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ID Date Authorup Type Category Subject
  7794   Wed Dec 5 17:38:41 2012 RijuHowTo Photodiode transimpedance

I have started making the circuit to measure the transimpedance for the photodiode PDA10CF using Jenne's laser. I will continue it tomorrow.

  7817   Wed Dec 12 17:26:47 2012 RijuUpdate Testing AG4395A+GPIB

I repeated my experiment to get noise level. To get that I disconnected the bandpass filter SBP-10.7  from channel A of network analyzer AG4395A and terminated both the open ends (open end of filter and open end of channel A) with 50ohm terminator.

Reference level had been corrected, signal and noise data had been collected separately w.r.t that level.

Command for GPIB:   ./netgpibdata.py -i 192.168.113.105 -d AG4395A -a 10 -f filename

The result is as follows

 

Attachment 1: TFbandpassfilter.pdf
TFbandpassfilter.pdf
  7834   Fri Dec 14 14:40:31 2012 RijuUpdate Photodiode transimpedance

Photodiode PDA10CF was under test. The RF out signal of AG4395A had been divided by splitter with one output of the splitter going to R channel of the network analyzer and the other to the laser. The splitted laser beams - splitted with beam splitter - fall on two photodiodes - one reference and the other on PDA10CF. The outputs of these two photodiodes go to channel B and A respectively of the network analyzer. The measured transimpedance data had been collected using the GPIB connection.

The result is as follows:

Attachment 1: PDA10CF.pdf
PDA10CF.pdf
  7870   Fri Dec 21 19:49:39 2012 RijuUpdate Photodiode transimpedance

I have repeated the transimpedance measurement of PDA10CF. Also made the dark current noise measurement by connecting the PDA10CF output to the A channel of network analyzer.  The results are as follows. I I started to take the reading for shot noise intercept current using a light bulb in front of the PD, changing the current through the bulb, but at higher current the bulb filament got broken, so the experiment is incomplete.

Attachment 1: PDA10CFrepeat.pdf
PDA10CFrepeat.pdf
Attachment 2: darknoiseVpda10cf.pdf
darknoiseVpda10cf.pdf
Attachment 3: darknoiseApda10cf.pdf
darknoiseApda10cf.pdf
Attachment 4: PDA10CF_z.pdf
PDA10CF_z.pdf
  7874   Thu Jan 3 20:34:43 2013 RijuUpdate Photodiode transimpedance

Today I have measured the transimpedance and dark-noise of the MC-REFL PD.

For transimpedance measurement I first collected the data of the reference Newfocus PD connecting it at channel B of Network-analyzer using the set-up of Jenne's laser. The data for the MC-REFL PD had been collected by connecting it to the A channel of Network Analyzer. To do that I shifted the Jenne's Laser to the table of MC-REFL PD, I moved the laser output on the table and fixed a lens and a mirror on the table. Taking the ratio of the two sets of datas I got the required trans-impedance.

Dark-noise readings were taken keeping the laser off.

I will upload the corresponding plots tomorrow.

  7880   Tue Jan 8 14:01:21 2013 RijuUpdate Photodiode transimpedance

 Here I upload the plots corresponding to my last day's measurements.

 

Attachment 1: TFreflpd.pdf
TFreflpd.pdf
Attachment 2: REFL_z.pdf
REFL_z.pdf
Attachment 3: darknoiseVreflpd.pdf
darknoiseVreflpd.pdf
Attachment 4: darknoiseAreflpd.pdf
darknoiseAreflpd.pdf
  7881   Tue Jan 8 14:07:04 2013 RijuUpdateElectronicsPhotodiode transimpedance

Quote:

You have to correct this transimpedance ratio by correcting for the different levels of DC photocurrent in the two devices.

For the dark noise, you must always include a trace showing the noise of the measurements device (i.e. the analyzer noise must be less than the dark PD noise) with the same input attenuation setting.

 Hi,

The correction for different levels of DC photocurrent in the two devices had been taken care by one MATLAB code, the code that originally was made by Koji.

The analyzer noise I had not recorded; today I am going to record it.

Riju

  7882   Tue Jan 8 15:28:41 2013 RijuUpdateElectronicsPhotodiode transimpedance

Quote:

Quote:

You have to correct this transimpedance ratio by correcting for the different levels of DC photocurrent in the two devices.

For the dark noise, you must always include a trace showing the noise of the measurements device (i.e. the analyzer noise must be less than the dark PD noise) with the same input attenuation setting.

 Hi,

The correction for different levels of DC photocurrent in the two devices had been taken care by one MATLAB code, the code that originally was made by Koji.

The analyzer noise I had not recorded; today I am going to record it.

Riju

 Here is the data for AG4395A network/spectrum analyzer noise data. I collected the data by putting 50ohm terminator on channel A with same input attenuation setting (0dB attenuation).

Attachment 1: analyzernoiseV.pdf
analyzernoiseV.pdf
  7887   Wed Jan 9 19:32:24 2013 RijuUpdate Photodiode transimpedance

Summary:

Today I have tested the MC transmission-end RF photodiode PDA255 for transimpedance and dark noise using Jenne's Laser and AG4395A network/spectrum analyzer. The dark noise voltage distribution for the transmission and reflection PDs of MC and the analyzer has been compared.

Motivation:

I am to do the input mode cleaner cavity mode scan. The electronic and shot noise of the components used , particularly photodiode noise, will affect the peak position  of the modes, indicating the uncertainty in the measured frequencies of the modes. That will in turn give the uncertainty in the measured change of radius of curvature of the mirrors in presence of the laser beam, from which we will be able to calculate the uncertainty in the mirror-absorption  value.

Method:

For PD transimpedance measurement I used Jenne's laser along with AG4395 network analyzer. The RF out signal of AG4395A had been divided by splitter with one output of the splitter going to R channel of the network analyzer and the other to the laser. The splitted laser beams - splitted with beam splitter - fall on two photodiodes - one reference(Newfocus1617? PD, the DC and RF transimpedance values were taken from its datasheet ) and the other on PDA255. The outputs of these two photodiodes go to channel B and A respectively of the network analyzer. The measured transimpedance data had been collected using the GPIB connection. It had been ensured that the PD under test is not going to saturation, for that the source power level was kept to -40dBm. transimpedance measurements were compensated by the ratio of DC photocurrent.

For dark noise measurement the output of the PD was connected to the A channel of the AG4395A, when there was no light falling on it. The response is collected using GPIB. The attenuation of channel A was made 0dB. ( AG4395A was kept in Spectrum analyzer mode in Noise Format).

