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ID Date Author Type Category Subject
9440   Wed Dec 4 15:43:13 2013 JenneSummaryLSCPut LSC DAQ channels back

Last week, Koji cleaned up the LSC model to make it much more readable, while he was working on piping the ALS signals to the LSC model.  However, somehow the DAQ Channels block got deleted before the model was committed to the svn.  Since there were 2 months between svn checkins for c1lsc.mdl, it's possible that someone had the model open just to look at, and the block got deleted, and that's the version that Koji started with.

Anyhow, thankfully we have the svn, so Koji and I found that the DAQ Channels block was (as expected) in the previously checked-in version of the LSC model.  I put a copy of the old model onto my desktop, opened it up, copied the DAQ Channels block, and then pasted it into the new cleaned-up version of the model.  (Jamie - is there a way to conveniently download a previous version through the web interface?)

I have checked it in, compiled and restarted the lsc model.  The _DQ channels are back now.

4138   Tue Jan 11 18:41:43 2011 JenneUpdateIOOPut MC PZT offset onto MC board, instead of on awkward cart

[Larisa and Jenne]

We wanted to get rid of the awkward cart that was sitting behind the 1Y1 rack.  This cart was supplying a +5V offset to the PZT driver, so that we could use the MC length signal to feedback to lock the laser to the MC cavity.  Instead, we put the offset on the last op amp before the servo out on the Mc Servo Board.  Because we wanted +5V, but the board only had +5, +15, -15V as options, and we needed -5 to add just before the op amp (U40 in the schematic), because the op amp is using regular negative feedback, we made a little voltage divider between -15V and GND, to give ourselves -5V.  We used the back side of the voltage test points (where you can check to make sure that you're actually getting DC voltage on the board), and used a 511Ohm and 1.02kOhm resistor as a voltage divider.

Then we put a 3.32kOhm resistor in ~"parallel" to R124, which is the usual resistor just before the negative input of the op amp.  Our -5V goes to our new resistor, and should, at the output, give us a +5V offset.

Sadly, when we measure the actual output we get, it's only +2.3V.  Sadface.

We went ahead and plugged the servo out into the PZT driver anyway, since we had previously seen that the fluctuation when the mode cleaner is locked was much less than a volt, so we won't run into any problems with the PZT driver running into the lower limit (it only goes 0-10V).

Suresh has discovered that the op amp that we're looking at, U40 on the schematic, is an AD829, which has an input impedance of a measely 13kOhm.  So maybe the 3.32kOhm resistors that we are using (because that's what had already been there) are too large.  Perhaps tomorrow I'll switch all 3 resistors (R119, R124, and our new one) to something more like 1kOhm.  But right now, the MC is locked, and I'm super hungry, and it's time for some arm locking action.

I've attached the schematic.  The stuff that we fitzed with was all on page 8.

Attachment 1: D040180-B.pdf
4140   Wed Jan 12 01:38:52 2011 KojiUpdateIOOPut MC PZT offset onto MC board, instead of on awkward cart

I can not think of any reason that the input impedance of 13kOhm between the pos/neg inputs produces such a big change at the output. In any case, the differential voltage between the pos/neg inputs produces a big output. But the output was just 2V or so. This means that the neg input was actually about zero volt. This ensures the principle of the summing amplifier of this kind.

Because the input impedance of the summing node (the additional resister you put at the negative input) is not infinity, the voltage divider is not perfect and shows 10% reduction of the voltge (i.e. the output will have +4.5V offset instead of +5V). But still it is not enough to explain such a small output like 2.3V.

What I can think of is that the earlier stages somehow have the offset for some reason. Anyway, it is difficult to guess the true reason unless all of the nodes around the last stage are checked with the multimeters.

At least, we can remove the voltage divider and instead put a 10k between -15V and the neg input in order to impose +5V offset at the output. This costs 1.5mA instead of 10mA.

4147   Wed Jan 12 22:39:16 2011 SureshUpdateIOOPut MC PZT offset onto MC board, instead of on awkward cart

Quote:

I can not think of any reason that the input impedance of 13kOhm between the pos/neg inputs produces such a big change at the output. In any case, the differential voltage between the pos/neg inputs produces a big output. But the output was just 2V or so. This means that the neg input was actually about zero volt. This ensures the principle of the summing amplifier of this kind.

Because the input impedance of the summing node (the additional resister you put at the negative input) is not infinity, the voltage divider is not perfect and shows 10% reduction of the voltge (i.e. the output will have +4.5V offset instead of +5V). But still it is not enough to explain such a small output like 2.3V.

What I can think of is that the earlier stages somehow have the offset for some reason. Anyway, it is difficult to guess the true reason unless all of the nodes around the last stage are checked with the multimeters.

At least, we can remove the voltage divider and instead put a 10k between -15V and the neg input in order to impose +5V offset at the output. This costs 1.5mA instead of 10mA.

[Koji, Suresh]

We looked at the board and found that the resistor R119 (the feed back) is 1.65k instead of the 3.32k that was needed for unity gain.  The gain has been intentionally reduced to 0.5 so that output range would be close to the 0-10V that is required at the input range of the PZT driver which follows.   A note to this effect is already present in the D040180-B, page 8.

The voltage divider with 1k and 0.5k provides 4.5V (ref Koji's note above) this provides 2.25V at the output due to the gain of 0.5.  To get to the original goal of introducing a 5V offset on the output, we introduced the modification shown in the  'D040180-B with 5V offset.pdf' uploaded below.  Please check page 8, the changes are marked in red.  We checked to make sure that the output is 5V when the input is disconnected.

The PCB pics at the end are also attached.  The 4.99k resistor is glued onto the PCB with epoxy and placed as close to the opamp possible.

Attachment 1: P1120508.JPG
Attachment 2: P1120509.JPG
5858   Wed Nov 9 21:32:38 2011 MirkoUpdateAdaptive FilteringPut accelerometers 4-6 on top of MC2 tank

Put the accelerometers on top of MC2. Orientated as the arms,GUR1 and STS1:

Should be fixed a bit more rigidly.

Looking into the signals at a quiet time:

Hmm. Either the acc. are mislabeled or there is really bad x-y coupling. The connectors in the back of the acc. power supply / amplifier box are in ascending order.

Attachment 3: Coherence_quiet_time.fig
4029   Wed Dec 8 17:05:39 2010 josephbUpdateCDSPut in dolphin fiber between c1sus and c1lsc

[josephb,Suresh]

We put in the fiber for use with the Dolphin reflected memory between c1sus and c1lsc (rack 1X4 to rack 1Y3).  I still need to setup the dolphin hub in the 1X4 rack, but once that is done, we should be able to test the dolphin memory tomorrow.

6314   Fri Feb 24 16:10:48 2012 mikeUpdateComputersPyNDS and a Plot

Power Spectral Density plot using PyNDS, comparing 5 fast data channels for ETMX.

