Jeff K and I saw that Phase 3b (in-vacuum) TFs had not yet been taken for the OMC and OMs suspensions, therefore, I've taken a complete set this morning, prior to next weeks planned vent of HAM6, for reference and acceptance purposes.

I've taken undamped DTT TFs, with the HAM-ISI isolated and damped via Guardian.

All suspension alignment offsets remained ON throughout the measurement. However, it soon became evident that OM1 was struggling in all DOFs, see snapshots of OM1 TFs below, the red trace is a good reference, the black trace raises some concerns. I turned OFF the alignment offsets for OM1, but the issue persisted. I then noticed that the ISC signal path is biassing OM1 and saturating the DAC output. Turning OFF the ISC path restored OM1s performance.

A 7 day trend for OM1 is attached below, apart from some transient glitches, the alignment offsets have remained steady. However, the ISC bias has transitioned between +/-4000 counts. The ISC_LOCK Guardian state is also included, noting that an index >500 indicates the IFO is locked with DC readout.

There was also a minor issue obtaining V-V DOF TFs on the OMC suspension, which resulted in the incorrect scaling when compared to the model (all other DOFs were fine). After investigating the signal chain, I discovered a gain of -500 in the TEST_FILTERS bank. I returned this to the nominal gain of +1, which rectified the problem.   

The OMC and OMs TF measurements have been compared with previous Phase 3a (in-air) measurements, as well with identical suspensions at LLO and are available below.

Summary:

Transfer functions for both OMC and OM suspensions are consistent with previous measurements, and similar suspensions at LLO (with no biases applied to OM1). However, the HAM6 vent (and swap on the OM1 optic) may provide an ideal opportunity to offload some OM1 alignment, if it's deemed necessary.

All data, scripts and plots have been committed to the sus svn as of this entry.

Last night, we again became unable to damp the roll modes (see previous experience in alog 17378) with the usual damping settings. After some random experiments, we became able to damp it with the usal damping settings for some reason. We have no idea why the mode occasionally behave in this way. Note that we use AS_WFS_A for damping them.

(The roll modes)

After the recycling gain study (alog 17645) and ASC study (alog 17646), we fully locked the interferometer with DC readout and 10 W. We immediately noticed that the DARM spectrum was extremely noisy which turned to be high roll modes saturating the OMC DC PDs at the ADC. Looking at the frequency of the peak in the DARM spectrum, we could idenfity the mode -- it was at 13.8 Hz which is the one from ITMX. The peak height was as high as 10^-12 m/sqrtHz in the DARM spectrum with 0.1 Hz BW. We went back to ASQ in order to address the issue. The PSL power remained at 10 W. Evan tried different phases (e.g. +-60 deg) and even the negative sign in the damping gain, but none of them seemed to work. This is exactly the same situation as the one previously reported (alog 17378).

(Damping experiments)

- ITMX

Since I knew that it was mostly from ITMX, I first disabled the damping on ETMY in order to make the experiment straightforward. Then I narrowed the pass band on ITMX, which is nominally 1 Hz wide with a center frequency of 13.9 Hz, to 100 mHz passband with a center frequency of 13.8 Hz. They are 4th order butterworth filters. According to foton, this change causes an extra phase rotation of 30 deg, which I did not try to correct as this seemed small enough. Engaging the narrower butterworth, I was able to damp the mode with the same positive gain. This brought the peak height in the DARM spectrum to as low as 10^-14 m/sqrtHz.

- ETMY

I then moved onto ETMY to propagate the same modification. ETMY also had a 1 Hz bandpass 4th order butterworth with a center frequency of 13.9 Hz. I tried a 100 mHz passband with a center frequency of 14 Hz. This again caused a 30 deg phase shift, but I neglected it. After engaging the narrower bandpass on both ITMX and ETMY, however the modes slowly started growing up. I tried different phases and negative damping gain on ETMY, but none of them helped. I also tried several configurations -- e.g. disabling ETMY and keeping ITMX, disabling ITMX and running ETMY, and etc. But I did not succeed in damping the modes. Moreover they kept growing on a time scale of a couple minutes.

