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ID Date Author Type Categoryup Subject
  6338   Wed Feb 29 01:02:06 2012 DenUpdatePEMseis box measured

I've measured the input signal to the seismic box from seismometer Guralp 1. The spectrum of the signal in the "input +" (TP 1) is



The spectrum below 1 Hz is ~250 uV/sqrt(Hz). As the input is differential, then the input voltage is 0.5 mV/sqrt(Hz). The spectrum of the "output +" signal (TP 2) is



So the gain at ~ 1Hz is ~20. I've measured the transfer function between the "input +" and "output +" (TP1 and TP2) for all 9 circuits


The channels 1-6 are of new modification and have gain ~20 at the frequencies 0.2 - 100 Hz. Below 0.2 Hz the gain is reduced. 100 Hz - cut off frequency of the low-pass filters. Meanwhile channels 7-9 (old configuration) have much more gain and 10_50 Hz filters work here.

The coherence between  "input +" and "output +" (TP1 and TP2) for 9 circuits is



We can see that channel VERT 3 is very bad. For others coherence is lost below 0.2 Hz. The spectrum analyzer noise measured is ~1000 times less then the signal at these frequencies. I'll pay more attention to this loss of coherence at low frequencies. Something is noisy.

  6343   Thu Mar 1 00:05:23 2012 DenUpdatePEMseis box noise

I've moved GUR1 seismometer from MC2 to the working tables in order not to disturb the MC while working with the seismometer box. The new place for the GUR1 for a few days is near the printer, cables and blue boxes. I've cleaned all mess and wires from the floor, so that seismometer now looks like that


I've connected 2 inputs of the N/S 1 circuit of the seismometer box with a 50 Ohm resistor and measured the noise at the output. The comparison with the seismic signal is


The noise increased at 0.5 Hz and is pretty big. This might explain the loose of coherence at low frequencies.

  6345   Thu Mar 1 21:48:34 2012 DenUpdatePEMseis box noise


The noise increased at 0.5 Hz and is pretty big. This might explain the loose of coherence at low frequencies.

 This is because spectrum analyzer did not plot the real noise spectrum at the first few points at low frequencies. I've remeasured the noise at 1mHz - 3Hz at "output -" (TP9) and compared it to the seismometer signal


The noise seems to be much less then the signal. I've measured the noise several times and once I got a huge amount of noise



I made another measurement in some time and got the low noise again. A circuit might have a bad contact somewhere.

The plan is to change AD620 adjustable resistor (R2) from 5.49kOhm to 500Ohm to increase the gain from 20 up to 200.

  6346   Fri Mar 2 11:05:28 2012 DenUpdatePEMseis box gain

I've replaced R2 resistor that adjusts the gain of the AD620 amplifier. Previous value 5491Ohm, new value 464Ohm, so the gain should increase up to ~200-250. Only at the N/S 1 circuit!

LISO simulation of the circuit transfer function and noise are



LISO predicts gain ~45-46 dB = 200 and noise at the level of 10uV at 1Hz. The transfer function and noise measured are



The noise measured is 5 times higher then predicted by LISO. Though I described AD620 as an ordinary amplifier with 49.9kOhm resistor connecting output and inverted input. I specified the noise spectrum 10 nV and 1/f corner frequency 30 Hz. In the AD620 datasheet noise spectrum is 10 - 100 nV depending on the gain. However, the gain is 200 and noise spectrum should be 10 nV. May be in reality it is not the case. It also possible that the noise model used by LISO is not valid for AD620 as it is not an ordinary operational amplifier.

  6349   Fri Mar 2 18:55:06 2012 DenUpdatePEMseis box

I've put the seismometer box back to the 1x1, Guralp is back under MC2. When the seismometer is not plugged in, the noise is


Now, I'm going to collect some data from GUR 1 and MC_F and see if the problem with adaptive filter (increasing errror while decreasing mu) will be gone.


  6356   Mon Mar 5 15:15:15 2012 DenUpdatePEMRCG

[Alex / Den]

I've encountered a problem that C1:PEM-SEIS_GUR1_X_IN1 is saved in the int format. It turned out that inside the code the signal is also in the int format.  It is not just a saving error. It should not be so as ADC works at 64k and the model runs at 2k.

Why? There is a bug somewhere in the generation of the code. c1pem.c looks suspicious to Alex because there is a mismatch in the ADC numbers with the simulink model.