**EDIT** Script here:

import nds
import numpy as np
import matplotlib.pyplot as plt
import time
daq=nds.daq('fb', 8088)
channels=daq.recv_channel_list()
e=0
start=int(time.time()-315964819)
rqst=['C1:SUS-ETMX_SENSOR_UR','C1:SUS-ETMX_SENSOR_UL','C1:SUS-ETMX_SENSOR_LL','C1:SUS-ETMX_SENSOR_LR','C1:SUS-ETMX_SENSOR_SIDE']    #Requested Channels
for c in channels:
if c.name in rqst:
daq=nds.daq('fb', 8088)
data=daq.fetch(start-100, start, c.name)
vars()['psddata'+str(e)], vars()['psdfreq'+str(e)]=plt.psd(data[0],NFFT=16384,Fs=c.rate)
vars()['label'+str(e)]=c.name
e+=1
plt.figure(1)
plt.clf()
plt.title('PSD Comparison')
plt.grid(True, which='majorminor')
plt.xlabel(r'Frequency $Hz$')
plt.ylabel(r'Decibels $\frac{dB}{Hz}$')
for x in np.arange(0,e):
plt.loglog(psdfreq0, 10*vars()['psddata'+str(x)], label=vars()['label'+str(x)])
plt.legend()
plt.show()

Attachment 1: PSD_Comparison.png
6316   Fri Feb 24 18:59:04 2012 JenneUpdateComputersPyNDS and a Plot

 Quote: Power Spectral Density plot using PyNDS, comparing 5 fast data channels for ETMX.

Is there any stuff to install, etc?  Y'know, for those of use who don't really know how to use computers and stuff....

6341   Wed Feb 29 17:32:11 2012 MikeUpdateComputersPyNDS and a Plot

Quote:

 Quote: Power Spectral Density plot using PyNDS, comparing 5 fast data channels for ETMX.

Is there any stuff to install, etc?  Y'know, for those of use who don't really know how to use computers and stuff....

No new stuff for these computers.  Everything should be installed already.

4157   Fri Jan 14 17:13:39 2011 josephbUpdateCamerasPylon driver for Basler Cameras installed on Megatron

After getting some help from the Basler technical support, I was directed to the following ftp link:

ftp://Pylon4Linux-ro:h50UZgkl@ftp.baslerweb.com

I went to the pylon 2.1.0 directory and downloaded the pylon-2.1.0-1748-bininst-64.tar.bz2 file.  Inside of this tar file was another one called pylon-bininst-64.tar.bz2 (along with some other sample programs). I ran tar -jxf on pylon-bininst-64.tar.bz2 and placed the results into the /opt/pylon directory.  It produced a directory of includes, libraries and binaries there.

After playing around with the make files for several sample programs they provided, I finally have been able to compile  them.  At several places I had to have the make files point to /opt/pylon/lib64 rather than /opt/pylon/lib.  I'll be testing the camera with these programs on Monday.  I'd also like to see if this particular distribution will work on Centos machines.  There's some comments in one of the INSTALL help files suggesting packages needed for an install on Fedora 9, which may mean its possible to get this version working on the Centos machines.

12937   Mon Apr 10 16:00:26 2017 rebeccaUpdateCamerasPylon installation warning

When trying to install an older version of Pylon packaged for Debian that Joe B. had sent, it gave the warning that the package was of bad quality along with the details below.

Is it safe to ignore the warning? Or should I hold off on the installation?

Use of uninitialized value \$ENV{"HOME"} in concatenation (.) or string at /usr/bin/lintian line 108.
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12938   Mon Apr 10 18:42:09 2017 johannesUpdateCamerasPylon installation warning

It looks like we may not need to use this old Pylon version after all. Gautam and I looked into installing SnapPy with the makefile in scripts/GigE/SnapPy/ that he modified (removed the linkage to paths that don't exist in Pylon 5). Compiling took a while (~10 minutes) but eventually succeeded. The package was installed to /ligo/apps/linux-x86_64/camera/

GV 10pm April 10 2017: We didn't actually try executing an image capture or change some settings using the python utilities, that remains to be done..

10209   Wed Jul 16 01:18:02 2014 ranaSummaryLSCPython Wavelet peak finding for dramatic ALS - Red Resonance finding speedup

New script called scripts/ALS/findRedResonance.py finds the IR resonance in less than 20 seconds.

1. Do a ~2 FSR scan of the arm over 10 seconds using the Phase Tracker servo offset ramp. (dt = 10 s)
2. Load the frame data for the TR_OUT and the Phase Tracker phase. (dt = 2 s)
3. Use Python (modern) SciPy to find all peaks with moderate SNR (dt = 3 s)
4. Take the top 3 peaks (all presumably TEM00) and choose the one closest to zero and go there.

The above is the gist of what goes on, but there were several issues to overcome to get the code to run.

1. None of our workstations have a modern enough Python distro to run either the ipython notebooks or the new SciPy with wavelets, so I installed Anaconda Python in the controls home directory.
2. In order to get the peak finder function to work well I gave it a range of peak widths to look for. If we change the speed of the ALS scan by more than 3x, we probably have to change the width array in the function.
3. I've used the find_peaks_cwt function in SciPy. This uses a Ricker ('Mexican Hat') wavelet to find peaks by doing multi-res transforms and looking for ridges in the wavelet space (I think)
4. To make the code run fast, I downsample from 16 kHz to 1 kHz right at the top. Would be better if we had downsampling in v2 of the getData function.

Attachment 1: findRedResonance.pdf
10211   Wed Jul 16 01:35:16 2014 KojiSummaryLSCPython Wavelet peak finding for dramatic ALS - Red Resonance finding speedup

From the last plot:

- Subtracting the offset of 0.0095, the modulation depth were estimated to be 0.20 for 11MHz, 0.25 for 55MHz

- Carrier TEM00 1.0, 1st order 0.01, 2nd order 0.05, 3rd order 0.002, 4th order 0.004

==> mode matching ~93%, dominat higher order is the 2nd order (5%).

Eric: now we have the number for the mode matching. How much did the cavity round-trip loss be using this number?

1075   Thu Oct 23 18:45:18 2008 AlbertoOmnistructureComputer Scripts / ProgramsPython code for GPIB devices developed for the Absl length experiment
I wrote two Python scripts for my measurement that can be also used/imitated by others: sweepfrequency. py and HP8590.py. The first is is the one that we run by a Python interpreter (just typing "python <name script> <parameters>"from the terminal). It manages the parameters that we have to pass it for the measurement and calls the second one, HP8590.py which actually does most of the job.

Here what it does. It scans the frequency of the Marconi and, for each step, searches the highest peak in the Spectrum Analyzer (which is centered 50 KHz around the frequency of the Marconi). It then associates the amplitude of the peak to the frequency of the Marconi and write the two number in two columns of a file.
The file name, the GPIB-to/LAN interface IP address, the frequency range, the frequency step amplitude and the number of measures we want it to average for each step, are all set by the parameters when we call sweepfrequency.py.
More details are in the help of the function or just looking at the header of the code.

