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ID Date Author Type Category Subjectup
  12603   Mon Nov 7 17:24:12 2016 gautamUpdateGreen LockingGreen beat setup on PSL table

I've been trying to understand the green beat setup on the PSL table to see if I can explain the abysmal mode-matching of the arm and PSL green beams on the broadband beat PDs. My investigations suggest that the mode-matching is very sensitive to the position of one of the lenses in the arm green path. I will upload a sktech of the PSL beat setup along with some photos, but here is the quick summary.

  1. I first mapped the various optical components and distances between them on the PSL table, both for the arm green path and the PSL green path
  2. Next, setting the PSL green waist at the center of the doubling oven and the arm green waist at the ITMs (in vacuum distances for the arm green backed out of CAD drawing), I used a la mode to trace the Gaussian beam profile for our present configuration. The main aim here was to see what sort of mode matching we can achieve theoretically, assuming perfect alignment onto the BBPDs. The simulation is simplified, the various beam splitters and other transmissive optics are treated as having 0 width
  3. It is pretty difficult to accurately measure path lengths to mm accuracy, so to validate my measurement, I measured the beam widths of the arm and PSL green beams at a few locations, and compared them to what my simulation told me to expect. The measurements were taken with a beam profiler I borrowed from Andrew Wade, and both the arm and PSL green beams have smooth Gaussian intensity profiles for the TEM00 mode (as they should!). I will upload some plots shortly. The agreement is pretty good, to within 10%, although geometric constraints on the PSL table limited the number of measurements I could take (I didn't want to disturb any optics at this point)
  4. I then played around with the position of a fast (100mm EFL) lens in the arm green path, to which the mode matching efficiency on the BBPD is most sensitive, and found that in a +/- 1cm range, the mode matching efficiency changes dramatically

Results:

Attachments #1 and 2: Simulated and measured beam profiles for the PSL and arm green beams. The origin is chosen such that both beams have travelled to the same coordinate when they arrive at the BBPD. The agreement between simulation and measurement is pretty good, suggesting that I have modelled the system reasonably well. The solid black line indicates the (approximate) location of the BBPD

     

Attachment #3: Mode matching efficiency as a function of shift of the above-mentioned fast lens. Currently, after my best efforts to align the arm and PSL green beams in the near and far fields before sending them to the BBPD results in a mode matching efficiency of ~30% - the corresponding coordinate in the simulation is not 0 because my length measurements are evidently not precise to the mm level. But clearly the mode matching efficiency is strongly sensitive to the position of this lens. Nevertheless, I believe that the conclusion that shifting the position of this lens by just 2.5mm from its optimal position degrades the theoretical maximum mode matching efficiency from >95% to 50% remains valid. I propose that we align the beams onto the BBPD in the near and far fields, and then shift this lens which is conveniently mounted on a translational stage, by a few mm to maximize the beat amplitude from the BBPDs. 

Unrelated to this work: I also wish to shift the position of the PSL green shutter. Currently, it is located before the doubling oven. But the IR pickoff for the IR beat setup currently is located after the doubling oven, so when the PSL green shutter is closed, we don't have an IR beat. I wish to relocate the shutter to a position such that it being open or closed does not affect the IR beat setup. Eventually, we want to implement some kind of PID control to make the end laser frequencies track the PSL frequency continuously using the frequency counter setup, for which we need this change...

  12609   Wed Nov 9 23:21:44 2016 gautamUpdateGreen LockingGreen beat setup on PSL table

I tried to realize an improvement in the mode matching onto the BBPDs by moving the lens mentioned in the previous elog in this thread. My best efforts today yielded X and Y beats at amplitudes -15.9dBm (@37MHz) and -25.9dBm (@25MHz) respectively. The procedure I followed was roughly:

  1. Do the near-field far-field alignment of the arm and PSL green beams
  2. Steer beam onto BBPD, center as best as possible using the usual technique of walking the beam across the photodiode
  3. Hook up the output of the scope to the Agilent network analyzer. Tweak the arm and PSL green alignments to maximize the beat amplitude. Then move the lens to maximize the beat amplitude.

As per my earlier power budget, these numbers translate to a mode matching efficiency of ~53% for the X arm beat and ~58% for the Y arm beat, which is a far cry from the numbers promised by the a la mode simulation (~90% at the optimal point, I could not achieve this for either arm scanning the lens through a maximum of the beat amplitude). Looks like this is the best we can do without putting in any extra lenses. Still a marginal improvement from the previous state though...

  11700   Mon Oct 19 16:20:52 2015 ericqUpdateLSCGreen beatnote couplers installed

Last Friday, I installed some RF couplers on the green BBPDs' outputs, and sent them over to Gautam's frequency divider module. At first I tried 20dB couplers, but it seemed like not enough power was reaching the dividers to produce a good output. I could only find one 10dB coupler, and I stuck that on the X BBPD. With that, I could see some real signals come into the digital system.

I don't think it should be a problem to leave the couplers there during other activities.

  11714   Mon Oct 26 18:59:25 2015 gautamUpdateLSCGreen beatnote couplers installed

I found (an old) 10 dB coupler in the RF component shelves near MC2 - it has BNC connectors and not SMA connectors, but I thought it would be worth it to switch out the 20dB coupler currently on the X green beat PD on the PSL table with it. I used some BNC to SMA adaptors for this purpose. It appears that the coupler works, because I am now able to register an input signal on the X arm channel of the digital frequency counter (i.e. the coupled output from the green beat PD). I thought it may be useful to have this in place and do an IR transmissions arm scan using ALS for the X arm as well, in order to compare the results with those discussed here. However, the beat note amplitude on the analyzer in the control room looks noticeably lower - I am not sure if the coupler is responsible for this or if it has to do with the problems we have been having with the X end laser (the green transmission doesn't look glitchy on striptool though, and the transmission itself is ~0.45). In any case, we could always remove the coupler if this is hindering locking efforts tonight. 

