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  16492   Tue Dec 7 10:55:25 2021 Ian MacMillanSummaryComputersQuantization Noise Calculation Summary

[Ian, Tega]

Tega and I have gone through the IIR Filter code and optimized it to make sure there aren't any areas that force high precision to be down-converted to low precision.

For the new biquad filter we have run into the issue where the gain of the filter is much higher than it should be. Looking at attachments 1 and 2, which are time series comparisons of the inputs and outputs from the different filters, we see that the scale for the output of the Direct form II filter shown in attachment 1 on the right is on the order of 10^-5 where the magnitude of the response of the biquad filter is on the order of 10^2. other than this gain the responses look to be the same. 

I am not entirely sure how this gain came into the system because we copied the c code that actually runs on the CDS system into python. There is a gain that affects the input of the biquad filter as shown on this slide of Matt Evans Slides. This gain, shown below as g, could decrease the input signal and thus fix the gain. However, I have not found any way to calculate this g.

 

 

With this gain problem we are left with the quantization noise shown in Attachment 4.

State Space:

I have controlled the state space filter to act with a given precision level. However, my code is not optimized. It works by putting the input state through the first state-space equation then integrating the result, which finally gets fed through the second state-space equation. 

This is not optimized and gives us the resulting quantization noise shown in attachment 5.

However, the state-space filter also has a gain problem where it is about 85 times the amplitude of the DF2 filter. Also since the state space is not operating in the most efficient way possible I decided to port the code chris made to run the state-space model to python. This code has a problem where it seems to be unstable. I will see if I can fix it

 

 

  16498   Fri Dec 10 13:02:47 2021 Ian MacMillanSummaryComputersQuantization Noise Calculation Summary

I am trying to replicate the simulation done by Matt Evans in his presentation  (see Attachment 1 for the slide in particular). 

He defines his input as x_{\mathrm{in}}=sin(2\pi t)+10^{-9} sin(2\pi t f_s/4) so he has two inputs one of amplitude 1 at 1 Hz and one of amplitude 10^-9 at 1/4th the sampling frequency  in this case: 4096 Hz

For his filter, he uses a fourth-order notch filter. To achieve this filter I cascaded two second-order notch filters (signal.iirnotch) both with locations at 1 Hz and quality factors of 1 and 1e6. as specified in slide 13 of his presentation

I used the same procedure outlined here. My results are posted below in attachment 2.

Analysis of results:

As we can see from the results posted below the results don't match. there are a few problems that I noticed that may give us some idea of what went wrong.

First, there is a peak in the noise around 35 Hz. this peak is not shown at all in Matt's results and may indicate that something is inconsistent.

the second thing is that there is no peak at 4096 Hz. This is clearly shown in Matt's slides and it is shown in the input spectrum so it is strange that it does not appear in the output.

My first thought was that the 4kHz signal was being entered at about 35Hz but even when you remove the 4kHz signal from the input it is still there. The spectrum of the input shown in Attachment 3 shows no features at ~35Hz.

The Input filter, Shown in attachment 4 shows the input filter, which also has no features at ~35Hz. Seeing how the input has no features at ~35Hz and the filter has no features at ~35Hz there must be either some sort of quantization noise feature there or more likely there is some sort of sampling effect or some effect of the calculation.

To figure out what is causing this I will continue to change things in the model until I find what is controlling it. 

I have included a Zip file that includes all the necessary files to recreate these plots and results.

  16836   Mon May 9 15:32:14 2022 Ian MacMillanSummaryComputersQuantization Noise Calculation Summary

I made the first pass at a tool to measure the quantization noise of specific filters in the 40m system. The code for which can be found here. It takes the input to the filter bank and the filter coefficients for all of the filters in the filter bank. it then runs the input through all the filters and measures the quantization noise at each instance. It does this by subtracting the 64-bit output from the 32-bit output. Note: the actual system is 64 bit so I need to update it to subtract the 64-bit output from the 128-bit output using the long double format. This means that it must be run on a computer that supports the long double format. which I checked and Rossa does. The code outputs a number of plots that look like the one in Attachment 1. Koji suggested formatting a page for each of the filters that is automatically generated that shows the filter and the results as well as an SNR for the noise source. The code is formatted as a class so that it can be easily added to the IFOtest repo when it is ready.

I tracked down a filter that I thought may have lower thermal noise than the one that is currently used. The specifics of this will be in the DCC document version 2 that I am updating but a diagram of it is found in attachment 2. Preliminary calculations seemed to show that it had lower quantization noise than the current filter realization. I added this filter realization to the c code and ran a simple comparison between all of them. The results in Attachment 3 are not as good as I had hoped. The input was a two-toned sin wave. The low-level broadband signal between 10Hz and 4kHz is the quantization noise. The blue shows the current filter realization and there shows the generic and most basic direct form 2. The orange one is the new filter, which I personally call the Aircraft Biquad because I found it in this paper by the Hughes Aircraft Company. See fig 2 in paper. They call it the "modified canonic form realization" but there are about 20 filters in the paper that also share that name. in the DCC doc I have just given them numbers because it is easier. 

Whats next:

1) I need to make the review the qnoisetool code to make it compute the correct 64-bit noise. 

        a) I also want to add the new filter to the simulation to see how it does

2) Make the output into a summary page the way Koji suggested. 

3) complete the updated DCC document. I need to reconcile the differences between the calculation I made and the actual result of the simulation.

  17127   Fri Sep 2 13:30:25 2022 Ian MacMillanSummaryComputersQuantization Noise Calculation Summary

P. P. Vaidyanathan wrote a chapter in the book "Handbook of Digital Signal Processing: Engineering Applications" called "Low-Noise and Low-Sensitivity Digital Filters" (Chapter 5 pg. 359).  I took a quick look at it and wanted to give some thoughts in case they are useful. The experts in the field would be Leland B. JacksonP. P. VaidyanathanBernard Widrow, and István Kollár.  Widrow and Kollar  wrote the book "Quantization Noise Roundoff Error in Digital Computation, Signal Processing, Control, and Communications" (a copy of which is at the 40m). it is good that P. P. Vaidyanathan is at Caltech.

Vaidyanathan's chapter is serves as a good introduction to the topic of quantization noise. He starts off with the basic theory similar to my own document on the topic. From there, there are two main relevant topics to our goals.

The first interesting thing is using Error-Spectrum Shaping (pg. 387). I have never investigated this idea but the general gist is as poles and zeros move closer to the unit circle the SNR deteriorates so this is a way of implementing error feedback that should alleviate this problem. See Fig. 5.20 for a full realization of a second-order section with error feedback.

The second starts on page 402 and is an overview of state space filters and gives an example of a state space realization (Fig. 5.26). I also tested this exact realization a while ago and found that it was better than the direct form II filter but not as good as the current low-noise implementation that LIGO uses. This realization is very close to the current realization except uses one less addition block.

Overall I think it is a useful chapter. I like the idea of using some sort of error correction and I'm sure his other work will talk more about this stuff. It would be useful to look into.

One thought that I had recently is that if the quantization noise is uncorrelated between the two different realizations then connecting them in parallel then averaging their results (as shown in Attachment 1) may actually yield lower quantization noise. It would require double the computation power for filtering but it may work. For example, using the current LIGO realization and the realization given in this book it might yield a lower quantization noise. This would only work with two similarly low noise realizations. Since it would be randomly sampling two uniform distributions and we would be going from one sample to two samples the variance would be cut in half, and the ASD would show a 1/√2 reduction if using realizations with the same level of quantization noise. This is only beneficial if the realization with the higher quantization noise only has less than about 1.7 times the one with the lower noise. I included a simple simulation to show this in the zip file in attachment 2 for my own reference.

Another thought that I had is that the transpose of this low-noise state-space filter (Fig. 5.26) or even of LIGO's current filter realization would yield even lower quantization noise because both of their transposes require one less calculation.

  1888   Tue Aug 11 23:55:04 2009 rana, richSummaryOMCQuantum Efficiency and Dark Current measurements of eLIGO Photodiodes

Rich Abbott, Rana

Summary: We found that the 3mm InGaAs photodiodes from eGTRAN which are being used for the DC Readout in eLIGO are bad. The QE is ~50%. We will have to replace them ASAP.

Valera and Nic Smith have pointed out out a factor of ~2 discrepancy between the estimated power transmission to the dark port in H1 and L1. So we decided to measure the QE of the accused diodes.

 The data of the QE and dark current are attached here.

We used a 1064 nm CrystaLaser (which does not have a very stable power output). We attenuated the light with an ND1.0 for all measurements.

The photocurrent is estimated by reading out the voltage across one leg of the differential drive of the DC PD preamp. The photocurrent goes across a 100 Ohm resistor and then through 2 gain of  1 stages to get to this testpoint, so the overall transimpedance gain is 100 Ohms for this measurement.