I guess that one can perform other similar measurement just with little changes in the code so I think it could turn out useful to anyone else.
Attachment 1: HP8590.py
# This function provides the measuremeent of the peak amplitude on the spectrum analyzer
# HP8590 analyzer while sweeping the excitation frequency on the function generator.
#
# Alberto Stochino 2008

import re
import sys
import math
from optparse import OptionParser
from socket import *

... 55 more lines ...
Attachment 2: sweepfrequency.py
## sweepfrequency.py [-f filename] [-i ip_address] [-a startFreq] [-z endFreq] [-s stepFreq] [-m numAvg]
#
## This script sweeps the frequency of a Marconi local oscillator, within the range
## delimited by startFreq and endFreq, with a step set by stepFreq. An arbitary
## signal is monitored on a HP8590 spectrum analyzer and the scripts records the
## amplitude of the spectrum at the frequency injected by the Marconi at the moment.

## The GPIB address of the Marconi is assumed to be 17, that of the HP Spectrum Analyzer to be 18

## Alberto Stochino, October 2008

... 51 more lines ...
15021   Thu Nov 7 17:55:37 2019 shrutiUpdateComputer Scripts / ProgramsPython packages on donatella

Today I realized that pip and other python2,3 packages were installed in the conda base environment, so after running

conda activate

I could run the python-GPIB scripts to interface with the Agilent.

Although, I did have to add a python2 kernel to jupyter/ipython, which I did in a separate conda environment:

conda create -n ipykernel_py2 python=2 ipykernel
source activate ipykernel_py2
python -m ipykernel install --user
 Quote: I've installed pyepics on Donatella running sudo yum install pyepics Pip and ipython did not seem to be installed yet.

15055   Wed Nov 27 18:51:22 2019 Gavin WallaceUpdateIMCQ Measurement of Test Masses

[Yehonathan, Gavin]

As the resonant modes of the 40m TMs are at high frequencies (starting at 28.8 kHz) we started background checks to understand if we would be able to see resonant frequency excitations in the DCPD output. We used the SR785 in the Q_OUT_DEMODULATOR port of the INPUT_MODE_CLEANER to measure around this frequency. Currently we could not see any natural excitation about the noise floor indicating it may not be possible to see such a small excitation. In any case we are conducting additional measurements in the I_MON port of 1Y2_POY11 to understand if this is a certainty.

15065   Tue Dec 3 14:52:13 2019 ranaUpdateIMCQ Measurement of Test Masses

 Quote: [Yehonathan, Gavin]
1. Lock IMC
2. Lock one of the arms (only) using the IR PDH signal feeding back to an ETM.
3. Excite the ITM using the SR785 near 28.8 kHz
4. Look for the resulting peak using the SR785 spectra of the POX or POY error signal from the demod board
5. Based on the calibrated noise level of the POX/POY, estimate what the SNR will be of the internal mode peak.
15076   Thu Dec 5 08:44:44 2019 GavinUpdateLoss MeasurementQ Measurements of Test Masses

[Yehonathan, Gavin]

Measuring POX11_Q_MON and injecting a signal into the ITMX_UL_IN port a signal could not be seen on the function generator. After debugging the source of the issue was two fold:

• By using the quadrant drives for coils (UL, UR etc) a signal has to pass through a switch before reaching the driver. To resolve this the signal input was switched to POS_IN (driving the entire coil at once rather than in quadrants) which has no switch to bypass.
• The averaging on the Stanford SR785 was set too low. By increasing the averages from 10 to 25 the signal became more visible.

Unrelated to these issues the signal input was switched to POY11_Q_MON and ITMY_POS_IN as part of the debugging process. The function generator used was switched from the Stanford to the Siglant SDG 1032X.

An unrelated issue but note worthy was the Lenovo 40m laptop used to measure the IFO state (locked or unlocked) ran out of battery in a very short timespan.

To gauge where the resonance of the test masses are FEA model of a simple 40m test mass was computed to give an esitimate at what frequency the eigenmodes exist. For the first two modes the model gave resonances at 20.366 kHz (butterfly mode) and 28.820 kHz (drumhead mode). Then by measuring with an acquisition time of 1 s at they frequencies on the SR785 and injecting broad band white noise with a mean of 0 V and a stdev of 2 V, small peaks were seen above the noise at 20.260 kHz and 28.846 kHz. By then injecting a sine wave at those frequencies with 9 Vpp, the peak became clearly visible above the noise floor.

The last step is to measure the natural decay of these modes when the excitation is turned off. It is difficult to tell currently if these are indeed eigenmodes or just large cavity injections with an associated stabilisation time (what could appear as a ringdown decay). More investigation is required.

Attachment 1: 20191205_132158.jpg
3303   Tue Jul 27 23:46:45 2010 JenneUpdateSUSQ measurements of 2 TTs

[Koji, Jenne]

We took measurements of the Q of all the modes that we could think of for TT#4, and then repeated several of the same measurements for TT#2.  We noticed that when we took off the backplane and then replaced it on TT#4, the pitch pointing had changed, so we had to repeat the balancing procedure by slightly shifting the position of the wire clamps relative to the mirror holder. No fun. We decided to quit removing the backplanes.

The main conclusion of this evening's measurements of TT#4 is that everything looks very close to the design ideas.  Good work team!

TT#4:

'Free Swinging' values (just for interest)

Vert, no damping:   Q = 31.4

Pitch, no damping (ECD backplane removed): Q = ~700

Yaw, no ECDs: Q = ~900

Pos, no ECDs (no measurement) - we had already put the backplane back on, and didn't want to take it off again.

Damped Values:

Vert, with damping: Q = 14.3

Pitch, with ECDs: overdamped, so Q < 1/2

Yaw, with ECDs: Q = 2.3

Pos, with ECDs: Q = 1.4

Side, with ECDs: Q = 1.9

We also measured the resonant frequency of each of the ECDs for this TT (since we had the backplane removed anyway...)

ECD UL: 10.05Hz

ECD UR: 10.15Hz

ECD LL: 10.21Hz

ECD LR: 10.21Hz

TT#2:

Yaw, with ECDs: Q = 7.0

Pitch, with ECDs: overdamped, so Q < 1/2

Vert: Problematic.  No damping, f = 25.9Hz, Q = 36.  With rubber dampers, f = 20.0Hz, Q = 42.   Yes, you read that right.  The frequency is lower, and the Q is higher *with* the damping.  Perhaps our brains are fried.  Perhaps we've discovered new, inconsistent physics (awfully unlikely....). We'll revisit this again tomorrow to figure out what mistake we're making.

3710   Thu Oct 14 00:04:46 2010 yutaUpdateSUSQ-value adjustment for MC dampings

Background:
We need MC to be locked soon, so MC suspensions should be damped well(Q~5).

What I did:
1. Set the correct filters and turn all the damping servo on.

2. Kick the optics by adding some offset into the control loop.

3. Measure the Q-value of the ringdown with my eye.

4. If Q-value seems to be around 5, go to step #5. If not, change the filter gain and go to step #2.

5. Done! Do step #1-4 for all MCs.

All parameters I used for the servo are automatically saved here;
/cvs/cds/caltech/burt/autoburt/snapshots/2010/Oct/13/20:07/c1mcs.epics

Result:
Q-values of the damping servo for all MCs are set to around 5.
Attached is the ringdown of MC2 for example.
As you can see, my eye was very rough......

