Bubba and I were able to crane the Genie manlift over the Y beam manifold this morning in order to continue the crane rail work.
GV5 and GV7 were soft closed for the duration from UTC 16:15 to 16:53.
The crane behaved normally.
Are complete. I will post plots when I get a chance.
Here are the plots.
Laser Status:
SysStat is good
Front End power is 32.63W (should be around 30 W)
Frontend Watch is GREEN
HPO Watch is RED
PMC:
It has been locked 11.0 days, 23.0 hr 23.0 minutes (should be days/weeks)
Reflected power is 3.203Watts and PowerSum = 25.7Watts.
FSS:
It has been locked for 0.0 days 12.0 h and 23.0 min (should be days/weeks)
TPD[V] = 1.415V (min 0.9V)
ISS:
The diffracted power is around 8.004% (should be 5-9%)
Last saturation event was 0.0 days 12.0 hours and 23.0 minutes ago (should be days/weeks)
12 Counts on HAM5
Den made some modifications to our DRMI that he thinks might help us lock faster.
We had all of our integrators zero history immediately, Den added 1 second ramps to the 4:0 in MICH and the 10:0.1 in PRCL with the idea that this can reduce transients when they turn on.
He also changed our triggering so that SRCL and MICH are triggered together at 20 counts off at 10 coutns (this is about 1/3 of the power build up of POP18). Before SRCL was triggered at 2 counts.
Den also increased the PRCL gain from 11 to 15, removed the triggering of PRCL FM3 (10:0.1) and engaged it by hand after it locked. (the idea for higher gain being that it is better to supress PRCL well in the SRCL error signal).
He set the SRCL gain to -20 from -45.
DRMI locked in about two minutes. Its probably worth testing these settings out more and maybe making an alternate DRMI locking guardian state for testin new settings to see if we can reliably get a faster DRMI time.
We had an unusual HEPI trip (ETMX) just now. There doesn't seem to be much happening seismically except for some small wind gusts (not reaching 20mph). HEPI tripped as well as stage 1 of the ISI, but we are re isolated now and don't seem to have any problems.
We've just had another similar trip of ETMX HEPI, this time at the same time as a 40 moh gust of wind. The plotting tool didn't work.
1635 -1700 hrs. local -> To and from Y-mid Behaviour a little different today. ~5 minutes after opening the LLCV bypass valve 1/2 turn open there was no indication of vapor at the exhaust. It took an additional 5 minutes after opening a full turn before complete. As found, the exhaust pipe was noticeably absent most of the semi-permanent ice build up - warmer ambient temps? Next over-fill to be Tuesday, Feb. 16th before 4:00 pm
Re: this and the previous entry about exhaust LPM, it will depend on beam tube temperature (thermal radiation). We should model that and see if it improves predicted consumption. Do we have thermometer channels?
{Rana, Evan}
This evening we looked at the coupling of DCPD bias voltage into DARM.
Each DCPD is biased with +12 V from a linear regulator with a 1 Ω output resistor. We wanted to inject extra bias noise, so we exposed the bias lines with a breakout board at the DCPD chassy in the HAM6 rack (see D1300502). Then we summed in the output of an SR785 across an impedance of 10 kΩ in series with 20 µF (see diagram; green shows the normal DCPD electronics and red shows the addition). The 10 kΩ gives a 1:104 ratio of bias fluctuation to drive voltage, and the capacitor ac-couples the drive so that it does not pull on the bias at dc.
With the SR875 we drove a 1 Vpk line first at 187.3 Hz and then at 62.4 Hz (i.e., the bias fluctuation was 70 µV rms). We looked at the response in DARM (at 2 W dc readout, with DARM still controlled by EX). We had 10 mA dc on each PD, in the 400 Ω transimpedance configuration.
For 187.3 Hz (from 02:03:00 to 05:22:00 Z), the magnitude in DARM was 1.13×10−18 m rms, which implies a coupling of 1.6×10−14 m/V. The noise of the regulator at this frequency was 0.9 µV/Hz1/2, which implies a DARM noise of 1.4×10−20 m/Hz1/2.
For 62.4 Hz (from 05:33:00 to 05:56:30 Z), the magnitude in DARM was 1.4×10−18 m rms, which implies a coupling of 2.0×10−14 m/V. The noise of the regulator at this frequency was 1.9 µV/Hz1/2, which implies a DARM noise of 3.7×10−20 m/Hz1/2. Note that there is some room for error here because the DARM control configuration here is not exactly the same as the low-noise configuration. However, the ugf and phase margin should not be too different in the two configurations.
This is very close to the current low-noise DARM noise floor. However, if DARM is limited by voltage noise of the regulators, we should either expect that the DCPD null stream is equal in magnitude to the DCPD sum (it isn't), or the regulator noises are coherent (they aren't).
I am not sure if there are any contradictions in these numbers. DARM calibration at DC is C [W / m] = 4 * pi * G_arm / lambda * sqrt(G_prc * P_in * P_as / G_src) = 1.5e9 and 5e9 for input power 2W and 22W and 26mW at the AS port. This means that the response you measured is ~2e-5 A/V. If the input power is 22W, 1uV/sqHz projects to 4e-21 m/sqHz around 100Hz. This number is what you have in your noise budget plots.
The freerunning DARM channel may not be properly calibrated in the low-power state with EX control, so the numbers I gave originally could be too high.
We directly measured 1.2×10−6 mA rms in DCPD B at 187.3 Hz, which implies a coupling of 0.017 mA/V, which implies the bias noise shows up in DCPD B at 1.5×10−8 mA/Hz1/2. The shot noise with 10 mA on the PD is 5.7×10−8 mA/Hz1/2. So it is a factor of 4 or so below the DARM shot noise, assuming DCPD A is similar. That's close to the dark noise, but the dark noise is flat down to a few tens of hertz while the regulator noise has some negative slope.
