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  1790   Sat Jul 25 13:49:28 2009 KojiUpdateGeneralMultiply Resonant EOM Update

Quote:

After speaking with Rana and realizing that it would be better to use smaller inductances in the flying-component circuit (and after a lot of tinkering with the original), I rebuilt the circuit, removing all of the resistors (to simplify it) and making the necessary inductance and capacitance changes. A picture of the circuit is attached, as is a circuit diagram.

A plot of the measured and simulated transfer functions is also attached; the general shape matches between the two, and the resonant frequencies are roughly correct (they should be 11, 29.5, and 55 MHz). The gain at the 55 MHz peak is lower than the other two peaks (I'd like them all to be roughly the same). I currently have no idea what the impedance is doing, but I'm certain it is not 50 Ohms at the resonant peaks, because there are no resistors in the circuit to correct the impedance. Next, I'll have to add the resistors and see what happens.

Stephanie, 

This is a quite nice measurement. Much better than the previous one.

1) For further steps, I think now you need to connect the real EOM at the end in order to incorporate
the capacitance and the loss (=resistance) of the EOM. Then you have to measure the input impedance
of the circuit. You can measure the impedance of the device at Wilson house.
(I can come with you in order to consult with Rich, if you like)

Before that you may be able to do a preparatory measurement which can be less precise than the Wilson one,
but still useful. You can measure the transfer function of the voltage across the input of this circuit,
and can convert it to the impedance. The calibration will be needed by connecting a 50Ohm resister
on the network analyzer.

2) I wonder why the model transfer function (TF) has slow phase changes at the resonance.
Is there any implicit resistances took into account in the model?

If the circuit model is formed only by reactive devices (Cs and Ls), the whole circuit has no place to dissipate (= no loss).
This means that the impedance goes infinity and zero, at the resonance and the anti-resonance, respectively.
This leads a sharp flip of the phase at these resonances and anti-resonances.

The real circuit has small losses everywhere. So, the slow phase change is reasonable.

  1804   Wed Jul 29 12:00:49 2009 StephanieUpdateGeneralMultiply Resonant EOM Update

For the past couple of days I have been trying to understand and perform Koji's method for impedance measurement using the Agilent 4395A Network Analyzer (without the impedance testing kit). I have made some headway, but I don't completely understand what's going on; here's what I've done so far.

I have made several transfer function measurements using the attached physical setup (ImpedanceTestingPhysicalSetup.png), after calibrating the setup by placing a 50 Ohm resistor in the place of the Z in the diagram. The responses of the various impedances I've measured are shown in the attached plot (ImpResponses.png). However, I'm having trouble figuring out how to convert these responses to impedances, so I tried to derive the relationship between the measured transfer function and the impedance by simplifying the diagram Koji drew on the board for me (attached, ImpedanceTestingSetup.png) to the attached circuit diagram (ImpedanceTestingCktDiagram.png), and finding the expected value of VA/VR. For the circuit diagram shown, the equation should be VA/VR = 2Z/(50+Z). 50 Ohms is good to use for calibration because the expected value of the transfer function for this impedance is 1 (0 dB).

So I used this relationship to find the expected response for the various impedances, and I also calculated the impedance from the actual measured responses. I've attached a plot of the measured (red) and expected (black) response (top) and impedance (bottom) for a 1 nF capacitor (1nF.png). The expected and measured plots don't really match up very well; if I add extra inductance (7.6 nH, plots shown in blue), the two plots match up a little better, but still don't match very well. I suspect that the difference may come from the fact that for my analysis, I treated the power splitter as if it were a simple node, and I think that's probably not very accurate.

Anyway, the point of all this is to eventually measure the impedance of the circuit I created on Friday, but I don't think I can really do that until I understand what is going on a little better.

Attachment 1: ImpedanceTestingPhysicalSetup.png
ImpedanceTestingPhysicalSetup.png
Attachment 2: ImpResponses.png
ImpResponses.png
Attachment 3: ImpedanceTestingSetup.png
ImpedanceTestingSetup.png
Attachment 4: ImpedanceTestingCktDiagram.png
ImpedanceTestingCktDiagram.png
Attachment 5: 1nF.png
1nF.png
  1813   Thu Jul 30 19:55:23 2009 KojiUpdateGeneralMultiply Resonant EOM Update

Quote:

For the past couple of days I have been trying to understand and perform Koji's method for impedance measurement using the Agilent 4395A Network Analyzer (without the impedance testing kit). I have made some headway, but I don't completely understand what's going on; here's what I've done so far.

I have made several transfer function measurements using the attached physical setup (ImpedanceTestingPhysicalSetup.png), after calibrating the setup by placing a 50 Ohm resistor in the place of the Z in the diagram. The responses of the various impedances I've measured are shown in the attached plot (ImpResponses.png). However, I'm having trouble figuring out how to convert these responses to impedances, so I tried to derive the relationship between the measured transfer function and the impedance by simplifying the diagram Koji drew on the board for me (attached, ImpedanceTestingSetup.png) to the attached circuit diagram (ImpedanceTestingCktDiagram.png), and finding the expected value of VA/VR. For the circuit diagram shown, the equation should be VA/VR = 2Z/(50+Z). 50 Ohms is good to use for calibration because the expected value of the transfer function for this impedance is 1 (0 dB).

So I used this relationship to find the expected response for the various impedances, and I also calculated the impedance from the actual measured responses. I've attached a plot of the measured (red) and expected (black) response (top) and impedance (bottom) for a 1 nF capacitor (1nF.png). The expected and measured plots don't really match up very well; if I add extra inductance (7.6 nH, plots shown in blue), the two plots match up a little better, but still don't match very well. I suspect that the difference may come from the fact that for my analysis, I treated the power splitter as if it were a simple node, and I think that's probably not very accurate.

Anyway, the point of all this is to eventually measure the impedance of the circuit I created on Friday, but I don't think I can really do that until I understand what is going on a little better.

 I checked the setup and found RF reflection at the load was the cause of the unreasonable response in the impedance measurement.
So, I have put a total 22dB attenuation (10+6+6 dB) between the power splitter and the load to be measured. See the picture.
This kind of attenuators, called as PADs, is generally used in order to improve the impedance matching, sacrificing the signal amplitude at the load.

Then, It looks the measurements got reasonable up to 100MHz (at least) and |Z|<1kOhm.
For the measurements, I just followed the procedure that Stephanie described.
Stephanie has measured the impedance of her resonant circuit.


As a test of the method, I measured impedances of various discrete devices. i.e. 50Ohm, 10-1000pF Cap, Inductances, circuit opened.

a) 50Ohm (marine-blue) was calibrated to be recognized as 50Ohm.

b) The mica capacitances (orange 10pF, yellow 100pF, green 1000pF) appeared as the impedances f^-1 in the low freq region. It's nice.
At high frequency, the impedances deviate from f^-1, which could be caused by the lead inductance. (Self Resonance)
So 1000pF mica is not capacitance at 50MHz already.

c) Open BNC connector (Red) looks have something like 5pF. (i.e. 300Ohm at 100MHz)

d) I could not get good measurements with the inductors as I had 200nH (and some C of ~5pF) for a Pomona clip (blue).
This is just because of my laziness such that I avoid soldering the Ls to an RF connector!