  10372   Wed Aug 13 03:03:37 2014 ericqUpdateGeneralGreen beatnote troubles

[Jenne, Rana, ericq]

No luck locking tonight, as spent a while trying to figure out the complete absence of the green beatnotes. Long story short, we ended up having to adjust the pointing on the PSL table.

Unrelated to this, we also turned on the noise eater on the PSL laser because why not. 


We hooked the BBPDs directly up to a 300MHz scope to try to see the beat as it happened. We witnessed a very strange intermittent ~800MHz oscillation on the Y BBPD, and weirder still, on both the RF and DC outputs of the PD, and the frequency was independent of the laser temperatures. This is to be investigated in the future, but was not related to the beat note state. 

Some progress was made when we took some components out, and looked at the far field of the PSL-Ygreen overlap, and saw some misalignment, and corrected it. Putting the end laser temperature in the usual area allowed the beat note to be found, with the eventual amplitude of ~-40dBm directly out of the BBPD. The Y green alignment was pretty bad throughout, so this can be improved to bring the beat amplitude up. We should also check and make sure we're well aligned to the SHG with the PSL light. We're leaving the X beat for tomorrow, now knowing that we should be able to get it with careful alignment. 

  3763   Fri Oct 22 18:15:21 2010 kiwamuUpdateLockingGreen era: found a green beat note finally

finally we found it !

 green_beatnote.jpg

  3766   Fri Oct 22 21:28:27 2010 AidanUpdateLockingGreen era: found a green beat note finally

Nice work!

Quote:

finally we found it !

 green_beatnote.jpg

 

  3800   Wed Oct 27 21:33:42 2010 SureshUpdateLockingGreen from the far end re-obtained

 

The mirror which was moved during the mode matching of PSL light to the MC (ref elog #3791) has been repositioned.  We once again have the green light from the NPRO on the X (south) arm available on the PSL table. 

This light was supposed to be collimated by the two plano convex lenses (f=200mm and f=50mm  ref to elog #3771) but it was converging.  So I moved the f=50mm lens backwards to make the beam collimated.  I checked the beam collimation by introducing an Al coated mirror infront of th PD and diverting the beam temporarily in a free direction.  I could then check the collinearity and collimation of both the green beams over a meter.  After alignment the mirror was removed and the light is now incident on the PD once again.  We can now proceed to look for green beats.

The power from the PSL NPRO was attenuated for the MC locking work of yesterday.  It has now been increased to the maximum by rotating the Half Wave Plate (HWP).  The power after the PSL is now about 450mW  (500mW - 10% picked off for the doubling).

 

 

 

  12085   Thu Apr 21 14:25:52 2016 gautamUpdateendtable upgradeGreen light recovered

I've made progress on the new layout up to the doubling oven. After doing the coarse alignment with the diode current to the NPRO at ~1A, I turned it back up to the nominal 2A. I then rotated the HWP before the IR Faraday such that only ~470mW of IR power is going into the doubler (the rest is being dumped on razor beam dumps). After tuning the alignment of the IR into the doubling oven using the steering mirror + 4 axis translation stage on which the doubling oven is mounted, I get ~3.2mW of green after the harmonic separator and a HR mirror for green. The mode looks pretty good to the eye (see attachment #1), and the conversion efficiency is ~1.45%/W - which is somewhat less than the expected 2%/W but in the ballpark. It may be that some fine tweaking of the alignment + polarization while monitoring the green power can improve the situation a little bit (I think it may go up to ~4mW, which would be pretty close to 2%/W conversion efficiency). The harmonic separator also seems to be reflecting quite a bit of green light along with IR (see attachment #2) - so I'm not sure how much of a correction that introduces to the conversion efficiency. 

While doing the alignment, I noticed that some amount of IR light is actually transmitted through the HR mirrors. With ~500mW of incident light at ~45 degrees, this transmitted light amounts to ~2mW. Turns out that this is also polarization dependant (see attachment #3) - for S polarized light, as at the first two steering mirrors after the NPRO, there is no transmitted light, while for P-polarized light, which is what we want for the doubling crystal, the amount transmitted is ~0.5%. The point is, I think the measured levels are consistent with the CVI datasheet. We just have to take care find all these stray beams and dump them.

I will try and optimize the amount of green power we can get out of the doubler a little more (but anyway 3mW should still be plenty for ALS). Once I'm happy with that, I will proceed with laying out the optics for mode-matching the green to the arm.

  1941   Tue Aug 25 03:30:23 2009 YoichiSummaryWIKI-40M UpdateGreen lock and phase noise
While Koji and I were discussing about the green laser lock, we wondered if the common motion of the cavity mirrors,
which won't be suppressed by the green laser servo, will cause any problem to the locking.

Since the common motion of the cavity mirrors is equivalent to the change of the path length from the laser to the
input mirror, it will show up as a phase noise in the error signal.
Unfortunately, since we inject the green laser from the end mirror, this phase noise has opposite sign for the
PSL and the green laser.

I calculated the magnitude of the phase noise using an extremely rough estimate of the common motion of the mirrors.
It is explained in the 40m wiki.
http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_09/GreenLock

The result plot is attached.
(Probably the seismic noise I used is an over estimate.)
  8133   Thu Feb 21 19:55:02 2013 ManasaUpdateLockingGreen locking in arms

[Yuta, Manasa]

We have aligned the Y-arm to lock in green. The green beams at the PSL table were clipping at the attenuation optics we installed for the vent (HWP-PBS-HWP). We had to move the polarization changing wave plate to get the green beam on the steering mirror. We installed the GRNT camera on the PSL table and aligned the arms to get TEM00 flashing. Green TRX PD was then installed and the trans power was brought to a maximum of 210uW.
We will use this to align the IR to the arm when we are back in full power tomorrow.