Next work:
- Make a script that does steps #2-5 automatically.
I need pyNDS module installed to get data using Python.
I already wrote the rest of the script.
We'll have Leo help us install pyNDS tomorrow.

Attachment 1: MC2ringdown.png
15687   Mon Nov 23 23:27:43 2020 KojiSummaryASCQ3000 characterization

Last week and this week I've been working on the characterization of the Q3000 QPDs. The QPDs were named 81, 82, 83, and 94.

• Dark current [OMC LAB ELOG 402]: All the segments looked similar and acceptable except for the seg1 of #82. It has a smaller reverse breakdown voltage (~6V) but even this is an acceptable level.
• Impedance [OMC LAB ELOG 403]: All the segments showed a ~300pF junction capacitance with no reverse bias. This looks quite normal.
• Dark noise [OMC LAB ELOG 404]: All the segments showed ~5pA/rtHz dark noise above 1Hz.

My recommendation is to use #81 and #84 as they have similar dark current characteristics between the segments. But basically, all the QPDs look fine.

The actual junction capacitance and the RF dark noise should be characterized by the actual WFS head circuit.

The QPD packages were labeled and returned to Gautam to be implemented in the WFS heads.

gautam: S/N #84 was installed as the AS WFS QPD. The remaining 3 are stored in the clean cabinet at EX (where the rest of the RF photodiodes are).

8381   Mon Apr 1 16:13:50 2013 ChloeUpdate QPD

Because we would like to get started on testing mount vibrations as soon as possible, I've been trying to get one of the other QPDs we found to work with the summing/subtracting circuit on a breadboard. I've been using a power supply that I think Jamie built 15 years ago... which seems to be broken as of today, since I no longer read any signal from it with an oscilloscope.

I tried using a different power supply, but I still can't read any change in signal with the QPD for any of the quadrants when using a laser pointer to shine light on it. I'll be working with Eric on this later this week. In the meantime, I'll try and come up with a shopping list for the nicer QPD circuit that'll be a longer term side project.

8511   Tue Apr 30 12:25:23 2013 ChloeUpdate QPD

Annalisa and I met yesterday and fixed the voltage regulator on the breadboard so the QPD circuit is working. We will meet with Eric on Thursday to determine the course of action with measurements.

10997   Tue Feb 10 18:37:17 2015 ericqUpdateASCQPD ASC ready to go

I've remeasured the QPD ASC sensing coefficients, and figured out what I did weird with the actuation coefficients. I've rearranged the controller filters to be able to turn on the boost in a triggered way, and written Up/Down scripts that I've tested numerous times, and Jenne has used as well; they are exposed on the ASC screen.

All four loops (2 arms * pit,yaw), have their gains set for 8Hz UGF, and have 60 degrees of phase margin. The loop shape is the same as the previous ELOG post. Here is the current on/off performance. The PDH signals (not shown, but in attached xml) show no extra noise, and the low frequency RIN goes down a bit, whic is good. The oplevs error signals are a bit noisier, but I suppose that's unavoidable. The Y-arm performs a bit better than the X-arm.

The up/down scripts don't touch the filters' trigger settings at all, just handles switching the input and output and clearing history. FM1 contains the boost which is intended to have a longer trigger delay than the filters themselves.

Attachment 1: Feb10_loops_offOn.png
Attachment 2: Feb10_newLoops_offOn.xml.zip
10920   Mon Jan 19 18:27:16 2015 ericqUpdateASCQPD ASC saga continues.

# Herein, I will try to paint a more thorough picture of this whole QPD ASC mess.

## Motivation for QPD ASC loops:

• We would like to use the QPDs as a DC arm pointing reference during locking attempts, or over multiple days, if possible.
• It would be nice if the QPDs could complement the oplevs to reduce angular motion of the cavity.
• We must not make the single arm longnitudinal noise or RIN worse, because anything observable in the single arm case will be catastrophic at full sensitivity

## Actuation design:

As mentioned in a previous ELOG, in single arm lock, I measured the QPD response with respect to the calibrated oplev signals. They were:

YARM ETMY: QPD PIT / OPLEV PIT =   22.0 count/urad       QPD YAW / OPLEV YAW =   17.1 count/urad ITMY: QPD PIT / OPLEV PIT =   -6.0 count/urad       QPD YAW / OPLEV YAW =    5.9 count/urad
XARM ETMX: QPD PIT / OPLEV PIT = 16.6 count/urad       QPD YAW / OPLEV YAW = -9.3 count/urad ITMX: QPD PIT / OPLEV PIT =  4.0 count/urad       QPD YAW / OPLEV YAW = -6.0 count/urad

For reference, one microradian of either ITM or ETM motion produces about 60um of ETM beam spot displacement, compared to the spot size of ~5mm.

However, given the lenses on the end tables that are used for green mode matching, that the IR transmitted beam also passes through, the QPDs are not directly imaging the ETM spot position; if they were, they would have equal sensitivity to ITM and ETM motion due to our flat/curved arm geometry.

From this data, I calculated the actuation coefficients for each DoF as $A_{ETM} = \frac{d_{ETM}}{\sqrt {d_{ETM}^2 + d_{ITM}^2}}$, and similarly for the ITMs, where the d's come from the table above. However, it occurs to me that maybe this isn't the way to go... I'll mention this later.

## Loop design:

Up until now, at every turn, I had not properly been thinking about how the oplev loop plays into all of this. I went to the foton filters, and grabbed the loop and plant models for the ETMY oplev, and constructed the closed loop gain, 1/1+G, and the modified plant, P/1+G, which is what the ASC loop sees as its plant.

Here, the purple trace explains all of the features I was confused about earlier.

With this in hand, I set up to design a loop to satisfy our motivations.

• Bounce/roll mode notches to avoid exciting them
• 1/f UGF crossing at a few Hz, limited by the gain margin at ~10Hz, which is where the phase will hit 180, due to the notches
• 4th order Elliptic lowpass at 100, to avoid contaminating the longnitudinal signals
• 1/f^2 at low frequencies for DC gain

To do this, I inverted the oplev closed loop plant pole around 4Hz to smooth the whole thing out. Here's a comparison of the measured OLG with what I modelled.

There's a little bit of phase discrepency around 10Hz, but I think it looks about right overall.

## Evaluation:

So, here's the part that counts: How does this actually perform? I took spectra of the QPD error signals, the relevant OpLev signals as out of loop sensors, the PDH error signal and transmitted RIN while single arm locked, with this loop off, and on for all 4 DoFs simultaneously.

Verdict:

• In-loop signals get small, unsurprisingly.
• Cavity signals unchanged.
• ITM oplev signals are unchanged (and not plotted, to not clutter the plots (This isn't surprising since the loops mostly actuate on the ETMs).
• ETM oplev signals get smaller around the 3Hz peak, but are louder in other bands.

This is what makes me think I may need to revisit the actuation matrix. If I did it wrong, I am driving the "invisible" quadrant of the cavity angular DoFs, and this could be what is injecting noise into the oplevs.