Solution: upgrade to 2.4 version - most probably it was fixed there. If not, Alex will handle this problem.

  6372   Wed Mar 7 13:30:17 2012 JimUpdatePEMadded TPs and JIMS channels to PEM front-end model

[Jim Ryan]

The PEM model has been modified now to include a block called 'JIMS' for the JIMS(Joint Information Management System) channel processing. Additionally I added test points inside the BLRMS blocks that are there. These test points are connected to the output of the sqrt function for each band. I needed this for debugging purposes and it was something Jenny had requested.

The outputs are taken out of the RMS block and muxed, then demuxed just outside the JIMS block. I was unable to get the model to work properly with the muxed channel traveling up or down levels for this. Inside the JIMS block the information goes into blocks for the corresponding seismometer channel.

For each seismometer channel the five bands are processed by comparing to a threshold value to give a boolean with 1 being good (BLRMS below threshold) and 0 being bad (BLRMS above threshold). The boolean streams are then split into a persistent stream and a non-persistent stream. The persistent stream is processed by a new library block that I created (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):




The EPICS variables for the persist step size are of the form:




I have set all of the persist values to 2048 (1 sec.) for now. The threshold values are currently 200,140,300,485,340 for the GUR1X bands and 170,105,185,440,430 for the GUR1Y bands.

The values were set using ezcawrite. There is no MEDM screen for this yet.

PEM model was restarted at approx. 11:30 Mar. 7 2012 PST.


  6389   Fri Mar 9 10:17:06 2012 steveHowToPEMdo not leave tables open

Type: How not to

Please do not leave optical tables open! You will be held responsible for creating dirty optics.

Attachment 1: P1080547.JPG
  6427   Sun Mar 18 00:29:24 2012 DenUpdatePEMsts-2

I've turned off the power of the STS-2 readout box as it provides outputs with ~10 Volts DC offset! AA filter box works in the range -2 +2 Volts, so we do not have any useful information anyway. I'll adjust the mass positions in the seismometer.

  6430   Tue Mar 20 16:53:48 2012 steveUpdatePEMcranes maintenance & certified inspection of 2012

Fred Goodbar of Konecrane has completed the annual certified crane inspection and maintenance of our cranes as required in safety document.

They are in good working condition and safe to use.

  6468   Thu Mar 29 20:13:21 2012 jamieConfigurationPEMPEM_SLOW (i.e. seismic RMS) channels added to fb master

I've added the PEM_SLOW.ini file to the fb master file, which should give us the slow seismic RMS channels when the framebuilder is restarted. Example channels:


I also updated the path to the other _SLOW.ini files.


I will do it first thing in the am tomorrow, when Kiwamu is not busy getting real work done.

Here's is a the diff for /opt/rtcds/caltech/c1/target/fb/master:h

controls@pianosa:/opt/rtcds/caltech/c1/target/fb 1$ diff -u master~ master
--- master~	2011-09-15 17:32:24.000000000 -0700
+++ master	2012-03-29 19:51:52.000000000 -0700
@@ -7,11 +7,12 @@
controls@pianosa:/opt/rtcds/caltech/c1/target/fb 1$


  6484   Wed Apr 4 13:25:29 2012 jamieConfigurationPEMPEM_SLOW (i.e. seismic RMS) channels aquiring


I've added the PEM_SLOW.ini file to the fb master file, which should give us the slow seismic RMS channels when the framebuilder is restarted. Example channels:


 The framebuilder seems to have been restarted, or restarted on it's own, so these channels are now being acquired.

Below is a minute trend of a smattering of the available RMS channels over the last five days.


  6499   Fri Apr 6 19:04:35 2012 JenneUpdatePEMSTS releveled, GUR2 plugged in

[Den, Jenne]

We were wondering why the STS-2 signal was funny.  When I went to look at it, the X-axis indicator was pointing ~45deg from the x-axis, so that it was pointing between the arms of the IFO.  Also, the bubble in the level was totally stuck on one side.  We locked the masses, and I put the seismometer back to the correct orientation, and then leveled it.  We unlocked the masses and turned the power back on, and hit the auto-zero button a few times.  Right now the X-axis signal is fine, but Y and Z are still railed, but it's been like 24 seconds, not 24 hours since we last hit auto zero, so there's still some time to wait.