Attachment 1: imepedance.png
imepedance.png
Attachment 2: impedance_meas.jpg
impedance_meas.jpg
  1815   Fri Jul 31 09:52:38 2009 StephanieUpdateGeneralMultiply Resonant EOM Update

I was able to make an impedance measurement of the flying-component circuit using Koji's method for impedance measurement. I first measured the impedance of the circuit with a 10 pF capacitor in the place of the EOM (as shown in the circuit diagram). This impedance plot is attached. I then added resistance to adjust the impedance slightly, attached the circuit to a New Focus KTP 4064 EOM, and took another impedance measurement (circuit diagram and impedance plot attached). The peaks are relatively close to 50 Ohms; they are at least the same order of magnitude.

Attachment 1: BuiltCkt2_Simplified_EOM.png
BuiltCkt2_Simplified_EOM.png
Attachment 2: ImpedanceAG4395A_with10pF.png
ImpedanceAG4395A_with10pF.png
Attachment 3: BuiltCkt2_Simplified_EOM_R.png
BuiltCkt2_Simplified_EOM_R.png
Attachment 4: ImpedanceAG4395A_withEOM.png
ImpedanceAG4395A_withEOM.png
  1816   Fri Jul 31 11:04:42 2009 StephanieUpdateGeneralMultiply Resonant EOM Update

I put the flying-component circuit in a box; a photo is attached. I also measured the impedance; it looks exactly the same as it looked before I put the circuit in the box.

Attachment 1: BoxPic.png
BoxPic.png
Attachment 2: BoxPic2.png
BoxPic2.png
  1834   Wed Aug 5 11:49:49 2009 StephanieUpdateGeneralMultiply Resonant EOM Update

I have spent the past couple of days gathering optics and mounts so that I can observe the modulation of the EOM attached to the circuit I built using the optical spectrum analyzer (OSA). A rough diagram of the planned layout is attached.

I also built a short SMA cable so that the EOM did not have to be connected directly to the circuit box. The cable is shown attached to the EOM and circuit box in the attached photo. After checking to make sure that all of the connections in the cable were sound, I remeasured the input impedance of the circuit; the impedance measurement (black) is shown in the attached plot with the impedance before the SMA cable was added with and without the box (green and blue, respectively--these two are almost identical). The new impedance has a strange shape compared to the original measurements; I'd like to understand this a little better, since adding extra inductance in LTSpice doesn't seem to have that effect. Since I had already taken apart the setup used for the previous impedance measurements, I had to rebuild and recalibrate the setup; I guess the difference could be something about the new calibration, but I don't really think that that's the case.

Attachment 1: OSASetup.png
OSASetup.png
Attachment 2: SMAPic.png
SMAPic.png
Attachment 3: WithSMA.png
WithSMA.png
  1835   Wed Aug 5 15:18:12 2009 StephanieUpdateGeneralMultiply Resonant EOM Update

Quote:

I have spent the past couple of days gathering optics and mounts so that I can observe the modulation of the EOM attached to the circuit I built using the optical spectrum analyzer (OSA). A rough diagram of the planned layout is attached.

I also built a short SMA cable so that the EOM did not have to be connected directly to the circuit box. The cable is shown attached to the EOM and circuit box in the attached photo. After checking to make sure that all of the connections in the cable were sound, I remeasured the input impedance of the circuit; the impedance measurement (black) is shown in the attached plot with the impedance before the SMA cable was added with and without the box (green and blue, respectively--these two are almost identical). The new impedance has a strange shape compared to the original measurements; I'd like to understand this a little better, since adding extra inductance in LTSpice doesn't seem to have that effect. Since I had already taken apart the setup used for the previous impedance measurements, I had to rebuild and recalibrate the setup; I guess the difference could be something about the new calibration, but I don't really think that that's the case.

 

After investigating this a bit further, I discovered that some of the components in the circuit were pressed firmly up against the inside of the box, and when they were moved, the impedance plot changed shape dramatically. I think that originally, the components were not pressed against the box, but the box's SMA joint was rather loose; when I connected this to the SMA cable, I tightened it, and this seems to have twisted the circuit around inside the box, pushing the components up against the side. I have fixed the twisting, and since the SMA joint is now tight, the circuit should no longer have any twisting problems.

A new plot is attached, showing the impedance of the circuit with nothing attached (blue), with the SMA cable and EOM attached (green), and with the EOM attached directly to it taken last friday with the old calibration of the setup (red). All three curves look roughly the same; the center peak is shifted slightly between the three curves, but the circuit with SMA and EOM is the version we'll be using, and it's central peak is close to the correct value.

Attachment 1: SMA.png
SMA.png
  1886   Tue Aug 11 14:15:28 2009 StephanieUpdateGeneralMultiply Resonant EOM Update

I was able to observe the three sets of modulation sidebands created by the EOM + triply resonant circuit yesterday. Quantitative results will be posted later.

  1891   Wed Aug 12 12:08:16 2009 StephanieUpdateGeneralMultiply Resonant EOM Update

I measured the magnitude of modulation as a function of frequency using the optical spectrum analyzer and an oscilloscope while generating signals using a Marconi signal generator; the results are shown in the attached plot and are compared to the expected modulation given the measured transfer function of the circuit and the nominal modulation index of the EOM used (13 mrad/V). Using the oscilloscope, I found the resonant peaks to be at 11.11 MHz, 29.57 MHz, and 54.70 MHz. There are several different colors on the plot; this is because I had to take the data in several different segments and had to switch to measuring a different sideband partway through the measurment. I also separately found the modulation at each resonant peak for each sideband. The magnitude of modulation was measured  by finding the ratio between the magnitude of the carrier and sideband powers using an oscilloscope, and calculating the magnitude of modulation from this. This method was also used to quantify the dependence of modulation magnitude on input power at each resonant peak; these results are also attached. These same results can also be plotted as modulation magnitude as a function of voltage into the resonant circuit; this is also attached (I'm not sure which is more useful).

In order to produce these results (get the measurements in mrad/V) it was necessary to measure the gain of the amplifier. I used the signal generator to input signals of varying power and measured the output signal voltage using the oscilloscope; I then repeated this process at each resonant frequency. From this I was able to calculate the gain of the amplifier to be 28.1 dB at 11.11 MHz, 27.4 dB at 29.57 MHz, and 25.7 dB at 54.70 MHz. These values are in the same ballpark as the values in the Mini Circuits data sheet (all values are ~25-28 MHz).

Attachment 1: Modulation.png
Modulation.png
Attachment 2: Linearity.png
Linearity.png
Attachment 3: Linearity_V.png
Linearity_V.png
  14763   Tue Jul 16 15:00:03 2019 gautamUpdateSUSMultiple small EQs

There were several small/medium earthquakes in Ridgecrest and one medium one in Blackhawk CA at about 2000 UTC (i.e. ~ 2 hours ago), one of which caused BS, ITMY, and ETM watchdogs to trip. I restored the damping just now.