## Conclusion:

In the end, I have a better understanding of what is going on, and I don't think we're quite there yet.

Attachment 1: oplevPlant.pdf
Attachment 2: loopDesignComparison.pdf
10921   Tue Jan 20 02:39:49 2015 ericqUpdateASCQPD ASC saga continues.

Although the QPD loops are less than ideal right now, I made changes to the ASC model to trigger the QPD loops on and off politely, depending on TRX and TRY. The settings are exposed on the ASC screen. However, I have not yet exposed the FM triggering that I also set up to make sure the integrator doesn't misbehave if the arm loses lock. We probably don't want to trigger them on at anything lower than arm powers of about 1.0.

I've tested the triggering by randomly turning LSC mode on and off, and making sure that the optics don't recieve much of a kick as the QPD loops engage a few seconds after the LSC boosts do, or when lock is lost. This works as long as there isn't much of a DC offset befire the loops are engaged. (Under 20 counts or so is fine)

As a side note, I was going to use the TRIG_SIG signals sent via the LSC model via SHMEM blocks for the ASC triggering, but oddly, the data streams that made it over were actually the MICH and SRCL TRIG_SIGs, instead of XARM and YARM as labelled. I double checked the simulink diagrams; everything seemed fine to me. In any case, ASS was already recieving TRX and TRY directly via RFM, so I just piped those over to the ASC block. This way is probably better anyways, because it directly references the arm powers, instead of the less obvious LSC triggering matrix.

8233   Tue Mar 5 17:23:06 2013 ChloeUpdate QPD Adding/Subtracting Circuit

Today I finished building the adding/subtracting circuit for the QPD and tested that the QPD could see a laser moving across its visual field for both pitch and yaw. It didn't seem to behave weirdly (saturate) at the edges, but I need to test this more carefully to be sure.

However, this circuit uses many op amps, which will cause problems for building the actual circuit to fit into the QPD box. I am trying to figure out how to do this with fewer op amps (both with a quad op amp for amplifying the signals from the QPD and by summing/subtracting the signals with a single op amp instead of 3).

I finally got around to asking Steve to order more breadboards! Trying to determine what would be a good QPD to order for the final circuit, since we do not have any unmounted QPDs that aren't ancient. I'll read up on things I don't know enough about (namely op amps).

8873   Thu Jul 18 19:09:08 2013 gautamConfigurationendtable upgradeQPD Calibration for PZT Calibration

Summary

I have been working on setting up a QPD which can eventually be used to calibrate the PZT, and also orient the PZT in the mount such that the pitch and yaw axes roughly coincide with the vertical and horizontal.

The calibration constants have been determined to be:

X-axis: -3.69 V/mm

Y-axis: -3.70V/mm

Methodology:

I initially tried using the QPD setup left behind by Chloe near MC2, but this turned out to be dysfunctional. On opening out the QPD, I found that the internal circuitry had some issues (shorts in the wrong places etc.) Fortunately, Steve was able to hand me another working unit. For future reference, there are a bunch of old QPDs which I assume are functional in the cabinet marked 'Old PDs' along the Y-arm.

I then made a circuit with which to read out the X and Y coordinates from the QPD. This consists of 4 buffer amplifiers (one for each quadrant), and 3 summing amplifiers (outputs are A+B+C+D = sum, B+C-A-D = Y-coordinate, and A+B-C-D = X-coordinate) that take the appropriate linear combinations of the 4 quadrants to output a voltage that may be calibrated against displacement of the QPD.

The output from the QPD is via a sub-D connector on the side of the pomona box enclosing the PD and the circuitry, with 7 pins- 3 for power lines, and 4 for the 4 quadrants of the QPD. It was a little tricky to figure the pin-out for this connector, as there was no way to use continuity checking to map the pins to quadrants. Therefore, I used a laser pointer, and some trial and error (i.e. shine the light on a given quadrant, and check the sign of the X and Y voltages on an oscilloscope) to map the pin outs. Steve tells me that these QPDs were made long before colour code standardisation, but I note here the pin outs in any case for future reference (the quadrant orientations are w.r.t the QPD held with all the circuitry above it, with the active surface facing me):

Red= +Vcc

Black= -Vcc

Green = GND

Blue = Upper Left Quadrant

White = Upper Right Quadrant

Purple = Lower Left Quadrant

Grey = Lower Right Quadrant

Chloe had noted that there was some issue with the voltage regulators on her circuit (overheating) but I suspect this may have been due to the faulty internal circuitry. Also, she had used 12 V regulators. I checked the datasheet of the QPD, Op-Amp LF347 (inside the pomona box) and the OP27s on my circuit, and found that they all had absolute maximum ratings above 18V, so I used 15V voltage regulators. The overheating problem was not a problem anymore.

I then proceeded to arrange a set up for the calibration (initially on the optical bench next to MC2, but now relocated to the SP table, and a cart adjacent to it). It consists of the following:

• He-Ne laser source
• Y2 2-inch mirror (AR and HR coated for 532nm) glued onto the PZT and mounted on a machined Newport U100P  - see this elog for details.
• QPD mounted on a translational stage whose micrometers are calibrated in tenths of an inch (in the plots I have scaled this to mm)
• A neutral density filter (ND = 2.0) which I added so that the QPD amplifier output did not saturate. I considered using a lens as well to reduce the spot size on the QPD but found that after adding the ND filter, it was reasonably small.
• High-voltage power supply (on cart)
• Two SR power supplies (for the PZT driver board and my QPD amplifier
• SR function generator
• Laser power source
• Two oscilloscopes
• Breadboard holding my QPD amplifier circuit

Having set everything up and having done the coarse alignment using the mirror mount, I proceeded to calibrate the X and Y axes of the QPD using the translational stage. The steps I followed were:

• Centre spot on QPD using coarse adjustment on the mirror mount: I gauged this by monitoring the X and Y voltage outputs on an oscilloscope, and adjusted things till both these went to zero.
• Used the tilt knob on the translational stage to roughly decouple the X and Y motion of the QPD.
• Kept Y-coordinate fixed, took the X-coordinate to close to its maximum value (I gauged this by checking where the voltage stopped changing appreciably for changes in the QPD position.
• Using this as a starting point, I moved the QPD through its X range, noting voltage output of the X-coordinate (and also the Y) on an oscilloscope.
• Repeated the procedure for the Y-coordinate.
• Analysis follows largely what was done in these elogs. I am attaching the script I used to fit an error function to the datapoints, this is something MATLAB should seriously include in cftool (note that it is VERY sensitive to the initial guess. I had to do quite a bit of guessing).

The plots are attached, from which the calibration values cited above are deduced. The linear fits for the orthogonal axis were done using cftool. There is some residual coupling between the X and Y motions of the QPD, but I think this os okay my purposes.

My next step would be to first tweak the orientation of the PZT in the mount while applying a small excitation to it in order to decouple the pitch and yaw motion as best as possible. Once this is done, I can go ahead and calibrate the angular motion of the PZT in mrad/V.

