

The signal still changes by about 400 counts between the IMC locked and unlocked statuses, and the RF part seems to be fine as the IMC locks regularly.

By inserting a breakout board at the input of the interface, we did verify that the power supply readings (+-18 V) were normal and that the offset came in fact from a bias of about 2.2 V on the REFL_DC readout. It does thus appear to be a problem with the head, or anyhow with something downstream of the interface.

It is curious to note how all the WFS channels show something going on at the exact same moment that the offset appeared (see attached plot IMC_REFL_DC_zoom). It is not clear if the problems seen on the WFS (see entry 5207) are related to this, if working on WFS debuging triggered the problem on the REFL_DC or if the two things are completely unrelated.

Summary: In an attempt to better understand the high magnetic coupling to the test masses, I measured magnetic fields at the locations of the 8 PUM magnets for an isolated reaction mass, the fields around ITMY in situ in BSC1, the moments of the 2 types of magnets, and searched for other possible coupling locations. While I have not been able to account for the high coupling, I did find that large parts of the UIMs and the PUM reaction mass were magnetic. I will try to measure the magnetic moments of these masses when I return.

Gradient scales at the PUM magnets

10 Hz

I used a fluxgate magnetometer and measured fields at the positions of the 8 PUM magnets (2 in each flag) for an isolated PUM reaction mass (Figure 1). In the table below the fields B1 and B2 were at sites 2.7 cm apart, close to the separation of magnets in the PUM flag. The measurements were used to estimate how well the paired magnets in each flag could cancel. The last column gives approximate gradients from the field differences for the two sites. The magnets were not in place for the measurements.

At the UL site, I also looked for higher gradients on a smaller scale (smaller movements) and found B/gradB values of 0.012 m for 6mm displacements right at the location of the flag magnet in the AOSEM. Of course the fluxgate’s ability to measure high gradients that extend only over short distances is limited by the scale of the sensor, which is 1.8 cm long. The magnets are 0.6 cm long so they could be subject to localized gradients that would have been averaged down by the fluxgate. For calculations of the magnetic coupling, I halved the 0.12m scale to 0.06 m because of the possibility of  more localized gradients.

100 Hz

I also made a couple of measurements at 100 Hz. For a 2.7 cm difference at UL, my estimate of B/gradB was 0.012 instead of the 0.021 at 10 Hz.

Measurements of fields and gradients around the quad in-situ inside BSC1

I measured injected magnetic fields around the ITMY quad in BSC1 (Figure 2) in order to make sure that the field at the ITM during my coupling measurements was similar to my estimates made with a magnetometer mounted outside BSC1, under its center. The average of injected field values inside was 37% lower than I estimated from my outside measurement. Thus the coupling  should be 37% higher (worse) than I previously reported.

The scale of gradients across the back face of the reaction mass chain were measured to be:

(B/gradB: 5.26 m, 1.10 m, 0.58 m, 0.53 m). These measurements were used to estimate how well magnets at different actuators could cancel. The arm cavity baffle was not installed for these measurements, and the BSC door was open.

Magnet moments

I measured the moments of one large (M0, L1) and one small (L2) magnets using a magnetometer at a distance large compared to the magnet size (Figure 3). For the small magnet I measured 0.013 J/T and for the large one, 0.717 J/T (or Am^2).

Estimates of residual moment from magnets

I used the fields measured at the positions of the 2 magnets in the PUM flags to estimate the residual moment for the pairs in each flag. I also used the larger scale gradients from the in-chamber measurements to estimate how well the different locations would cancel (e.g. how well will UL cancel LR). I estimated a residual moment of 1/3 of the moment of a single one of the 8 magnets, if all magnets were oriented properly, and a residual moment of about twice the single magnet value if one magnet was mis-oriented. For the estimates below of coupling at the UIM, I used the same gradient scales as I measured for the PUM.

Magnetized 304 steel in the UIM and PUM reaction mass

Figure 4 demonstrates that magnets stick to many parts of the UIMs and PUM reaction masses (L1, R1 and R2). Many of the large parts of the main and reaction UIM, as well as the reaction PUM are called out as 304 or 316 steel (shops choice). The relative permeability of cold worked 304 steel can be several orders of magnitude higher than 316 steel and is reported to reach 10 or 20. So magnets stick to many parts of the UIM and PUM reaction mass, and which parts are magnetic varies with the particular run of parts. About ½ of the volume of the PUM reaction mass in BSC1 is magnetic and at least ½ of the UIM and reaction UIM are as well.

Estimates of coupling from magnets and magnetized 304 steel

I used the measurements of magnet moments and estimates of  the residual moments along with the estimated field gradients and moment arms to estimate torques on the PUM and UIM. To compare to the angular motions I observed in the magnetic coupling measurements, I used Mark Barton’s functions for force or torque at the various quad levels to displacement, pitch and yaw of the test mass.

To estimate motion produced by the magnetized 304 steel, I assumed that the parts were magnetized by the large DC field from the earth (I used 3e-5T), giving them a magnetic moment and causing them to couple to the small AC fields: m = chi/mu0 BearthV. This does not include the magnetization from the permanent magnets, but estimates that I have made do not suggest that this could increase the moment by more than a factor of a couple. I used a relative permeability of 10, at the high end of permeability for 304 steel. I will try to measure the magnetic moment of parts directly when I return. I have also not examined the connectors.

Attached are plots of dust counts > .3 microns and > .5 microns in particles per cubic foot from approximately 5 PM Jan. 21 to 5 PM Jan. 22. Also attached are plots of the modes to show when they were running/acquiring data. Dust monitor 10 in the H1 PSL enclosure is still indicating a calibration failure. I did not plot the counts in the labs, since this IOC was rebooted and put 'nan' in the data. The IOC was timing out communicating with the dust monitors, but the Comtrol was still on. Rebooting the IOC seemed to fix it.

Giacomo, Lisa, Matt

While yesterday's "MC2-M2 as a low frequency offload path for M3" approach worked for signals well below 100mHz, it did little to save M3 from saturation due to signals around the microseism.  It was also not sufficient for ISI testing.

Through more measurements we found that the MC2 M2-M3 cross-over had a small region of stablity between 10 and 20Hz with only the old 100:1 filter engaged.  The maximum phase margin in this region was about 10dg, which really doesn't sound like enough to be reliable, so I started another filter design cycle.  The result is shown in the attached plot: unconditionally stable up to 20Hz, but not really optimized in terms of gain (we could have a lot more if we are willing to invert the plant features).  This was sufficient to keep the M3 drive RMS below 10k counts (at LOCK filter output, so 2.5k at the DAC), which is about a factor of 10 better than before and about a factor of 40 from saturation.

Mark B.

Commencing another round of Matlab TFs on PR3.