By far, the Ophir power meter is the biggest source of error. Its absolute calibration is only 5% and the variation across the sensor face is ~5%. There are some hot and not hot spots on the face which can make even more variation, but we tried to avoid these.

We also inserted the power meter very close to the time when we read the voltage, so that the photocurrent and power estimates are made within 10 seconds of each other. This should reduce the error from the laser's power fluctuations.

All diodes still had the glass case on. We measured the reflected power to be ~5-7% of the incident power. This reflected power is NOT accounted for in these estimates.

 

Punch line: The eGTRAN diodes that we currently use are definitely bad. The JDSU and EG&G 2mm diodes have a better QE. We should immediately purchase 3 mm versions and get them cut and measured to be ready for the Sep. 1 commissioning surge.

  3760   Fri Oct 22 03:37:56 2010 KevinUpdatePSLQuarter Wave Plate Measurements

[Koji and Kevin]

We measured the reflection from the PBS as a function of half wave plate rotation for five different quarter wave plate rotations. Before the measurement we reduced the laser current to 1 A, locked the PMC, and recorded 1.1 V transmitted through the PMC. During the measurements, the beam was blocked after the faraday isolator. After the measurements, we again locked the PMC and recorded 1.2 V transmitted. The current is now 2.1 A and both the PMC and reference cavities are locked.

I will post the details of the measurement tomorrow.

  3768   Sat Oct 23 02:25:49 2010 KevinUpdatePSLQuarter Wave Plate Measurements

Quote:

[Koji and Kevin]

We measured the reflection from the PBS as a function of half wave plate rotation for five different quarter wave plate rotations. Before the measurement we reduced the laser current to 1 A, locked the PMC, and recorded 1.1 V transmitted through the PMC. During the measurements, the beam was blocked after the faraday isolator. After the measurements, we again locked the PMC and recorded 1.2 V transmitted. The current is now 2.1 A and both the PMC and reference cavities are locked.

I will post the details of the measurement tomorrow.

I measured the reflected power from the PBS as a function of half wave plate rotation for five different quarter wave plate rotations.

The optimum angles that minimize the reflected power are 330° for the quarter wave plate and 268° for the half wave plate.

The following data was taken with 2.102 A laser current and 32.25° C crystal temperature.

For each of five quarter wave plate settings around the optimum value, I measured the reflected power from the PBS with an Ophir power meter. I measured the power as a function of half wave plate angle five times for each angle and averaged these values to calculate the mean and uncertainty for each of these angles. The Ophir started to drift when trying to measure relatively large amounts of power. (With approximately 1W reflected from the PBS, the power reading rapidly increased by several hundred mW.) So I could only take data near the minimum reflection accurately.

The data was fit to P = P0 + P1*sin^2(2pi/180*(t-t0)) with the angle t measured in degrees with the following results:

lambda/4 angle (°) t0 (°) P0 (mW) P1 (mW) chi^2/ndf V
318 261.56 ± 0.02 224.9 ± 0.5 2016 ± 5 0.98 0.900 ± 0.001
326 266.07 ± 0.01 178.5 ± 0.4 1998 ± 5 16.00 0.918 ± 0.001
330 268.00 ± 0.01 168.2 ± 0.3 2119 ± 5 1.33 0.926 ± 0.001
334 270.07 ± 0.02 174.5 ± 0.4 2083 ± 5 1.53 0.923 ± 0.001
342 273.49 ± 0.02 226.8 ± 0.5 1966 ± 5 1.41 0.897 ± 0.001

where V is the visibility V = 1- P_max/P_min. These fits are shown in attachment 1. We would like to understand better why we can only reduce the reflected light to ~150 mW. Ideally, we would have V = 1. I will redo these measurements with a different power meter that can measure up to 2 W and take data over a full period of the reflected power.

  3776   Mon Oct 25 02:25:21 2010 KojiUpdatePSLQuarter Wave Plate Measurements

Q1. Suppose the laser beam has a certain (i.e. arbitrary) polarization state but contains only TEM00. Also suppose the PSB is perfect (reflect all S and transmit all P). What results do you expect from your expereiment?

Q2. Suppose the above condition but the PBS is not perfect (i.e. reflects most of S but also small leakage of P to the reflection port.) How are the expected results modified?

Q3. In reality, the laser may also contain some thing dirty (e.g. deporarization in the laser Xtal, higher order modes in a certain polarization but different from the TEM00's one, etc). What actually is the cause of 170mW rejection from the PBS? Can we improve the transmitted power through the PBS?

Q4. Why is the visibility for the lambda/4 with 330deg better than the one with 326deg? Yes, as I already explained to Kevin, I suppose it was caused by the lack of the data points in the wider angle ranges.

Quote:

I measured the reflected power from the PBS as a function of half wave plate rotation for five different quarter wave plate rotations.

The optimum angles that minimize the reflected power are 330° for the quarter wave plate and 268° for the half wave plate.

The following data was taken with 2.102 A laser current and 32.25° C crystal temperature.

For each of five quarter wave plate settings around the optimum value, I measured the reflected power from the PBS with an Ophir power meter. I measured the power as a function of half wave plate angle five times for each angle and averaged these values to calculate the mean and uncertainty for each of these angles. The Ophir started to drift when trying to measure relatively large amounts of power. (With approximately 1W reflected from the PBS, the power reading rapidly increased by several hundred mW.) So I could only take data near the minimum reflection accurately.

The data was fit to P = P0 + P1*sin^2(2pi/180*(t-t0)) with the angle t measured in degrees with the following results:

lambda/4 angle (°) t0 (°) P0 (mW) P1 (mW) chi^2/ndf V
318 261.56 ± 0.02 224.9 ± 0.5 2016 ± 5 0.98 0.900 ± 0.001
326 266.07 ± 0.01 178.5 ± 0.4 1998 ± 5 16.00 0.918 ± 0.001
330 268.00 ± 0.01 168.2 ± 0.3 2119 ± 5 1.33 0.926 ± 0.001
334 270.07 ± 0.02 174.5 ± 0.4 2083 ± 5 1.53 0.923 ± 0.001
342 273.49 ± 0.02 226.8 ± 0.5 1966 ± 5 1.41 0.897 ± 0.001

where V is the visibility V = 1- P_max/P_min. These fits are shown in attachment 1. We would like to understand better why we can only reduce the reflected light to ~150 mW. Ideally, we would have V = 1. I will redo these measurements with a different power meter that can measure up to 2 W and take data over a full period of the reflected power.

 

  3747   Wed Oct 20 21:33:11 2010 KevinUpdatePSLQuarter Wave Plate Optimization

[Suresh and Kevin]

We placed the quarter wave plate in front of the 2W laser and moved the half wave plate forward. To make both wave plates fit, we had to rotate one of the clamps for the laser. We optimized the angles of both wave plates so that the power in the reflection from the PBS was minimized and the transmitted power through the faraday isolator was maximized. This was done with 2.1 A injection current and 38°C crystal temperature.

Next, I will make plots of the reflected power as a function of half wave plate angle for a few different quarter wave plate rotations.

  15404   Wed Jun 17 16:27:51 2020 gautamUpdateVACQuestions/comments on vacuum

I missed the vacuum discussion on the call today, but I have some questions/comments:

  • Isn’t it true that we didn’t digitally monitor any of the TP diagnostic channels before 2018 December? I don’t have the full history but certainly there wasn’t any failure of the vacuum system connected to pump current/temp/speed from Sep 2015-Dec2018, whereas we have had 2 interruptions in 6 months because of flaky serial communications.
  • According to the manuals, the turbo-pumps have their own internal logic to shut off the pump when either bearing temperature exceeds 60C or current exceeds 1.5A. I agree its good to have some redundancy, but do we really expect that our outer interlock loops will function if the internal ones fail?
  • In what scenario do we expect that all our pressure gauge readbacks fail, but not the TP readbacks? If so, won’t the differential pressure conditions protect the vacuum envelope, and the TPs internal shutoffs will protect the pumps? Except during the pump down phase perhaps, when we want to give a little more headroom to the small TPs to stress them less?

At the very least, I think we should consider making the interlock code have levels (like interrupts on a micro controller). So if the pressure gauges are communicating and are reporting acceptable pressure readings, we should be able to reject unphysical readbacks from the TP controllers.

I still don’t understand why TP2 can’t back TP1, but we just disable all the software interlock conditions contingent on TP2 readbacks. This pump is far newer than TP3, and unless I’ve misunderstood something major about the vacuum infrastructure, I don’t really see why we should trust this flaky serial readbacks for any actionable interlocks, at least without some AND logic (since temperature, current and speed aren’t really independent variables).

I also think we should finally implement the email alert in the event the vacuum interlock is tripped. I can implement this if no one else volunteers.

This might also be a good reminder to get the documentation in order about the new vacuum system.