Voltage noise of bias (pin #8 of the d-sub), measured with BNC clip doodle and SR785 (with AC coupling).
Sheila, Rana
We continued the investigation. Today we hooked up a DAC channel to the bias to make sweeps and noise injection. No surprises relative to yesterday. Still seems so close to DARM as to be unbelievable. Maybe the 1 Ohm resistor in the bias circuit is not stuffed?
We also injected random noise into PZT2 to look for upconversion there. We saw the usual kinds of quadratic coupling; noise at a level ~500x above the quiesscent HVmon noise level was able to be just visible in DARM in the baseband as well as by injecting noise close to the 4100 Hz dither frequency.
0554 UTC, leaving it in 'low noise mode'. The BS coil driver is in some mixed low noise state giving us increased DAC noise below 50 Hz, but the noise above there is as good as ever.
Can't get the photodiode D's off the DCC at the moment (outage???), but surely there must be a biga$$ cap (ideally several in ||) from the pd cathode to ground??
Yes, in the in-vacuum preamp, there is a 1 uF capacitor from the Bias to ground. At the LM317T (voltage regulator that sets the bias), there is a 10 uF cap to ground, on the regulator side of the 1 ohm resistor (it's not shown in Rana's sketch above). In any case, the projection given above relies on the 1e4:1 scaling of the injected signal - can't you just measure directly the drive on the bias line, rather than assuming the 1e4:1 ratio?
Bigger caps are unlikely to help much. The noise is due to the internal burried zener diode which serves as the voltage reference. The BW of the regulator is about 10kHz here. A bigger C may reduce this, but may also increase gain peaking. Just use a low noise supply such as the one here. Noise performance: T1000025.
Den, Rana
We directly measured the voltage noise on pin8 and confirmed that our injection through the 9.09k resistor (not 10k as indicated above) scales as expected. It seems that the 1 Ohm resistor is really 1 Ohm (+/- 20%).
From MZ, we have http://www.edn.com/electrical-engineer-community/industry-blog/4422750/2/Simple-circuits-reduce-regulator-noise-floor.
This indicates that some larger caps may reduce the regulator output noise at 100 Hz by a factor of 5 or so. Could be easy to try if we have a spare whitening chassis sitting around.
Rana, Sheila, Den We have measured the bias noise with a better resolution and found that this noise is almost flat below 60Hz. Then made a projection of this noise to DARM when the input power was 22W and power on each OMC PD was 10mAmps. For PD A the coupling is 1.5e-15 m/V while for PD B is 3e-15 m/V. Attached plot shows the projection of bias noise to DARM. It is factor of ~4 below the current sensitivity.
According to the noise budget and measurement of the dark noise, this noise is above the dark noise level. This means that the noise is present only when the DC photocurrent is present.
Suggests QE compression due to bias reduction. For higher P it may be wise to not only improve bias voltage noise, but to fix anode-cathode potential. Either a true transimpedance preamp, or a tracking supply at the rack.
We drove PD_B bias and measured the coupling of the bias noise to OMC NULL channel for different current levels. Plot is attached. The coupling is close to zero when there is no power. The coupling scales linear for small currents and stays almost constant for large currents (>10mA on each diode). We have also double checked that the optical signal scales linear with the current by driving an intensity line.
Kiwamu, Den We have digitized bias channels (LSC:EXTRA_AI_2 channel) and double checked coupling to DARM. Attached plots show coupling of PD_B bias to DARM. There is a calibration line at 62.4Hz of this coupling.
[Evan; Rana; Kiwamu];
We restored the 20 dB gains (that have been commented out for long time) in all the soft loos. We still have some suspicision that the ISS may be doing something bad causing locklosses. In order to separate the issues, we decided to gain them up. If one wants to get rid of them, just comment out lines 1990-1993 in the ISC_LOCK guardian.
The ASC loops had a slow oscillation with these 20 dB gains today, so we commented them out again.
The new ISS digital AC coupling caused the diffracted power to oscillate by ~1% with a period much less than 1Hz. I tried turning the gain down on the servo, but we lost lock (we were in NomLowNoise).
Later, I locked the interferometer to nominal low noise in order to check the behavior of the ISS. The 2nd loop was able to automatically engage the servo. I did not see a fault behavior with the ISS at least after twenty minutes in full lock.
Perhaps what Jenne saw is a type of oscillation that reported in alog 24665 ? Since the interferometer is locked, I am leaving it undistrubed. By the way OMC DCPDs are seemingly with low transimpedance. Noise in DARM below 50 Hz seems higher than the reference curve. I did not pay attention to the calibration at all.
The attached show an overnight trend (for 12 hours) of the relevant channels. As Jenne pointed out, the diffraction power indeed fluctuated (below 1 Hz) by 1 % or so all the time, but this is a known behavior (alog 24665) -- the 2nd loop changes the operating point of the first loop since the 2nd loop still has some gain at low frequencies even though it is digitally AC-coupled. As Gabriele pointed out, we think this fluctuation is added by the angular motion of the input mode cleaner (alog 24677). If we want to improve fluctuations in the diffraction power, the next attacking point would be the input mode cleaner.
Tagging SEI and CDS in this. If this problem (this aLOG and LHO aLOG 24665) has moved into the "we keep re-discovering it" category, perhaps the ISC team should request that CDS to work with SEI to push fixing HAM3's 0.6 [Hz] oscillation problems, and allow some non-Teusday time to do so.
Average LVEA temperature quickly came back but there are jumps in indivisual sensors, some show large change (0.5 to 0.8 C).