As mentioned in the previous alog (alog 16780), I suspected that the linearization in the ESD may not be behaving as expected.

We have been assuming that the ESD linearization does not change the actuator gain from the non-linearized case, but this turned out to be wrong according to a measurement (and analytical calculation).

It seems that either fixing this behavior in the actual system or correctly incorporating the linerization in the suspension model would reduce the discrepancy between the model and measured ESD response to a level of several 10 %.

On the other hand, I got another mystery where I am unable to explain the amount of change between the linearized and nonlinearized cases. The work continues.

(A single frequency measurement)

I did a quick measurement in this morning, comparing the linearized and non-linearized cases on ETMY (which was the only available ETM in this morning with the green light locked). I drove ETMY ESD at 2.261 Hz with an amplitude of 300000 cnts at L3_LOCK_L_EXC. The amplitude is set close to saturation at the DAC in order to get highest signal-to-noise ratio. The bias voltage was set to 9.5 V. There were no filters between the excitation point and the DAC. The L2P and L2Y were disabled. The oplev damping was active at the L2 stage only in pitch. The force coefficient was set to -180000 cnts in order to be identical to ETMX.

I used the green PDH control signal to monitor the displacment on the test mass. Also, since I used the green PDH signal instead of the IR locking signal this time, I was not able to get great SNR at 13 Hz which is the ferquency I have been using.

(Results)

The attachment shown below is the result.

As I switched the linerization on, the peak height at the excitation frequency increased by a factor of roughly 1.65. In addition, the 2nd harmonic peak decreased as the linearization is supposed to eliminate the nonlinear terms. The residual in the 2nd harmonic could be due to some charge on the test mass.

If this is true in ETMX as well, this will reduce the discrepancy between the suspension model and measurement down to 25% (which was previously reported to be discrepancy of a factor of 2.07 in alog 16780).

(Analytical calculation does not match the measurement)

On the other hand, according to my math (see the second attachment), the linerization was expected to increases the response only by a factor of 1.45 instead of 1.65. Although the difference between the two is only 13%, this still makes me think that something is not right as this calculation is relatively straightforward. Just for reference, I also attach the liearization simulink model that we use on ETMs.

If my math is correct, in order for the ESD to have the same actuator response gain, the absolute value of the force coefficient has to be the same as the bias counts at the DAC. Since we use bias voltage of 9.5 V (or 125418.4 cnts), the force coefficient should be -124518.4 cnts as well, but it was set to -1800000 cnts in reality. Since the response gain is proportional to the force coefficient, this should give us an extra increment of 1800000/124518.4 = 1.45 in the gain. I have no idea why the measurement differs from the expected.

I will repeat the measurement at some point soon when I get a chance.

PR3 oplev died at about Feb 17 2015 20:00:00 UTC, that's about noon local time.

The commissioners had to stop using PR3 oplev for some ASC purpose yesterday evening.

H1BROADCAST0.ini has 3 additional channels in r9856. h1broadcast0 was restarted, its channel count increased from 686 to 689.

Additional channels are:

+[H1:LSC-PD_DOF_MTRX_1_1]
+[H1:LSC-TR_X_QPD_B_SUM_OUTPUT]
+[H1:LSC-TR_Y_QPD_B_SUM_OUTPUT]

 

LVEA: Laser Hazard
Observation Bit: Commissioning  

08:21 Betsy – Running TFs on ETMX and SR2
08:23 Corey – 3IFO work in H2 Squeezer bay
08:25 Filiberto – Pulling cables at HAM6
08:49 Mitch – 3IFO work in West Bay
08:55 Cris – Cleaning at Mid-X
08:55 Karen – Cleaning at End-Y
09:03 Mitch – Out of LVEA
09:15 Travis – Going into the LVEA looking for tooling 
09:22 Doug – Going to optics cabinet near H1-PSL enclosure
09:35 Travis – Out of the LVEA
09:39 Corey – Going to End-Y
09:41 Apollo – Starting up A/C units for DCS
09:55 Richard – Swap IR Spool (X arm) camera zoom lens
10:20 Jodi & Travis – Going to Mid-X and Mid-Y to look for parts
10:24 Elli – Going to X-Arm Spool 
10:52 Dan – Giving a tour of LVEA for students   
10:53 Jodi & Travis – Back from the Mid stations
10:55 King Soft on site to take water samples
11:10 Richard – Out of LVEA
13:07 Filiberto & Ed – Going to End-Y to remove 3IFO power supplies 
14:25 Corey – Going into the LVEA
14:31 Corey – Out of the LVEA
15:00 Guardian training in OSB large conference room 