- Ending up with the same old configuraion

After all, I switched the bandpss filters back to the 1 Hz passband ones to see if I can damp them. Yes, I was able to damp them. The decay time was approximately on a time scale of a couple minutes. No extra phases or sign flips were needed. Unsatisfactory (✖╭╮✖)

In order to try and keep the diffracted power at a nominal 8%, I tried a simple ezcaservo to do this.
Running the following on opsws2
ezcaservo -r "H1:PSL-ISS_DIFFRACTION_AVG" -s 8.0 -g -0.001 -f 0.05 -t 240 "H1:PSL=ISS_REFSIGNAL"
This timed out after 4 minutes.

Increasing the gain to -0.01 seems okay.  -0.1 is too high. -0.05 is too high.  -0.02 seems okay.

The attached plot shows two manually introduced excursions from the reference signal set point and
the recovery done by ezcaservo, which seems to work okay.  The final command issued was
ezcaservo -r "H1:PSL-ISS_DIFFRACTION_AVG" -s 8.0 -g -0.02 -f 0.05 -t 240 "H1:PSL-ISS_REFSIGNAL"

The command timed out and is no longer running.  It would be worth taking out for a longer test
drive at a later time.

Summary: H1:SUS-ETMX_M0_DAMP_L_IN1_DQ looks to have been saturating during the long lock and making glitches in DARM at 9Hz. 

In Detchar we're looking at the 2015-04-02 lock from ~8-13 UTC, which had good sensitivity and some amount of undisturbed time. The hveto page for that day has several interesting glitch classes. The first round winner is a series of glitches centered at around 9Hz and associated with the SUS ETM* L1/M1 L channels. These glitches seem to only show up in this high sensitivity lock and not the low sensitivity locks around it (perhaps higher RMS on M0 in low-noise configuration?). Checking the raw data, it appears that H1:SUS-ETMX_M0_DAMP_L_IN1_DQ is saturating.

• Figure 1 shows a time-frequency map of all glitches (black circles) and the glitches associated with this mechanism (red pluses).
• Loads of omega scans showing how these glitches show up in DARM and in the SUS channels can be found here. 
• Figure 2 shows a spectrogram of the SUS channel lined up with its timeseries. I think the wavy cutoff at the top of the timeseries indicates saturation somewhere a little bit of filtering away from this channel.
• Figure 3 shows the spectrogram of the SUS channel lined up with the spectrogram of DARM. The broad SUS glitches up to 10Hz correlate with DARM glitches at around 8-9Hz. 

Note: CIS says this channel is calibrated in um. I don't know whether this is a digital saturation or some physical thing - will consult a SUS expert. 

One mystery, to me, is why the glitches occur at GPS times ending in .000, .250, .500, and .750. This might be due to time domain clustering in our glitch algorithm. At first I thought it indicated a digital origin for the glitches, which turns out to have been a red herring. 

Below are the trends from the last 10 days

Do not forget: Meetings are back to their normal Monday, Wednesday, Friday @ 830 schedule.

SEI: HAM3 is currently experiencing some issues, please stay away until the problem is sorted out.

SUS: Stuart is taking TFs this morning

CDS: Quiet day

VAC/FAC:

• Ready for HAM door removal
• Fans are currently on (for Commissioners: do NOT leave the fans off for more than 5 min)
• Dust monitors are on and ready for vent
• contamination control is ready for vent

OpLev: wants to put new OpLev on HAM3, they will coordinate with SEI

We've had some difficulties locking today, in part because sometimes when the ASC comes on, it misalings things and causes mode hopping. 

When we did lock, we planned to work on reducing the ETMY DAC glitches (alog 17555), first by pushing up the L1/L3 crossover then by turning off the linearization.  We got as far as measuring the crossover, screenshot attached.  We designed a lead filter to give us some phase to push the crossover up to about 2 Hz, but ran into trouble with locking and now HAM3 HEPI.