Results:

The plots corresponding to the measurements are attached.

Discussion:

The comparison for the dark noise voltage levels of the MC transmission PD (PDA255) with MC REFL PD has been made with analyzer dark noise voltage. It is shown in the attachment (I will upload the dark noise current comparison too....since the output darknoise depends on the gain of the circuit, it is important to divide this voltage spectra by transimpedances.)

Attachment 1: PDA255.pdf
PDA255.pdf
Attachment 2: PDA255_z.pdf
PDA255_z.pdf
Attachment 3: darknoiseVpda255.pdf
darknoiseVpda255.pdf
Attachment 4: darknoiseApda255.pdf
darknoiseApda255.pdf
Attachment 5: darknoise_comparison.pdf
darknoise_comparison.pdf
  7907   Wed Jan 16 18:58:08 2013 RijuUpdate Photodiode transimpedance

Today I have taken the reading for shot noise intercept current for the PDA255 - MC transmission RF PD. To do that I have put an incandescent bulb (JKL lamps, 222 bulbs, voltage and current rating 2.25V and 0.25A) in front of the PD and varied the current through it from 0A to 0.29A at 2.2V. I measured the corresponding DC voltage and took the noise data (4395A spectrum analyzer/ format noise, channel attenuation 0dB) through GPIB .

I will process the data and upload the result soon.

  7926   Tue Jan 22 17:29:29 2013 RijuUpdate Photodiode transimpedance

Riju

Summary:  I am stuck with the measurement of shot-noise-intercept-current of PDA255. Seeking help.

Motivation: It is to measure the shot noise intercept current for PDA255 - the MC transmission RF photodiode to get an idea for the noise current for the detector.

Method: It is as described in the elog  7907 

Result: The plot is attached here.

Discussion: The result I got is really unexpected, the noise voltage should increase with the DC current level that corresponds to the increment of light level too. But actually it is decreasing. Three times I have repeated this experiment and got the same result. I want some suggestion on this regard.

Attachment 1: pda255shotnoiseintercept.pdf
pda255shotnoiseintercept.pdf
  7929   Wed Jan 23 11:43:19 2013 RijuUpdate Photodiode transimpedance

Quote:

- The data should be plotted in a log-log scale.
- The data points were only taken in the high current region.

- The plot may suggest that the amplifier saturate at the RF.

PDA255 has the nomial transimpedance gain of 10^4 Ohm.
The DC current of 10^-3 gives the output of 10V.
This plot may tell that the saturation starts even at the 1/10 of the full DC range.

The plot doesn't have many points below 0.1mA.
Consult with my plots for the similar measurements.
The measured points are logarithmically spaced. Use the same technique.

- It is also very unknown that how the noise level is calculated. No info is supplied in the plot or the elogs.

 Here I am attaching the plot in loglog scale. I have taken the data-points from no light condition to the maximum light condition, the minimum variation possible in the current supply was 0.01A. The noise was visibly decreasing at higher light level.

For the noise level calculation I took the average of total noise in the range 7-60MHz. For each range the formula used was

noisevalue= sqrt(data(:,2)*100)/sqrt(2)/sqrt(channel BW);     -- this conversion is needed since the data was collected in the 2 column format: frequency, spectrum(W).

Attachment 1: pda255shotnoiseintercept1.pdf
pda255shotnoiseintercept1.pdf
  7933   Wed Jan 23 20:27:05 2013 RijuUpdate Photodiode transimpedance

Today I have repeated the expt for shot noise intercept current. Koji found that the Spectrum analyzer is going to saturation, so we have used one DC blocker (MCL - 15542 model) in PD signal.

I will analyze the data and report.

Ed by Koji: DC BLOCK is  BLK-89-S

  7946   Mon Jan 28 17:59:02 2013 RijuUpdate Photodiode transimpedance

Summary: Measurement and plot of shot-noise-intercept-current for PDA255.

Motivation:It is to measure the shot noise intercept current for PDA255 - the MC transmission RF photodiode to get an idea for the noise current for the detector

Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 3.06mA

Discussion:

The plot is for the measured data of Noise voltage (V/sqrt(Hz)) vs DCcurrent(A). The fitted plot to this measured data follows the noise equation

Vnoise = gdet* sqrt[ 2e (iDC+idet)] ,  where gdet= transimpedance of the PD in RF region as described in manual of PDA255 (i.e. 5e3 when it is not in High-impedance region).

On the other hand for DCcurrent calculation we must use the high-impedance value for the transimpedance i.e. 1e4 Ohm. idet is the shot noise intercept current.

For the rough calculation of the noise level we may use the following formulae:

Vnoise = gdet*sqrt[2e (iDC+idet)] = gdet*sqrt(2e in), when in=iDC+idet;

For say, in1=1mA; Vnoise1=gdet*sqrt(2e *in1)

and sqrt(2e *in1)~18pA/sqrt(Hz)

In current case dark noise is ~1.5e-7 V/sqrt(Hz)

Therefore dark current(in2) ~dark noise voltage/RF transimpedance = 30pA/sqrt(Hz)

i.e. sqrt(2e *in2)=30pA/sqrt(Hz)

i.e. sqrt(in2/in1)=30/18

therefore, in2~3mA (since in1=1mA)

For, iDC=0, in=idet.

Therefore the shot-noise-intercept current will be ~3mA

Then Vdc = in2*1e4 = 30V

According to the experiment  and also from the PDA255 manual the DC voltage level never goes beyond ~10V. Therefore following the photodiode characteristics(we work in reverse bias) we may infer that it can never become shot noise limited.

Also, from PDA255 manual, at 1650nm the dark noise is 30pW/sqrt(Hz) and the responsivity is 0.9A/W. Therefore the noise current level will be = noise power* responsivity ~27pA/sqrt(Hz). The value matches well with our expectation.

 

Attachment 1: shotnoiseinterceptpda255.pdf
shotnoiseinterceptpda255.pdf
  7956   Tue Jan 29 18:40:20 2013 RijuUpdate Photodiode transimpedance

Today I have taken data for shot noise intercept current for PDA10CF. I will process the data and report.

Note: GPIB address changed, new command for AG4395A network/spectrum analyzer: ./netgpibdata.py -i 192.168.113.108 -d AG4395A -a 10 -f filename

  7972   Thu Jan 31 12:44:42 2013 RijuUpdate Photodiode transimpedance

Today I collected the data for shot noise intercept current for MC REFL PD. I didn't get many data points at higher DC voltage of the photodiode, cause the incandescent bulbs get burnt at that level; two bulbs I have burnt today. I will process the data and report.