At 12:19pst 18 Feb, the servo was back running--no glitch whatsoever for the platforms.  The EPICS SCAN rate is now 1 sec but the PID parameters are those JeffK calcuated for a 10mHz UFG in alog 16782.

Bottom line--If we collect fewer channels, that is, if the database has fewer Analog inputs to process, the database process time changes.  This may seem obvious, but come on, we are collecting 15 pressure sensors, doing  two or three calcs and the PID.  Oh yeah, there is the 1 sec heartbeat, so sure, this processor is really stressed!

The first two attachments are matlab histograms of the DT field of the the epics PID.  This is the time between the PID process iterations used in the PID calculation.  In alog 16619 JeffK reports a DT value of 0.55sec; this is with 15 sensors collected and the epics running at 10 hz---the processor is only getting to the PID calculation every .55 sec!  When I reduce the number of channels collected to 7, DT drops to 0.312 secs (first attachment.)  In the second attachment is the histogram when the epics is set to run at a 1 second SCAN rate.  Here, the PID record is processing at ~1second but is multimodal with about a 1mhz variation. 

The third attachment is the Power Spectra of the Differntial Pressure running the Pump Servo and its coherence with the HEPI L4Cs at the BS.  In the spectra you can see the zero related to the update period of the PID: Blue--15 sensors 10hz epics ==> 0.55sec update= 1.88hz; Red--7 sensors 10hz epics ==>0.312sec=3.2hz.  And clearly Red: 15 chanels at 1hz ==> 1 sec update=1 hz.

The lower panel of the third plot shows the coherence with the Pressure to the BS HEPI L4Cs, it shows just H3 which had the strongest coherence in our normal configuration early Tuesday morning.  The Blue Trace is that normal configuration of 15 sensors collected at a 10hz epics scan; the Green trace is when the sensors collected dropped to 7 as does our coherence with the reduced gain peaking.  When we shift the process to 1hz scan shown in the Red trace (without adjusting the PID parameters!) the gain peaking increases as does our coherence again.  As Jeff has done in alog 16782, we need to recalculate the PID parameters if we wish to reduce the epics scan rate.

Except for the known FSS issues (alogs 16605, 16645), everything looks normal; no significant changes from last week.

Following up on our adjustment of the FSS RefCav alignment on 2/10/2015 (alog 16605) I've attached a 10 day trend of the signal H1:PSL-FSS_TPD_DC_OUT_DQ.  In this you can see our 2/10/2015 adjustment, where we left the TPD reading ~1.6V.  It starts to decay early Monday morning, 2/16/2015 (~11:00:00 UTC) and is currently reading ~1.3V.  Will keep an eye on this over the next few days, we may need to go in the PSL and adjust this again (most likely during the next Tuesday maintenance).

While running DBB scans this morning I noticed the ISS diffracted power was up around 12.2%.  I adjusted the RefSignal from 2.08V to 2.13V, bringing the diffracted power to 7.4%.  Running a trend shows the diffracted power started increasing slowly early Sunday morning (see attached).

   To accommodate the remaining 3IFO work before the end of project there will be extended noise hours until the end of March. Each Tuesday from 08:00 to 16:00 will be open for noisy work around the site. Floor access after 10:00 on the other days may be allowed with commissioner’s approval. 
 
   Seismic - Working on HEPI pump commissioning

   Suspensions – Running transfer functions on ETMX and SR2

   Vacuum – Preparing to start pumping at HAM1. Will coordinate with Daniel before starting work

   Electrical – Will be moving racks from End-Y to the H2 electronics building in the near future

   Safety Meeting – John reviewed the melted plug/receptacle extension cord problem from last week. The portable transformers will be shut down, and extension cords removed as the LVEA and VEAs are cleaned up for the ER run. Each subsystem should be looking into shutting down unused equipment and removing any extension cords wherever possible.    