  7241   Tue Aug 21 01:59:33 2012 JenneUpdateGreen LockingGreen locking needs help!

The green beam for the Xarm is flashing a pretty nice 00 mode, but isn't catching lock.

The green beam for the Yarm isn't flashing at all that I can tell from just the camera views.  I don't have energy to start this sometimes monumental task tonight, so I leave it for Future Jenne to work on.

  2835   Fri Apr 23 18:30:49 2010 Aidan, Jenne, KojiSummaryGreen LockingGreen means GO!

Jenne, Koji and I assembled the Covesion Oven today, inserted a PPKTP crystal from Raicol, aligned the crystal to a 50mW focus and
got some green beam coming out.

Covesion Oven assembly

The oven contains a brass clip that can clamp a crystal up to 10mm wide x 0.5mm high x 40mm long (according to the instructions). According to the correspondence from Covesion the clip can accomodate a crystal up to 1.5mm high. Our crystal is 1mm x 1mm x 30mm.

  1. We removed the brass springs from the clip - see Koji's photos
  2. We placed the Raicol PPKTP crystal (#725) into the clamp with the long polished surfaces facing out to the sides and the roughened surfaces facing up and down.
  3. We balanced the 10mm x 40mm x 1mm glass plate on top of the crystal.
  4. We replaced the brass springs in the top of the clip but only tightened the screws a couple of turns so they wouldn't fall out.
  5. Very carefully and slowly, I tightened the screws a few turns in a star-shaped order to distribute the pressure evenly across the glass top
  6. Each time I tightened all eight screws, I jiggled each of the four springs to see if there was any compression in them
  7. Once the springs started to show signs of compression I stopped tightening them and tested the stability of the glass plate - a reasonable amount of pressure was required to move the plate - about the same amount required to push a SR560 across an optical table with your index finger.
  8. We loosely attached the lid and moved the oven to the table

Alignment of the crystal to the focus

The oven was mounted on a 4-axis Newport translation stage. We plonked the assembly onto the table, removed the lid and adjusted the rough position so that a focus of the 1064nm beam, from a 100mm lens, was positioned near the center of the crystal - then it was clamped down to the table. From here we adjusted the alignment of the stage, using an IR card and a viewer to guide us, until we eventually saw some green beam coming out. We were all very excited by this! We optimized the alignment as best we could using the IR card and then we replaced the lid on the oven. At this point the temperature of the PPKTP was around 26.5C and the green beam coming out look quite dim. We turned the oven up to around 36 degC and observed the beam getting much brighter and we approached the optimum phase-matching condition.

We haven't done anyway quantitative measurements yet but we were pleased with how easy this first stage was.

 

[Edit by Koji] More photos are on Picasa album

  16883   Tue May 31 17:30:01 2022 YehonathanUpdateBHDGreen shutters fixed

[Paco, Yehonathan]

We fixed the slow control over the green beam shutters.

At the Y arm the wrong BNC was connected to the shutter driver. We connected the correct BNC to the driver and switched the remote mode. The green Y shutter now works but in reverese, meaning that sending 1 to C1:AUX-GREEN_Y_Shutter closes the shutter and vice versa. This needs to be fixed.

At the X end the problem was a bit more complicated. Previously, the shutter was controlled by c1auxey. We figured that c1auxex has a lot of spare bio channels. We found an Acromag BNC front panel (with wires already soldered to the BNCs) lying around in the lab and installed it on the c1auxex Acromag chassie. We then connected the topmost BNC to channel 0 on XT1111A in the chassie. The BNC was connected to the green shutter driver on the X end.

EPIC channel was added to the c1auxex db file while it was commented out on the psl shutters db file. Modbus was restarted on c1auxex and c1psl. c1psl had to be burt restored to regain MC lock. Now the green X shutter works properly.

  9405   Tue Nov 19 00:07:16 2013 JenneUpdateLSCGreen status

After I aligned the IR interferometer (no ASS - we still need to figure out what's going on with that), I am trying to find the green beatnotes for each arm.

First, I locked the green lasers to each arm.

I then went out to the PSL table and aligned the Green Yarm path by overlapping the near-field and far-field of the yarm transmission and the PSL green pickoff.  I then turned on the power for the Beat PDs, since it was off (I confirmed that the outputs were plugged into the beatbox, so they are seeing 50 ohms).  I assume that the beat PDs were off since Manasa pulled the Beatbox last week, but there is no elog reference!!  Anyhow, after seeing a real signal, I maximized the DC power on the beat PD for the Yarm.  I then maximized the light on the DC transmission PD for the Yarm.

I looked at the Xarm, and the near-field alignment looks okay, but I haven't checked the far-field.

I started looking for the beatnotes from the control room:

I am changing the SLOW_SERVO2_OFFSETs by 30 counts, and then unlocking and relocking the arms, and checking to see if I see a peak on the RF spectrum analyser. 

The Y offset started at -10320, and I found a beatnote at -11230 (beatnote is about 26MHz).  The X offset started at 4500.  Going larger seemed to get me to a less bright TEM00 mode, so I switched and have been searching by going down in offset, but haven't yet found the beatnote.  I suspect that I actually need to align the X path on the PSL table.  The Y beatnote is very small, about -30dBm, so I also need to tweak the alignment by maximizing the peak value.