X-Axis                                                                                                                                Y-axis

Attachment 3: Error_Function_Fitting.zip
8111   Tue Feb 19 17:14:56 2013 ChloeUpdate QPD Circuit

I finished working out the circuit and figured out where the broken connections were. This is diagrammed in my notebook (will draw up more nicely and include in future elog post). Within the QPD circuitry, it seems like there are already opamps which regulate the circuit. I need to discuss the final diagram further with Eric.

I rewired the circuit inside the QPD box, which took awhile because it was difficult to solder the wires to such small locations without having multiple wires touch. This is completed, and on Friday I will begin to make the circuit to add/subtract signals to give pitch and yaw.

8173   Tue Feb 26 17:36:28 2013 ChloeUpdate QPD Circuit

I corrected the circuit diagram I constructed last time - it would read 0 output most of the time because I made a mistake with the op amps. This will be attached once I discuss it with Eric.

I searched the 40m lab and ended up finding a breadboard in the Bridge lab. I then spent awhile trying to remove the QPD from the circuit board it was on, which was difficult since it had 6 pins. After that, I soldered wires to the QPD legs and began constructing the circuit on the breadboard. I also spent time showing Annalisa the setup and explaining my project.

On Friday I will try and reconstruct all of the circuitry from before for the QPD.

8346   Mon Mar 25 23:27:26 2013 ChloeUpdate QPD Circuit

In order to test the mount vibrations, I will likely try and make a different circuit work (with the summing/subtracting on an external breadboard) and designing an optimal circuit will be a side project. This is the circuit with the power supply Rana came up with, and the design I had in mind for the rest of the circuit. In my free time, I will try to figure out what parts to get that reduce noise and slowly work on building this, since it would be useful to have in the lab.

https://www.circuitlab.com/circuit/7sx995/qpd-circuit/#postsave_access_control_settings

8295   Thu Mar 14 16:56:16 2013 ChloeUpdate QPD Circuit Design

I have sketched out the circuit design for the QPD. However, it seems like even when using a different opamp configuration, which I talked to Eric about on Friday, space will be a problem. It may be possible to squeeze everything onto a single circuit board to fit in the QPD box but what I think is more likely is that I will need to have 2 separate circuit boards both mounted within the box, one which integrates the signal from the QPD and the other which adds/subtracts (this involves many resistors which will take up a lot of space). I will continue to think about the best design for this.

I will try to have the circuit built in the next week or so, which may be difficult since I just started finals which will take most of my time. I spent most of this week writing up an ECDL proposal for a SURF with Tara. I'll make up for whatever work I miss since I'll be here for my spring break and doing little besides working in lab.

15039   Wed Nov 20 17:20:24 2019 YehonathanUpdateLSCQPD Investigation

{Gautam, Yehonathan}

In search of the source of discrepancy between the QPD readings in the X and Y arms, we look into the schematics of the QPD amplifier - DCC #D990272.

We find that there are 4 gain switches with the following gain characteristics (The 40m QPD whitening board has an additional gain of 4.5):

S4 S3 S2 S1 V/A
0 0 0 0 2e4
0 0 0 1 2e5
0 0 1 0 4e4
0 0 1 1 4e5
0 1 0 0 1e5
0 1 0 1 1e6
0 1 1 0 2e5
0 1 1 1 2e6
1     0 5e2
1     1 5e3

Switch 4 bypasses the amps controlled by switch 2 and 3 when it is set to 1 so they don't matter in this state.

Note that according to elog-13965 the switches are controlled through the QPD whitening board by a XT1111a Acromag whose normal state is 1.

Also, according to the QPD amplifier schematics, the resistor on the transimpedance, controlled by switch 1, is 25kOhm. However, according to the EPICS it is actually 5kOhm. We verify this by shining the QPD with uniform light from a flashlight and switching switch1 on and off while measuring the voltages of the different segments. The schematics should be updated on the DCC.

Surprisingly, QPDX switches where 0,0,0,0 while QPDY switches where 1,0,0,1. This explains the difference in their responses.

We check by shining a laser pointer with a known power on the different segments of QPDX that we get the expected number of counts on the ADC and that the response of the different segments is equal.

gautam edits:

1. Lest there be confusion, the states of the switches in the (S1, S2, S3, S4) order are (0,0,0,0) for QPDX and (0,1,0,1) for QPDY.
2. The Acromag XT1111 is a sinking BIO unit - so when the EPICS channel is zero, the output impedance is low and the DUT (i.e. MAX333) is shorted to ground. So, the state of the MAX333 shown on the schematics corresponds to EPICS logic level 1, and the switched state corresponds to logic level 0.
3. For the laser pointer test, we used a red laser pointer. Using a power meter, we measured ~100uW of 632nm power. However, we think this particular laser pointer had failing batteries or something because the spot looked sometimes brighter/dimmer to the eye. Anyways, we saw ~10,000 ADC counts when illuminating a single segment (with the QPD gain switches at the 0,0,0,0 setting, before we changed anything). We expect 100uW * 0.4 A/W * 500 V/A * 10 * 40 * 4.5 * 3267.8 cts/V = ~12000 cts. So everything seems to check out. We changed the gain to the 5kohm setting and bypassed the subsequent gain stages, and saw the expected response too. The segments were only balanced to ~10%, but presumably this can be adjusted by tweaking digital gains.
15040   Wed Nov 20 17:52:00 2019 gautamUpdateLSCQPD MEDM screen update

Koji and I had noticed that there was some discrepancy between the switchable gain stages of the EX and EY QPDs. Sadly, there was no indication that these switches even exist on the QPD MEDM screen. Yehonathan and I rectified this today. Both EX and EY Transmon QPDs now have some extra info (see Attachment #1). We physically verified the indicated quadrant mapping for the EX QPD (see previous elog in this thread for the details), and I edited the screen accordingly. EY QPD still has to be checked. Note also that there is an ND=0.4 + ND=0.2 filter and some kind of 1064nm light filter installed in series on the EX QPD. The ND filters have a net transmission T~25%.

After making the EX and EY QPDs have the same switchable gain settings (I also reset the trans normalization gains), the angular motion witnessed is much more consistent between the two now - see Attachment #2. The high-frequency noise of the sum channel is somewhat higher for EX than EY - maybe the ND filters are different on the two ends?

Note that there was an extra factor of 40 gain on the EX QPD relative to EY during the lock yesterday. So really, the signals were probably just getting saturated. Now that the gains are consistent between the ends, it'll be interesting to see how balanced the buildup of the two arms is. There still remains the problem that the MICH loop was too unstable, which probably led to to excess arm power fluctuations.

There is a mark on the QPD surface that is probably dirt (since we never have such high power transmitted through the ETM to damage the QPD). I'll try cleaning it up at the next opportunity.

Attachment 1: newLookQPD.png
Attachment 2: TRX_TRY_comparison.pdf
Attachment 3: IMG_8186.JPG
3244   Mon Jul 19 14:14:03 2010 nancy, kojiUpdateIOOQPD Response Transfer Function

Friday night myself and Koji measured the Transfer function of the QPD circuit at MC2 side using a chopper . Following was our procedure :

We connected some wires at the input and output of the filter circuit to one of the segment of teh QPD. - seg 1.