Evan, Sheila, Koji

We ran into some difficulty tonight with HAM3 seismic, both HEPI and the ISI are tripping.  We've tried several things:

• disabled ISC outputs, the IMC-MCL output, and the isc inputs to MC2. There were no signals going to PR2. 
• turned off all ISI sensor correction by setting gains to 0 in the MATCH filter banks
• The HPI sensor correction was off already
• things still tripped, so we switched the GS13s to low gain mode.  
• It seems that if we leave HEPI tripped and isolate the ISI, it stays isolated without tripping, so HEPI must be the problem.  We looked at the pump servo screen but nothing seems obviously wrong....

This is a follow up entry of LHO ALOG 17601.

A couple of days ago, the discrepancy of the response for DCPDA and DCPDB were found. This was basically caused by misadjusted filter modules for the anti-whitening filters. Some of them were using design values (like Z10:P1) and some others were just left as they had been imported from the LLO setup.

In order to correctly take the whitening transfer functions into account, the wiring of the in-vacuum and in-air connections were necessary to be tracked down. The 1st attachment shows the sufficiently detailed wiring chain for this task. Using the test data (links indicated in the diagram), we can reconstruct what the correct anti-whitening filters should be. The summary can be found below.

[Trivia for Rich: DCPD1 (Transmission side of the OMC BS) is connected to HEAD2, and DCPD2 (Relfection side of the OMC BS) is connected to HEAD1. This is because of twisted D1300369. This cable has J2 for HEAD2 and J3 for HEAD1. This twist exists in LLO and LHO consistently, as far as I know]

=======
Characteristics of the DCPD electronics chain
Complex poles/zeros are expressed by f0 and Q

DCPD A
(DCPD at the transmission side of the OMC DCPD BS)
- Preamp D060572 SN005
Transimpedance: Z_LO = 100.2, Z_HI = 400.0
Voltage amplification ZPK: zeros: 7.094, 7.094, (204.44 k, 0.426), poles: 73.131, 83.167, 13.71k, 17.80k, gain: 1.984

- Whitening filter D1002559 S1101603
(This document defines the gain not at the DC but at a high frequency. The gain below is defined as a DC gain.)
CH5 Whitening
Filter 1: zero 0.87, pole 10.07, DC gain 10.36/(10.07/0.87)
Filter 2: zero 0.88, pole 10.15, DC gain 10.36/(10.15/0.88)
Filter 3: zero 0.88, pole 10.20, DC gain 10.36/(10.20/0.88)
Gain: “0dB”: -0.051dB (nominal), “3dB”: 2.944dB, “6dB”: 5.963dB, “12dB”: 11.84dB, “24dB”: 24.04dB

DCPD B
(DCPD at the reflection side of the OMC DCPD BS)
- Preamp D060572 SN004
Transimpedance: Z_LO = 100.8, Z_HI = 400.9
Voltage amplification ZPK: zeros: 7.689, 7.689, (203.90 k, 0.429), poles: 78.912, 90.642, 13.69k, 17.80k, gain: 1.983

- Whitening filter D1002559 S1101603
CH6 Whitening
Filter 1: zero 0.88, pole 10.13, DC gain 10.41/(10.13/0.88)
Filter 2: zero 0.87, pole   9.96, DC gain 10.40/(  9.96/0.87)
Filter 3: zero 0.88, pole 10.15, DC gain 10.41/(10.15/0.88)
Gain: “0dB”: -0.012dB (nominal), “3dB”: 2.982dB, “6dB”: 6.007dB, “12dB”: 11.87dB, “24dB”: 24.04dB

=======

Now we put these transfer functions into the model and check if we can reproduce the observed relative difference (Attachment 2). In deed, the measurement is well explained by the model below 30Hz where the measurement S/N was good. As we saw in the previous entry, the difference of the DCPDA and DCPDB after the whtening compensation is 20% max. Note that further inspection revealed that this 20% difference is, in fact, mostly coming from the difference of the preamp transfer functions rather than the miscompensation.