These are trends for the last 10 days:

model restarts logged for Mon 16/Feb/2015

no restarts reported

model restarts logged for Tue 17/Feb/2015

2015_02_17 10:53 h1hpietmx
2015_02_17 10:53 h1iopseiex
2015_02_17 10:53 h1isietmx
2015_02_17 11:05 h1alsex
2015_02_17 11:05 h1iopiscex
2015_02_17 11:05 h1pemex
2015_02_17 11:07 h1iscex
2015_02_17 11:07 h1odcx
2015_02_17 11:22 h1hpietmy
2015_02_17 11:22 h1iopseiey
2015_02_17 11:23 h1hpietmy
2015_02_17 11:23 h1iopseiey
2015_02_17 11:23 h1isietmy
2015_02_17 11:26 h1iopsusex
2015_02_17 11:26 h1susetmx
2015_02_17 11:26 h1sustmsx
2015_02_17 11:27 h1susetmx
2015_02_17 11:33 h1iopsusey
2015_02_17 11:35 h1susetmy
2015_02_17 11:35 h1sustmsy
2015_02_17 11:42 h1iopiscey
2015_02_17 11:44 h1alsey
2015_02_17 11:44 h1iscey
2015_02_17 11:44 h1odcy
2015_02_17 11:44 h1pemey
2015_02_17 22:39 h1fw0

Maintenance day. One unexpected restart. Removal of RFM card in SEI end station computers. EX Beckhoff computer reboot after fortnight freeze.

Alexa, Evan, Peter, Lisa, Sheila

Today we increase the gain in the fast path off the common mode servo gain to 7dB rom 3dB.  This was needed to fix the problem in the ALS COMM loop shape (alog 17649. ) We originally tuned our TR CARM transition at an input power of 10.8 Watts, and we are now running at 2.8 Watts.  The IMC guardian is partially correciting the IMC servo gain for this change, but not compeletely, so the fast path gain was a bit different than what we had when we originally tuned the transition.  The new ALS COMM open loop gain is attached.  If we deicde to change the input power for the locking sequence we might need to revisit this, or do a better job compensating for optical gain changes in the IMC. 

With this gain adjusted, we were able to do the TR CARM transition without a problem, (at the original gain of -16dB in the common mode board input 1).  The new TR CARM open loop gain  (with improved phase as described in alog 16766)  is attached to alog 16766

We then moved on to redcing the CARM offset, and lost the lock severl times on the way (possibly due to bad alingment).  We have now moved the transition to RF DARM to a higher CARM offset (8 times the single arm power). We have attempted to turn on the DHARD WFS at the same CARM offset that we had been using (25 times the single arm power) but only PITCH was working. With just pitch running and manually alinging YAW, we have been able to go through the locking sequence but not transition CARM to REFL 9.

One thing we have noticed tonight is that the Y arm alingment that is good for green is verry different from the alingment that reduces AS DC.  This probably means that we could make the process easier by adjusting the camera position that the Y arm green WFS use durring intial alingment.  

J. Kissel

Since the original study on coherence with pump servos focused on the corner station (see LHO aLOG 16239), I attach some plots (first and second attachment) showing how bad the coherence is between each stations pump servo and the chamber motion. Further, the original study used the HEPI L4Cs -- but these were proven to be sensor noise limited at the boundaries of the coherence. Using the ISI T240s, one can resolve the coherence better, and see that it's worse over a more broad frequency band. Turns out T240s are better sensors than L4Cs. Shocking, I know. Note that I only have shown the Z, RX, RY, and RZ DOFs because (a) X & Y don't show coherence anywhere in either the L4Cs or T240s, and (b) I didn't look at the HP / VPs because there's no combination of the T240s that could reconstruct these DOFs.

Great, but this is sort of old news now. We know the parameters we have installed are bad given all the other flaws in the system (see LHO aLOG 16619). 