A laser light was shined on to the QPD, it was pulsed using a chopper. The frequency of rotation of the chopper was varied.

These wires were then fed to the spectum analyser , and a transfer funstion was observed, It was nearly a low pass filter

The chopper frequency was then made variable by giving the chopper a signal from the spectrum analyser. This signal just swiped a large range of the rpm of the chopper.

Now the input signal looked like a sine wave of varying frequency. the transfer function looked like a perfect LPF, with a small SNR.

Attaching the plot of the TF in the next e-log (this one is on windows and can't access /cvs/cds)

3245   Mon Jul 19 14:16:01 2010 nancy, kojiUpdateIOOQPD Response Transfer Function

 Quote: Friday night myself and Koji measured the Transfer function of the QPD circuit at MC2 side using a chopper . Following was our procedure :   We connected some wires at the input and output of teh filter circuit to one of the segment of teh QPD. - seg 2. A laser light was shined on to  the QPD, it was pulsed using a chopper. The frequency of rotation of teh chopper was varied. These wires were then fed to the spectum analyser , and a transfer funstion was observed, It was nearly a low pass filter The chopper frequency was then made variable by giving the chopper a signal from teh spectrum analyser. This signal just swiped a large range of the rpm of the chopper. Now the input signal looked like a sine wave of varying frequency. the transfer functino looked like a perfect LPF, with a small SNR. Attaching the plot of the TF in the next e-log (this one is on windows and cant access /cvs/cds)

8403   Wed Apr 3 16:03:59 2013 ChloeUpdate QPD Voltage Regulators

The voltage regulator on the QPD breadboard seems to be having problems... yesterday Eric helped me debug my circuit and discovered that the +12V regulator was overheating, so we replaced it. Today, I found that the -12V regulator was also doing the same thing, so I replaced it. However, it's still overheating. We checked all of the setup for the power regulators yesterday, so I'm not sure what's wrong.

I've also noticed that not all the connections on the breadboard that I've been using seem to work - I may search for a new breadboard in this case. Need to check I'm not doing something stupid with that.

8406   Wed Apr 3 18:27:03 2013 KojiUpdate QPD Voltage Regulators

Breadboards may not be suitable for a reliable work. Why don't you switch to any protoboard and real soldering?

626   Wed Jul 2 18:30:01 2008 JohnUpdateIOOQPD alignment
I aligned the beams on the following QPDs

IP POS
IP ANG
MC TRANS
IOO POS
Attachment 1: IOO080702.png
Attachment 2: MC080702.png
14219   Sun Sep 30 20:14:51 2018 yukiConfigurationASCQPD calibration

[ Yuki, Gautam, Steve ]

Results:
I calibrated a QPD (D1600079, V1009) and made sure it performes well. The calibration constants are as follows:

X-Axis: 584 mV/mm
Y-Axis: 588 mV/mm

Details:
The calibration of QPD is needed to calibrate steeing PZT mirrors. It was measured by moving QPD on a translation stage. The QPD was connected to its amplifier (D1700110-v1) and +-18V was supplied from DC power supplier. The amplifier has three output ports; Pitch, Yaw, and Sum. I did the calibration as follows:

• Center beam spot on QPD using steering mirror, which was confirmed by monitored Pitch and Yaw signals that were around zero.
• Kept Y-axis micrometer fixed, moved X-axis micrometer and measured the outputs.
• Repeated the procedure for the Y-axis.

The results are attached. The main signal was fitted with error function and I drawed a slope at zero crossing point, which is calibration factor. I determined the linear range of the QPD to be when the output was in range -50V to 50V, then corresponding displacement range is about 0.2 mm width. Using this result, the PZT mirrors will be calibrated in linear range of the QPD tomorrow.

• Some X-Y coupling existed. When one axis micrometer was moved, a little signal of the other direction was also generated.
• As Gautam proposed in the previous study, there is some hysteresis. That process would bring some errors to this result.
• A scale of micrometer is expressed in INCH!
• The micrometer I used was made to have 1/2 inch range, but it didn't work well and the range of X-axis was much narrower.

Reference:
previous experiment by Gautam for X-arm: elog:40m/8873, elog:40m/8884

Attachment 1: QPDcalibrationXaxis.pdf
Attachment 2: QPDcalibrationYaxis.pdf
14221   Mon Oct 1 13:33:55 2018 yukiConfigurationASCQPD calibration
 Quote: I assume this QPD set is a D1600079/D1600273 combo. How much was the SUM output during the measurement? Also how much were the beam radii of this beam (from the error func fittings)? Then the calibration [V/m] is going to be the linear/inv-linear function of the incident power and the beam radus. You mean the linear range is +/-50mV (for a given beam), I guess.
• The SUM output was from -174 to -127 mV.
• The beam radii calculated from the error func fittings was 0.47 mm.
• Total optical path length measured by a ruler= 36 cm.
• Beam power measured at QPD was 2.96 mW. (There are some loss mechanism in the setup.)

Then the calibration factor of the QPD is

X axis: 584 * (POWER / 2.96mW) * (0.472mm /  RADIUS) [mV/mm]
Y axis: 588 * (POWER / 2.96mW) * (0.472mm /  RADIUS) [mV/mm].

Attachment 1: Pic_QPDcalibration.jpg
8139   Fri Feb 22 17:33:38 2013 ChloeUpdate QPD circuit diagram

Today I tested the circuitry within the QPD to make sure I had put it back together correctly. The output was able to detect when a laser pointer was shone on different quadrants of the QPD when hooked up to the oscilloscope, so fixing the QPD worked!

Following this, I spent awhile understanding what was going on with the circuit reading from the QPD. I concluded that the opamp on the QPD circuit acted as a low pass filter, with corner frequency of about 17 kHz, which serves our purposes (we are only interested in frequencies below 1 kHz). I diagrammed the circuit that I plan to build to give pitch and yaw (attached). It will be necessary to make small modifications to the circuitry already built (removing some resistors), which I have started on.

Next time, I will construct the circuit that adds/subtracts signals on a breadboard and test it with the QPD circuit that is already built.

Attachment 1: IMG_0377.JPG
8090   Fri Feb 15 17:11:13 2013 ChloeUpdate QPD circuit pictures

I took better pictures of the circuits of the QPD and spent a couple of hours with a multimeter trying to figure out how all the connections worked. I will continue to do so and analyze the circuits over the weekend to try to understand what is going on. I also have an old SURF report that Eric sent me that is similar to the design I was planning to use to sum the pitch and yaw signals. I will try and look at this over the weekend.

Attachment 1: IMG_0337.JPG
Attachment 2: IMG_0338.JPG
8067   Tue Feb 12 17:26:31 2013 ChloeUpdate QPD circuitry to test mount vibrations

I spent awhile today reading about op-amps and understanding what would be necessary to design a circuit which would directly give pitch and yaw of the QPD I am using. After getting an idea of what signals would be summed or subtracted, I opened up the QPD to take better pictures than last time (sorry, the pictures were blurry last time and I didn't realize). It turns out some of the connections have been broken inside the QPD, which would explain why we saw an unchanging signal in Ch2 on the oscilloscope yesterday when trying to test the laser setup.