So this was the relative calibration between DCPDA and DCPDB. How is the compensation performance of each one? The 3rd attachment shows how much of current we get at the output as H1:OMC-DCPD_A_OUT, H1:OMC-DCPD_B_OUT, and H1:OMC-DCPD_SUM_OUT, if we give 1mA of photocurrent to DCPD_A, DCPD_B, or both (half and half). Ideally, this should be the unity. The plot shows how they have not been adjusted. For the our main GW channel we take sum of two DCPDs. The individual deviations were averaged and thus the sum channel has max 10% deviation from the ideal compensation. This shows up in the GW channel.

=======

So let’s implement correct compensation. Basically we can place the inverse filter of the each filters. The preamplifier, however, includes some poles and zeros whose frequency are higher than the nyquist frequency. Here we just ignore them and assess how the impact is.

The result is shown as the 4th attachment. Upto 1kHz, the gain error is less than 1%. This increases to 5% above 3kHz.  The phase error is 7deg at 1kHz. This increases to 20deg above 3kHz. These are the effect of the ignored pole/zeros. Note that these are static error. In fact, the phase error is quite linear to the frequency. Thus this behaves as a time delay of ~18.5us. Since the phase delay at 100Hz is small, the impact to the DARM feedback servo is minimal. For the feedforward subtraction, however, this might cause some limitation of the subtraction performance. In practice, we measure the coupling transfer function in order to adjust the subtraction, in any case. Therefore this delay would not be a serious problem.

The filter bank to implement the new compensation was already configured. The filter file is attached as foton_DCPDfilters.txt.

Sheila, Elli

We tried to move ASC inputs to MICH and SRC1 from AS_B_RF36 to AS_A_RF36 as outlined in Sheila's alog 17623.  We are trying to use ASC-AS_A_RF36_I to control the SRM using SRC1 and ASC-AS_B_RF36_Q to control the BS using MICH.

Today we tried to rephase the AS_B WFS to minimise the effect of SRM misalignment in the Q phase.  Yesterday we tried this by injecting a 12Hz pitch signal into the SRM and minimising the 12Hz line in the ASC-AS_A_RF36_[Q1/Q2/Q3/Q4]_ERR for each of the four quadrants (Q1/Q2/Q3/Q4).  Today we tried a similar thing, except we excited both pitch and yaw on SUS-SRM_M3_LOCK_Y_EXC and SUS-SRM_M3_LOCK_P_EXC at 10 and 12 Hz respectively.  We tried to set the phase of each AS_A_RF36 quadrant to minimise the 10Hz and 12Hz lines simultaneously.  We changed Q1 from -50 to -40, Q2 from -90 to -70, Q3 from -60 to -50, and Q4 from -50 to -20.  It looked like we ended up with smaller signals in the Q-quadrature than we started with.

We also reset the dark offsets on AS_A_RF36.  We unlocked the IMC to do this.

After rephasing AS_A_RF36 and rezoeroing the dark offset, we went to DRMI_LOCKED on ISC_LOCK, and looked for the zero crossing of the AS_A_RF36.  We did this by turning of either MICH or SRC1 ASC and then we changed the BS/SRM alignment and looked for a zero crossing in the relevant AS_A_RF36 signal.  This did not look promising, and we couldn't find a zero crossing at a good alignment for any degree of freedom except for SRM pitch/AS_A_RF36_I_YAW. 

With that we are leaving this task for today, untill we think of a smarter way to rephase the AS_A_RF36.

This morning I moved ITMX pit by -3.8 urad to get more recycling gain. The recycling gain increased from 26 to 30. Assuming that the ASC loops (DHARD and CHARD) suppressed the angle of the misalignment but not the translation, I must have introduced a translation of 7.4 mm upward. In addition, when I increased the PSL power from 3 to 10 W in the full lock, I saw that both ITMs tilted only in pitch by roughly +0.5 urad according to the oplev signals. This means that the beam on ITMs were lower than the center of the optic by roughly 5 mm (see Evan's calculation in alog 16344), though, to be accurate, one has to take the ASC loops into account which I did not. Anyways, I believe that my move on ITMX also improved the centering on ITMX as well. We should check the optical torque when the interferometer is fully locked.