  7976   Thu Jan 31 15:34:22 2013 RijuUpdateRF SystemPhotodiode transimpedance

Quote:

Quote:

Today I collected the data for shot noise intercept current for MC REFL PD. I didn't get many data points at higher DC voltage of the photodiode, cause the incandescent bulbs get burnt at that level; two bulbs I have burnt today. I will process the data and report.

 This work was done in-situ, so no optics on the AS table were moved.  The PSL shutter was blocked since the IR beam was not necessary, and would scatter off the bulb Riju put in front of the PD. 

 Thanks Jenne.

  7977   Thu Jan 31 15:56:38 2013 RijuUpdate Photodiode transimpedance

Summary: Measurement and plot of shot-noise-intercept-current for PDA10CF. 

Motivation:It is to measure the shot noise intercept current for PDA10CF.

Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 0.21mA

Discussion:

The plot is for the measured data of Noise voltage (V/sqrt(Hz)) vs DCcurrent(A). The fitted plot to this measured data follows the noise equation

Vnoise = gdet* sqrt[ 2e (iDC+idet)] ,  where gdet= transimpedance of the PD in RF region as described in manual of PDA255 (i.e. 5e3 when it is not in High-impedance region).

To get an approximate idea of the shot noise intercept current, we may follow the same procedure described in 7946 

In the present case dark-noise is 4.3e-08 V/sqrt(Hz)

Therefore dark current(in2) ~dark noise voltage/RF transimpedance = 8.6pA/sqrt(Hz)

 

 

Therefore the approximate shot noise intercept current ~ (8.6/18)^2=0.22mA

This value matches well with the fitted data.

From PDA10CF manual, NEP=1.2e-11W/sqrt(Hz) and responsivity~0.9A/W. Therefore the noise current level will be ~10pA.

 

 

Attachment 1: shotnoiseinterceptpda10cf.pdf
shotnoiseinterceptpda10cf.pdf
  7984   Fri Feb 1 14:47:17 2013 RijuUpdate Photodiode transimpedance

 Summary: Measurement and plot of shot-noise-intercept-current for MC REFL PD. 

Motivation:It is to measure the shot noise intercept current for MC REFL PD.

 

Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 0.041mA

Discussion:

 

The plot is for the measured data of Noise voltage (V/sqrt(Hz)) vs DCcurrent(A). The fitted plot to this measured data follows the noise equation

Vnoise = gdet* sqrt[ 2e (iDC+idet)] ,  where gdet= transimpedance of the PD in RF region as described in manual of PDA255 (i.e. 5e3 when it is not in High-impedance region).

To get an approximate idea of the shot noise intercept current, we may follow the same procedure described in 7946 

In the present case minimum noise value is 2.03e-08 V/sqrt(Hz)

Therefore dark current(in2) ~dark noise voltage/RF transimpedance = 4.06pA/sqrt(Hz)

Therefore the approximate shot noise intercept current value is (4/18)^2 ~ 0.049mA, which is close to the fitted value.

 

 ... hard to believe these numbers. Wrong DC transimpedance? (KA)

Attachment 1: shotnoiseinterceptmcreflpd.pdf
shotnoiseinterceptmcreflpd.pdf
  8027   Thu Feb 7 19:24:57 2013 RijuUpdate Photodiode transimpedance

 Summary: Measurement and plot of shot-noise-intercept-current for MC REFL PD. 

Motivation:It is to measure the shot noise intercept current for MC REFL PD.

 

Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 1.9mA

Discussion:

 

The plot is for the measured data of Noise voltage (V/sqrt(Hz)) vs DCcurrent(A). The fitted plot to this measured data follows the noise equation

Vnoise = gdet* sqrt[ 2e (iDC+idet)] ,  where gdet= transimpedance of the PD in RF region ~600

To get an approximate idea of the shot noise intercept current, we may follow the same procedure described in 7946 

In the present case minimum noise value is 1.46e-08 V/sqrt(Hz)

Therefore dark current(in2) ~dark noise voltage/RF transimpedance ~25pA/sqrt(Hz)

Therefore the approximate shot noise intercept current value is (25/18)^2 ~ 1.92mA, which matches well to the fitted value.

 

 

Attachment 1: reflshotnoise.pdf
reflshotnoise.pdf
  8186   Wed Feb 27 17:43:54 2013 RijuUpdate Photodiode transimpedance

Here is the transimpedance for the other PD used for MC REFL

Attachment 1: TFnewreflpd.pdf
TFnewreflpd.pdf
Attachment 2: NewREFL_z.pdf
NewREFL_z.pdf
  8188   Wed Feb 27 18:17:05 2013 RijuUpdate Photodiode transimpedance

Quote:

How much is the exact resonant frequency?

And what's the unit of the plot? The resonant "transimpedance" in the unit of Ohm can not be ~100.

 The exact resonant frequency is 29.38MHz. I ve uploaded the other plot. It was the output of Vectfit.

  8189   Wed Feb 27 18:38:51 2013 RijuUpdate Photodiode transimpedance

Quote:

Quote:

How much is the exact resonant frequency?

And what's the unit of the plot? The resonant "transimpedance" in the unit of Ohm can not be ~100.

 The exact resonant frequency is 29.38MHz. I ve uploaded the other plot. It was the output of Vectfit.

 Is the DC transimpedance now 10010 Ohm? I ve used 50 Ohm. Which one is correct?

  8484   Wed Apr 24 14:24:40 2013 RijuUpdate PD frequency response

 Here I am attaching the first schematic diagram of the PD frequency response set-up, I will keep updating it with relevant informations with the progress of the work.

Description: Our objective is to set-up one simultaneous transfer-function measurement system for all the RF-PDs present in 40m lab. A diode laser will be used to illuminate the PDs. The diode laser output will be divided by 1x16 fiber splitter and will be sent to all the PDs through single-mode fiber. The transfer function of the PDs will be measured using network analyzer(Agilent 4395A). The output of the PDs will be fed to network analyzer via one RF-switch. The diode laser will be controlled by the controller ILX LDC 3744C. The scanning frequency signal will be fed to this controller from network analyzer through its external modulation port. The output of the controller will be splitted  into two parts: one will go to laser diode and the other will be used as reference signal for network analyzer.

 

 

Attachment 1: PD_freq_resp.pdf
PD_freq_resp.pdf
  8488   Thu Apr 25 00:59:37 2013 RijuUpdateRF SystemPD frequency response

Quote:

I think you have the splitter that splits the RF signal from the network analyzer in the wrong place. 