  9407   Tue Nov 19 01:11:19 2013 JenneUpdateLSCGreen status

I am able to lock the Yarm ALS, but not at the full gain that I should be.  I attribute this to my mediocre alignment of the path on the PSL table.  EDIT: Manasa pointed out that I forgot to set the PSL FSS slow adjust to ~zero, so the PSL temperature was off, so there wasn't really any hope for me last night.

However, I decided that I should write down the ALS locking procedure, as shown to me by Masayuki on 29Oct2013, that is written in one of the Control Room notebooks.  So, here it is.  I will write channel names and DTT template names for the Y arm, but the procedure is the same for both arms.

  1. Lock and align arms using IR.
  2. Lock green beams to arms.
  3. Align green beams to arms.
  4. Check beatnote alignment on PSL table.
  5. Find beatnote by changing end laser temperature (C1:ALS-Y_SLOW_SERVO2_OFFSET) in steps of ~30, watch spectrum analyser for peak.  Easier if arms are locked in IR, but disable LSC system before moving to step 6.  Beatnote should be less than ~50 MHz, and should have a peak height of about -20dBm or more.  When doing 2 arms, be careful that beatnotes of the different arms do not overlap in frequency.  Manasa reminds me that you must also remember to set the PSL FSS SLOW actuator adjust to near zero, to get the PSL back near its nominal temperature.
  6. Check UGF of phase tracker loop.  (DTT template in /users/Templates/ALS/YALS_PT_OLTF.xml) Want UGF to be ~2kHz.  Change C1:ALS0BEATY_FINE_PHASE_GAIN as necessary.
  7. Start the watch script from the ALS screen to watch for lockloss.
  8. Look at the PHASE_OUT spectrum (DTT template in /users/Templates/ALS/ALS.xml).
  9. Clear history of Phase Tracker Loop (clear hist button on C1:ALS-BEATY-FINE_PHASE screen).  Very important to do this before step 10, every time you get to step 10  (i.e. if you lose lock and are starting over)!
  10. Check sign of loop gain by using + or - 0.1 for the gain (C1:ALS-YARM_GAIN).  Beatnote should immediately stop moving if you have the sign right.  Otherwise, it'll zip around (if it does, repeat step 9, step 10).
  11. Turn gain of ALS up to ~15.  Watch the PHASE_OUT spectrum, look for the servo bump.  When you see it, back off the gain a little.  Gain of ~15 is usually about the right ballpark.
  12. Turn on FM 2, 3, 6, 7, 8 of C1:ALS-YARM.  (FM5 should already have been on).
  13. Wait for PHASE_OUT spectrum to come down.  Turn on FM10 of C1:ALS-YARM.
  14. Check UGF of ALS loop (DTT template in /users/Templates/ALS/YALS_OLTF.xml).  Want UGF to be about 150 or 170 Hz (at the peak of the phase bubble).  Adjust C1:ALS-YARM_GAIN as necessary.
  15. ALS is locked!  Use something like the "Scan Arm" script from the ALS screen to find IR resonance, or do whatever measurement you want.  Dataviewer template /users/Templates/Dataviewer_Templates/ALSdtv.xml may be useful.
  9411   Tue Nov 19 14:47:59 2013 manasaUpdateLSCGreen status

Quote:

After I aligned the IR interferometer (no ASS - we still need to figure out what's going on with that), I am trying to find the green beatnotes for each arm.

First, I locked the green lasers to each arm.

I then went out to the PSL table and aligned the Green Yarm path by overlapping the near-field and far-field of the yarm transmission and the PSL green pickoff.  I then turned on the power for the Beat PDs, since it was off (I confirmed that the outputs were plugged into the beatbox, so they are seeing 50 ohms).  I assume that the beat PDs were off since Manasa pulled the Beatbox last week, but there is no elog reference!!  Anyhow, after seeing a real signal, I maximized the DC power on the beat PD for the Yarm.  I then maximized the light on the DC transmission PD for the Yarm.

I looked at the Xarm, and the near-field alignment looks okay, but I haven't checked the far-field.

I started looking for the beatnotes from the control room:

I am changing the SLOW_SERVO2_OFFSETs by 30 counts, and then unlocking and relocking the arms, and checking to see if I see a peak on the RF spectrum analyser. 

The Y offset started at -10320, and I found a beatnote at -11230 (beatnote is about 26MHz).  The X offset started at 4500.  Going larger seemed to get me to a less bright TEM00 mode, so I switched and have been searching by going down in offset, but haven't yet found the beatnote.  I suspect that I actually need to align the X path on the PSL table.  The Y beatnote is very small, about -30dBm, so I also need to tweak the alignment by maximizing the peak value.

 I found the beatnotes for both the X and Y arm ALS this morning. The beat amplitudes measured -5dBm and -18dBm respectively and occurred at SLOW SERVO2 OFFSET 4550 and -10340. I had to only tweak the Y green PSL alignment to increase the beat amplitude.

I locked both the arms using ALS and they were stably locked until MC unlocked for a moment (nearly 16 minutes).

The only thing missing in the list of things you looked into is the status of the PSL slow actuator adjust. Check if this is near zero.

  8958   Thu Aug 1 22:49:31 2013 manasaUpdateGeneralGreen status after PR3 flipping investigated

[EricQ, Koji, Manasa]

We opened the BS chamber to check the status of the green beams. The X green has 3 steering mirrors before they hit periscope1 and the Y green transmits through all the optics giving no way to steer it.

We agreed to start fixing the Y green. The wedge angle of PR3 is steering the transmitted beam away in both pitch and yaw. Since we are restricted only to yaw movement (done by moving the periscope), we want he wedge angle to be oriented in the yaw as well.