Also, GUR2 was unplugged on both ends of the cable.  We plugged it back in.  However, it looks like the *seismometer* labeled #1 is now plugged into *channels* GUR2, and the seismometer labeled #2 is plugged into channels GUR1.  Recall that Den has only modified X, Y, Z for GUR1 channels, not any other channels in the breakout box.

  6529   Thu Apr 12 20:56:07 2012 DenUpdatePEMdaq

GUR1 XYZ, GUR2 XYZ, MC_F channels are now recorded at 256 Hz.

EDIT by JCD:  What Den means to say here is that (a) he modified some .ini files, and (b) he restarted the fb.

  6536   Mon Apr 16 09:10:37 2012 DenUpdatePEMgur2_x

Already not for the first time I notice that GUR2 readjusts its X zero position



As a result the coherence between GUR1X and GUR2X is lost, but between GUR2X and GUR2Y shows up. It seems that these two signals mix at some point.


  6537   Mon Apr 16 09:44:54 2012 JenneUpdatePEMgur2_x


Already not for the first time I notice that GUR2 readjusts its X zero position

As a result the coherence between GUR1X and GUR2X is lost, but between GUR2X and GUR2Y shows up. It seems that these two signals mix at some point.

 Can you go back in time before the X-position jumped to plot the x1-x2 and x2-y2 coherences?  Just to see what things look like?

  6538   Mon Apr 16 14:37:01 2012 DenUpdatePEMgur2_x



Already not for the first time I notice that GUR2 readjusts its X zero position

As a result the coherence between GUR1X and GUR2X is lost, but between GUR2X and GUR2Y shows up. It seems that these two signals mix at some point.

 Can you go back in time before the X-position jumped to plot the x1-x2 and x2-y2 coherences?  Just to see what things look like?

DAQ is not working now but ordinary the coherence between GUR1X and GUR2X is ~1 at 0.1 - 10 Hz and between GUR2X and GUR2Y is ~0.

  6557   Mon Apr 23 23:20:07 2012 DenUpdatePEMmicrophones

Tonight I wanted to measure the ambient noise level using Blue Bird mics and figure out if Panasonic WM61a or Primo EM172/173 will be good enough or not. Blue Bird that is in the control room does not seem to work. May be the problem is with the pre-amplifier. The output measured by ADC/Oscilloscope is noise ( amplitude=5mV ). I will return to this issue tomorrow.

  6558   Tue Apr 24 09:58:37 2012 steveUpdatePEMearthquake 3.9 magnitude

Local eq shakes the lab

Attachment 1: eq3.9.png
  6559   Tue Apr 24 11:27:51 2012 steveUpdatePEMnew chairs

We received 6 new  chairs stools for the work benches that have 36" heights.

The control room east side and general office desks require 18" seat height. The new chairs stools have  minimum seat heights  26"

Please label chairs that we are getting rid of.


  6563   Tue Apr 24 16:15:24 2012 DenUpdatePEMmicrophones

I've installed Blue Bird microphone to listen to the acoustic noise at the PSL near PMC.

DSC_4271.JPG     DSC_4272.JPG

Coherence between MC_F and Blue Bird output (C1:PEM-ACC_MC2_Z for now) is changing from low to high value at frequencies 20 - 200 Hz with period ~1 min. Maybe HEPA works with some periodicity. Now it works pretty hard, ~80% of max.

micro_mc_low.png    micro_mc_high.png

  6564   Tue Apr 24 22:16:59 2012 DenUpdatePEMBlue Bird Pre-Amplifier

 I detached Clyde (pre-amp that was in the control room) to understand why it is not working. I seems that the board circuit is burnt near R40, R47, R45.

DSC_4273.JPG     DSC_4274.JPG

  6565   Wed Apr 25 00:20:01 2012 DenUpdatePEMacoustic noise at 40m

 Blue Bird Mic is suspended close to PMC now and outputs ~10 counts when pre-amp gain is 8 dB. This means that the mic outputs ~2.42 mV. Its sensitivity is 27 mV/Pa => acoustic noise is ~0.1 Pa or ~75 dB SPL.