I updated the green camera reference position of ITMs from 241.6 to 248.5 and from 216.5 to 218.0 for ITMX and ITMY respectively. After a lockloss by accident, we confirmed that we could lock back to this new high recycling gain point without re-tuning the ITMX angle. I could not finish optimizing the angle of ITMX or check the yaw alignment yet due to the lock loss. We know that we can get a recycling gain of 33 (alog 17158), so this work continues.

827 Jim W., Krishna - to EX for BRS restart and CPS check

832 Betsy - Retrieving item from W. Bay

842 Betsy - Back

911 Jim W., Krishna - Back

1241 Karen/Cris - To Mid Y/X

1330 Karen - Back

1501 Jeff B. - Cleaning area for vent prep

1536 Jeff B. - Back

J. Kissel, S. Dwyer, K. Venkateswara, J. Warner, T. Shaffer

I stumbled in on a conversation between the four listed above about how to deal with wind, so I immediately started taking notes. Here're some of the conclusions:

- There are *three* fault conditions of the beam rotation sensor (BRS) at EX. Under these conditions the BRS should *not* be used for sensor correction:
   (1) The BRS software is dead. In this case, the raw time series of the ADC input for the sensor has flatlined and does not show the usual ~8 [mHz] sine wave resonance of the beam's suspension.
   (2) The BRS has rung up. If the raw input shows the 8 [mHz] resonance, but the amplitude exceeds ~200 [ct] then the sensor output begins to go non-linear and should not be used. Note that the analog USB DAC that is pushing the analysis software's output into the CDS system is the limit on the signal. This is why, last week, we were seeing what looked like an 8 [mHz] square wave in the time series -- the rotation sensor was so rung up, that the software's requested output signal exceeded the 20 [Vpp] (+/-10 [Vp]) range of the USB DAC. This occurs at +/-16k [ct] in the CDS ADC.
   (3) The BRS's gravitational damper is on. If the gravitational damper is ON, then the BRS has rung up enough that (2) is happening.

- If none of the above error conditions are present, then the BRS can be used to subtract tilt from the GND T240 sitting next to it, and therefore can improve sensor correction. HOWEVER, it won't improve any-and-all sensor correction: the sensor correction filters need to have authority in the frequency region where we expect the GND instrument is dominated by tilt. Therefore, in the current nominal configuration of the BSC-ISIs at LHO -- where we're using Dr. DeRosa's notch-like sensor correction filter that only has authority in a narrow band around 0.5 [Hz] and otherwise using the ISI T240s in feed back down to 45 [mHz] -- improving the GND T240 sensor with the BRS  won't do you any good, because the GND T240 is typically only dominated by tilt only below 90 [mHz].

- Krishna's data from LHO aLOG 16465 demonstrates that even during 5-10 [mph] winds, the following configuration for the ETMX BSC-ISI is equivalent to the nominal configuration:
   (1) Push the blend up to using the 90 [mHz] blends on the X DOF only.
   (2) Use the tilt-corrected GND T240 + BRS super sensor
   (3) Switch to using the Mittleman, low-frequency, "tilt free" sensor correction filters which have authority down to 10 [mHz]
As such, we suggest that this should be the windy configuration for ETMX.

- Jim plans to accelerate his campaign to get the tuned sensor correction MATCH gains pushed into filter banks, such that the nominal value for the *actual* gain of the MATCH bank is 1.0

- T.J. Is going to write us the beginnings of an ISI Configuration manager in order to make it easier to remember all of this.
It will do the following
   To go to windy configuration (in order):
   (1) Switch ETMX ST1 X and ETMY ST1 Y blends from 45 [mHz] to 90 [mHz] (wait to finish)
   (2) Ramp OFF the gain (ramp to zero) of the ETMX Sensor Correction MATCH bank.
   (3) Switch ETMX GND STS X direction input matrix element from using STSB to STSC (i.e. turn ON the BRS correction)
   (4) Switch the ETMX ST1 X Sensor Correction filter from the "SC-rdr" (i.e. the 0.5 [Hz] notch-style DeRosa filter) to the "Mitt_SC" (i.e. the Mittleman, low-frequency filter)
   (5) Wait for the ETMX ST1 X output to settle (which should be the impulse response time of the Mitt_SC filter, ~100 [sec]) -- should be 100 [sec]
   (6) Ramp ON the gain (ramp to one) of the ETMX ST1 X sensor correction MATCH bank.