  2244   Wed Nov 11 20:57:06 2009 kiwamuUpdateElectronicsMulti-resonant EOM --- LC tank circuit ---

I have been working about multi-resonant EOM since last week.

In order to characterize the behavior of the each components, I have made a simple LC tank circuit.

You can see the picture of the circuit below.

DSCN0160.JPG

Before constructing the circuit, I made an "ideal" calculation of the transfer function without any assumptions by my hand and pen.

Most difficult part in the calculation is the dealing with a transformer analytically. Eventually I found how to deal with it in the analytical calculation.

The comparison of the calculated and measured transfer function is attached.

 It shows the resonant frequency of ~50MHz as I expected. Those are nicely matched below 50MHz !!

For the next step, I will make the model of the circuit with stray capacitors, lead inductors, ... by changing the inductance or something. 

 

Attachment 2: LCtank_complete.png
LCtank_complete.png
  2340   Wed Nov 25 20:44:48 2009 kiwamuUpdateElectronicsMulti-resonant EOM --- Q-factor ----

Now I am studying about the behavior of the Q-factor in the resonant circuit because the Q-factor of the circuit directly determine the performance as the EOM driver.

Here I summarize the fundamental which explains why Q-factor is important.

 --------------------------------------

The EOM driver circuit can be approximately described as shown in figure below

trans.png

Z represents the impedance of a resonant circuit.

In an ideal case, the transformer just raise the voltage level n-times larger.  Rin is the output impedance of the signal source and usually has 50[Ohm].

The transformer also makes the impedance Z 1/n^2 smaller. Therefore this configuration gives a following relation between Vin and Vout.

eq1.png

 Where G is the gain for the voltage. And G goes to a maximum value when Rin=Z/n2. This relation is shown clearly in the following plot.

 

impedance.png

 Note that I put Rin=50 [Ohm] for calculating the plot.

Under the condition  Rin=Z/n2( generally referred as impedance matching ), the maximum gain can be expressed as;

eq2.png

 

It means that larger Z makes more efficient gain. In our case, interested Z is considered as the impedance at a resonance.

So what we should do is making a resonant circuit which has a higher impedance at the resonance (e.g. high Q-resonant circuit).

 

 

  2341   Thu Nov 26 02:08:34 2009 KojiUpdateElectronicsMulti-resonant EOM --- Q-factor ----

The key point of the story is:
"The recipe to exploit maximum benefit from a resonant EOM"
- Make a resonant EOM circuit. Measure the impedance Z at the resonance.
- This Z determines the optimum turn ratio n of the step-up transformer.
 
(n2 = Z/Rin where Rin is 50Ohm in our case.)
- This n gives the maximum gain Gmax (= n/2) that can be obtained with the step up transformer.
  And, the impedance matching is also satisfied in this condition.

OK: The larger Z, the better. The higher Q, the Z larger, thus the better.
(Although the relationship between Z and Q were not described in the original post.)

So, how can we make the Q higher? What is the recipe for the resonant circuit?
=> Choose the components with smaller loss (resistance). The details will be provided by Kiwamu soon??? 


When I was young (3 months ago), I thought...

  • Hey! Let's increase the Q of an EOM! It will increase the modulation!
  • Hey! Let's use the step-up transformer with n as high as possible! It will increase the modulation!
  • Hey! Take the impedance matching! It will increase the modulation!

I was just too thoughtless. In reality, they are closely related each other.

A high Q resonant circuit has a high residual resistance at the resonant frequency. As far as the impedance is higher than the equivalent output impedance of the driving circuit (i.e. Z>Rin n2), we get the benefit of increasing the turn ratio of the transformer. In other words, "the performance of the resonant EOM is limited by the turn ratio of the transformer." (give us more turns!)

OK. So can we increase the turn ratio infinitely? No. Once Rin n2 gets larger than Z, you no longer get the benefit of the impedance transforming. The output impedance of the signal source yields too much voltage drop.

There is an optimum point for n. That is the above recipe. 

So, a low Q resonant EOM has a destiny to be useless. But high Q EOM still needs to be optimized. As far as we use a transformer with a low turn ratio, it only shows ordinary performance.

 

 

  3069   Fri Jun 11 15:04:25 2010 josephbUpdateCDSMulti-filter matrix medm screens finished and script for copying filters from SOS file

I've finished the MEDM portion of the RCG FiltMuxMatrix part.  Now it generates an appropriate medm screen for the matrix, with links to all the filter banks.  The filter bank .adl files are also generated, and placed in a sub directory with the name of the filter matrix as the name of the sub directory.

The input is the first number and the output is the second number.  This particular matrix has 5 inputs (0 through 4) and 15 outputs (0 through 14). Unfortunately, the filter names can't be longer than 24 characters, which forced me to use numbers instead of actual part names for the input and output.

 

The key to the numbers is:

Inputs:

DARM 0
MICH 1
PRC 2
SRC 3
CARM 4

Outputs:

AS_DC 0
AS11_I 1
AS11_Q 2
AS55_I 3
AS55_Q 4
POP_DC 5
POP11_I 6
POP11_Q 7
POP55_I 8
POP55_Q 9
REFL_DC 10
REFL11_I 11
REFL11_Q 12
REFL55_I 13
REFL55_Q 14

To get this working required modifications to the feCodeGen.pl and the creation of mkfiltmatrix.pl (which was based off of mkmatrix.pl).  These are located in /cvs/cds/caltech/cds/advLigoRTS/src/epics/util/

In related news, I asked Valera if he could load the simulated plant filters he had generated, and after several tries, his answer was no.  He says it has the same format as those filter they pass to the feed forward banks down in Livingston, so he's not sure why they won't work.

I tested my script, FillFotonFilterMatrix.py, on some simple second order section filters (like gain of 1, with b1 = 1.01, b2 = 0.02, a1 = 1.03, a2 = 1.04), and it populated the foton filter file correctly, and was parsed fine by Foton itself.  So I'm going to claim the script is done and its the fault of the filters we're trying to load.  This script is now living in /cvs/cds/caltech/chans/ , along with a name file called lsp_dof2pd_mtrx.txt which tells the script that DARM is 0, CARM is 1, etc.  To run it, you also need a SOS.txt file with the filters to load, similar to the one Valera posted here, but preferably loadable.

I also updated my progess on the wiki, here.

Attachment 1: FiltMatrixMedm.png
FiltMatrixMedm.png
  839   Fri Aug 15 11:52:32 2008 josephbConfigurationCamerasMulti-computer display and recording of digital camera output
Through the magic of gstreamer, I've been able to live play on one machine, compress the image, send it to another machine via udp, and also display it there. The "tee" function also allows one to save at the same images at time as well.