  15406   Thu Jun 18 11:00:24 2020 JonUpdateVACQuestions/comments on vacuum
Quote:
  • Isn’t it true that we didn’t digitally monitor any of the TP diagnostic channels before 2018 December? I don’t have the full history but certainly there wasn’t any failure of the vacuum system connected to pump current/temp/speed from Sep 2015-Dec2018, whereas we have had 2 interruptions in 6 months because of flaky serial communications.

Looking at images of the old vac screens, the TP2/3 rotation speed and status string were digitally monitored. However I don't know if there were software interlocks predicated on those.

Quote:
  • According to the manuals, the turbo-pumps have their own internal logic to shut off the pump when either bearing temperature exceeds 60C or current exceeds 1.5A. I agree its good to have some redundancy, but do we really expect that our outer interlock loops will function if the internal ones fail?

The temperature and current interlocks are implemented precisely because the pumps can shut themselves off. The concern is not about damaging the pumps (their internal logic protects against that); it's that a pump could automatically shut down and back-vent the IFO to atmosphere. Another interlock (e.g., the pressure differentials) might catch it, but it would depend on the back-vent rate and the scenario has never been tested. The temperature and current interlocks are set to trip just before the pump reaches its internal shut-down threshold.

One way we might be able to reduce our reliance on the flaky serial readbacks is to implement rotation-speed hardware interlocks. The old vac documentation alludes to these, but as far as Chub and I could determine in 2018, they never actually existed. The older turbo controllers, at least, had an analog output proportional to speed which could be used to control a relay to interrupt the V4/5 control signals. I'll look into this for the new controllers. If it could be done, we could likely eliminate the layer of serial-readback interlocks altogether.

 
  • I also think we should finally implement the email alert in the event the vacuum interlock is tripped. I can implement this if no one else volunteers.

That would be awesome if you're willing to volunteer. I agree this would be great to have.

  15407   Thu Jun 18 12:00:36 2020 gautamUpdateVACQuestions/comments on vacuum

I agree there were MEDM fields, but I can't find any record of these channels being recorded till 2018 December, so I don't agree that they were being digitally monitored. You can also look back in the elog (e.g. here and here) and see that the display fields are just blank. I would then assume that no interlocks were dependent on these channels, because otherwise the vacuum interlocks would be perpetually tripped.

Looking at images of the old vac screens, the TP2/3 rotation speed and status string were digitally monitored. However I don't know if there were software interlocks predicated on those.

Sorry but I'm having trouble imagining a scenario how the pressure gauges wouldn't register this before the IFO volume is compromised. Is there some back of the envelope calculations I can do to understand this? Since both the pressure gauges and the TP diagnostic channels are being monitored via EPICS, the refresh rate is similar, so I don't see how we can have a pump temperature / speed / current threshold tripped but NOT have this be registered on all the pressure gauges, seems like a bit of a contrived scenario to me. Our thresholds currently seem to be arbitrary numbers anyway, or are they based on some expected backstreaming rate? Isn't this scenario degenerate with a leak elsewhere in the vacuum envelope that would be caught by the differential pressure interlocks?

The temperature and current interlocks are implemented precisely because the pumps can shut themselves off. The concern is not about damaging the pumps (their internal logic protects against that); it's that a pump could automatically shut down and back-vent the IFO to atmosphere. Another interlock (e.g., the pressure differentials) might catch it, but it would depend on the back-vent rate and the scenario has never been tested. The temperature and current interlocks are set to trip just before the pump reaches its internal shut-down threshold.

For the email alert, can you expose a soft channel that is a flag - if this flag is not 1, then the service will send out an email.

That would be awesome if you're willing to volunteer. I agree this would be great to have.
  15408   Thu Jun 18 14:13:03 2020 JonUpdateVACQuestions/comments on vacuum
I agree there were MEDM fields, but I can't find any record of these channels being recorded till 2018 December, so I don't agree that they were being digitally monitored. You can also look back in the elog (e.g. here and here) and see that the display fields are just blank. I would then assume that no interlocks were dependent on these channels, because otherwise the vacuum interlocks would be perpetually tripped.

Right, I doubt they were ever recorded or used for interlocks. But the readbacks did work at one point in the past. There's a photo of the old vac monitor screen on p. 19 of E1500239 (last updated 2017) which shows the fields once alive.

Sorry but I'm having trouble imagining a scenario how the pressure gauges wouldn't register this before the IFO volume is compromised. Is there some back of the envelope calculations I can do to understand this? Since both the pressure gauges and the TP diagnostic channels are being monitored via EPICS, the refresh rate is similar, so I don't see how we can have a pump temperature / speed / current threshold tripped but NOT have this be registered on all the pressure gauges, seems like a bit of a contrived scenario to me. Our thresholds currently seem to be arbitrary numbers anyway, or are they based on some expected backstreaming rate? Isn't this scenario degenerate with a leak elsewhere in the vacuum envelope that would be caught by the differential pressure interlocks?​

I don't disagree that the pressure gauges would register the change. What I'm not sure about is whether the change would violate any of the existing interlock conditions, triggering a shutdown. Looking at what we have now, the only non-pump-related conditions I see that might catch it are the diffpres conditions:

  • abs(P2 - PTP2) > 1 torr (for a TP2 failure)

  • abs(P3 - PTP3) > 1 torr (for a TP3 failure)

  • abs(P1a - P2) > 1 torr (for either a TP2 or TP3 failure)

For the P1a-P2 differential, the threshold of 1 torr is the smallest value that in practice still allows us to pump down the IFO without having to disable the interlocks (P1a-P2 is the TP1 intake/exhaust differential). The purpose of the P2-PTP2/P3-PTP3 differentials is to prevent V4/5 from opening and suddenly exposing the spinning turbo to high pressure. I'm not aware of a real damage threshold calculation that any one has done; I think < 1 torr is lore passed down by Steve.

If a turbo pump fails, the rate it would backstream is unknown (to me, at least) and likely depends on the failure mode. The scenario I'm concerned about is if the backstream rate is slower than the conduction time through the pumspool and into the main volume. In that case, the pressure gauges will rise more or less together all the way up to atmosphere, likely never crossing the 1 torr differential pressure thresholds.

For the email alert, can you expose a soft channel that is a flag - if this flag is not 1, then the service will send out an email.

There's already a channel C1:Vac-error_status, where if the value is anything other than an empty string, there is an interlock tripped. Does that work?

  15410   Thu Jun 18 15:46:34 2020 gautamUpdateVACQuestions/comments on vacuum

So why not just have a special mode for the interlock code during pumpdown and venting, and during normal operation we expect the main volume pressure to be <100uTorr so the interlock trips if this condition is violated? These can just be EPICS buttons on the Vac control MEDM screen. Both of these procedures are not "business as usual", and even if we script them in the future, it's likely to have some operator supervising, so I don't think it's unreasonable to have to switch between these modes. I just think the pressure gauges have demonstrated themselves to be much more reliable than these TP serial readbacks (as you say, they worked once upon a time, but that is already evidence of its flakiness?). The Pirani gauges are not ultra-reliable, they have failed in the past, but at least less frequently than this serial comm glitching. In fact, if these readbacks are so flaky, it's not impossible that they don't signal a TP shutdown? I just think the real power of having these multi-channel diagnostics is lost without some AND logic - a turbopump failure is likely to result in an increase in pump current and temperature increase and pump speed decrease, so it's not the individual channel values that should be determining if an interlock is tripped.

I definitely think that protecting the vacuum envelope is a priority - but I don't think it should be at the expense of commissioning time. But if you think these extra interlocks are essential to the safety of the vacuum system, I withdraw my request.

I don't disagree that the pressure gauges would register the change. What I'm not sure about is whether the change would violate any of the existing interlock conditions, triggering a shutdown. Looking at what we have now, the only non-pump-related conditions I see that might catch it are the diffpres conditions:

It would be better to have a flag channel, might be useful for the summary pages too. I will make it if it is too much trouble.

There's already a channel C1:Vac-error_status, where if the value is anything other than an empty string, there is an interlock tripped. Does that work?
  15413   Fri Jun 19 07:40:49 2020 JonUpdateVACQuestions/comments on vacuum

I think we should discuss interlock possibilities at a 40m meeting. I'm reluctant to make the system more complicated, but perhaps we can find ways to reduce the reliance on the turbo pump readbacks. I agree they've proven to be the least reliable.

While we may be able to improve the tolerance to certain kinds of hardware malfunctions (and if so, we should), I don't see interlocks triggering on abnormal behavior of critical equipment as the root problem. As I see it, our bigger problem is with all the malfunctioning, mostly end-of-lifetime pieces of vacuum equipment still in use. If we can address the hardware problems, as I'm trying to do with replacements [ELOG 15412], I think that in itself will make the interlocking much less of an issue.