   To come back from windy configuration (in order):
   (1) Ramp OFF the gain (ramp to zero) of the ETMX ST1 X sensor correction MATCH bank
   (2) Switch the ETMX ST1 X Sensor Correction filter from "Mitt_SC" back to the "SC-rdr"
   (3) Switch ETMX GND STS X direction input matrix element from using STSC to STSB (i.e. turn OFF the BRS correction)
   (4) Wait for the ETMX ST1 X output to settle (the SC-rdr filter's impulse response is smaller and shorter, so maybe ~30 [sec] is fine)
   (5) Ramp ON the gain (ramp to one) of the ETMX ST1 X sensor correction MATCH bank.
   (6) Switch ETMX ST1 X and ETMY ST1 Y blends from 90 [mHz] to 45 [mHz] (wait to finish)
   
This above process assumes that the MATCH TRAMP time has been set to 15 [sec] and is monitored by the SDF system, that Jim has moved the Mitt_SC filter into the MATCH bank (and removed it from the IIR SC bank) and has moved the tuned match gains into filters.

----------
For a description of the Derosa 0.5 [Hz] notch-like sensor correction, see SEI aLOG 645.
For plots and design of the Mittleman low-frequency, tilt-free, (typically used in Z) sensor correction filter, see SEI aLOG 594

Posted are the OpLev trends for the past 7 days. No apparent concerning trends noted. These trends are consistent with 30 and 60 day trends.   

Nutsinee, Dan, Jeff K, Angus

This is a follow up on the alog17529. Below you'll find the list of violin mode frequencies we found and averaged frequencies including possible alternatives. The fiber is determined using data gathered in alog16614 (which cites alog11184, alog9359, alog11044, and alog6858). The air frequency included in the last column. 

The way alternatives work is that, if you choose to use one, you have to use the next alternative as well. For instant, if you decide for 508.00075 line to be averaged violin mode for the ETMY FR, you have to use 508.176 as the ETMY FL line. Or if you were to pick 508.21725 as the ETMY FL, you have to use 508.213 as the ETMY BL. This seems a little bit confusing so I attached the original Excel file as well. 

Any comments, questions, and suggestions welcome.

Ps. I don't know why alog keeps making new entries everytime I add things to the table and update the file. Sorry for the spam!

Koji, Sheila, Dan, Evan

Summary

Noise coupling measurements for MICH, SRCL, PRCL, intensity, and frequency have been taken.

We also tried a few small noise-hunting activities.

Details

Coupling measurements

For PRCL, MICH, and SRCL, we excited each dof with a swept sine and then recorded the transfer function from the error signal (IN1) to the DARM channel. MICH was already done previously.

For intensity, we did the same as described earlier.

For frequency, we used the same DAC channel (LSC-EXTRA_AO_2) to drive the common-mode board excitation point with a few millivolts of swept sine. Then we recorded the transfer function from REFL_A_9I (which is out of loop) to the DARM channel.

The dtt files are attached. More analysis to follow.

Other

Koji and I saw that ASC-MICH_P had significant cohrence with the DARM spectrum between 20 and 40 Hz. We took an OLTF and found that the UGF was 2 Hz with 60° of phase. We installed an elliptic LPF at 20 Hz, which removed most of this coherence (see attached). Correspondingly, the DARM spectrum dropped by a factor of 1.5 or so around 30 Hz.

We then tried to tune the bias of the EX ESD to see if we could improve the DARM spectrum. We could not find a sharp optimum; rather, anything from −190 V to 0 V seemed to be OK.

Koji then suggested trying to excite a scattering shelf in DARM by driving the OMC suspension. We drove the suspension longitudinally, transversely, and then vertically by a few microns at 0.15 Hz, but we found we could not make anything appear in the DARM spectrum.

Twice today the high voltage for the OMC PZT tripped, requriring the power supply to be reset by hand. The voltage is set at 100 V and the current limit is 2 mA. The quiescent draw is 0.8 mA.