Right now, the wedge is oriented at about 20-30 deg off (The mark on the side of the mirror does not indicate the wedge). So we see a pitch as well as yaw misalignment in the transmitted beam. The pitch misalignment is making the beam fall off the mirrors in periscope2. 

We have decided to get the wedge angle set right for PR3 and redo the alignment for IR. Once we are aligned for the IR, we will modify the green layout.

  1994   Wed Sep 23 17:32:37 2009 robAoGComputersGremlins in the RFM

A cosmic ray struck the RFM in the framebuilder this afternoon, causing hours of consternation.  The whole FE system is just now coming back up, and it appears the mode cleaner is not coming back to the same place (alignment).

 

rob, jenne

  1996   Wed Sep 23 20:02:11 2009 JenneAoGComputersGremlins in the RFM

Quote:

A cosmic ray struck the RFM in the framebuilder this afternoon, causing hours of consternation.  The whole FE system is just now coming back up, and it appears the mode cleaner is not coming back to the same place (alignment).

 

rob, jenne

 Jenne, Rana, Koji

The mode cleaner has been realigned, using a combination of techniques.  First, we used ezcaservo to look at C1:SUS-MC(1,3)_SUS(DOF)_INMON and drive C1:SUS-MC(1,3)_(DOF)_COMM, to put the MC1 and MC3 mirrors back to their DriftMon values.  Then we looked at the MC_TRANS_SUM on dataviewer and adjusted the MC alignment sliders by hand to maximize the transmission.  Once the transmission was reasonably good, we saw that the spot was still a little high, and the WFS QPDs weren't centered.  So Koji and I went out and centered the WFS, and now the MC is back to where it used to be.  The MC_TRANS QPD looks nice and centered, so the pointing is back to where it used to be.

  11517   Wed Aug 19 07:58:25 2015 SteveUpdatePEMGur interface box

Koji and Steve,

We took transferfunctions of each channel yesterday. They were identical ?. I will check the cables from ADC to DAQ next.

  11520   Thu Aug 20 11:31:55 2015 KojiUpdatePEMGur interface box

As reported previously, the transfer functions of the channels look fine. (i.e. All channels almost identical.)
I checked the chain from the unit input to the DAQ BNC connectors. They were all OK.

Today I have been checking the signals on the unit with the long DB37 cables connected.
I could not see anything on the Gur2 channels on the board. I looked at the DB37 for Gur2 and felt something is wrong.

I opened the housing of the cable and realized that all the pins are not fully inserted.
The wires were crimped improperly and prevents them to be fully inserted.

=> We need to redo the crimping to insert them.
=> We need to check the other side too.

  11523   Fri Aug 21 17:15:13 2015 SteveUpdatePEMGur interface box

 

Quote:

As reported previously, the transfer functions of the channels look fine. (i.e. All channels almost identical.)
I checked the chain from the unit input to the DAQ BNC connectors. They were all OK.

Today I have been checking the signals on the unit with the long DB37 cables connected.
I could not see anything on the Gur2 channels on the board. I looked at the DB37 for Gur2 and felt something is wrong.

I opened the housing of the cable and realized that all the pins are not fully inserted.
The wires were crimped improperly and prevents them to be fully inserted.

=> We need to redo the crimping to insert them.
=> We need to check the other side too.

I'm making a new long cable. Both connector ends of this X arm long cable were terrible. It was removed from the cable tray yesterday.

The Y arm Guralp is running fine. The interface box is open in front of 1X1 on a cart and it is alive!    Please be aware of it !

  11537   Fri Aug 28 17:04:12 2015 SteveUpdatePEMGur interface box cable
Ara! Onara suru tsu-mori datta keh-do, un-chi ga de-chatta...
Quote:

 

Quote:

As reported previously, the transfer functions of the channels look fine. (i.e. All channels almost identical.)
I checked the chain from the unit input to the DAQ BNC connectors. They were all OK.

Today I have been checking the signals on the unit with the long DB37 cables connected.
I could not see anything on the Gur2 channels on the board. I looked at the DB37 for Gur2 and felt something is wrong.

I opened the housing of the cable and realized that all the pins are not fully inserted.
The wires were crimped improperly and prevents them to be fully inserted.

=> We need to redo the crimping to insert them.
=> We need to check the other side too.

I'm making a new long cable. Both connector ends of this X arm long cable were terrible. It was removed from the cable tray yesterday.

The Y arm Guralp is running fine. The interface box is open in front of 1X1 on a cart and it is alive!    Please be aware of it !

The new cable was made this way:

Pins were located with ohm meter for locations and both ends were cut off.The Belden 1424A cable than was soldered to DB37 and Guralp circular connector " IKPT06F16-26S-ND "

This cable will connect the ADC interface box CCD# DO 60506 to Guralp seismometer at the sout end.

The Guralp's each 3 axies will be connected through a twisted pair to the differential input op amp

Gur  ouput  vertical axis + -  on circular connector   A, B  to DB37 pin 1 &20

Gur output        N/S axis + -  on circular connector   C, D to DB37 pin 2 & 21

Gur output       E/W axis + -  on circular connector   E, F to DB37 pin 3 & 22

Power +12 VDC  from DB37 pin 29 to Gur circular connector pin c (lower case)

Power -12 VDC  from DB37 pin 24 to Gur circular connector pin  M Note: this connection was absent at the first test of this cable!

Ground              from DB37 pin 10 to Gur circular connector pin b (lower case)

Summery: I may destored the opamp  at the Guralp A at the south end.

 

 

  11540   Fri Aug 28 20:20:26 2015 ranaUpdatePEMGur interface box cable

To help find out if Steve really melted the inside of our precious seismometer, lets hook it up using the handheld seismo wand and see if it produces volts when we shake the ground.