If we buy Panasonic WM61A with their sensitivity -35 dB => they will output ~1.7 mV. We can amplify this signal without adding significant noise. For WM61A S/N ratio is given to be 62 dB. This is for some standard signal that is not specified. For Blue Bird mic it is specified according to IEC 651. So I assume SPL of the standard signal = 94 dB => noise level of WM61A is 32 dB (pretty bad compared to 7 dB-A of Blue Bird). But in our case for PSL S/N ratio is ~43 dB that is not too bad. PSL is noisy due to HEPA, acoustic noise level close to MC2 stack will be less. So we may want to consider Primo EM172/173 where the noise level is claimed to be 18 dB less. I think we should buy several WM61A and EM172.

  6566   Wed Apr 25 11:45:34 2012 JenneUpdatePEMBlue Bird Pre-Amplifier

It looks like we should change the "R40" and "R47" diodes.  If you do it this week, ask Jamie or Koji to check that you've got them oriented correctly before soldering them and plugging it in.

  6567   Wed Apr 25 18:59:47 2012 ranaUpdatePEMBlue Bird Pre-Amplifier

Usually R is for resistors and D is for diodes. Do you think from the schematic that we should put diodes into the R slots?

  6568   Wed Apr 25 19:32:57 2012 DenUpdatePEMBlue Bird Pre-Amplifier


Usually R is for resistors and D is for diodes. Do you think from the schematic that we should put diodes into the R slots?

 That guys are resistors.

  6572   Thu Apr 26 11:56:10 2012 DenUpdatePEMBlue Bird Pre-Amplifier



Usually R is for resistors and D is for diodes. Do you think from the schematic that we should put diodes into the R slots?

 That guys are resistors.

 You are right, they just looked like they were too small to be resistors when I glanced at them. 

  6581   Fri Apr 27 13:32:06 2012 DenUpdatePEMseism channels

A few weeks ago I found that GUR2_X signal is biased from 0 to 800 counts in average. I decided that the corresponding channel in the readout box is bad - adds DC voltage to the signal. I stopped using GUR2_XYZ channels of the seism readout box. Now the same thing happened with the GUR1_XYZ channels. I checked the signals coming out from the seism box with the oscilloscope and they were fine. So the problem is not in the readout box. Then I applied 1 V sine wave to the input of AA board to the GUR1_X and ACC_MC1_Z channels. GUR1_X channel still shows noise. Something is wrong with these channels inside the AA board or in the ADC.



Edited by Den: GUR1_XYZ_IN1 signals are empty though GUR1_XYZ are fine. So the problem is just that GUR1_XYZ_IN1 are not acquired for now though some of the ACC_IN1 channels contain the signal. I need to correct .ini files.

  6593   Wed May 2 19:47:20 2012 DenUpdatePEMEM 172 nonlinearities

I've checked new small EM172 microphones for nonlinearities using Koji's Mac Book speakers. EM172 + Mac nonlinearities are presented at the figure


The Mac's sound frequency was specified to be 500 Hz. Harmonics are seen at 1k, 1.5k, but their amplitude is ~30 times less.

  6594   Wed May 2 21:04:06 2012 DenUpdatePEMEM 172 coherence

I measured coherence between 2 EM 172 microphones in a "quiet room" with SR785


High-frequency noise (>2k) is SR785 noise - I'm not using any amplifier now, the signal from microphone is sent directly to SR785 and is weak at high frequencies.

  6610   Sun May 6 01:41:55 2012 DenUpdatePEMseismic in x,y arms

I locked x,y arms and measured coherence between POS{X,Y}11_I_ERR, MC_F and seismometer signals.


Surprisingly, coherence between POSY and GUR1Y is low, but with GUR1X is relatively high. I wonder if this is due to MC that brings this x-axis noise to the arms.

  6651   Sun May 20 19:57:51 2012 DenUpdatePEMmicrophones

I've soldered EM172 microphones to BNC connectors to get data from them.

DSC_4287.JPG    DSC_4285.JPG

Then I've build an amplifier for them. The circuit is


I've build 6 such circuits inside 1 box. It needs +15 V to A3 and GND to A2. A1 power channel is not used.

DSC_4284.JPG     DSC_4286.JPG

LISO model for this scheme was created and simulation results were compared to measurement of each channel

freq_resp.png   noise.png

Measured noise curve (green) is the SR785 own noise.

  6664   Tue May 22 23:36:02 2012 DenUpdatePEMmircophones

I've put 5 EM172 microphones close together and measured there signal and coherence. They are plugged in to accelerometer channels.