The command line used on the "server", say Rosalba or Mafalda is:

CamServe -F 'Mono8' -c 44058 -E 20000 -X 0 -Y 0 -H 480 -W 752 -l 0 -m 100 | gst-launch-0.10 fdsrc fd=0 blocksize=360960 ! video/x-raw-gray, height=480, width=752, bpp=8,depth=8,framerate=60/1 ! tee name=t1 t1. ! video/x-raw-gray, height=480, width=752, bpp=8,depth=8,framerate=60/1 ! ffmpegcolorspace ! ximagesink t1. ! video/x-raw-gray, height=480, width=752, bpp=8,depth=8,framerate=60/1 ! ffmpegcolorspace ! queue ! smokeenc keyframe=8 qmax=40 ! udpsink host="131.215.113.103" port=5000

This both displays the image and sends it to the host 131.215.113.103 in this case.

I've written a primitive shell script that does most of this.

It requires at the minimum an IP address. You can also give it a number of images (the -m number) and also the exposure value (-E 20000).

Currently in /cvs/cds/caltech/target/Prosilica/40mCode/SnapCode/ there is a script called CameraServerScript.

Typing in "CameraServerScript 131.215.113.107" would send it to that IP address.

Typing in "CameraServerScript 131.215.113.107 500 40000" would run for 500 images at an exposure value of 40000.

To actually receive, you need gstreamer installed and run the following command:

gst-launch udpsrc port=5000 ! smokedec ! queue ! ffmpegcolorspace ! ximagesink sync=false

Make sure you have the right IP address to send to.

Still working on multicasting (basically a server is constantly sending out images, and the client subscribes to the multicast).
  102   Wed Nov 14 16:54:54 2007 pkpUpdateOMCMuch better looking vertical transfer functions
[Norna Pinkesh]

So after Chub did his wonderful mini-surgery and removed the peek from the cables and after Norna and I aligned the whole apparatus, the following are the peaks that we see.
It almost exactly matches Norna's simulations and some of the extra peaks are possibly due to us exciting the Roll/longitudnal/yaw and pitch motions. The roll resonance is esp prominent.

We also took another plot with one of the wires removed and will wait on Chub before we remove another wire.
Attachment 1: VerticalTransPreampwireremovedNov142007.pdf
VerticalTransPreampwireremovedNov142007.pdf VerticalTransPreampwireremovedNov142007.pdf VerticalTransPreampwireremovedNov142007.pdf VerticalTransPreampwireremovedNov142007.pdf
Attachment 2: VerticalTranswiresclampedNov142007.pdf
VerticalTranswiresclampedNov142007.pdf VerticalTranswiresclampedNov142007.pdf VerticalTranswiresclampedNov142007.pdf VerticalTranswiresclampedNov142007.pdf
  16392   Mon Oct 11 18:29:35 2021 AnchalSummaryCDSMoving forward?

The teststand has some non-trivial issue with Myrinet card (either software or hardware) which even teh experts are saying they don't remember how to fix it. CDS with mx was iin use more than a decade ago, so it is hard to find support for issues with it now and will be the same in future. We need to wrap up this test procedure one way or another now, so I have following two options moving forward:


Direct integration with main CDS and testing

  • We can just connect the c1sus2 and c1bhd FE computers to martian network directly.
  • We'll have to connect c1sus2 and c1bhd to the optical fiber subnetwork as well.
  • On booting, they would get booted through the exisitng fb1 boot server which seems to work fine for the other 5 FE machines.
  • We can update teh DHCP in chiara and reload it so that we can ssh into these FEs with host names.
  • Hopefully, presence of these computers won't tank the existing CDS even if they  themselves have any issues, as they have no shared memory with other models.
  • If this works, we can do the loop back testing of I/O chassis using the main DAQ network and move on with our upgrade.
  • If this does not work and causes any harm to exisitng CDS network, we can disconnect these computers and go back to existing CDS. Recently, our confidence on rebooting the CDS has increased with the robust performance as some legacy issues were fixed.
  • We'll however, continue to use a CDS which is no more supported by the current LIGO CDS group.

Testing CDS upgrade on teststand

  • From what I could gather, most of the hardware in I/O chassis that I could find, is still used in CDS of LLO and LHO, with their recent tests and documents using the same cards and PCBs.
  • There might be some difference in the DAQ network setup that I need to confirm.
  • I've summarised the current c1teststand hardware on this wiki page.
  • If the latest CDS is backwards compatible with our hardware, we can test the new CDS in teh c1teststand setup without disrupting our main CDS. We'll have ample help and support for this upgrade from the current LIGO CDS group.
  • We can do the loop back testing of the I/O chassis as well.
  • If the upgrade is succesfull in the teststand without many hardware changes, we can upgrade the main CDS of 40m as well, as it has the same hardware as our teststand.
  • Biggest plus point would be that out CDS will be up-to-date and we will be able to take help from CDS group if any trouble occurs.

So these are the two options we have. We should discuss which one to take in the mattermost chat or in upcoming meeting.

  5171   Wed Aug 10 13:52:23 2011 Manuel , IshwitaUpdatePEMMoving Seismometers

We turned off the power of the seismometers and moved the Guralp1 close to the STS. Both are now situated below the center of the mode cleaner vacuum tube.

We oriented the X axis of the STS & Guralp1 along the X axis of the interferometer. Then we turned on the power again, but the STS channels don't give any signal. We think this is, because we didn't push the auto zero button.

  5186   Thu Aug 11 10:56:08 2011 Ishwita, ManuelUpdatePEMMoving Seismometers

Quote:

We turned off the power of the seismometers and moved the Guralp1 close to the STS. Both are now situated below the center of the mode cleaner vacuum tube.

We oriented the X axis of the STS & Guralp1 along the X axis of the interferometer. Then we turned on the power again, but the STS channels don't give any signal. We think this is, because we didn't push the auto zero button.

 After pressing the auto-zero button (a lot of times) of the STS breakout box & aligning the bubble in the STS, we could finally get data from STS (Bacardi). So, now STS2 (Bacardi - Serial NR. 100151) is working!

  10531   Wed Sep 24 11:02:38 2014 manasaUpdateLSCMoving SRM

I looked at the CAD layout and it seems like we will clearly be clipping POY if we move SRM by 7.5cm. Since POY is not visible at low power, we cannot be sure about the clipping.

We should have a plan B before we move everything. I suggest we move a combination of SRM and SR2 to get the desired SRC length.
Moving SR2 will require extra effort to walk the beam unclipped through all the 6 output steering mirrors that follow; but there will be little room for error if we use irides to propagate the beam through the first 4 mirrors that are in the BS and ITMY chamber.

  16488   Tue Nov 30 17:11:06 2021 PacoUpdateGeneralMoved white rack to 1X3.5

[Paco, Ian, Tega]

We moved the white rack (formerly unused along the YARM) to a position between 1X3, and 1X4. For this task we temporarily removed the hepas near the enclosures, but have since restored them.