Also, please stop using names like GurA or Gur1 or GurSuzy. We have GurX and GurY because they are at those ends. Anything else is confusing.

  11505   Fri Aug 14 09:07:45 2015 SteveUpdatePEMGur interface box is wonky

Atm1, Before cable swap

Atm2, The long cables were swapped at the input of the interface box.

We can conclude that the problem is in the interface box

I wonder if interface box input 3 is wired?

  11506   Fri Aug 14 12:10:08 2015 KojiUpdatePEMGur interface box is wonky

Let's dismantle the I/F unit from the rack and connect the cable with the lid open.
We need to trace the signal.
 

  11507   Fri Aug 14 17:20:01 2015 JenneUpdatePEMGur interface box is wonky

IIRC, the Guralp box's 3rd set of channels do not have all of the modifications that were made on channels 1 and 2.

  11514   Tue Aug 18 11:16:17 2015 SteveUpdatePEMGur interface box is wonky

The Guralp ADC  interface box  D060506 is ready for inspection. It is in front of 1X1 with open top and running.cool

Obviously c7 as 1 miroF cap is missing.blush

Quote:

Let's dismantle the I/F unit from the rack and connect the cable with the lid open.
We need to trace the signal.

 

  3205   Tue Jul 13 11:51:19 2010 JenneUpdatePEMGur1 has no signal?!?!?!?!

[Sanjit, Jenne]

Sanjit discovered that the Gur1 channels are all digital 0.  We determined that this began on July8, 04:00 UTC (~9pm on the 7th?).

It's digital zero, so we suspect a software thing.  Just to check, we put a sine wave in, and didn't see anything.  Gur2 seems totally fine, and the sine wave input showed up nicely on dataviewer.  What's going on? Sabotage to prevent this paper from getting done?  Dmass trying to get his paper done before me???

Investigations are ongoing.... Joe claims it's not his fault, since his shenanigans near the PEM rack were on days before, and days after this, but not on the 7th.  

  3211   Tue Jul 13 23:20:37 2010 JenneUpdatePEMGur1 has no signal?!?!?!?!

Quote:

[Sanjit, Jenne]

Sanjit discovered that the Gur1 channels are all digital 0.  We determined that this began on July8, 04:00 UTC (~9pm on the 7th?).

It's digital zero, so we suspect a software thing.  Just to check, we put a sine wave in, and didn't see anything.  Gur2 seems totally fine, and the sine wave input showed up nicely on dataviewer.  What's going on? Sabotage to prevent this paper from getting done?  Dmass trying to get his paper done before me???

Investigations are ongoing.... Joe claims it's not his fault, since his shenanigans near the PEM rack were on days before, and days after this, but not on the 7th.  

 I just rebooted c0dcu1, which didn't help anything.  Joe said he'd try to give me a hand tomorrow.

  11497   Wed Aug 12 11:44:13 2015 ericqUpdatePEMGur2 Channels still wonky

In previous elogs, we saw that the X and Y spectra out of GUR2 (X end Guralp seismometer) looked strange (i.e. inconsistent with the GUR1 spectra). 

This morning, Steve and I brought the handheld control unit to the Guralp to center the test mass, by adjusting the centering potentiometers inside the unit while monitoring the voltage readout corresponding to the DC mass position (manual has instructions). 

At first glance, this seemed like the likely culprit, as the offsets for the horizontal directions were much larger than the vertical one. We zeroed all three to within a mV or two. Unfortuntately, the spectra look the same as they did 10 hours ago. no

Since we already had the kit out, we checked the offsets for GUR1. Only the "East/West" had an offset over 50mV, so we zeroed that one, but left the others alone. 

  2170   Mon Nov 2 15:27:08 2009 JenneUpdatePEMGur2 cables have been moved

The cables labeled "Gur2" which were connected to channels 2,3,4 of the PEM-ADCU have been moved to the PCIX ADC which is connected directly to the ASS machine.  This means that until I (a) put the cables back or (b) figure out how to route channels from the ASS ADC to the RFM, we won't be able to use these channels for environmental monitoring, nor will they be saved. 

The Gur2_X, Gur2_Y, Gur2_Z channels are now connected to the 2nd, 3rd and 4th ADC channels respectively, on the ASS ADC (the first channel / TP1 is ADC0_0, which is the 1pps signal.).  The sketchy thing about the setup is the connection between the cables and the new ADC board.  The PCIX card is connected to the ASS via a white ribbon cable, and the board is just sitting on top of the computer box.  The 1pps (which has been hooked up for a long time) goes into the board via clip-doodles.  The regular channels have a SCSI cable connector, so I used a SCSI cable to connect up the ADC tester board, and connected my seismometer inputs to this tester board via more clip doodles.  Clearly this is a sketchy solution, and not okay for more than a day or so.  But we'll see how it goes. 

I'm going to, on the SimuLink Diagram, change the input source of these channels, from the RFMN to the ADC.  Then we'll see if that fixes our timing problem, and magically makes everything relating to the OAF work, and subtract huge amounts of noise. 

  2503   Mon Jan 11 14:16:59 2010 JenneUpdatePEMGur2 cables reconnected to the PEM ADCU

So that we can use both Guralps for Adaptive stuff, and so that I can look at the differential ground motion spectra, I've reconnected the Guralp Seismometers to the PEM ADCU, instead of where they've been sitting for a while connected to the ASS ADC.  I redid the ASS.mdl file, so that the PEM and PEMIIR matricies know where to look for the Gur2 data.  I followed the 'make ass' procedure in the wiki.  The spectra of the Gur1 and Gur2 seismometers look pretty much the same, so everything should be all good.