Quote:

So why not just have a special mode for the interlock code during pumpdown and venting, and during normal operation we expect the main volume pressure to be <100uTorr so the interlock trips if this condition is violated? These can just be EPICS buttons on the Vac control MEDM screen. Both of these procedures are not "business as usual", and even if we script them in the future, it's likely to have some operator supervising, so I don't think it's unreasonable to have to switch between these modes. I just think the pressure gauges have demonstrated themselves to be much more reliable than these TP serial readbacks (as you say, they worked once upon a time, but that is already evidence of its flakiness?). The Pirani gauges are not ultra-reliable, they have failed in the past, but at least less frequently than this serial comm glitching. In fact, if these readbacks are so flaky, it's not impossible that they don't signal a TP shutdown? I just think the real power of having these multi-channel diagnostics is lost without some AND logic - a turbopump failure is likely to result in an increase in pump current and temperature increase and pump speed decrease, so it's not the individual channel values that should be determining if an interlock is tripped.

Ok, this can be added pretty easily. Its value will just be toggled between 1 and 0 every time the interlock server raises/clears the existing string channel. Adding the channel will require restarting the whole vac IOC, so I'll do it at a time when Jordan is on hand in case something fails to come back up.

Quote:

It would be better to have a flag channel, might be useful for the summary pages too. I will make it if it is too much trouble.

  15415   Fri Jun 19 09:57:35 2020 gautamUpdateVACQuestions/comments on vacuum

For this particular email service, ideally the email should be sent out as soon as the interlock is tripped, so this would require a line of code to be added to the main interlock code. Which I guess would require a restart of the interlock service. So let me know when you guys plan to do the dry-pump tip seal replacement operation (when I presume valves will be closed anyways) so that we can do this in a minimally invasive way.

Quote:

Ok, this can be added pretty easily. Its value will just be toggled between 1 and 0 every time the interlock server raises/clears the existing string channel. Adding the channel will require restarting the whole vac IOC, so I'll do it at a time when Jordan is on hand in case something fails to come back up.

  8509   Mon Apr 29 23:02:48 2013 KojiConfigurationLSCQuestons

Q. How much Schnupp asymmetry we want in order to improve the signal ratio between PRCL/MICH in REFL ports?

Q. How much can we increase Schnupp asymmetry in the practical constraints?

Q. How PRCL/MICH ratio is different the REFL ports?
=> My modeling (many years ago) shows the ratio of {115, 51, 26, 23} for REFL{11, 33, 55, 165}.
These numbers should be confirmed by modern simulation of the 40m with updated parameters.
I should definitely use 55MHz but also prepare better 165MHz too.

Q. How the TT/PRM motions are affecting the lock stability? How can we quantify this effect? How can we mitigate this issue?

Q. Can we somehow change the sensing matrix by shifting the modulation frequency?

Q. Is normalization by POP22 or POP110 actually working well?
=> Time series measurement of error signals & servo inputs

  9850   Thu Apr 24 16:25:31 2014 ericqUpdateLSCQuick CM servo prep

I added ~1m of cable to the LO side of the REFL11 Demodulator, which brought its PRCL demod phase to about 8 degrees. According to my simulations, PRCL and CARM have the same angle (but opposite sign) at resonance. There seems to be a severe lack of SMA cables in the lab, so I didn't tune it to be any closer. Cos(8 degrees)=.99, so I think it should be fine to use it for the CARM servo, since none of the other signals are going to be nearly as big. I plugged analog REFL 11 I back into the CARM servo IN1. 

As for IN2, I threw together a temporary setup for using REFLDC as a complementary signal. I T'd off the REFLDC signal (which is the DC signal out of REFL55), and sent it into an SR560 to subtract an offset. The offset comes from a 1Hz-passive-pomona-box-low-passed C1:IOO-TT4_LR output, since there are 8 DAC channels set up for the nonexistent tip tilts 3 and 4 actively running. The output of the SR560 is sent to the CARM servo IN2. 

I adjusted the offset by turning on only IN2 in the CARM servo MEDM screen, and looking at the CM_SLOW signal in data viewer. I adjusted gains and such to get it to look just like REFLDC with the PRC locked. There was good coherence and no appreciable phase difference from DC out to some kHz, albeit a dip in coherence to about .8-.9 from ~40 to 300Hz, for some reason. (This included turning on the unWhite FM in the REFLDC filter bank)

If this signal turns out to be useful, it will be relatively straightforward to put together a little box that does the offset subtraction nicely, but this should do for our immediate needs.

Lastly, I hung up this plot in the control room to give us information about the DC values of different signals as the CARM offset changes. This is helpful to see what our CARM offset is, based on the transmission we se, when different signals start to have length dependence, where they start/stop being linear, etc. The TRX curve is scaled to a maximum of 600, REFLDC is normalized to input power = 1, and all the rest are arbitrarily scaled to fit on the plot. I've assumed 75ppm loss on all mirrors in my simulation (PRM, BS, 2xITM, 2xETM), mostly to get some realistic profile of REFLDC. 

carmOffsetProfiles.pdf

  12591   Wed Nov 2 12:05:00 2016 ericqUpdateASCQuick WFS thoughts

I poked around a bit thinking about what we need for a single AS WFS. 

New things that we would need:

Things we have:

  • Many Eurocard-style Whitening chassis, such as we use for all of the LSC PDs. 
  • Enough ADC (c1ioo has two ADCs, but doesn't even use 32 channels, so we can steal one, and throw it into c1lsc)

We'd have 12 new signals to acquire: 4 quadrants x DC, I, Q. In principle the DC part could go into a slow channel, but we have the ADC space to do it fast, and it'll be easier than mucking around with c1iscaux or whatever.

Open question: What to do about AA? A quick search didn't turn up any eurocard AA chassis like the ones we use for the LSC PDs. However, given the digital AA that happens from 64kHz->16kHz in the IOP, we've talked about disabling/bypassing the analog AA for the LSC signals. Maybe we can do the same for the QPD signals? Or, modify the post-demod audioband amplifer in the demod chassis to have some simple, not too agressive lowpass.

  11594   Mon Sep 14 16:50:12 2015 ericqUpdateLSCQuick note

Just a heads up while I'm out for a bit: the delay line is currently installed in the 55MHz modulation path. 

I'll be back later, and will revert the setup.

  11508   Fri Aug 14 21:40:26 2015 IgnacioUpdateLSCQuick static offline subtractions of YARM

Plotte below are the resultant subtractions for YARM using different witness configurations,

The best subtraction happens with all the channels of both the GUR1 and T240 seismometers, but one gets just as good subtraction without using the z channels as witnesses. 

Also, why is the T240 seismometer better at subtracting noise for YARM compared to what GUR1 alone can acomplish? Using only the X and Y channels for the T240 gave the third best subtraction(purple trace). 

My plan for now is as follows:

1) Measure the transfer function from the ETMY actuator to the YARM control signal

2) Collect data for YARM when FF for MCL is on in order to see what kind of subtractions can be done.

  8156   Mon Feb 25 13:01:39 2013 KojiSummaryGeneralQuick, compact, and independent tasks

- IMC PDH demodulation phase adjustment

- Permanent setup for green transmission DC PDs  on the PSL table

  1010   Tue Sep 30 19:50:27 2008 JenneUpdatePSLQuicky Summary - more details later
Quicky summary for now, more details later tonight / tomorrow morning:

PMC notch: It's tuned up, but it is out, and it is staying out. It looks like the 18.3kHz junk isn't being helped by the brick, in fact the brick makes it worse. And the notch isn't enough to make the peak go away. Rana's and my conclusions about the PMC: the 18.3kHz resonance is associated with the way the PMC touches its mount. Depending on where we push (very gently, not much pressure) on the PMC, we can make the peak come and go. Also, if the PMC happens to be set nicely on its ball bearings, the peak doesn't appear. More notes on this later.

PMC's RF modulation depth: Since with the PMC's brick off, and the PMC sitting nicely on its ball bearings, we don't see any crazy oscillations, we were able to take the gain slider on the PMC screen all the way up to 30dB. To give us more range, we changed the modulation depth of the RF to 2V, from its previous value of 1V.

Phase of PMC servo: Since the phase of the PMC servo hasn't been set in a while, I eyeballed it, and set the phase to: Phase Flip = 180, Phase Slider = 4.8000 . I measured many points, and will plot a calibration curve later.

I also measured the actual value of the RF out of the PMC's LO board, when changing the RF output adjust slider. Again, will post the calibration later.

The attached PNG shows the PMC spectra from now and from Aug. 30 (ref). As you can see there's been some good reduction in the acoustic noise (red v. orange). The large change in the error signal is because of the much higher gain in the servo now. We'll have to redo this plot once Jenne measures the new UGF.
  6494   Fri Apr 6 11:32:09 2012 JenneUpdateComputersRAID array is rebuilding....

Suresh reported to Den, who reported to me (although no elogs were made.....) that something was funny with the FB.  I went to look at it, and it's actually the RAID array rebuilding itself.  I have called in our guru, Jamie, to have a look-see.