Usually you split the signal immediately after the RF Out, so that half of the signal goes to the A-input of the Analyzer, and the other half goes to your controller (here, the laser diode controller).  Then you would take the output of your controller and go straight to the actual laser diode, with no splitting in this path.

 Here our device under test is the photodiode. So for the reference I wanted to retain the response of the laser diode controller. Otherwise I have to consider the transfer function of that LDC too. I may check both the options at the time of experiment.

Thanks

  8492   Thu Apr 25 17:56:28 2013 RijuConfiguration PD frequency response

 [Eric, Riju]

Today we have routed the fibers from 1x16 fiber splitter to POX table for POX11 PD and POP55 PD. Also we labeled the fibers on AP table, they have been fixed on the table. The photo of the table after work is attached here. We will do it for POX table tomorrow. 

Attachment 1: IMG_0495.JPG
IMG_0495.JPG
  8497   Fri Apr 26 17:08:42 2013 RijuConfiguration PD frequency response

Quote:

No.... what I told was to put the roll next to the splitter, not on the table.
The table area is more precious than the rack space.

Koji> The slack of the fibers should be nicely rolled and put together at the splitter side.

 Ok, will do it on the coming week.

  8506   Mon Apr 29 17:26:22 2013 RijuConfigurationRF SystemPD frequency response

 Today I have rerouted the fibers on AP table to remove the fiber rolls out of the AP table.  I removed the fibers one by one from both ends - from the 1x16 splitter and from the AP table - keeping the fiber roll intact, and then connected it in reverse way, i.e. the fiber end which was on AP table now is connected to the splitter (since length of the outside the roll is shorter that side) and the fiber end connected to splitter is now rerouted on AP table.

We need to keep the fibers in such a fashion so that no sharp bending occurs anywhere, and also it does not get strained due to its weight, particularly near the 1x16 splitter. Jenne suggested to use a plastic box over the splitter rack to keep the fiber rolls for time-being. We discussed a lot how this can be done nicely; in future we may use array of hooks, Koji suggested to use cable hangers and to tie the rolls using more than one hanging point, Jenne suggested to use the bottom shelf of the rack or to use one plastic box with holes. We tried to make holes on the plastic box using drill, but it developed crack on the box. So ultimately I used the opened box only and put it over the rack.

The corresponding photographs are attached herewith.

Tomorrow we will reroute the fibers for POX table.  

Attachment 1: IMG_0504.JPG
IMG_0504.JPG
Attachment 2: IMG_0503.JPG
IMG_0503.JPG
Attachment 3: IMG_0505.JPG
IMG_0505.JPG
Attachment 4: IMG_0506.JPG
IMG_0506.JPG
Attachment 5: IMG_0508.JPG
IMG_0508.JPG
Attachment 6: IMG_0509.JPG
IMG_0509.JPG
Attachment 7: IMG_0510.JPG
IMG_0510.JPG
  8512   Tue Apr 30 19:39:14 2013 RijuConfigurationRF SystemPD frequency response

Today I have rerouted the fibers on POX table. The aim was to lay it overhead through the plastic pipe. A pipe ~50ft (~15.5m) long was taken for this purpose. I disconnected the two 25m long fibers for POP55 and POX11 PD (those had been already routed) from both of their ends - i.e. from the POX table and also from 1x16 splitter. Jenne and Koji suggested that we may have another two PDs ( POP22 and POP110) on POX table in future. So we used another 25m long fiber for these two (POP22/POP110). We could not use two fibers for these two since we have only four 25m long fibers and one of them we need for POY11 PD on POY table. Jenne and me put the three fibers inside the pipe using a copper tube. The tube then was put on the overhead rack, Manasa helped me to do it. The fiber ends were finally laid on the POX table at one end and connected to the 1x16 splitter at the other end.

The corresponding photos are attached herewith.

Attachment 1: IMG_0511.JPG
IMG_0511.JPG
Attachment 2: IMG_0512.JPG
IMG_0512.JPG
Attachment 3: IMG_0513.JPG
IMG_0513.JPG
Attachment 4: IMG_0514.JPG
IMG_0514.JPG
Attachment 5: IMG_0515.JPG
IMG_0515.JPG
  8520   Wed May 1 17:36:26 2013 RijuConfigurationRF SystemPD frequency response

 Today I routed fiber from 1x16 splitter to POY table. Manasa helped me doing that. The fiber(25m) was laid on overhead rack through plastic pipe of length ~76ft. We put the fiber inside the pipe using one copper tube, and then tied the plastic pipe on the overhead rack. Finally one end of the fiber was laid on POY table and the other end was connected to the 1x16 splitter. The photographs corresponding are attached. There is no picture of splitter end, cause it was dark that time.

Attachment 1: IMG_0517.JPG
IMG_0517.JPG
Attachment 2: IMG_0518.JPG
IMG_0518.JPG
Attachment 3: IMG_0519.JPG
IMG_0519.JPG
  8573   Tue May 14 19:52:58 2013 RijuConfigurationRF SystemPD frequency response

 [Eric, Riju, Annalisa]

Today we have cleared up the fiber spool near AP table. We have put the 1x16 fiber splitter and a box (we made two openings on it) for fiber spool on a different part of the rack. Also put a plastic tubing or the fibers coming out of AP table. Now the fibers coming out from AP table and also from POX table first enter the box through one opening and the end of the fibers come out of the other opening to get connected to to splitter. Photographs of the work are attached. I don't think enough fiber is there to make a similar loop for fiber coming from POY table.

 

 

Attachment 1: IMG_0520.JPG
IMG_0520.JPG
Attachment 2: IMG_0521.JPG
IMG_0521.JPG
  7486   Thu Oct 4 23:01:49 2012 RijuparnaConfiguration cavitymode scan

 Here I am attaching the schematic diagram of the experimental set-up for IMC cavitymode scanning. A 30- 45MHz scanning signal generated by Agilent 4395A network analyzer enters EOM, which in turn modulates the laser beam entering IMC. The cavity response can be verified from reflected/transmitted beam.

I worked with the reflected beam last days. But I got no clue about the percentage of  reflected light reaching the photodiode and also the photodiode response. I would like to measure the power reaching photodiode and also would like to perform the test with transmitted beam - on wednesday if possible.