There's a problem with DataViewer though:  After selecting signals to plot, whenever I hit the "Start" button for the realtime plots, DataViewer closes abruptly. 

When I open dataviewer in terminal, I get the following output:

allegra:~>dataviewer
Warning: communication protocol revision mismatch: expected 11.3, received 11.4
Warning: Not all children have same parent in XtManageChildren
Warning: Not all children have same parent in XtManageChildren
Warning: Not all children have same parent in XtManageChildren
Warning: Not all children have same parent in XtManageChildren
Warning: Not all children have same parent in XtManageChildren
Warning: communication protocol revision mismatch: expected 11.3, received 11.4
msgget: No space left on device
allegra:~>framer4 msgget:msqid: No space left on device

Does anyone have any inspiration for why this is, or what the story is?  I have GR class, but I'll try to follow up later this afternoon.

  786   Sun Aug 3 20:53:54 2008 ranaConfigurationPEMGuralp
We got our repaired Guralp back in the mail from England (s/n T4157). I plugged it in
to Ben's 3-Guralp breakout box (http://www.ligo.caltech.edu/docs/D/D060506-00.pdf) and
verified that it is not oscillating (like it was before) and that it responds to us
jumping around.

The breakout box has way too much gain, however. The ADC wants +/-2 V and the box puts out
~5 Vpk in the night time.

Looking at the schematic, it has a DC gain of 200 and a double whitener (50,50:10,10) so that
there's a gain of 5000 from 50-2000 Hz. The Guralp has a transduction gain of 800 V/(m/s) and
so we can just calculate what the frequency dependent noise figure of the box has to be. I've
pulled it out, put it on the bench, and started reworking it. I am looking for a soldering/
testing volunteer.

The other kink in the problem is that since we want to use this for the adaptive noise cancellation,
we have to make the noise floor of the readout better than the ambient noise by the same factor
with which we want to cancel the noise.
  1760   Fri Jul 17 18:04:54 2009 ClaraUpdatePEMGuralp Box Fail

I've been trying for most of the week to get noise measurements on the output of the Guralp box as well as scross the AD640 chip. The measurements haven't really been making sense, and, being at a loss as to what else I should try, I decided to redo the resistors on the N/S 2 and E/W 2 channels. (I had been comparing the VERT1 and VERT2 channels, as VERT1 has been restuffed and VERT2 has not.) I don't need all three of the second set of channels to do more measurements, so it seemed like a good use of time.

The first thing I noticed was that the VERT2 channel was missing two resistors (R24 and R25). I probably should have noticed this sooner, as they are right by the output points I had been measuring across, but it didn't occur to me that anyone did anything to the VERT2 channel at all. So, probably the measurements on VERT2 are no good.

VERT2_missing_resistors.png

Note the existence of 100 kOhm resistors on the top channel, and none on the bottom channel (VERT2).

 

Then, while I was soldering in some 100 Ohm resistors, I happened to notice that the resistors I was using had a different number (1001) on them than the corresponding ones on the already redone channels (1003). I checked the resistance, and the ones on the already redone channels turned out to be 100 kOhm resistors, rather than 100 Ohms. So, I double checked the circuit diagram to make sure that I had read it correctly, and there were a number of resistors that had been relabeled as 100 Ohms and several relabeled as 100 kOhms. On the board, however, they were ALL 100 kOhms. Clearly, one of them is wrong, and I suspect that it is the circuitboard, but I don't know for sure.

resistors_diagram.png

resistors_board.png

The diagram clearly shows that R6 should be a 100k resistor, while R5 and R8 should be 100 Ohm resistors, but they are all the same (100k) on the board. I suspect this may have something to do with larger-than-expected noise measurements. But, it's possible the diagram is wrong, not the board. In any case, I didn't really know what to do, since I wasn't sure which was right, so I just replaced all the resistors I was sure about and removed the 100k and 100 Ohm resistors without replacing them with anything. Incidentally, the box of 100kOhm resistors seems to be missing, so I wouldn't have been able to finish those anyway.

  1761   Sat Jul 18 19:49:48 2009 ranaUpdatePEMGuralp Box Fail
That's terrible: R5 & R8 should definitely be 100 Ohm and not 100kOhm. 100k would make it a noise disaster. They should also be metal film (from the expensive box, not from the standard box). This is the same for all channels so might as well stuff them.

The circuit diagram between TP3 and TP4 appears to be designed to make the whitening not work. That's why R6 & R7 should be 100k. And R2 should be metal film too.

Basically, every time we want good low frequency performance we have to use the metal film or metal foil or wirewound resistors. Everything else produces a lot of crackling noise under the influence of DC current.

I'm also attaching the voltage and current noise spectra for the AD620 from the datasheet. These should allow us to compare our measurements to a reasonable baseline.
  1765   Mon Jul 20 17:06:29 2009 JenneUpdatePEMGuralp Box Fail

Quote:
That's terrible: R5 & R8 should definitely be 100 Ohm and not 100kOhm. 100k would make it a noise disaster. They should also be metal film (from the expensive box, not from the standard box). This is the same for all channels so might as well stuff them.

The circuit diagram between TP3 and TP4 appears to be designed to make the whitening not work. That's why R6 & R7 should be 100k. And R2 should be metal film too.

Basically, every time we want good low frequency performance we have to use the metal film or metal foil or wirewound resistors. Everything else produces a lot of crackling noise under the influence of DC current.

I'm also attaching the voltage and current noise spectra for the AD620 from the datasheet. These should allow us to compare our measurements to a reasonable baseline.