  6495   Fri Apr 6 14:39:21 2012 JamieUpdateComputersRAID array is rebuilding....

The RAID (JetStor SATA 416S) is indeed resyncing itself after a disk failure.  There is a hot spare, so it's stable for the moment.  But we need a replacement disk:

    RAID disks:  1000.2GB Hitachi HDT721010SLA360

Do we have spares?  If not we should probably buy some, if we can.  We want to try to keep a stock of the same model number.

Other notes:

The RAID has a web interface, but it was for some reason not connected.  I connected it to the martian network at 192.168.113.119.

Viewing the RAID event log on the web interface silences the alarm.

I retrieved the manual from Alex, and placed it in the COMPUTER MANUALS drawer in the filing cabinet.

  1973   Tue Sep 8 15:14:26 2009 rana, alexConfigurationDAQRAID update to Framebuilder: directories added + lookback increased

 Alex logged in around 10:30 this morning and, at our request, adjusted the configuration of fb40m to have 20 days of lookback.

I wasn't able to get him to elog, but he did email the procedure to us:


1) create a bunch of new "Data???" directories in /frames/full
2) change the setting in /usr/controls/daqdrc file
       set num_dirs=480;

my guess is that the next step is:

3) telnet fb0 8087

    daqd>  shutdown

I checked and we do, in fact, now have 480 directories in /frames/full and are so far using up 11% of our 13TB capacity. Lets try to remember to check up on this so that it doesn't get overfull and crash the framebuilder.

  6082   Wed Dec 7 18:47:36 2011 JenneUpdateRF SystemRAM Mon is now being demodulated

There were 2 open outputs on the splitter in the RAMmon (formerly known as Stochmon) box underneath the BS oplev table.  The input to the splitter comes from the Thorlabs PD that we're using as our RAM monitoring PD.  2 of the outputs go to the RMS detection of 11 and 55 MHz.  Now the other 2 (previously terminated) outputs go over to the LSC rack via SMA cable.  The signal on both channels is ~200mV pk-pk, so -10dBm.  One is plugged into the AS11 demod board (which didn't have a PD input yet), and the other goes to POP55's demod board, so POP55 is not what you think it is for now.

Koji is working on checking out the Rich box, which has 4 demodulators, which we will use eventually.  Right now we're just using the already-plugged-in demod boards so we can start looking at some trends of RAM.  We're going to need to find some channels when we're ready for the switchover.

Zach is nearing completion of the mini-update to the temp sensing system.  Once we have the new more sensitive temp sensor in place, we can have a look-see at the similarities between EOM temperature and RAM levels.

  6084   Thu Dec 8 00:04:50 2011 ranaUpdateIOORAM Mon is now being demodulated

Monitoring good, but remember that the EOM alignment must be done carefully to minimize the RAM before we can use these trends.

  6059   Thu Dec 1 12:27:51 2011 ZachMetaphysicsRF SystemRAM diagnosis/suppression plan?

It seems like there is some confusion---or disagreement---amongst the lab about how to proceed with the RAM work (as Rana mentioned at the TAC meeting, we will henceforth refer to it only as "RAM" and never as "RFAM"; those who refuse to follow this protocol will be taken out back and shot).

I would like to provide a rough outline and then request that people reply with comments, so that we can get a collective picture of how this should work. I have divided this into two sections: 1) Methodology, which is concerned with the overall goal of the testing and the procedure for meeting them, and 2) General Issues, which are broadly important regardless of the chosen methodology.

1. Methodology

There are two broad goals:

  • Characterization of extant RAM
    • Measuring the RAM levels existing in an aLIGO-type interferometer without any suppression systems
    • Modeling to estimate the effect on IFO control and corroboration with measurements where possible
      • DC RAM levels contributing offsets to IFO operating point
      • Quasi-DC RAM levels affecting long term detector tuning (e.g., sensing matrix, MICH -> DARM feedforward, etc.)
      • Audio-frequency RAM contributing noise directly via error point modulation
    • Modeling to scale/adapt results from 40m -> aLIGO
  • Mitigation
    • Developing and assessing systems for suppressing RAM
      • Passive: thermal shielding and isolation
      • Active: EOM temperature control
        • Simple temperature stabilization
        • RAM error signal

The question is: which is our goal? The first, the second, or both? If both, what priority is given to which and can/should they be done in parallel? Also, task distribution.

 

2. General Issues

These are loosely related, so they are in random order:

  • Sensing
    • Temperature
      • What is the priority/urgency of a precision AC-bridge-readout temperature sensor?
      • If priority/urgency is low, what is the priority/urgency of upgrading breadboard controller to protoboard version? The common answer will be "make the protoboard version now", but if the urgency of the final AC sensing is high, it may make sense to focus on finalizing that design (after all, other experiments are waiting on a precision temperature controller, and it is not cost-effective to make many temporary controllers as I have done for the 40m).
      • Sensor noise issues
        • What is the sensor-noise-limited temperature stabilization level?
        • What is our willingness to tolerate the thermal low-passing of the EOM can itself (i.e., what is our sensitivity to gradients)?
        • To answer the above questions, we need to perform stabilization tests with several sensors on the same can, with some in loop (averaged) and some out of loop.
        • If we determine that gradients are a problem, we may need to:
          • Design a casing for outside the EOM (inside the foam box) to make the heating uniform, or
          • We may be able to get away with a more customized heater (instead of heating the can from one side as we do now).
    • Optical RAM
      • Stochmon is a nice diagnostic tool, but do we want something better? In particular, we want to have linear signals about a zero-DC-RAM point, which requires phase
        • Where will this sensor be located?
        • What kind of PD will it be? Broadband? Multi-resonant?
        • What sort of electronics will we need? If we are going to use this as an error signal for controlling the EOM temperature, it is just as important as any other IFO readout, since it may couple into all of them.
          • RF pickup is a BIG ISSUE HERE
          • How will the demodulation phases be selected? It should be possible to take TF measurements in certain misaligned (i.e., non-resonant) conditions and adjust the relative phase between the RAM readouts and standard IFO RF readouts such that they are in phase, but this will require some thinking.
          • Lots more, I'm sure
  • Control
    • Method (overlaps some with methodology portion)
      • What is better, simple temperature stabilization or RAM feeback? (More likely, "how much better is RAM feedback?")
      • If RAM feedback is difficult or impossible to implement effectively (see below), is temperature stabilization good enough?
    • Regime
      • Depending on extant RAM levels and on achievable sensing noise, it will be unwise and/or unnecessary to have a RAM control bandwidth above some relatively low frequency (~sub Hz)
        • Gain where RAM suppression is not needed only injects noise into the system
        • This cutoff frequency is largely determined by the thermal response of the system, but additional filtering will likely be necessary to reduce higher-frequency noise coupling (e.g., nonlinear downconversion of high-frequency signals into heater dissipation, etc.)
    • Efficacy
      • If we do RAM feedback, which signal (i.e. which frequency and quadrature) do we minimize?
        • Do we achieve large common-mode reduction across all RF signals, or is there some differential component?
        • In particular, do we make some or all other control signals noisier by stabilizing/minimizing RAM in one channel?
        • If the answer is yes, can we derive an effective control signal from a linear combination of some or all individual RAM signals?

 

There are probably many other issues I have neglected, so please comment on this rough draft as you see fit!

  6069   Mon Dec 5 09:46:21 2011 ZachMetaphysicsRF SystemRAM diagnosis/suppression plan?

Since no one has made any comments, I will assume that everyone is either 100% satisfied with the outline or they have no interest in the project. Under this assumption, I will make decisions on my own and begin planning the individual steps in more detail.

In particular, I will assume that our goal comprises BOTH characterization of RAM levels and mitigation, and I will try to find the best way that both can be achieved as simultaneously as possible. 

  10625   Fri Oct 17 17:52:55 2014 JenneUpdateLSCRAM offsets

Last night I measured our RAM offsets and looked at how those affect the PRMI situation.  It seems like the RAM is not creating significant offsets that we need to worry about.


Words here about data gathering, calibration and calculations.

Step 1:  Lock PRMI on sideband, drive PRM at 675.13Hz with 100 counts (675Hz notches on in both MICH and PRCL).  Find peak heights for I-phases in DTT to get calibration number.

Step 2:  Same lock, drive ITMs differentially at 675.13Hz with 2,000 counts.  find peak heights for Q-phases in DTT to get calibration number.

Step 3:  Look up actuator calibrations.  PRM = 19.6e-9/f^2 meters/count and ITMs = 4.68e-9/f^2 meters/count.  So, I was driving PRM about 4pm, and the ITMs about 20pm.

Step 4:  Unlock PRMI, allow flashes, collect time series data of REFL RF siganls.

Step 5: Significantly misalign ITMs, collect RAM offset time series data.

Step 6: Close PSL shutter, collect dark offset time series data.

Step 7: Apply calibration to each PD time series.  For each I-phase of PDs, calibration is (PRM actuator / peak height from step 1).  For each Q-phase of PDs, calibration is (ITM actuator / peak height from step 2).