So let's design new PID loops with parameters that are better, given the constraints of this sub-par ADC/DAC system, and given our knowledge of the plant (see LHO aLOG 16601).

Assuming we reduce the sampling frequency of the EPICs record that processes the analog input, PID, and output to 1 [Hz] (instead of the claimed 10 [Hz], which was actually some slower frequency due to extra slow processing time), we now know that the integrator coefficient's value will depend on that sampling frequency so we must design accordingly. We also know that SMOO parameter low-pass filters are bad (at least ones that are so close the UGF). We also know that the ADC noise is terrible, and we haven't really resolved when the pressure sensor signal gets above the ADC noise, even though we've measured all the way down to 3 [mHz] (see LHO aLOG 16500). In any event we know that reducing the UGF of the loop does good things -- or at least reduces the bad (see LHO aLOG 16466). As such, I've modeled the right parameters to get a UGF of 10 [mHz]:
         P     I [cycles/min]
Corner   5     0.13   
EX       5     0.04
EY       5     0.04
For plots supporting the model, see the last attachment. 

Why 10 [mHz] you ask? I'm glad you're curious.
- As mentioned above and elsewhere, the sensor signals don't get above the ADC noise floor -- at least down to 3 [mHz] -- but they look like they're on the way up and may surpass the noise by 1 [mHz]. Why not a 1 [mHz] UGF then? Well, one could claim the SR785 measurement of the raw pressure sensor voltage may not have been valid at its lowest frequency points. It'd be a stretch, especially for the return pressure sensor signal, but I'll humor you.
- Do we really have the patience to commission / characterize a 1 [mHz] loop? Not really.
- Do we have to have patience anyway, because the pump servos are causing noise down at these frequencies whether we like it or not? This got me launched on using the T240s. They show the coherence rolls off at a lower frequencies than the L4Cs report BUT the coherence drops BEFORE the T240s hit their noise floor. This drop off happens by 10 [mHz].
- We want to get *some* suppression on these things on the 100 [s] time scale, because when free running, we do see the pressure drift around on the several minute time-scale. Not a lot, but it does. An unagressive UGF of 10 [mHz] gets us a suppression of 10 at 1 [mHz], and continues to increase proportional to 1/f. Should be plenty. 10 [mHz] also plenty far enough away from the sampling frequency that there's no funny phase business going on anymore.

Another side thought -- maybe we should just go back to using the supply pressure alone? It definitely has better SNR than the return pressure signal at these frequencies. We can use the one by the chamber as a compromise.

Hugh and I will post some data tomorrow showing that 
(a) a 1 [s] requested sampling rate reliably produces a 1 [Hz] sampling frequency.
(b) When we request to sample at 0.1 [s], the sampling frequency depends on the number of sensors read in, but the ADC noise floor does not change.
(c) We've permanently set the sampling time to 1 [s], installed the above new PID parameters, and there is no longer any coherence with the chamber's T240s (and hopefully the IFO).

-------
Data is taken from the template:
/ligo/svncommon/SeiSVN/seismic/HEPI/H1/Common/2015-02-16_H1HPI_EndStation_Coh_wISIT240s.xml

Filters were design with the script:
/ligo/svncommon/SeiSVN/seismic/HEPI/H1/Common/H1HPI_PumpServo_FilterDesign_Ts1Hz_UGF10mHz_20150217.m

Peter, Alexa

Summary

We measured the digital delay from the IR TR PDs at the end station to the CARM slow path at the corner to be ~50 deg at 300 Hz. This delay will include an end station model delay and two LSC delays. We have two LSC delays because TR CARM is in the LSC model, as well as the digital slow path after the IFO common mode board.  Our measurement is reasonable given Chris's delay plot (LLO#15933).

Details

We turned off the LSC-X_TR_A_LF_OUT (IR TR PD at END X) input and sent in an excitation with an amplitude of 100 cts. We turned off any filters along the TR CARM path (i.e. LSC-TR_CARM --> LSC-REFLBIAS --> ALS-C_REFL_DC_BIAS path), modulo some gains, and measured the transfer function at LSC_REFL_SERVO_SLOW_OUT. See LHO#15489 for the path.

