Scott L. Ed P. Chris S.

Yesterday the crew cleaned 52 meters of tube and 67 meters today to X-1-8 double doors. Results are posted here.

The extraordinary accomplishment of cleaning over 90 meters on 3-31 was very much appreciated, however I have asked the crew to consider a more reliable pace and not burn themselves out. I reminded them that we are only 20% complete with the overall task.

Monday will be spent relocating equipment, lights, and support vehicles. 

Measurements were carried out on the ETMX effective charge voltage over a period of 3.5 hours this morning. 

Firstly, some housekeeping, I svn'd up the charge scripts directory to obtain updates from LLO /ligo/svncommon/SusSVN/sus/trunk/QUAD/Common/Scripts/ and persevered local changes.

ETMX was selected since it does not currently have low-pass filters installed on each quadrant. It was not necessary to re-align the ETMX optic, since the OpLev was already well centred. Linearization was bypassed (turned off) for the duration of these measurements. The ESD_UL_LL_UR_LR_charge_07-H1.py script was run to drive the ESD at 4 Hz with an amplitude of 130k counts. The script attempts to write a bias to H1:SUS-ETMX_L3_LOCK_BIAS_OFFSET, however, this is nominally turned OFF at LHO. Therefore, it will need to be engaged, and the bias in DAC counts residing in H1:SUS-ETMX_L3_LOCK_INBIAS set to zero. Also, the ramp time should be reduced from 10s to 5s for the duration of the charge measurements.

Data was processed using the ESD_UL_LL_UR_LR_analysis_07_H1.m script, charging and charge deviations from today’s measurement can be seen below (all times in UTC).

A significant negative effective voltage is observed on the lower quadrants, which are quite variable. Upper quadrants exhibit less charge and are more stable (similar to what was seen for LLO ETMY, before it was discharged) n.b. there is also a large discrepancy between the effective charge reported by OpLev Pitch and Yaw.

Previous automated charge measurements carried-out on ETMX by Brett after the most recent vent did not show as larger effective charge (see LHO aLOG entry 16057). Follow-up measurements, may help determine how the charge is evolving. The infrastructure is in place to help determine if any future discharging is successful.

Processed results, and analysis scripts have been committed to the sus svn, raw data files have not.

Today has been a rough day for the input HAM chambers. This morning we found that a channel went dead in expansion chassis (see Richards alog for the resolution), and troubleshooting involved a lot of restarts of SEIH23. This afternoon, after that problem was sorted, Evan found that the SEI MEDM screens for HAM2&3 were frozen. Dave and JimB should be posting a log about the resolution of that issue.

It would be very good if Detchar could at do some comparisons of the H3 IPS  on HAM3 HEPI with other sensors to see if the failure that took out this chamber this morning (killing commissioning efforts until ~now) gave us any warning. I attach some dataviewer trends of the IPS blend ins, and I can kind of convince myself that the horizontal loops all look a little noisier 18 hrs ago versus now. Not necessarily true, I haven't looked in any detail and I'm just guessing based on the max/min being noisier 18 hours ago.

All models on the h1seih23 computer stopped running.  A quick check showed that the I/O chassis appeared to be powered down, as no cards were reported from the I/O chassis with a lspci -v command.  We assumed the power supply had failed, so we removed the computer from the Dolphin network, stopped the models, and powered off the computer.  We then examined the I/O chassis only to find that it was powered up and appeared to be running OK.  

After examining the one-stop cable to make sure it was seated properly and showed no signs of having been kinked or otherwise damaged, the I/O chassis was powered down, then back up, and the computer restarted.  All models started normally with only a slight IRIG-B deviation into a negative value which quickly recovered.

Bottom line is we don't know what happened.

645 Jeff B. - LVEA CC stuff HAM6

713 Karen - LVEA

805 Jim W. - LVEA inspect HAM3

815 Jeff B. - Back

818 Jim W. - Back

840 Doug, Jason - LVEA prepping OpLev

909 Jim W. - LVEA more inspection

939 Doug, Jason  - Back

946 Sudarshan - LVEA

1002 SEI HAM2,3 FE model restart

1024 Suresh, Doug, Jason - Tweak HAM3 OpLev

1031 Richard - LVEA swapping ADC

1039 Jeff B. - LVEA

1039 Ed M. - LVEA

1047 Richard - Back

1047 Ed M. - Back

1048 Jeff B. - Back

1052 Sudarshan - Back

1112 Richard - LVEA replace ribbon cable

1122 Richard - back

1204 Doug, Jason, Ed M, Suresh - LVEA adjusting OpLev

1225 Sudarshan - LVEA

1229 Sudarshan - Back

1232 Doug, Jason, Ed M. - Back

1300 Suresh - Back

1340 - Restarting IO chasis for HAM2,3

This is posted early since I have to go to the airport

Jim Warner reported a problem with the Pier 3 IPS horizontal.  Investigating we found that the signals into the IO expansion chassis had a problem. Large offset and the noise as viewed on dataviewer was not the same as the others.  I replace the ADC interface card the ribbon cable and the ADC in an attempt to get the system back on line quickly.  We could narrow down the problem in the test stand.  I had replace the ribbon cable a second time as the one I found had a problem with channel 1.  Once this was complete the system seems to be fine.  I believe it is the ribbon cable that is the problem but further investigation is needed.   Thanks to Jim Batch for taking the system out of the dolphin network and shutting down the computer (multiple times) for me so the work could proceed.

J. Kissel, J. Batch

Exploring why the optical gain compensation calculation wasn't working, Jim reminded me of what I'd already discovered when building the front-end model: The user-defined amplitude of the given calibration line is determined by a built-in EPICs variable inside the oscillator of the DEMOD simulink library part. This amplitude is needed for the math used to compute the optical gain compensation (see T1500121). However, the oscillator part (and therefore the DEMOD part) doesn't spit out a front-end graspable version of the amplitude, only the line itself and the sine and cosine. So I'd had to create *another* EPICs variable to feed into the front-end math, with the intent of *always* keeping it in sync with the oscillator's amplitude.

My problem? I turned on the oscillator amplitude, but I forgot to put the parallel EPICs variable on the MEDM screen, so I forgot to set it when I set the amplitude of the calibration line (back in LHO aLOG 17622).

I've added the variable to the MEDM screen (and committed to the repo), and set it appropriately. Now we just need a DARM spectrum to further debug the computation!

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

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.