Step 8:  Look at DC difference between RAM offset and dark offset of each PD.  This is the first 4 rows of data in the summary table below.

Step 9:  Look at what peak-to-peak values of signals mean.  For PRCL, I used the largest pk-pk values in the plots below.  For MICH I used a calculation of what a half of a fringe is - bright to dark.  (Whole fringe distance) = (lambda/2), so I estimate that a half fringe is (lambda/4), which is 266nm for IR.  This is the next 4 rows of data in the table.

Step 10: Divide.  This ratio (RAM offset / pk-pk value) is my estimate of how important the RAM offset is to each length degree of freedom. 


Summary table:

  PRCL (I-phase) MICH (Q-phase)
RAM offsets    
11 4e-11 m 2.1e-9 m
33 1.5e-11 m ~2e-9 m
55 2.2e-11 m ~1e-9 m
165 ~1e-11 m ~1e-9 m
Pk-pk (PDH or fringes) PDH pk-pk from flashes MICH fringes from calculation
11 5.5e-9 m 266e-9 m
33 6.9e-9 m 266e-9 m
55 2.5e-9 m 266e-9 m
165 5.8e-9 m 266e-9 m
Ratio: (RAM offset) / (pk-pk)    
11 7e-3 8e-4
33 2e-3 7e-3
55 9e-3 4e-3
165 2e-3 4e-3

 


Plots (Left side is several PRMI flashes, right side is a zoom to see the RAM offset more clearly):

RAM_PRMI_PRMIflashing_REFL11I.pdfRAM_PRMI_Zoom_REFL11I.pdf

RAM_PRMI_PRMIflashing_REFL11Q.pdfRAM_PRMI_Zoom_REFL11Q.pdf

RAM_PRMI_PRMIflashing_REFL33I.pdfRAM_PRMI_Zoom_REFL33I.pdf

RAM_PRMI_PRMIflashing_REFL33Q.pdfRAM_PRMI_Zoom_REFL33Q.pdf

RAM_PRMI_PRMIflashing_REFL55I.pdfRAM_PRMI_Zoom_REFL55I.pdf

RAM_PRMI_PRMIflashing_REFL55Q.pdfRAM_PRMI_Zoom_REFL55Q.pdf

RAM_PRMI_PRMIflashing_REFL165I.pdfRAM_PRMI_Zoom_REFL165I.pdf

RAM_PRMI_PRMIflashing_REFL165Q.pdfRAM_PRMI_Zoom_REFL165Q.pdf

  6417   Wed Mar 14 16:33:20 2012 keikoUpdateLSCRAM simulation / RAM pollution plot

In the last post, I showed that SRCL element in the MICH sensor (AS55I-mich) is chaned 1% due to RAM.

Here I calculated how is this 1% residual in MICH sensor (AS55 I-mich) shown in MICH sensitivity. The senario is:

(1) we assume we are canceling SRCL in MICH by feed forward first (original matrix (2,3) element).

(2) SRCL in MICH (matrix(2,3) is changed 1% due to RAM, but you keep the same feed forward with the same feedforward gain

(3) You get 1% SRCL residual motion in MICH sensor. This motion depends on how SRCL is quiet/loud. The assumed level is

Pollution level = SRCL shot noise level in SRCL sensor  x  SRCL closed loop TF  x  1% residual .... the following plot.

 

 

AS sensor = AS55I-mich  --- SN level 2.4e-11 W/rtHz ------- MICH SN level 6e-17 m/rtHz

SRCL sensor = AS55 I-SRCL --- SN level 2e-11 W/rtHz ---  SRCL SN level 5e-14 m/rtHz

 

 

RAMexampleplot.png

 

 

Quote:

Adding some more results with more realistic RAM level assumption.

(4) With 0.1% RAM mod index of PM (normalized by (1) )

  PRCL MICH SRCL
REFL11I 0.99999 -0.001807 -0.000148
AS 55 Im 0.000822 1.000002 0.000475
AS 55 Is 1.068342 906.968167 1.00559
 

 

 

 

 

  6475   Mon Apr 2 18:24:34 2012 keikoUpdateLSCRAM simulation for Full ifo

 I extended my RAM script from DRMI (3DoF) to the full IFO (5DoF).

Again, it calculates the operation point offsets for each DoF from the opt model with RAM. Then the position offsets are added to the model, and calculates the LSC matrix. RAM level is assumed as 0.1% of the PM modulation level, as usual, and lossless for a simple model.

 

 

Original matrix without RAM:

REFL f1 : 1.000000    0.000000    0.000008    -0.000005    0.000003 

  AS f2 : 0.000001    1.000000    0.000005    -0.003523    -0.000001 

 POP f1 : -3956.958708    -0.000183    1.000000    0.019064    0.000055 

 POP f2 : -32.766392    -0.154433    -0.072624    1.000000    0.024289 

 POP f2 : 922.415913    -0.006625    1.488912    0.042962    1.000000 

 

(MICH and SRCL uses the same sensor, with optimised demodulation phase for each DoF.) 

Operation position offsets are:

PRCL   -3.9125e-11 m

SRCL    9.1250e-12 m

CARM  5.0000e-15 m  

and no position offsets for DARM and MICH (because they are differential sensor and not affected by RAM offsets).

 

Resulting matrix with RAM + RAM offsets, normalised by the original matrix:  

REFL f1 : 0.001663    -0.000000    0.003519    0.000005    -0.000003 

  AS f2 : 0.000004    0.514424    0.000004    -0.001676    -0.000001 

 POP f1 : 7.140984    -0.001205    15.051807    0.019254    0.000417 

 POP f2 : 0.029112    -0.319792    0.042583    1.000460    0.024298 

 POP f2 : -0.310318    -0.014385    -1.761519    0.043005    0.999819 

 

As you can see in the second matrix, the CARM and DARM rows are completely destroyed by the RAM offsets! The signals are half reduced in the DARM case, so the mixture between DARM and MICH are about 50% degraded.

 I also would like to extend this script to use the DC readout, but don't know how to calculate the postion offset for AS_DC because the error signal is not zero-crossing for AS_DC anymore. Do you have any suggestions for me?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  6478   Tue Apr 3 01:52:15 2012 ZachUpdateLSCRAM simulation for Full ifo

Quote:

 I also would like to extend this script to use the DC readout, but don't know how to calculate the postion offset for AS_DC because the error signal is not zero-crossing for AS_DC anymore. Do you have any suggestions for me?

 I don't think I understand the question. AS_DC should not have a zero crossing, correct?

  6480   Tue Apr 3 14:11:33 2012 keikoUpdateLSCRAM simulation for Full ifo

Quote:

Quote:

 I also would like to extend this script to use the DC readout, but don't know how to calculate the postion offset for AS_DC because the error signal is not zero-crossing for AS_DC anymore. Do you have any suggestions for me?

 I don't think I understand the question. AS_DC should not have a zero crossing, correct?

 That's right. I calculate the offset of the operation point (when you have RAM) from the zero-crossing point of the PDH signals. I don't know how to do that for AS_DC, because it doesn't cross zero anymore anytime.

  6481   Tue Apr 3 14:17:18 2012 keikoUpdateLSCRAM simulation for Full ifo

I add a flow-chart drawing what the scripts do and how the scripts calculate the LSC matrix.

flowchart.png

 

(1) First, you calculate the LSC matrix WITHOUT RAM or anything, just for a reference. This is the first matrix shown in the quoted post.

(2) The script calculates the LSC matrix with RAM. Also, the heterodyne signals for all 5 DoF are calculated. The signals have offsets due to the RAM effect. The operating position offsets are saved for the next round.

(3) The script calculates the LSC matrix again, with RAM plus the offset of the operation points. The matrix is shown in the last part of the quoted post.

 

Now I am going to check (A) LSC matrices (matrix 2, the second matrix of above chart) with different RAM levels (B) Are pos-offsets degrade the CARM and DARM so much (See, the quated result below), is that true?

Quote:

Original matrix without RAM:

REFL f1 : 1.000000    0.000000    0.000008    -0.000005    0.000003 

  AS f2 : 0.000001    1.000000    0.000005    -0.003523    -0.000001 

 POP f1 : -3956.958708    -0.000183    1.000000    0.019064    0.000055 

 POP f2 : -32.766392    -0.154433    -0.072624    1.000000    0.024289 

 POP f2 : 922.415913    -0.006625    1.488912    0.042962    1.000000 

 

(MICH and SRCL uses the same sensor, with optimised demodulation phase for each DoF.) 

Operation position offsets are:

PRCL   -3.9125e-11 m

SRCL    9.1250e-12 m

CARM  5.0000e-15 m  

and no position offsets for DARM and MICH (because they are differential sensor and not affected by RAM offsets).