Attachment 1: IMG_8749.JPG
IMG_8749.JPG
Attachment 2: IMG_8750.JPG
IMG_8750.JPG
  5700   Wed Oct 19 15:48:20 2011 MirkoUpdatePEMMoved the STS1 from x-arm end to vortex

[Jenne, Mirko]

We moved our one STS1 from the x-arm end to the vortex. We record the data as STS1 in c1pem @ 256Hz. x is still north-south.

JD:  This is actually an STS-2.  We just call it C1:PEM-SEIS_STS1.... to differentiate the 3 STSs that we have from one another (assuming we plug in the other two).

19102011061.jpg

  14881   Mon Sep 16 12:00:16 2019 aaronHowToGeneralMoved some immovable optics

When I put away the lenses we had used for measuring the RF transfer functions of the QPD heads, I saw that I'd removed them from the cabinet containing green endtable optics, but hadn't noticed the sign forbidding their removal. I'll talk with Koji/Gautam about what happened and what should be done.

  16324   Mon Sep 13 18:19:25 2021 TegaUpdateComputer Scripts / ProgramsMoved modbus service from chiara to c1susaux

[Tega, Anchal, Paco]

After talking to Anchal, it was made clear that chiara is not the place to host the modbus service for the temperature sensors. The obvious machine is c1pem, but the startup cmd script loads c object files and it is not clear how easy it would integrate the modbus functionality since we can only login via telnet, so we decided to instead host the service on c1susaux. We also modified the /etc/motd file on c1susaucx which displays the welcome message during login to inform the user that this machine hosts the modbus service for the temperature sensor. Anchal plans to also document this information on the temperature sensor wiki at some point in the future when the page is updated to include what has been learnt so far.

We might also consider updating the database file to a more modern way of reading the temperature sensor data using FLOAT32_LE which is available on EPICs version 3.14 and above, instead of the current method which works but leaves the reader bemused by the bitwise operations that convert the two 16 bits words (A and B) to IEEE-754 32-bit float, via 

field(CALC, "(A&D?(A&C?-1:1):0)*((G|A&E)*J+B)*2^((A&D)/G-F)")

where 

   field(INPA, "$HiWord")
   field(INPB, "$LoWord")
   field(INPC, "0x8000")   # Hi word, sign bit
   field(INPD, "0x7F80")   # Hi word, exponent mask
   field(INPE, "0x00FF")   # Hi word, mantissa mask (incl hidden bit)
   field(INPF, "150")      # Exponent offset plus 23-bit mantissa shift
   field(INPG, "0x0080")   # Mantissa hidden bit
   field(INPJ, "65536")    # Hi/Lo mantissa ratio
   field(CALC, "(A&D?(A&C?-1:1):0)*((G|A&E)*J+B)*2^((A&D)/G-F)")
   field(PREC, "4")

as opposed to the more modern form

field(INP,"@asyn($(PORT) $(OFFSET))FLOAT32_LE")
  3799   Wed Oct 27 17:06:48 2010 josephbUpdateCDSMoved c1iscey chassis and host interface board to c1ioo

Problem:

Need a working IO chassis connected to c1ioo in order to bring the MC_L into the digital realm, and then via RFM transmit to the c1sus machine.

Attempted Solution:

Move the c1iscey IO chassis to c1ioo while the c1ioo chassis is at downs.

The c1iscey chassis however doesn't seem to be talking to the c1ioo computer.  I tried changing the host interface card on the c1ioo chassis.  I took out One Stop Systems HIB2-x4-H interface card with serial number 26638 from the c1ioo computer and put in the One Stop Systems HIB2-x4-H with serial number 35242 in from c1iscey into c1ioo.  Still didn't work.

All the lights are red on the interface card on the actual chassis and its cooling fan isn't spinning. 

Using dmesg on c1ioo shows that it does not see any of the ADC/DAC/BO cards.

Status:

I'm going to  wait until tomorrow morning when Rolf gets a chance to look at the c1ioo chassis over at Downs to determine the next step.  If we fix the c1ioo chassis, I'm move the c1iscey chassis and its host interface board back to the end.

  4368   Wed Mar 2 17:19:58 2011 AidanConfigurationGreen LockingMoved PDH PD on end table

As previously noted, there are multiple beams coming back from the ETM surface onto the PDH PD on the end table. They are spread out in a vertical pattern. All the spots swing together (as the ETM moves?).

I moved the PDH Green PD on the end table so that it was further away from the Faraday and I added an iris in between the Faraday and the PD. Now only the principle reflection from the ETM is incident on the PD. See attached photos. In order to sneak past the neighbouring optics, I had to steer the beam down a bit, so the PD is now lower than it previously was.

Just FYI: the angle between the returning beams is about 5 or 6 mrad at the PD. Before the beams get to the PD they go through a telescope that de-magnifies the beam by about 5 or 6 times. This implies that the angle between adjacent returning beams from the ETM is around 1 mrad at the ETM.

This does make the position of the spot on the PD more susceptible to the alignment of the ETM - we should use a short focal length lens and image the ETM plane onto the PD.

 

First image - overview of table

Second image - the three returning beams immediately before the IRIS

Third image - a close up of the IRIS and PDH PD. 

 

 

 

Attachment 1: P1000223-a.jpg
P1000223-a.jpg
Attachment 2: P1000218.jpg
P1000218.jpg
Attachment 3: P1000224.jpg
P1000224.jpg
  10392   Thu Aug 14 19:33:00 2014 JenneConfigurationIOOMoved MC2 spot

Last night, and again just now, I used the ./MC2_spot_[direction] scripts to center the MC2 spot on the trans QPD.  The MCWFS handled overall alignment to correct for the fact that the ratios in the script aren't perfect.  When I was finished, I ran the MC WFS relief script from the WFS screen.  Last night, and again today, things had drifted until the yaw spot was more than 0.5 counts off.

  11588   Thu Sep 10 01:09:20 2015 ranaUpdateLSCMoved LSC sensing matrix notch frequencies

We looked at the DRMI noise spectrum and chose new excitation frequencies such that the lines are lower in frequency than before (~300 Hz instead of 800 Hz) and also not in some noisy region.

New filters is saved and loaded for all LSC DOFs.

Attachment 1: NewLSCnotches.png
NewLSCnotches.png
  11589   Thu Sep 10 04:23:00 2015 ericqUpdateLSCMoved LSC sensing matrix notch frequencies

Frequencies are:

  • CARM: 309.21 Hz
  • DARM: 307.88 Hz
  • MICH: 311.1 Hz
  • PRCL: 313.31 Hz
  • SRCL: 315.17 Hz

POP110 and POP22 demod angles were adjusted for DRMI lock. 

Last week, I never achieved a fully 1F lock, REFL165 was used for SRCL. Tonight, we created input matrix settings for pure 1F locking, and did some signal mixing to reduce the PRCL to SRCL coupling. The PRCL to MICH coupling was already low, since AS55 is fairly insensitive to PRCL. 