 

Attachment 1: diagram1.pdf
diagram1.pdf
  7519   Wed Oct 10 15:31:59 2012 RijuparnaUpdate cavitymode scan

 Rijuparna, Jenne

Today I checked the optical lay-out in MC REFL board of the MC REFL path on the AS table (I will put the updated diagram in a few hours), and took a record of the reflected power of unlocked MC and power entering MC REFL PD. The power coming out of MC cavity when unlocked is 1.25W and power entering REFL PD 112mW (Jenne measured these powers for me). 

I also got a description of the MC demodulation board from Jenne.

(Edits by Jenne)

  7537   Fri Oct 12 15:31:03 2012 RijuparnaConfiguration cavitymode scan

 Rijuparna, Manasa

Today I have checked the optical layout of the MC transmission RFPD table and measured the laser powers at different points. Manasa helped me for that. I found the power entering the RF photodiode is 0.394mW while the transmitted power of the cavity is 2.46mW. (I will give the diagram later).

  7351   Thu Sep 6 17:06:25 2012 Rijuparna ChakrabortyConfigurationelogCavitymode scan

 Aim: to scan the cavitymodes of IMC

The circuit used: 

 Attachment4

Results obtained:

Attachment 1,2,3

 

Attachment 1: 3.pdf
3.pdf
Attachment 2: 2.pdf
2.pdf
Attachment 3: 1.pdf
1.pdf
Attachment 4: cavityscanconnections.pdf
cavityscanconnections.pdf
  7363   Fri Sep 7 15:58:29 2012 Rijuparna ChakrabortyUpdate cavitymode scan

 IMC transmission photodiode has been aligned.

  7368   Sat Sep 8 00:15:57 2012 Rijuparna ChakrabortyUpdate cavitymode scan

Quote:

Quote:

 IMC transmission photodiode has been aligned.

 Which PD?  The 'regular' DC one, or the newer one?  Why did it need realigning?  What mirrors did you touch to do the alignment?

Did you do anything else in the last 3 days?  I want to see ALL the gory details, because it can help people doing future measurements, or help us debug if something is wrong with the interferometer later.

MORE WORDS! Thanks.

 No, not the "regular DC one", the "newer one"  along with the controls of the corresponding mirror only i touched.

It needed to be realigned cause last week when we fitted a longer cable there, which may reach the network analyzer, it got misaligned since it got touched.

No other component in that box except that PD and the corresponding mirror controls I touched.

For my last 2 days work, I feel my last elog is reliable.

Today other than doing this, I checked for the higher order modes of the cavity, misaligning one of the MC mirror though the software only. I didn't mention it in my elog cause although I saw the presence of the higher order modes I didn't record it, so I can not upload any picture in support of such a statement.

Thanks

  7376   Wed Sep 12 19:26:08 2012 Rijuparna ChakrabortyUpdate cavitymode scan

 Summary: Recorded the presence of higher order modes in IMC

What I did: Misaligned the flat mirror MC1 by small amount in both pitch and yaw (it was needed to be done cause at the beginning of the experiment no higher order modes were present)  and scanned the cavity for frequency-range 32MHz to 45MHz.

I found the presence of higher order modes around 36.7MHz (1st order)  and 40.6MHz (2nd order) along with two other strong modes near 35MHz and 42.5MHz.

 

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  603   Mon Jun 30 14:07:26 2008 RobConfigurationPSLDon't put the bin in front of the air conditioning unit

Quote:
We spotted that the laser power was dropping.


the offending configuration:
Attachment 1: DSC_0140.png
DSC_0140.png
  1306   Sun Feb 15 15:53:21 2009 RobUpdateLSCLocking status

Quote:

I didn't get a chance to do much testing since the sus controller (susvme1) went nuts. In retrospect, this could be due to something in the script, so maybe we should try a burt restore to Friday afternoon next time someone wants to look at it.


I tried the burt restore today, it didn't work. Also tried some switching of timing cables, and multiple reboots, to no avail. This will require some more debugging. We might try diagnosing the clock driver and fanout modules, the penteks, and we can also try rebooting the whole FE system.
  623   Wed Jul 2 13:56:10 2008 Rob, Yoichi, JohnUpdateLocking24.5 Hz resonance
Work continues on trying to reduce the CARM offset using dc signals from PO_DC. Got up to arm powers of
~35 last night.

We found that progress was stymied by an oscillation around 24 Hz. This oscillation was clearly visible
in the intensity of the light at REFL, PO and TrX.

Initially we suspected that this oscillation was due to an instability in the CARM loop. We attempted to
solve the problem by tuning the crossover frequncy of the AO and MC_L paths and shaping the MC_L loop to
reduce the impact of the 24 Hz noise.

After some quick tests we found that the 24 Hz signal was present even when dc CARM was used. It appears
that the peak is in fact due to a SOS mechanical resonance. We currently suspect a roll mode.

We're going to check that PRC, MICH and DARM have filters to attenuate the 24 Hz line. We'll also look at the
SUS_POS bandstop filters to see where they are centred.

The ISS was behaving strangely again. Constantly saturated at 5dB of gain. Someone needs to look a this.
Attachment 1: locking080702.png
locking080702.png
  630   Thu Jul 3 13:12:32 2008 Rob, Yoichi, JohnUpdateLockingMore oscillations
Bounce/ roll filters were added to the short degrees of freedom to reduce the effect of the 24Hz line seen on Tuesday night.

However last night saw the arrival of a new oscillation at ~34Hz. This may be the second harmonic of the MOS roll mode. Reducing the arm offset would cause this oscillation to ring up and break the lock (first plot). This effect was repeatable.

No signal was seen in the oplevs or osems which leads us to rule out alignment problems, at least for now.

Although one can clearly see DARM_ERR increasing as arm power increases adding a resonant gain in the DARM loop had no effect.

We also noticed that x arm transmission was significantly more noisy than the Y (second plot). And showed greater coherence with the increase in DARM noise. Investigations showed that the PD was not the source of the difference.

Turning up the MC gain seems to help a little.

We're now looking at POX as a candidate for RF_CARM (third plot).
Attachment 1: LOL.png
LOL.png
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NoisyX080702.png
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POXforCARM080702.png
  13823   Mon May 7 20:01:14 2018 RorpheusUpdateGeneralUse anti-dewhitening + show CARMA/DARMA

What If I Told You - What If I Told You that bogus plots are fake news

example of plots illustrating DAC range / saturation

  6422   Thu Mar 15 08:48:40 2012 RyanSummaryCDSSummary of Syracuse Visit to 40m Mar 5-9 2012

JIMS Channels in PEM Model

The PEM model has been modified now to include the JIMS(Joint Information Management System) channel processing. Additionally Jim added test points at the outputs of the BLRMS.