 

Resulting matrix with RAM + RAM offsets, normalised by the original matrix:  

REFL f1 : 0.001663    -0.000000    0.003519    0.000005    -0.000003 

  AS f2 : 0.000004    0.514424    0.000004    -0.001676    -0.000001 

 POP f1 : 7.140984    -0.001205    15.051807    0.019254    0.000417 

 POP f2 : 0.029112    -0.319792    0.042583    1.000460    0.024298 

 POP f2 : -0.310318    -0.014385    -1.761519    0.043005    0.999819 

 

 

 

  6482   Tue Apr 3 15:50:58 2012 keikoUpdateLSCRAM simulation for Full ifo

Oops, Yesterday's results for DARM was wrong!

I got more convincing results now. 

 

> (B) Are pos-offsets degrade the CARM and DARM so much (See, the quoted result below), is that true? 

 

Here is the new results. It does change CARM a lot, but not DARM:
 
Matrix1 (normalised so that the diagonals are 1):
REFL f1 : 1.000000    0.000000    0.000008    -0.000005    0.000003 
  AS f2  : 0.000001    1.000000    0.000005    -0.003523    -0.000001 
 POP f1 : -3956.958708    -0.000183    1.000000    0.019064    0.000055 
 POP f2 : -32.766392    -0.154433    -0.072624    1.000000    0.024289 
 POP f2 : 922.415913    -0.006625    1.488912    0.042962    1.000000 
(=Matrix 2)
 
Position offsets:
only CARM, 4.6e-16 (this number changed because I increased the resolution of the calculation)
 
Matrix3 (normalised by matrix 1):
REFL f1 : 0.039780    -0.000000    0.003656    0.000005    -0.000003 
  AS f2  : 0.000008    1.000017    0.000005    -0.003499    -0.000001 
 POP f1 : 159.146819    -0.000138    15.605155    0.019393    0.000055 
 POP f2 : 1.277223    -0.154415    0.047344    1.000008    0.024289 
 POP f2 : -35.422498    -0.006633    -1.886454    0.042963    1.000000 

 

  • CARM got a small position offset which degrades CARM signal 2 orders of mag (still the biggest signal in the sensor, though).
  • DARM was not so bad, and probably the change of the DoF mixture is mostly not changed.
  • Matrices don't change only with 1e-4 RAM. It changes with position offsets.
  • I'll see how the matrix changes without position offsets but only with RAM effects, changing RAM levels.
  • Again, above is C1 configuration, 1e-4 RAM level of PM level.

 

 

Quote:

I add a flow-chart drawing what the scripts do and how the scripts calculate the LSC matrix.

flowchart.png

 

(1) First, you calculate the LSC matrix WITHOUT RAM or anything, just for a reference. This is the first matrix shown in the quoted post.

(2) The script calculates the LSC matrix with RAM. Also, the PDH signals for all 5 DoF are calculated. The PDH signals have offsets due to the RAM effect. The operating position offsets are saved for the next round.

(3) The script calculates the LSC matrix again, with RAM plus the offset of the operation points. The matrix is shown in the last part of the quoted post.

 

Now I am going to check (A) LSC matrices (matrix 2, the second matrix of above chart) with different RAM levels (B) Are pos-offsets degrade the CARM and DARM so much (See, the quated result below), is that true? 

 

  6483   Tue Apr 3 22:50:37 2012 keikoUpdateLSCRAM simulation for Full ifo

Koji and Jamie suggested me to include the coupling between DoFs when I calculate the last matrix. So far, I just add all the pos-offsets of 5 DoFs and re-calculate the matrix again. However, once I add one DoF pos-offset, it could already change the LSC matrix therefore different pos-offset to the other four DoF, we must iterate this process until we get the equilibrium pos-offsets for 5 DoFs.

I also noticed an error in the optical configuration file. AM mod levels were smaller than that supposed to be because of the hald power going through the AM-EOMs in the MZI paths. Also I have put PM-Mods in the MZT path which gives the smaller mod indexes. So, smaller mod levels were applied both for PM and AM. As PM-AM ratio is still kept in this, so the matrices were not very wrong, I assume. I'll modify that and post the results again.

  6486   Wed Apr 4 23:57:35 2012 keikoUpdateLSCRAM simulation for Full ifo

 I'm still wondering whether iteration version or simple version is closer approximation to the real situation. Sorry for few explanations here. I will try to present those on Friday.

 

Anyway, here is the results for both:

%*.*.*. Original matrix w/o RAM .*.*.*

REFL f1 : 1.000000        0.000000    -0.000003    -0.000005    0.000007 

  AS f2 : 0.000002        1.000000    0.000009    -0.003522    -0.000002 

 POP f1 : -3954.521443    -0.000965    1.000000    0.019081    -0.000152 

 POP f2 : -32.770726    -0.154433    -0.072594    1.000000    0.024284 

 POP f2 : 922.393978    -0.006608    1.488319    0.042948    1.000000 

 

*** Iteration *** 

%*.*.*. Resulting matrix w/ RAM .*.*.*

REFL f1 : 0.039125    -0.000000    0.003665       0.000005    -0.000007 

  AS f2 : 0.000010    1.000431    0.000009       -0.003500    -0.000002 

 POP f1 : 156.420221    -0.000246    15.586838    0.019406    -0.000154 

 POP f2 : 1.255806    -0.154275    0.047313       1.000008    0.024285 

 POP f2 : -34.814720    -0.006600    -1.884850    0.042950    1.000000 

Offsets converged to:

PRCL =  2.1e-15, MICH = 1.1e-17, SRCL = -3.8e-15, CARM = 2.2e-16, DARM = 0 

(POP CARMs became so much smaller compared with the other matrix below, because the offsets are added al of 5 DoFsl at once here.)

 

*** no iteration, offsets added for each DoF separately ***

REFL f1 : 0.020611        -0.000000    0.003600    0.000005    -0.000007 

AS f2   : 0.000002        1.000000    0.000009    -0.003522    -0.000002 

POP f1  : 1842.776419    -0.000198    21.533358    0.019404    -0.000132 

POP f2  : -32.700639    -0.153095    -0.072481    0.999995    0.024360 

 POP f2 : 922.393862    -0.006435    1.488298    0.042949    0.999982 

Added offsets:

PRCL =  7.5e-15, MICH = 6.25e-16, SRCL = -1.4e-14, CARM = 4.5e-16, DARM = 0

* So far, I used to add all the offsets at once. This time I add CARM and get the CARM row, add PRCL and get the PRCL row... and so on.

Quote:

Koji and Jamie suggested me to include the coupling between DoFs when I calculate the last matrix. So far, I just add all the pos-offsets of 5 DoFs and re-calculate the matrix again. However, once I add one DoF pos-offset, it could already change the LSC matrix therefore different pos-offset to the other four DoF, we must iterate this process until we get the equilibrium pos-offsets for 5 DoFs.

I also noticed an error in the optical configuration file. AM mod levels were smaller than that supposed to be because of the hald power going through the AM-EOMs in the MZI paths. Also I have put PM-Mods in the MZT path which gives the smaller mod indexes. So, smaller mod levels were applied both for PM and AM. As PM-AM ratio is still kept in this, so the matrices were not very wrong, I assume. I'll modify that and post the results again.

 

  6504   Sat Apr 7 00:31:12 2012 keikoUpdateLSCRAM simulation for Full ifo

I didn't understand how CARM can be decreased 2 orderes of magnitude and PRCL can be INCREASED by such small offsets (see the matrix quoted).

Apparently it was because of an optical-spring ish effect from the "detuning" (which is actually RAM position offsets). I put two plots which are CARM and PRCL tranfer functions to REFL f1 or POP f1, when there is a slight PRCL offset (0, 1e-14m, and 1e-15m cases are plotted). Looking at these plots, it was not a good idea to calculate the LSC matrix in DC because they are affected by this detuning a lot. I'll try f = 150 Hz for the matrix.

plot4a.pngplot4b.png

Quote:

*** Iteration *** 

%*.*.*. Resulting matrix w/ RAM .*.*.*

REFL f1 : 0.039125    -0.000000    0.003665       0.000005    -0.000007 

  AS f2 : 0.000010    1.000431    0.000009       -0.003500    -0.000002 

 POP f1 : 156.420221    -0.000246    15.586838    0.019406    -0.000154 

 POP f2 : 1.255806    -0.154275    0.047313       1.000008    0.024285 

 POP f2 : -34.814720    -0.006600    -1.884850    0.042950    1.000000 

Offsets converged to:

PRCL =  2.1e-15, MICH = 1.1e-17, SRCL = -3.8e-15, CARM = 2.2e-16, DARM = 0  

  6358   Mon Mar 5 18:12:00 2012 KeikoUpdateLSCRAM simulation update

 I wrote an RAM simulation script ... it calculates the LSC signal offset and the operation point offset depending on the RAM modulation index.

Configuration : RAM is added on optC1, by the additional Mach-Zehnder ifo before the PRM.

Mar5RAM3.pngMar5RAM2.png

 Both are for PRCL sweep result. Note that REFL33I is always almost zero. Next step: Check the LSC matrix with matrix at the offset operation point.