This is a brief and preliminary update of the calibration activity from today. I calibrated the ITMX and ETMX reponses using the usual free-swing Michelson fringe.

If I believe the measurement, I must have underestimated the ESD response by a factor of 5.3 (!?) in the previous calibration which is hard to believe for me. I would like to repeat the measuerment perhaps with different conditions (e.g. opelv on/off, L2P off, linearization off/on, different bias, different frequencies and etc) and on ETMY as well.

(MICH free swing)

The method is the same as what Joe described in LLO alog 14135. To obtain the ASQ_pkpk value, I did not run the fancy matlab code or anything, but I just picked up a highest peak value and lowest one in H1:LSC-MICH_IN1_DQ. The alignment was adjusted beforehand by locking MICH. The pk-pk value was measured to be 27.0 counts. Using the relation, d (ASQ)/d(ITMX) = 2 * pi * ASQ_pkpk / lambda, I get

ASQ optical gain = 1.59 x 10⁸ cnts/m

The input power to IMC was at 9.6 W, measured at the periscope bottom PD. ASAIR_ALF could get to 4550 counts at maximum and ASAIR_B_LF 1500 counts when MICH was freely swinging. The below are some dtails:

• ASAIR_A_RF45 whitening gain was set to 30 dB
• Whitening stage 1 and 2 were engaged (probably this was too much as it seemed already limited by some elecronics noise).
• I attach the time series.

(ITMX L2 stage calibration using MICH)

After locking MICH, I shook ITMX L2 stage at H1:LSC-SUS_ITMX_L2_LOCK_L_EXC with a drive level as high as possible without DAC saturation. I did a swept sine measurement to check how high frequency I would be able to get without loosing good signal-to-noise ratio. It seems that exctiation above 20 Hz is hopeless -- the drive signal dives into sensor noise. From this measurement I picked up one frequency point, 13.05 Hz where the ITM response was measured to be

ITMX L2 response = 8.41 x 10^-18 m/cnts @ 13.05 Hz

• L2 coil driver state was set to 2 to get the maximum range.
• No oplev damping loops were engaged.
• MICH loop correction was applied in the estimation of the L2 stage response as was done in Joe's alog 14135. Abs(1/(1+G)) = 0.817 @ 13.05, measured.
• I did not oberve a DAC saturation during the measurement.
• I attach a dtt file of the open loop measurement and ITMX response measurement.

(ETMX calibration using X arm)

Keeping the 9.6 W incident power, I locked the IR laser to the X arm with a UGF of 100-ish Hz. I did a swept sine measurement on ITMX and ETMX at different times but in the same lock strech. On ITMX, the L2 stage was driven again with the same setting as that of the MICH locking. On ETMX, I had set up the suspension filters such that they are the same as the full locking condition (e.g. drive signal goes not only ESD but also L1 stage and so on). Neverthelss, since my swept sine measurement does not go below 10 Hz, the ETMX response essentially represents the ESD response (with a small effect from the L2 stage which is almost two orders of magnitude smaller than the ESD in terms of displacement).

Taking the ratio between the two actuators, I confirmed that the ratio goes as f^2 as expected in a frequency range from 10 to 60 Hz. The ETMX/ITMX ratio was measured to be

ETMX_L3 / ITMX_L2 = 1.70 x 10² @ 13.05 Hz

ETMX_L3 response = 1.43 x 10^-15 m/cnts @ 13.05 Hz. This is almost 5.3 times stronger than what we have in the CAL-CS calibration.

• IM4 and PR2 were controlled by the REFL WFSs in order to maitain the high build up in the X arm all the time during the measurement.
• ETMX oplev pitch damping loops was on at the L2 stage with a gain of -9500.
• The swept sine excitation was injected at SUS_ETMX_L3_LOCK_L.
• The L2P and L2Y were kept engaged on L3 stage on ETMX.
• The L1 coil driver state was set to 2.
• The bias voltage was set to 9.5 V.
• The ESD liearization was on with a force coefficient of -1.8e5.
• I did not see a DAC saturation on ETMX.
• I attach the dtt files.