For each seismometer channel, five bands are compared to threshold values to produce boolean results.  Bands with RMS below threshold produce bits with value 1, above threshold results in 0.  These bits are combined to produce one output channel that contains all of the results.

A persistent version of the channel is generated by a new library block that called persist which holds the value at 0 for a number of time steps equal to an EPICS variable setting from the time the boolean first drops to zero. The persist allows excursions shorter than the timestep of a downsampled timeseries to be seen reliably.

The EPICS variables for the thresholds are of the form (in order of increasing frequency):
C1:PEM-JIMS_GUR1X_THRES1
C1:PEM-JIMS_GUR1X_THRES2
etc.
 
The EPICS variables for the persist step size are of the form:
C1:PEM-JIMS_GUR1X_PERSIST
C1:PEM-JIMS_GUR1Y_PERSIST
etc.

The JIMS Channels are being recorded and written to frames:

The two JIMS channels at 2048:
[C1:PEM-JIMS_CH1_DQ] Persistent version of JIMS channel. When bit drops to zero indicating something bad (BLRMS threshold exceeded) happens the bit stays at zero  for >= the value of the persist EPICS variable.
[C1:PEM-JIMS_CH2_DQ] Non-persistent version of JIMS channel.

And all of the BLRMS channels at 256:
Names are of the form:
[C1:PEM-RMS_ACC1_F0p1_0p3_DQ]
[C1:PEM-RMS_ACC1_F0p3_1_DQ]

For additional details about the JIMS Channels and the implementation, please see the previous elog entries by Jim.

 

Conlog

I have a working aLIGO Conlog/EPICS Log installed and running on megatron.

Please see this wiki page for the details of use:
https://wiki-40m.ligo.caltech.edu/aLIGO%20EPICs%20log%20%28conlog%29

I also edited this page with restart instructions for megatron:
https://wiki-40m.ligo.caltech.edu/Computer_Restart_Procedures#megatron

Please see Ryan's previous elog entries for installation details.

Future Work

  • Determine useful thresholds for each band
  • Generate MEDM Screens for JIMS Channels
  • Add a decimation option to channels
  • Add EPICS Strings in PEM model to describe bits in JIMS Channels
  • Add additional JIMS Channels: Testing additional characterization methods
  • Implement a State Log on Megatron: Will Provide a 1Hz index into JIMS Channels
  • Generate a single web page that allows access to aLIGO Conlog/EPICS Log and State Log

 

  6518   Wed Apr 11 12:25:11 2012 RyanUpdateComputersUpdating aLIGO Conlog

Over the next few days, I will be working on upgrading the aLIGO Conlog install to include new bugfixes distributed by Patrick T.  The currently running conlog *should* not be affected, but please let me know if it is (ryan.fisher@ligo.org).

  6539   Tue Apr 17 10:55:50 2012 RyanUpdateComputersUpdating aLIGO Conlog

Quote:

Over the next few days, I will be working on upgrading the aLIGO Conlog install to include new bugfixes distributed by Patrick T.  The currently running conlog *should* not be affected, but please let me know if it is (ryan.fisher@ligo.org).

 The upgrade to the aLIGO Conlog is completed.  The conlog is once again running on megatron in a screen session. (see http://nodus.ligo.caltech.edu:8080/40m/6396)

  6373   Wed Mar 7 13:59:07 2012 Ryan FisherSummaryComputer Scripts / ProgramsAlterations to base epics install for installing aLIGO conlog:

In order to install the necessary extensions to epics to make the aLIGO conlog work, I have edited one file in the base epics install that affects makefiles:

/cvs/cds/caltech/apps/linux64/epics/base/configure/CONFIG_COMMON

Jamie said he prefers diffs, so I regenerated the original file and did a diff against the current file:

megatron:configure>diff CONFIG_COMMON.orig.reconstructedMar72012 CONFIG_COMMON.bck.Mar72012
206,207c206,210
< USR_CPPFLAGS =
< USR_DBDFLAGS =
---
> USR_CPPFLAGS = -I $(EPICS_BASE)/include
> USR_CPPFLAGS += -I $(EPICS_BASE)/include/os/Linux/
> USR_CPPFLAGS += -I $(EPICS_BASE)/../modules/archive/lib/linux-x86_64/
> USR_DBDFLAGS = -I $(EPICS_BASE)/dbd
> USR_DBDFLAGS += -I $(EPICS_BASE)/../modules/archive/dbd

This is saved in CONFIG_COMMON.diff.Mar72012_1

  6377   Wed Mar 7 18:00:39 2012 Ryan FisherSummaryComputer Scripts / ProgramsAlterations to base epics install for installing aLIGO conlog:

Quote:

In order to install the necessary extensions to epics to make the aLIGO conlog work, I have edited one file in the base epics install that affects makefiles:

/cvs/cds/caltech/apps/linux64/epics/base/configure/CONFIG_COMMON

Jamie said he prefers diffs, so I regenerated the original file and did a diff against the current file:

megatron:configure>diff CONFIG_COMMON.orig.reconstructedMar72012 CONFIG_COMMON.bck.Mar72012
206,207c206,210
< USR_CPPFLAGS =
< USR_DBDFLAGS =
---
> USR_CPPFLAGS = -I $(EPICS_BASE)/include
> USR_CPPFLAGS += -I $(EPICS_BASE)/include/os/Linux/
> USR_CPPFLAGS += -I $(EPICS_BASE)/../modules/archive/lib/linux-x86_64/
> USR_DBDFLAGS = -I $(EPICS_BASE)/dbd
> USR_DBDFLAGS += -I $(EPICS_BASE)/../modules/archive/dbd

This is saved in CONFIG_COMMON.diff.Mar72012_1

 After following up with Patrick Thomas for a while trying to make the extensions to epics work within the currently installed epics, he decided that we should just start over with a fresh install of epics 3.14.10.

I am installing this in /ligo/apps/linux-x86_64/epics/base-3.14.10/

Prior to all of this, I had done a lot of installation and configuration of the packages needed to make LAMP work:

sudo apt-get install lamp-server^

sudo apt-get install phpmyadmin

I then continued to follow the instructions on Patrick's wiki:

https://awiki.ligo-wa.caltech.edu/aLIGO/Conlog#EDCU_library

I installed the c_string library into /ligo/apps/linux-x86_64/ according to his instructions.  (prior to my installs, there was no /ligo/ on this machine at all, so I made the needed parent directories with the correct permissions).