  6363   Tue Mar 6 15:22:02 2012 KeikoUpdateLSCRAM simulation update

Quote:

 I wrote an RAM simulation script ... it calculates the LSC signal offset and the operation point offset depending on the RAM modulation index.

Configuration : RAM is added on optC1, by the additional Mach-Zehnder ifo before the PRM.

Mar5RAM3.pngMar5RAM2.png

 Both are for PRCL sweep result. Note that REFL33I is always almost zero. Next step: Check the LSC matrix with matrix at the offset operation point.

 On the right figure, you see the non-zero operation points even when RAM mod index = 0. Apparently they come from non-zero loss of the model.  (Each mirror of 50ppm loss was assumed).

  6400   Mon Mar 12 01:04:18 2012 keikoUpdateLSCRAM simulation update, RAM LSC matrix

 I calculated the DRMI RAM LSC matrix with RAM and the operation point offsets.

  • configuration: C1 DRMI
  • RAM is added by an Mach-Zehnder ifo placed before the PRM
  • demodulation phases are optimised for each DoF
  • the operation points offset from the PDH signals are calculated and added to the optical configuration as mirror position offsets
  • Then the matrix is calculated with the offsets and the RAM
  • The set of the scrips are found as RAMmatrix.m, normMAT.m, newGetMAT.m,  on CVS/ifomodeling/40m/fullIFO_Optickle. They are a bit messy scripts at this moment.

Results:

(1) No RAM LSC matrix

  PRCL MICH SRCL
REFL11I 1 -0.001806 -0.000147
AS 55Q 0.000818 1 0.000474
AS 55 I 1.064561 902.292816 1

(2) With 1% RAM mod index of PM (normalised by (1) )

  PRCL MICH SRCL
REFL11I 1.000618 -0.001837 -0.000163
AS 55Q 0.000919 1.000521 0.000495
AS 55 I 1.169741 924.675187 1.018479
 

(3) With 5% RAM mod index of PM (normalised by (1) )

  PRCL MICH SRCL
REFL11I 0.999986 -0.001812 -0.000150
AS 55Q 0.000838 1.000028 0.000479
AS 55 I 1.084598 906.83668 1.003759
 

  6401   Mon Mar 12 18:57:58 2012 keikoUpdateLSCRAM simulation update, RAM LSC matrix

Quote:

 I calculated the DRMI RAM LSC matrix with RAM and the operation point offsets.

  • configuration: C1 DRMI
  • RAM is added by an Mach-Zehnder ifo placed before the PRM
  • demodulation phases are optimised for each DoF
  • the operation points offset from the PDH signals are calculated and added to the optical configuration as mirror position offsets
  • Then the matrix is calculated with the offsets and the RAM
  • The set of the scrips are found as RAMmatrix.m, normMAT.m, newGetMAT.m,  on CVS/ifomodeling/40m/fullIFO_Optickle. They are a bit messy scripts at this moment.

Results:

(1) No RAM LSC matrix

  PRCL MICH SRCL
REFL11I 1 -0.001806 -0.000147
AS 55Q 0.000818 1 0.000474
AS 55 I 1.064561 902.292816 1

(2) With 1% RAM mod index of PM (normalised by (1) )

  PRCL MICH SRCL
REFL11I 1.000618 -0.001837 -0.000163
AS 55Q 0.000919 1.000521 0.000495
AS 55 I 1.169741 924.675187 1.018479
 

(3) With 5% RAM mod index of PM (normalised by (1) )

  PRCL MICH SRCL
REFL11I 0.999986 -0.001812 -0.000150
AS 55Q 0.000838 1.000028 0.000479
AS 55 I 1.084598 906.83668 1.003759
 

Adding some more results with more realistic RAM level assumption.

(4) With 0.1% RAM mod index of PM (normalized by (1) )

  PRCL MICH SRCL
REFL11I 0.99999 -0.001807 -0.000148
AS 55Q 0.000822 1.000002 0.000475
AS 55 I 1.068342 906.968167 1.00559
 

(5) With 0.5% RAM mod index of  PM (normalized by (1) )

  PRCL MICH SRCL
REFL11I  0.999978  -0.001810    -0.000149 
AS 55Q 0.000830  1.000010  0.000476 
AS 55 I 1.075926 904.321433  1.001677
 

  6138   Mon Dec 19 23:50:23 2011 ZachUpdateRF SystemRAMmon

I have been looking at the swings in the RAMmon channels since the heater was reengaged, to compare them to the data from beforehand (with and without the foam box). With the large grains of salt that I will list after, it appears that the EOM temperature controller does in fact reduce the amplitude of the swings by a measurable factor.

Salt:

  1. The reason I have not included any plots here is because the data suck. What we should ideally have is a continuous stream of RAMmon signals split into three chunks: 1) no foam, no heat, 2) foam, no heat, and 3) foam and heat. Instead, we have pieces of each kind of data on different days, before and after the MC has been realigned, some in old channels and some in new so that the calibration is different, etc. This piecemeal shit will not do.
  2. I realized that the LF boost was not engaged on the heater when I turned it on most recently. For this reason, the EOM temperature has not been stabilized as well as it might have been on diurnal timescales, and so with the boost it could be that the noise reduction is greater. For posterity, the DC suppression level is ~20x without the boost.

It seems impractical to try and rope off essentially 3 straight days where nothign major can be done to the IFO just to take RAM data. Instead, I think we should figure out a way to mimic the diurnal temperature swings on ~hour timescales. The EOM can temperature follows PSL-FSS_RMTEMP almost exactly and with a very short delay, so we can probably even accomplish this by stepping the lab A/C temperature. If this won't work, we can use an incandescent lamp or something similar to heat up the area around the EOM by a noticeable amount.

I'll try to come up with a good way to do this so that we can get some reliable data...

  6109   Mon Dec 12 16:57:38 2011 JenneUpdateRF SystemRAMmon, 4 day trend

EOM was aligned to minimize the 11 and 55 MHz peaks in the RAMmon PD the other day (elog 6089), and was left with just the temperature sensor attached, no heater, no foam box.

Here is a 4 day trend:

EOM_tempSense_noFoam_noHeater_RAMmon_4days.png

I don't have a whole lot to say about this, other than there's a lot of stuff going on.  The craziness at the end is me realigning the PMC and MC since, as you can see, MC trans was way down.  The foam box was put on earlier today (elog 6104), so we'll see how that changes things over night.

  6111   Tue Dec 13 11:34:32 2011 JenneUpdateRF SystemRAMmon, 5 day trend

Now we've got another day of data, with the foam box on for the last 24hrs.

First plot is a 5 day trend so you can see that the RAM has gotten a little bit smaller, as has the temperature drift, but not by a whole lot.

EOM_tempSense_RAMmon_5days_last_day_withFoam_noHeater.png

Second plot is the last 19 hours (so excluding much of the time while I was realigning beams on the PSL table yesterday), to zoom in on just the time when the foam box was installed.

EOM_tempSense_withFoam_noHeater_RAMmon_1day.png

After lunch Zach and I are going to engage the heater to temperature stabilize the system, to see how that affects things.

In other news, the MC looks like it was fine for a good long time, and ~3 hours ago it went bad.  The mode that's flashing is really bad in both pitch and yaw.  I don't know what happened, but something is not so awesome. Edit: Steve said that he opened the PSL table at some point this morning to look around but not touch, and also it's Janitor Day, and Kevin comes in around 8ish. That doesn't mean I know the actual cause, but those are the only things that happened in the IFO room this morning that anyone is aware of.

  2805   Mon Apr 19 05:54:50 2010 ranaConfigurationPSLRC Temperature Servo Turned OFF temporarily

In order to measure the transfer function of the RC cavity's foam, I've turned off the servo so that the room temperature noise can excite it.

The attached plot shows a step response test from 2 weeks ago. Servo is nominally still working fine.

  2873   Mon May 3 17:49:41 2010 ranaConfigurationPSLRC Temperature Servo Turned OFF temporarily

Quote:

In order to measure the transfer function of the RC cavity's foam, I've turned off the servo so that the room temperature noise can excite it.

The attached plot shows a step response test from 2 weeks ago. Servo is nominally still working fine.

 I've just now re-enabled the temperature control of the reference cavity can. Trend of the last 8 days is attached.

  2875   Tue May 4 02:28:38 2010 ranaConfigurationPSLRC Temperature Servo Turned OFF temporarily

 

 My attempt to passively measure the transfer function of the foam failed fantastically.

As it turns out, the room temperature fluctuations inside the PSL box reach the 1 mK/rHz noise floor of the  AD590 (or maybe the ADC) at ~1-2 mHz. Everything at higher frequencies is noise.

So to see what the foam is doing we will have to do something smarter - we need a volunteer to disable the RC temperature servo from the EPICS screen and then cycle the PSL table lights every hour in the morning.

We'll then use our knowledge of the Laplace transform to get the TF from the step responses.

ELOG V3.1.3-