I found a couple other QPDs, which I will be using to help understand the circuit (and what is going on). I will be trying to use the same QPD box since it has banana cable and BNC cable adapters, which is helpful to have in the lab. Once I have concluded what the circuitry is like and designed electronics to add and subtract signals, I will build and mount all the circuits within the box (more sturdily than last time) so as to have a quality way of measuring the mount vibrations when I get there.

10174   Thu Jul 10 02:15:36 2014 JenneUpdateLSCQPD dark noise checkout

I have put beam dumps in front of both of the end transmission QPDs so that I could measure the dark noise.  They are still there.

I checked that the Yend QPD sliders and switches were doing things as I expected.  I couldn't do the Xend since c1auxex is still lost (elog 10165).  I'll post plots and actual information on this checkout, as well as my calculation of what this dark noise means in terms of meters for CARM when we're using 1/sqrt(trans) signals tomorrow morning.

10187   Fri Jul 11 20:05:34 2014 JenneUpdateLSCQPD dark noise checkout

## I put these things together to get a plot of transmission QPD noise vs. CARM offset, for a chosen set of analog settings.

Measurement of Yend transmission QPD dark noise

Since EricQ had already checked out the whitening filters (see elog 9637 and elog 9642), I didn't check on them.  I just left them (the analog whitening, and the digital antiwhitening filters) on.

First, I checked the noise vs. transimpedance gain. There are a few too many settings to put them all on one plot, so I have them sorted by the original transimpedance:  0.5 kOhms vs 5 kOhms.  It's a little tricky to see, but all of the spectra that begin with the 5k transimpedance have a little extra noise around 10 Hz, although I don't know why.  In the legend I have made note of what the settings were.  x1 x1 is my representation of the "inactive" setting.

I then looked at the noise with different whitening gain slider settings.  All but one of the traces are the 20 kOhm setting.

These .xml files are in /users/jenne/Arms/TransQPDnoise_July2014/

Calculation of inverse sqrt transmission sensitivity

I used Optickle to give me the power transmitted through the ETMs.  I first find the transmission in the FPMI case.  I use that to normalize the full PRFPMI transmission, so that the output units are the same as our C1:LSC-TR[x,y]_OUT units.

I take the square root of the transmitted power (sum of transmissions from each arm) at each CARM offset point, add 1e-3 as we do in the front end model to prevent divide-by-zero problems, and then take the inverse.

I find the slope by taking the difference in power between adjacent points, divided by the CARM offset difference between those points.

In this plot, I have taken the absolute value of the sensitivity, just for kicks.  I also display an arbitrarily scaled version of the log of the transmitted power, so that we can see that the highest sensitivity is at half the maximum power.

Calculate the QPD dark noise in terms of meters

Finally, I put it all together, and find the dark noise of the QPD in terms of meters.  Since the spectra were measured in units where the single-arm transmission is unity, the already match the units that I used to calculate the sqrtInv sensitivity.

I take the spectra of the QPD dark noise for the 20 kOhm case, and multiply it by the sensitivity calibration number at several different CARM offsets.  As we expect, the noise is the best at half-max transmission, where the sensitivity is maximal.

8618   Wed May 22 17:29:34 2013 JenneUpdateASCQPD for POP ASC tested

I fiddled around with the QPD that I'll use to replace Koji's temporary razor blade yaw sensor for detecting POP beam angular motion, and checked that it is working.

Using the Jenne Laser, I put beam onto the 4 different quadrants of the QPD, and saw that the Sum channel remained constant.

* I had the room lights off, since the PD elements are silicon.

* Beam size on the QPD as seen on an IR card was ~1mm diameter.

* With the beam on the QPD, I chose gain setting "G2" on the amplifier, since that was the only setting where neither the "current too high" nor the "current too low" LEDs were illuminated.  I didn't measure the power going to the PD, but the Jenne Laser puts out 1.2mW, and there's a 50/50 BS, so I was getting about 600uW.

* I turned off the "zero/cal" switch on the back of the box, since I don't know how to set the zero.  Since the X and Y channels are normalized by the Sum, you can't just block all light going to the PD and set the zero.  There isn't a big change in the output levels with the zero/cal switch off, so I think it should be fine.  (Previously, I set all 4 knobs - "zero" and "cal" for each X and Y - to approximately the center of their ranges.  Once you hit the end of the range, you can keep turning the knob, but something inside makes a clicking sound ~once per revolution, and the signal level stops changing (for the zero knobs). Much like centering a beam on a PD, I found each edge of the range for each knob, and set the knobs in the centers by counting the number of turns.  Anyhow, since I set the knobs to ~halfway, I think that explains why there isn't really a change whether the "zero/cal" switch is on or off.

* Using the steering mirror sending the beam to the QPD, I moved the beam around, and watched where I was going with an IR viewer.  I see that as I move from quad-to-quad, the X and Y channels respond as I expect.  If I only move the beam in X, I only see X response on a 'scope, and vice versa.

I can't do a real calibration until I get the QPD installed in place, so I can use the actual beam, but for now it looks like the QPD is responding nicely.  Since Annalisa and Manasa are using the Arms for the evening, I'll work on putting the QPD on the POX table tomorrow.

11056   Fri Feb 20 19:09:48 2015 ericqUpdateASCQPD frontend code unified

I have changed all of the oplevs and transmon QPDs to use the common ISC QPD library block, which differs mainly in its divide by zero protection.

c1scx.mdl and c1scy.mdl were directly changed for the transmon QPDs. The oplevs were done by changing the sus_single_control.mdl library part, which is used for all of the SOSs.

Then, because of the underscore introduced (i.e. OLPIT becomes OL_PIT because there is an OL block), I went on a sed safari to find and replace the new channel names into:

• The filter ini files
• various MEDM screens
• The optic misaligning scripts (which currently live in medm/MISC/ifoalign, and need to get moved to scripts/)
• A recent BURT snapshot, to restore all of the switches and settings easily.
• scripts/activateDQ.py, which is responsible for renaming OL_PIT_IN1_DQ to OPLEV_PERROR, etc.

I've fixed everything that occured to me, and the usual ways I'm used to interacting with the oplevs all seem to work at this time, but it's entirely possible I've overlooked something.

One important note is: because we are now using an effectively immutable QPD library block, the oplev urad conversion has to take place in the DoF matrix. The EPICS records C1:SUS-[OPTIC]_OL_[DOF]_CALIB still exist, but do not multiply the fast signals. Rather, the OL_MTRX elements are multiples of the CALIB value. I thought about making a new QPD_CALIBRATED part or something, but then we're right back to using custom code, which is what we're trying to avoid.

All of the oplev DoFs are stable, I checked a few loop TFs like ETMY pitch and PRM yaw, and they looked normal.

11057   Mon Feb 23 08:06:59 2015 ranaUpdateASCQPD frontend code unified

Might have to also get the OL screens that go with this new code to see, but the calibrations don't go into the matrix, but rather into the OLPIT/OLYAW filter banks which follow the division, but before the servo filter banks.

ELOG V3.1.3-