Then I've suspended microphones around the MC - 2 at MC2, 2 at MC1,3 and 1 at PSL. The amplifier box is above STS readout box.

 DSC_4288.JPG           DSC_4299.JPG       DSC_4304.JPG      DSC_4302.JPG

Microphone close to PSL gave a strong coherence with MC_F, as we already saw it using Blue Bird Microphone.

ACC_MC2_XY channels <=> MC2 microphones

ACC_MC1_XY channels <=> MC1,3 microphones

ACC_MC1_Z channel <=> PSL microphones



  6666   Wed May 23 11:30:39 2012 steveUpdatePEMnew emergency back up lights installed

New self checking emergency back up lights were installed at 13 locations in the 40m lab.

Attachment 1: IMG_1217.JPG
  6671   Thu May 24 02:55:36 2012 DenUpdatePEMacoustic noise in MCL

Mic in the PSL showed that fluctuations in the MCL in the frequency range 10 - 100 Hz are due to acoustic noise. I've measured MCL, MCL / PSL mic coherence 2 times with interval 300 seconds.

Surprisingly, acoustic noise level did not change but MC sometimes is more sensitive to acoustic noise, sometimes less.


  6674   Thu May 24 13:28:38 2012 DenUpdatePEMHEPA

HEPA filter was running at 90% of max. I reduced it to 20%. Acoustic noise moved down


The range of MCL oscillations has also decreased but fluctuations in the frequency range 10-100 are still present.

MCL is much more stable now.

mcl_90.png        mcl_20.png


  6692   Sat May 26 20:40:48 2012 DenUpdatePEMexperiments with seismic noise

I measured relative motion of 2 seismometers separated by 4, 18 and 38 feet.

DSC_4307.JPG         DSC_4308.JPG

Relative motion for difference distances between seismometers is presented below.

    psd_distance.png        ratio.png


Al frequencies f < fcrit relative motion becomes smaller then motion of each point. At these frequencies, the ratio relative / absolute motion can be approximated as ratio = C fa . The following table summarizes fcrit, C and a for different length between seismometers.


L, ft fcrit, Hz
C a
4 45 0.0074 1.30
18 30 0.0057 1.52
38 15 0.0208 1.43

Using this approximation we can estimate the desired noise floor of the seismometer to subtract seismic noise from MC_F


Desired seismometer noise should be 100 times less then Guralp's. ADC noise is still less then this level, so this will not be a problem.

Note: for longer cavities condition for seismometer noise becomes more week as fcrit decreases with length.

  6693   Sat May 26 23:57:11 2012 DenUpdatePEMGuralp noise

I've looked through the Guralp manual to figure out what noise do they declare. They present it in acceleration units in dB relative to 1 m2 / s4 / Hz. I've converted my measurements to this units and got


They declare much better noise. May be linoleum makes an effort. Do we have any isolation boxes?

  6695   Sun May 27 23:15:22 2012 DenUpdatePEMexperiments with seismometers

I wondered if linoleum is a reason of high Guralp noise. I measured Guralp noise in 3 cases: they stand on a very soft piece of paper, linulium and stone.

DSC_4309.JPG               DSC_4310.JPG                  DSC_4311.JPG

I've calibrated the noise to units m/s/sqrt(Hz). Using soft paper we get the worst noise, stone - the best, but noises do not differ that much and still much worse then declared noise in the manual.


  6696   Tue May 29 00:35:57 2012 DenUpdatePEMguralp readout box

I measured the frequency response of the Guralp readout box and noise by providing sin signal of amplitude 50 mV at 15 Hz for channels 1-3.


It turns out that the gain is ~250, while my liso model simulated it to be 200. This is because it is hard to approximate AD620 amplifier.

Noise of the box does not seem to be too bad at low frequencies.

  6697   Tue May 29 00:39:52 2012 DenUpdatePEMGuralp noise

I've connected Guralp output to the ADC without readout box. I've got the same noise at low frequencies and even worse noise at high frequencies. However, readout box was still used as DC supply and the signal was read from INPUT test points. I'll do the same experiment without touching readout box at all.


  6698   Tue May 29 00:48:51 2012 DenUpdatePEMsts readout box

STS readout box seems to be partly broken. I've terminated inputs from the seismometer and measured the output. I could not do this for vertical channel because it outputs 7 V DC + 500 mV AC signal. All the switches work fine, 5 V DC is indeed shown when auto zero, calibration, 1 sec resp, sig select are enables. The box has AC power supply that seems to work ok, all measured DC values are equal to the labels. Something is wrong with amplification.