Similarly, for the 3F signals, some signal mixing of REFL33I and REFL165Q was used to reduce the PRCL to MICH coupling. The PRCL to SRCL coupling in REFL165 isn't too bad, so no compensation was done. Interestingly, in this setting, the 3F MICH and SRCL signals agree with the 1F signals on their zero crossing, so no offsets are needed. REFL33 I does need an offset, however, to match the REFL11I PRCL zero crossing. 

The DRMI acquires faster with SRCL set to 165I. Once acquired, the 1F/3F can be made smoothly, and both settings are very stable. The sensing matrix in each setting is consistent with each other. (The PRCL and SRCL lines in AS55 change, but really I shouldn't even plot them, since they're not very coherent). 

For some reason, these show a sign flip relative to last week's measurements. The relative angles are consistent, though. 

Next up is finding the right coefficient for the SRM in the MICH output matrix, when actuating on the BS. 

Attachment 1: DRMI_1F.pdf
DRMI_1F.pdf
Attachment 2: DRMI_3F.pdf
DRMI_3F.pdf
  16476   Thu Nov 18 15:16:10 2021 AnchalUpdateGeneralMoved Chiara to 1X7 above nodus powered with same UPS

[Anchal, Paco]

We moved chiara to 1X7 above nodus and powered with same UPS from a battery backed port. The UPS is at 40% load capacity. The nameserver and nfs came back online automatically on boot up.

 

  7049   Mon Jul 30 12:38:45 2012 JamieUpdateCDSMove to RCG 2.5 tag release

I moved the RCG to the advLigoRTS-2.5 tag:

controls@c1iscey ~ 0$ ls -al /opt/rtcds/rtscore/release
lrwxrwxrwx 1 controls 1001 19 Jul 30 12:02 /opt/rtcds/rtscore/release -> tags/advLigoRTS-2.5
controls@c1iscey ~ 0$ 

There are only very minor differences between what we were running on the the 2.5 branch.  I have NOT rebuilt all the models yet.

I was hoping that there was something in the tagged release that might fix this hard-crash-on-filter-load issue that we're seeing in the c1tst model.  It didn't.  Still have no idea what's going on there.

  7086   Sun Aug 5 13:48:40 2012 DenUpdateCDSMove to RCG 2.5 tag release

Quote:

I moved the RCG to the advLigoRTS-2.5 tag

 After that RFM -> OAF communication through PCIE became bad again. Inside CommData2.c cache flushing is not allowed

// If PCIE comms show errors, may want to add this cache flushing
            #if 0
            if(ipcInfo[ii].netType == IPCIE)
                clflush_cache_range (ipcInfo[ii].pIpcData->dBlock[sendBlock][ipcIndex].data, 16);
            #endif

As a result, a significant part of MC_F and other signals is lost during RFM -> OAF transmission (270 - 330 out of 2048 per second)

erros.png   overview.png    oaf.png

 


Last time when I replaced 0 for 1, it suspended SUS machine because of the code bug. Alex modified a couple of files in the old version and it started to work. Do you know if this bug is fixed in the new version?

  1378   Mon Mar 9 19:27:16 2009 ranaConfigurationComputersMove of the CLIO Digital Controls test setup

Because of the network interference we've had from the CLIO system for the past 3-4 days, I asked the guys to remove

the test stand from the 40m lab area. It is now in the 40m control room. Since it needed an ethernet connection to get out

for some reason we've let them hook into GC. Also, instead of using a real timing signal slaved to the GPS, Jay suggested

just skipping it and having the Timing Slave talk to itself by looping back the fiber with the timing signal. Osamu will enter

more details, but this is just to give a status update.

  6178   Fri Jan 6 19:17:07 2012 Max De JongUpdateGeneralMounted projector

I mounted the new projector to the pipe where the old projector was attached. The mounting hardware wasn't designed for attaching to a pipe, but with Steve's help I mounted the projector. The projector is angled away from the area of the wall designated as the screen, and I am going to meet with Steve Monday to fix this.

  2995   Wed May 26 18:54:55 2010 AidanSummaryGreen LockingMounted Crystal 724 in the Doubling Oven

Andri and I mounted the Raicol Crystal #724 in one of the new Covesion Ovens. The procedure was the same as before - see elog entry here.

There was one issue - the glass plate that goes on top of the crystal is coated on one side with ITO (Indium-Tin Oxide) and it's not 100% certain that this was mounted in the correct orientation. It is virtually impossible to tell which side of the glass is coated.

The base plate of the oven was tapped for an M3 hole. We retapped it for an 8-32 and bolted it to a post and that one of the New Focus 4-axis translation stage. The assembly is currently bolted to the PSL table, awaiting use.

  8176   Wed Feb 27 00:56:01 2013 JenneUpdateASSMotivation for reactivating the ASS

I am putting a little bit of brain power into reviving the ASS, and I want to write down what the motivation is, and what the short and long-term plans are.

Why?

The IFO IR is not optimally aligned right now.  While we were at atmosphere, we should have taken the time to align the green beams to the arms until the greens were both resonating TEM00.  We were lazy, and excited to pump down, so we decided that locking on higher order modes was good enough to ensure the beams came out of vacuum.  Once we were pumped down, ITMY and ETMY were aligned to the green beam axis.  Then, the IR was aligned to this new Yarm cavity axis.  This would have been okay, and pretty close, if we had aligned the green beam all the way (used only the outside steering mirrors to resonate TEM00, after the cavity mirrors were aligned for flashing IR).  After the IR was aligned to the Ygreen axis, the rest of the IFO was aligned to this slightly-incorrect input pointing.  We want to measure the IR spot positions on ITMY and ETMY so that we can tweak the input pointing until we hit the center of both ITMY and ETMY.  Then we will align Ygreen's input pointing to this proper IR cavity axis.  The rest of the IFO alignment will also have to be redone.  This calls for a functioning A2L system, so the measurement part of the ASS.

The immediate motivation for measuring the spot positions is that the current Xarm IR axis is not at all very close to the Xgreen axis.  The other day while we were fixing up the Xend table (note in elog 8162), we found that the TRX beam to the TRX PD and the trans camera was clipped on the 2" harmonic separator (which is the first optic that the transmitted IR beam sees on the end tables).  It was clipping on the left side of the optic, if you are looking at the face of the optic.  This is the more east-erly side of the optic.  We moved that optic to the side so that we were not clipping.  Then, today when Manasa was trying to align the Xgreen beam, she found that it was clipping on the right side of the harmonic separator, the more west-erly side.  I remember seeing that the green beam was roughly centered on the harmonic separator when we were at atmosphere, so this clipping is certainly due to Yuta, Evan and my moving of the harmonic separator.  Since the end green steering optics are not very orthogonal in angle/translation, it is very difficult to translate the beam by a significant amount.  If we keep the current IR alignment, which surely isn't good anyway (you can see on the ETMXF camera that the beam isn't centered), we would probably have to move the Xgreen steering optics, which would be a total pain.  It seems that the better plan is to leave them where they are, and get the IR pointing in the correct direction, and move the harmonic separator back to where it was originally.