That should be everything up to installing epics (working on that now).

  6387   Thu Mar 8 17:18:19 2012 Ryan FisherSummaryComputer Scripts / ProgramsAlterations to base epics install for installing aLIGO conlog:
I have the aLIGO Conlog 'working' at http://192.168.113.209/conlog/conlog.php

The process is running inside a screen on megatron.

To start it running, you need to set your environment, and then run the startup.c1conlog script :

cd /cvs/cds/rtcds/caltech/c1/target/conlog/conlogepics

source conlog_environment.txt

./startup.c1conlog

This will leave you at an epics prompt, which means the code is running. (that's why I left it running in a screen for now).

To change the list of channels when the conlog is running, you need to edit the file (s):

/ligo/caltech/data/conlog/c1/add_channel_names
/ligo/caltech/data/conlog/c1/remove_channel_names

Then start up medm as follows:

cd ~/ryan/

medm -x -macro "IFO=C1" medm/CONLOG.adl

Then click the Add channel list button or Remove channel list button.

To change the channels before running the conlog from a blank database, you would edit:
/ligo/caltech/data/conlog/c1/use_channel_names (I believe this should be read whenever the conlog is restarted, but I'm only sure it does the first time you start conlog).




Documenting the rest of the installation:


Successful? Installation of Fresh EPICS and Extensions



Fresh Copy of EPICS 3.14.10


* We restarted (on Patrick's suggestion) with a fresh copy of EPICS 3.14.10 in:
/ligo/apps/linux-x86_64/epics
* I had to set a clean environment:
* Then I downloaded the tarball, unpacked it, and simply ran make within it, and it worked!
* Next, I followed Patrick's wiki instructions with only modifications to the configure/RELEASE files for the archive and ioc/conlog extensions.
* Then I realized that I had to rebuild conlog ioc after adding a directory:
/ligo/apps/linux-x86_64/epics/iocs/conlog/iocBoot/iocc1_conlog
* I had to copy the files from the h1 directory and modify them so that all reference to h1 now point to c1 in the new directory
* I then rebuilt the conlog ioc (I had to make sure setenv SCRIPTS was run again because I had logged out and back in, and I reset the whole environment properly again)

Rest of Install


* I was able to fairly trivially follow through the rest of the installation steps on Patrick's wiki, up to the "Design" section.
* Now, there is no obvious way to move forward (nothing is actually running I believe).

New Install Instructions:


"
You want to create the EPICS IOC boot directory by doing the following:

In the top level of the IOC (.../epics/iocs/conlog) with the appropriate
paths:

/epics/base/bin/linux-x86_64/makeBaseApp.pl -i -t ioc c1_conlog
What application should the IOC(s) boot?
The default uses the IOC's name, even if not listed above.
Application name? conlog

Then you will have to update the st.cmd it creates. You can compare the
st.cmd and st.cmd.backup files in the other directories to see what needs
to be changed.

I don't know if just copying the directory will work, it might.

You will also probably want to change the following line in
/epics/modules/archive/archiveApp/src/drvArchive.c:

queue = epicsMessageQueueCreate(100000000, sizeof(struct message_type));

and reduce 100000000 to something smaller depending on the amount of ram
available to the computer. I think sizeof(struct message_type) is
something like 112 bytes. Then recompile.

You basically put a file with the list of channels to use in the directory
path for "use channel list filepath" in the following command in st.cmd:
drvArchive_read_channel_list_filepaths <add channel list filepath>,<remove
channel list filepath>,<use channel list filepath>
I can send you the script that I currently use to generate that channel
list if you want, but it may need to be changed for your setup.

Once you start the ioc, open the medm which can be checked out from
subversion here: cds_user_apps/trunk/cds/common/medm/CONLOG.adl
with macro substitution for IFO: medm -x -macro "IFO=C1"
and click on the button for "Use channel list".
The number of monitored channels should increase to the number of channels
in the file.

-Patrick

...

The perl script and example file are attached, just redirect the output of
the perl script to a file. It scans autoBurt.req files in a particular
directory and its subdirectories for channel names that meet certain
criteria. All the file contains is a list of channel names, one on each
line. To start the IOC, go to the target directory and run
./startup.c1conlog.

"

{{rpfisher:scan_autoburt.pl.txt|scan_autoburt.pl.txt}}



{{rpfisher:use_channel_names.txt|use_channel_names.txt}}



My Notes Regarding These Instructions:


* Throughout the installation instructions, it probably should have been made clear that the ifo is lowercase: eg c1 (but in the end the installation mixed C1 and c1 in different places)
* Also throughout, one should be careful to replace lho with your site (eg caltech) wherever it appears
* After running the first perl script to generate the iocBoot/iocc1_conlog directory, the goal is to rebuild the whole conlog ioc by running make from epics/iocs/conlog, but before doing that:
* I needed to change the suggested line in the archive module to match the correct RAM size of the machine I am installing on (I actually gave it just less than half the free RAM), then:
* Remake the archive module
* Change into the ioc/conlog directory, remove the iocBoot I had made before for c1, rerun the perl script above, then run make from the ioc/conlog directory.
* Once that is done, you need to edit the file st.cmd to add lines for the reading and writing of channels, such as:
dbLoadRecords("db/conlog.db","IFO=C1")
drvArchive_mysql "C1_conlog","/data/mysql/C1_conlog_epics_user"
drvArchive_read_channel_list_filepaths "/ligo/caltech/data/conlog/c1/add_channel_names","/ligo/caltech/data/conlog/c1/remove_channel_names","/ligo/caltech/data/conlog/c1/use_channel_names"
drvArchive_write_channel_list_filepaths "/ligo/caltech/data/conlog/c1/channel_names","/ligo/caltech/data/conlog/c1/monitored_channel_names","/ligo/caltech/data/conlog/c1/unmonitored_channel_names"
* I also had to rerun this set of commands once that was all done:
controls: cd /opt/rtcds/<site>/<ifo>/target/conlog/conlogepics
controls: cp -r /ligo/apps/linux-x86_64/epics/iocs/conlog/db ./
controls: cp -r /ligo/apps/linux-x86_64/epics/iocs/conlog/dbd ./
controls: cp /ligo/apps/linux-x86_64/epics/iocs/conlog/iocBoot/ioc<ifo>_conlog/envPaths ./
controls: cp /ligo/apps/linux-x86_64/epics/iocs/conlog/iocBoot/ioc<ifo>_conlog/st.cmd ./
controls: echo ./bin/linux-x86_64/conlog st.cmd > startup.<ifo>conlog
controls: chmod a+x startup.<ifo>conlog
* This set of instructions seemed to be lacking, so I added this:

cp -r /ligo/apps/linux-x86_64/epics/iocs/conlog/bin/ ./

* Now the executable runs but doesn't work:
* Fixes needed:
* Need to use root permissions and make sure the files in /data/mysql have the right names for the users the code expects and also have the right passwords. (have to match capitalization appropriately for the <ifo> tag everywhere
* Might need to go into mysql and add a new user with the proper capitalization also
* Need to edit the ld_library_path to point to the new epics libraries (see the suggested environment below)
* Now, the code seems to work, but dumps me at an "epics> " prompt, I'm asking Patrick what to do next.
* I was impatient and loaded up the medm screen, and found out that the one channel I had picked was not readable (unmonitored)
* I ran a modified version of Patrick's perl script to search autoBert files for channels, and replaced my use_channel_names file with the output of the script
* Now, the medm screen shows lots of monitored channels, and the conlog is filling up! (can see it from phpmyadmin)
* Next step: I wanted to get the php pages working, so I edited the files inside /var/www/conlog:
megatron:~/ryan>diff -u /var/www/conlog/conlog.php /var/www/conlog/conlog.php.bck.Mar82012_1
--- /var/www/conlog/conlog.php  2012-03-08 15:31:53.152547771 -0800
+++ /var/www/conlog/conlog.php.bck.Mar82012_1   2012-03-08 15:28:23.062704171 -0800
@@ -19,7 +19,7 @@
        <form action="query.php" method="post">
                <h3><label for="database">Database:</label></h3>
                <select id="database" name="database">
-                       <option value="C1_conlog">C1</option>
+                       <option value="h2_conlog">h2</option>
                </select>
 
                <h3><label for="included_channels">Included channels:</label></h3>

megatron:~/ryan>diff -u /var/www/conlog/query.php /var/www/conlog/query.php.bck.Mar82012_1
--- /var/www/conlog/query.php   2012-03-08 15:33:45.122550303 -0800
+++ /var/www/conlog/query.php.bck.Mar82012_1    2012-03-08 15:32:31.772554679 -0800
@@ -168,8 +168,8 @@
        }
 
        $database_name = $_POST["database"];
-       if ($database_name == 'C1_conlog') {
-               $server = '192.168.113.209';
+       if ($database_name == 'h2_conlog') {
+               $server = 'cdsconlog';
        }
        else {
                die('Unknown database.');

* Finally, the mysql server was denying access from outside queries, so I fixed that:
megatron:~/ryan>diff -u /etc/mysql/my.cnf /etc/mysql/my.cnf.bck.Mar82012_1
--- /etc/mysql/my.cnf   2012-03-08 15:35:57.122548370 -0800
+++ /etc/mysql/my.cnf.bck.Mar82012_1    2012-03-08 15:35:10.652559315 -0800
@@ -49,7 +49,7 @@
 #
 # Instead of skip-networking the default is now to listen only on
 # localhost which is more compatible and is not less secure.
-#bind-address          = 127.0.0.1
+bind-address           = 127.0.0.1
 #
 # * Fine Tuning
 #
megatron:~/ryan>
* Now, I think everything is working * almost:
* It seems that when you first start the conlog up, it finds all the variables and inserts values of "Null" for everything, but after that it detects changes properly!


Conlog Environment


Need to source this to use the new environment:

megatron:~>cat ~/ryan/conlog_enviroment.txt
  6391   Fri Mar 9 11:02:56 2012 Ryan FisherSummaryComputer Scripts / ProgramsAlterations to base epics install for installing aLIGO conlog:

Too Many Fast Changing EPICS in New Conlog


I have been monitoring the new conlog, and it already has far too many rows.

I'm going through the list of channels to exclude in the update_channels script for the conlog that is currently running and removing them from
the monitored channels in the new conlog using the remove_channel_names file and the medm screen (we may want to just wipe out the tables
and start over after this is set properly, but for now I'm keeping them):
#-- Exclude a few uninteresting or obsolete categories
if ( $chan =~ m/^[BIJ]$/ ||
$chan =~ m/IOO-MC_PWR_IN/ ||
$chan eq "C1:PSL-FSS_SLOWDC" ||
$chan =~ m/PSL-STAT_.*_BITS/ ||
$chan =~ m/:IOO-PZTM[12]_(PIT|YAW)_BIAS$/ ||
$chan =~ m/DAQ.*_cycle/ ||
$chan =~ m/DAQ.*rtSeconds/ ||
$chan =~ m/C1:-.*/ ||
$chan =~ m/C1:SUP/ ||
$chan =~ m/C1:SP/ ||
$chan =~ m/C1:X/ ||
$chan =~ m/C1:TST/ ||
$chan =~ m/C1:RF/ ||
$chan =~ m/C1:UCT/ ||
$chan =~ m/C1:DU/ ||
$chan =~ m/C1:MCP/ ||
$chan =~ m/C1:MCS/ ||
$chan =~ m/C1:FEC/ ||
$chan =~ m/C1:PEM/ ||
$chan =~ m/C1:LSP/ ||
$chan =~ m/C1:NIO/ ||
$chan =~ m/C1:WFS/ ||
$chan =~ m/C1:ASC-WFS/ ||
$chan =~ m/C1:ASC-SP/ ||
$chan =~ m/C1:VG/ ||
$chan =~ m/C1:IOO-DOF/ ||
$chan =~ m/C1:IOO-EO/ ||
$chan =~ m/Name/ ||
$chan =~ m/DEFAULTNAME/ ||
$chan =~ m/:IOO-PZT.*OFFSET/ ||
$chan =~ m/PD_VAR$/ ||
$chan =~ m/_INMON$/ ||
$chan =~ m/_EXCMON$/ ||
$chan =~ m/_OUT16$/ ||
$chan =~ m/_OUTMON$/ ||
$chan =~ m/_OUTPUT$/ ||
$chan =~ m/_RSET$/ ||
$chan =~ m/_ALIVE$/ ||
$chan =~ m/VMon$/ ||
$chan =~ m/PDMon$/ ||
$chan =~ m/(BiasVMon|FE_PPOLL|MASTER_OVERFLOW|FSS_TIDALSET|CPU_LOAD|CDM
_STAT|State_Bits|INDCOFFSET)/ )

With these removals, only 15493 channels are being monitored now.
ELOG V3.1.3-