  6712   Tue May 29 22:48:37 2012 DenUpdatePEMGuralp noise

I've checked whether the Guralp noise that we see comes not from seismometer but from ADC or readout box. I did 2 separate measurements . First, I've split 1 signal from Guralp into 2 before the input to AA board and subtracted one from another using Wiener filter. Second, I've connected inputs of channels 1 and 4 of the seismometer readout box and put the signal from seismometer to channel 1.


The plot shows that ADC and readout box do not contribute too much to the Guralp noise.

  6721   Wed May 30 22:51:32 2012 DenUpdatePEMguralp isolation box

When I've put Guralps inside the isolation box, the signal from seismometers increased and was out of AA board range. I've reduced the gain of the readout box by a factor of 2. Now R2 for channels 1-6 is (2000, 1050, 1050, 2000, 1050, 1050) Ohm.

The signal increased in the frequency range 30-50 Hz. Guralp noise become better. That's good. However, it is still worse then in the manual.

As Yuta is dancing on the isolation box, Guralp signal is most time out of the AA board range. So I calculated the noise based on 5 min data. This may be enough, but I'll repeat the experiment later with 30 min data.


  6730   Thu May 31 11:38:19 2012 DenUpdatePEMisolation system

I've put Guralps into the Steve's 2 box isolation system. Noise got better, coherence between 2 seismometers improved. We still need better performance. Probably, one device is noisy and we can not determine which one using these 2 seismometers. We need more seismometers. Sadly, STS-2 readout box is not working.

lin_box_noise2.png    lin_box_coh.png

  6747   Sun Jun 3 01:30:07 2012 DenUpdatePEMsts-2 and guralp in isolation box

We have 2 sts-2 readout box - pink and blue. Pink outputs 12 DVC - this a problem of amplifier. This box has a rectifier (the box works from AC power) and an amplifier for velocity channels. Mass positions, calibration channels are connected by a wire from input to output. The amplifier for velocity channels does not work properly, so I connected velocity channels directly to the output - the signal from sts-2 is large enough even without amplification. When I plugged sts-2 to pink readout board, on the velocity output I saw ~4 VDC. Sts-2 was needed to be recentered. I pressed AUTOZERO command, but this did not work out. Before I had checked that this readout box indeed gives an autozero logical signal - 5VDC for ~2 sec. I think it does not provides sts-2  with enough current, seismometer needs 0.1 A in autozero regime.

Blue readout box after switching it to 1 sec regime and zeroing sts-2 started to output reasonable signal for gains = 10. I tried gains = 100, X velocity channel started to output noise. Now the gain is 10 and the response is 120 sec. But at least this box works. Still performance is not clear as well as noise level. To determine this I've put sts-2 to isolation box.

DSC_4315.JPG                    DSC_4319.JPG

After I've put Guralps in the isolation and waited for a couple of days, Guralp noise has been improved a little more.

lin_box_noise.png                 mcl_gur.png

  6754   Tue Jun 5 14:17:14 2012 steveUpdatePEMair cond maintenance


 Air conditioning maintenance is scheduled for tomorrow from 8 to 11am

  6782   Thu Jun 7 09:52:05 2012 steveUpdatePEMair cond maintenance



 Air conditioning maintenance is scheduled for tomorrow from 8 to 11am

 Jeff checked and  replaced filters  as needed. Job completed this morning.

Attachment 1: PEM800d.png
  6845   Thu Jun 21 09:10:08 2012 steveUpdatePEMflow bench must be running all times

The south end flow bench HEPA filter should be run all times. You can turn it off for a measurement or two but remember we are storing clean optics there.

The zero count bench will reach  room particle count  ~ 10,000 in one minute.

  6846   Thu Jun 21 12:13:35 2012 JenneUpdatePEMflow bench must be running all times


The south end flow bench HEPA filter should be run all times. You can turn it off for a measurement or two but remember we are storing clean optics there.

The zero count bench will reach  room particle count  ~ 10,000 in one minute.

 My bad.  I turned it off last night to see if it would help make the Xgreen more stable, and then when I woke up this morning I realized that I had forgotten to turn it back on.  Bad Jenne.

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