Short term (< few days):

Write the arm section of the existing MeasureSpotPositions.py script (in ....../scripts/ASS).  Write a wrapper script that, like ...../scripts/ASS/MC/mcassMCdecenter, calls sets up the lockins, runs MeasureSpotPositions.py, and calculates the calibrated spot positionsUse this information to hand tweak the input pointing, then realign the cavities to the new IR, and the greens to the new cavity axes.

All of the infrastructure for this is already in place in the c1ass model.   The only drawback to the current situation is the LSC output matrix only has one row for ASS, and so only one cavity can be measured at a time.  To make things faster, we could consider increasing the size of the LSC output matrix so that the 2 arms could be measured simultaneously.  This change is low priority for now.

Long term:

Make the full ASS system work. 

A major change from the current situation is that the current ASS cannot actuate on the input pointing (TT1 and TT2 for Yarm, BS for Xarm).  We want a low bandwidth servo to force the input beam to follow the cavity axis.  Implementing this will require some changes to the ASS model. 

Remeasure sensing matrix, test system.

  8178   Wed Feb 27 02:21:55 2013 JenneUpdateASSMotivation for reactivating the ASS

I have modified the MeasureSpotPositions.py script to accept the arms as valid cavities (it used to give an error "Sorry, this only works for MC right now").

There is still no wrapper script to turn on lockins and turn them off after the measurement, so I have not tested the arm A2L yet.  But I should be able to tomorrow, or whenever the IFO is next available.

To-do:

* Write the wrapper script (analog of mcassMCdecenter).

* Fix arm assOff, assDown, assOn, assUp scripts to match the current channel names (which were changed long ago to be human-readable, versus mysterious numbers).

* Test.

  4608   Tue May 3 10:41:35 2011 josephbUpdateCDSMorning maintenance

1) Filled in the C1SUS_BS_OLMATRIX properly so as to make the BS oplev work for Steve.

2) Turned on the ITMX damping.  Apparently it had tripped this morning, possibly due to work in the lab area.

3) The ETMX FE controller (c1scx) had ADC timed out and died sometime around 8:30 am.  The c1x01 (the IOP on the ETMX computer) was also indicating a FB status error (mismatch in DAQ channels).

The reported error in dmesg on c1iscex was:

[1628690.250002] c1spx: ADC TIMEOUT 0 3541 21 3605
[1628690.250002] c1scx: ADC TIMEOUT 0 3541 21 3605

Just to be safe, I rebuilt the c1x01 and c1scx models, ran ./activateDAQ.py, and used the scripts killc1spx, killc1scx, and killc1x01.

I finally restarted the process with startc1x01, startc1scx, and startc1spx.  Everything is currently alive and indicating all green.

  2159   Thu Oct 29 18:04:02 2009 JenneUpdateAdaptive FilteringMore work on saving coeffs on the OAF screen

[Sanjit,Jenne]

Sanjit has been working today on trying to get the OAF coefficients to save properly.  Alex got us most of the way, but right now it's looking like the filter that is being saved is totally constant (all the values are the same).  We're poking around trying to figure out why this is. 

Also, we're starting again (as we should have been for the last week or so since Alex came in to help us) to check in the TOP_XFCODE whenever we make changes to it, and when we recompile the front end code. 

  2160   Thu Oct 29 18:25:33 2009 SanjitUpdateAdaptive FilteringMore work on saving coeffs on the OAF screen

Quote:

[Sanjit,Jenne]

Sanjit has been working today on trying to get the OAF coefficients to save properly.  Alex got us most of the way, but right now it's looking like the filter that is being saved is totally constant (all the values are the same).  We're poking around trying to figure out why this is. 

Also, we're starting again (as we should have been for the last week or so since Alex came in to help us) to check in the TOP_XFCODE whenever we make changes to it, and when we recompile the front end code. 

 

We are manually restarting assepics, but the terminal logs us out after sometime and ass may crash. I set autologout=0 in the terminal for the time being. Once the testing process is over, assepics will start automatically when the computer is turned on, so we wont have to worry about this.

(if ass crashes tonight, it is not unexpected!)

 

  2171   Mon Nov 2 21:09:15 2009 SanjitUpdateAdaptive FilteringMore work on saving coeffs on the OAF screen

 

I made some changes in the code (all commented in the installed and SVN version) to print the filter coefficients. I got crazy output. Sometimes memory bugs lead to such crazy behavior. So far I could not find any bugs, but will have to spend more time on it.

 

  2199   Fri Nov 6 19:25:31 2009 Sanjit, Jenne, JoeUpdateAdaptive FilteringMore work on saving coeffs on the OAF screen

Quote:

 I made some changes in the code (all commented in the installed and SVN version) to print the filter coefficients. I got crazy output. Sometimes memory bugs lead to such crazy behavior. So far I could not find any bugs, but will have to spend more time on it 

 

Something strange was going on in the OAF code, printf would print a double precision number in %f format but not in %lf or %e format!

Since we know this problem now, we can move forward, but it will be important to know why printf was restricted and if there are other such constraints which we should remember while making changes in the codes.

 

  7097   Mon Aug 6 20:27:59 2012 JamieUpdateSimulationsMore work on getting simplant models running: c1lsp and c1sup

I'm trying to get more of the simplant models running so that we (me and Sasha Surf) can get a full real-time cavity simplant running.  As I reported last week, c1spx is running again on c1iscex.

The two new simplant models are c1sup, which holds the simplant for ITMX, and c1lsp, which holds the IFO simplant, specifically the one we're working on for XARM.

Here's the relevant info:

model  host     dcuid  cpu
c1spx  c1iscex  61     4
c1sup  c1sus    62     6
c1lsp  c1lsc    60     6

c1spx and c1sup will be running the sus_single_plant parts for ETMX and ITMX simplant.  All the simplant suspension channels will be names "SUP" (as opposed to "SUS" for control).

c1lsp is now running, but c1sup won't run for unknown reasons.  The c1sup model is not very complicated, and in fact is more-or-less identical to c1spx.  It compiles and installs and even loads, but it completely unresponsive after loading.  Unfortunately I've had enough CDS bullshit for today, so I'll try to figure out what's going on tomorrow.

  15686   Mon Nov 23 16:33:10 2020 gautamUpdateVACMore vacuum deliveries

Five Agilent pressure gauges were delivered to the 40m. It is stored with the controller and cables in the office area. This completes the inventory for the gauge replacement - we have all the ordered parts in hand (though. not necessarily all the adaptor flanges etc). I'll see if I can find some cabinet space in the VEA to store these, the clutter is getting out of hand again...
 

in addition, the spare gate valve from LHO was also delivered today to the 40m. It is stored at EX with the other spare valves. 

Quote:

It is stored along with the cables that arrived a few weeks ago, awaiting the gauges which are now expected next week sometime.

  14490   Thu Mar 21 12:46:22 2019 JonUpdateVACMore vac controls upgrades

The vac controls system is going down for migration from Python 2.7 to 3.4. Will advise when it is back up.

  14491   Thu Mar 21 17:22:52 2019 JonUpdateVACMore vac controls upgrades

I've converted all the vac control system code to run on Python 3.4, the latest version available through the Debian package manager. Note that these codes now REQUIRE Python 3.x. We decided there was no need to preserve Python 2.x compatibility. I'm leaving the vac system returned to its nominal state ("vacuum normal + RGA").

Quote:

The vac controls system is going down for migration from Python 2.7 to 3.4. Will advise when it is back up.

 

  6908   Tue Jul 3 18:58:14 2012 YaakovUpdateSTACISMore transfer functions and netGPIB status

I'm still having issues with the STACIS oscillating uncontrollably with the slightest extra vibration, but with some more added weight both x and z direction are stable if you don't disturb the setup.

I took more transfer functions of the STACIS. In the last data I took Jenne pointed out that the geophone signals were not correlated well with the driving signal, so I increased the amplitude of the driving signal and am looking in x and y too instead of just z. 

Details of the driving signal: 25 mV, swept sine from 0.1 to 100 Hz from the SR785. 

NOTE: The data below was all transferred from the SR785 using netGPIB, which works fine, if anyone was interested in using it.

Open loop in the y direction, taken with the y geophone (magnitude on top, phase on bottom):

geo_open_y.png

Open loop in the x direction, taken with the x geophone (with some extra weight to try to make the closed loop more stable):

 geo_open_x.png

Open loop in the x direction, taken with accelerometer instead of geophone:

accel_open_x.png

  15675   Thu Nov 12 14:55:35 2020 gautamUpdateElectronicsMore systematic noise characterization

Summary:

I now think the excess noise in this circuit could be coming from the KEPCO switching power supply (in fact, the supplies are linear, and specd for a voltage ripple at the level of <0.002% of the output - this is pretty good I think, hard to find much better).

Details:

All component references are w.r.t. the schematic. For this test, I decided to stuff a fresh channel on the board, with new components, just to rule out some funky behavior of the channel I had already stuffed. I decoupled the HV amplifier stage and the Acromag DAC noise filtering stages by leaving R3 open. Then, I shorted the non-inverting input of the PA95 (i.e. TP3) to GND, with a jumper cable. Then I measured the noise at TP5, using the AC coupling pomona box (although in principle, there is no need for this as the DC voltage should be zero, but I opted to use it just in case). The characteristic bump in the spectra at ~100Hz-1kHz was still evident, see the bottom row of Attachment #1. The expected voltage noise in this configuration, according to my SPICE model, is ~10 nV/rtHz, see the analysis note.

As a second test, I decided to measure the voltage noise of the power supply - there isn't a convenient monitor point on the circuit to directly probe the +/- HV supply rails (I didn't want any exposed HV conductors on the PCB) - so I measured the voltage noise at the 3-pin connector supplying power to the 2U chassis (i.e. the circuit itself was disconnected for this measurement, I'm measuring the noise of the supply itself). The output is supposedly differential - so I used the SR785 input "Float" mode, and used the Pomona AC coupling box once again to block the large DC voltage and avoid damage to the SR785. The results are summarized in the top row of Attachment #1.

The shape of the spectra suggests to me that the power supply noise is polluting the output noise - Koji suggested measuring the coherence between the channels, I'll try and do this in a safe way but I'm hesitant to use hacky clips for the High Voltage. The PA95 datasheet says nothing about its PSRR, and seems like the Spice model doesn't include it either. It would seem that a PSRR of <60dB at 100 Hz would explain the excess noise seen in the output. Typically, for other Op-Amps, the PSRR falls off as 1/f. The CMRR (which is distinct from the PSRR) is spec'd at 98 dB at DC, and for other OpAmps, I've seen that the CMRR is typically higher than the PSRR. I'm trying to make a case here that it's not unreasonable if the PA95 has a PSRR <= 60dB @100 Hz.

So what are the possible coupling mechanisms and how can we mitigate it?

  1. Use better power supply - I'm not sure how this spec of 10-50 uV/rtHz from the power supply lines up in the general scheme of things, is this already very good? Or can a linear power supply deliver better performance? Assuming the PSRR at 100 Hz is 60 dB and falls off as 1/f, we'd need a supply that is ~10x quieter at all frequencies if this is indeed the mechanism.
  2. Better grounding? To deliver the bipolar voltage rails, I used two unipolar supplies. The outputs are supposedly floating, so I connected the "-" input of the +300 V supply to the "+" input of the -300 V supply. I think this is the right thing to do, but maybe this is somehow polluting the measurement?
  3. Additional bypass capacitors? I use 0.1 uF, 700V DC ceramic capacitors as bypass capacitors close to the leads of the PA95, as is recommended in the datasheet. Can adding a 10uF capacitor in parallel provide better filtering? I'm not sure if one with compatible footprint and voltage rating is readily available, I'll look around.

What do the analog electronics experts think? I may be completely off the rails and imagining things here.


Update 2130: I measured the coherence between the positive supply rail and the output, under the same conditions (i.e. HV stage isolated, input shorted to ground). See Attachment #2 - the coherence does mirror the "bump" seen in the output voltage noise - but the coherence is. only 0.1,  even with 100 averages, suggesting the coupling is not directly linear - anyways, I think it's worth it to try adding some extra decoupling, I'm sourcing the HV 10uF capacitors now.

Attachment 1: powerSupplyNoise.pdf
powerSupplyNoise.pdf
Attachment 2: coherence.pdf
coherence.pdf
  15676   Thu Nov 12 15:40:42 2020 KojiUpdateElectronicsMore systematic noise characterization

Yes. The datasheet has a recommendation circuit with 10uF caps. Companies are careful to show reproducible, reliably functional circuit examples on datasheets. So, if the caps are there you should try to replicate the design.

Quote:

Additional bypass capacitors? I use 0.1 uF, 700V DC ceramic capacitors as bypass capacitors close to the leads of the PA95, as is recommended in the datasheet. Can adding a 10uF capacitor in parallel provide better filtering? I'm not sure if one with compatible footprint and voltage rating is readily available, I'll look around.

  15677   Mon Nov 16 00:02:34 2020 ranaUpdateElectronicsMore systematic noise characterization

true. also try to choose a cap with a goow high frequency response. In the Electronics Noise book by Ott there's some graph about this. I bet you good do a Bing search and also find something more modern. Basically we want to make sure that the self resonance is not happening at low frequencies. Might be tought to find one with a good HF response, a high voltage rating, and > 1uF.

Quote:

Yes. The datasheet has a recommendation circuit with 10uF caps. Companies are careful to show reproducible, reliably functional circuit examples on datasheets. So, if the caps are there you should try to replicate the design.

Quote:

Additional bypass capacitors? I use 0.1 uF, 700V DC ceramic capacitors as bypass capacitors close to the leads of the PA95, as is recommended in the datasheet. Can adding a 10uF capacitor in parallel provide better filtering? I'm not sure if one with compatible footprint and voltage rating is readily available, I'll look around.

ELOG V3.1.3-