While we're comparing things to other things, Ben Abbott just emailed me his measurement of the AD620 from back in the day. Clara's going to use this along with the specs to make sure that (a) we're not taking crazy measurements and (b) our AD620s aren't broken and in need of replacement. In this plot, we're looking at the GOLD trace, which has the AD620 set up with a gain of 10, which is how our AD620's are set up in the Guralp breakout box.

Just picking a single point to compare, it looks like at 1Hz, Ben saw ~130dBVrms/rtHz. Converting this to regular units [ 10^(#dB/20)*1Vrms = Vrms ], this is about 3*10^-7 Vrms. That means that Clara's measurements of our AD620 noise is within a factor of 2 of Ben's. Maybe the way we're connecting them up just isn't allowing us to achieve the ~50nV/rtHz that is claimed.
  1767   Tue Jul 21 13:55:08 2009 ClaraUpdatePEMGuralp Box Success!

There managed to be just enough 100 kOhm resistors to stuff all the "2" channels (VERT2, N/S2, E/W2) with the fancy low-noise resistors. The first six channels (VERT 1/2, NS 1/2, EW 1/2) are now completely done with the thin-film resistors, taking into account the changes that were made on the circuit diagram. I also replaced the C8 capacitor with the fancy Garrett ones and added capacitors on top of R4 and R13 (after painstakingly making sure that the capacitances are exactly the same for each pair) for the "2" channels. It looks like the capacitors on the "1" channels are the cheaper ones. I will compare the noise measurements later to see if there is any difference - if so, I can replace those as well (although, we're out of the 1 uF capacitors needed for C8).

Speaking of, we are now out of or very low on several types of the Garrett resistors/capacitors: 1 uF, 1kOhm, 100 Ohm, 14.0 Ohm, and 100 kOhm. I left the specifics on Steve's desk so that more can be ordered for the eventual time when the third set of channels needs to be restuffed.

  1131   Wed Nov 12 11:36:13 2008 JenneUpdatePEMGuralp Breakout Box is ~50% hooked up
The Guralp box is about halfway hooked up now. The seismometer is under the BSC, and the long cable from the seismometer to the breakout box is connected to "Guralps 1 Input" on the front panel. This corresponds to the set of 3 channels that Caryn stuffed with the new fancy-pants resistors few weeks ago. (When we finally get the other Guralp back from the company, we'll have to stuff the next set of 3 channels).

The Breakout Box is on the very top of 1Y1, sitting on top of the black power supplies. This should be fine, but it's pretty toasty hot up there, so if we find that there are problems with running the box at higher-than-room-temperature, step 1 will be to find a new spot for the box. (I'm not at this time anticipating a problem, but you never know....) Steve put a little foot between the Guralp box and the power supply to get some air circulation.

The ADC Octopus cable that Bob made is connected, and going up through the top of the rack. I am now going on a BNC cable hunt to extend this cable over to the PEM ADC. The PEM ADC is in 1Y7, so I'll need some medium-long BNC cable to get there.

The power cable is also ready to be connected to the rack's +/- 15VDC. I'll talk to Bob about getting this done.

Next step: pick some channels on the PEM ADC, and create them in the .ini files
  2802   Fri Apr 16 17:26:23 2010 JenneUpdatePEMGuralp Breakout Box pulled

I pulled the Guralp breakout box from the rack, and it's sitting on the EE bench here.  The game plan is to check out the Gur2X channel.  

Rana and Steve have been investigating, and found that the X channel has been funky (which has been known for ~a month or two) when the seismometer has been plugged in, and also when the seismometers have been unplugged, but the box is left on.  The funkyness goes away when the box is turned off.  Since it's not there when the box is off, it seems that it's not a problem with the cable from the box to the ADC, or in the ADC channel.  Since it is there when the box is on, but the seismometer is unplugged, it's clear that it's probably in the box itself.  

Preliminarily, I've connected a set of BNC clipdoodles to the input testpoints, and another set to the output.  They're both connected to a 'scope (which is on it's battery so it's not connected to any Ground), and when I tap on the circuit board the input trace is totally unchanged, but the output trace goes kind of crazy, and gets more fuzzy, and picks up a DC offset.  Koji is concerned that some of the big capacitors may have an iffy connection to the board. 

Investigations will continue Monday morning. 

  2811   Tue Apr 20 00:32:30 2010 JenneUpdatePEMGuralp Breakout Box put back

Quote:

I pulled the Guralp breakout box from the rack, and it's sitting on the EE bench here.  The game plan is to check out the Gur2X channel.  

Rana and Steve have been investigating, and found that the X channel has been funky (which has been known for ~a month or two) when the seismometer has been plugged in, and also when the seismometers have been unplugged, but the box is left on.  The funkyness goes away when the box is turned off.  Since it's not there when the box is off, it seems that it's not a problem with the cable from the box to the ADC, or in the ADC channel.  Since it is there when the box is on, but the seismometer is unplugged, it's clear that it's probably in the box itself.  

Preliminarily, I've connected a set of BNC clipdoodles to the input testpoints, and another set to the output.  They're both connected to a 'scope (which is on it's battery so it's not connected to any Ground), and when I tap on the circuit board the input trace is totally unchanged, but the output trace goes kind of crazy, and gets more fuzzy, and picks up a DC offset.  Koji is concerned that some of the big capacitors may have an iffy connection to the board. 

Investigations will continue Monday morning. 

 The Guralp Box appears to be back in working order.  It's reinstalled with the 2 seismometers plugged in.

In order:

* Koji suggested retouching the through-board solder joints on the broken channel (EW2 = Gur2X) with a bit of solder to ensure the connections were good.  Check.

* "C7", one of the giant 1uF capacitors on each channel is totally bypassed, and since that was one of the original suspects, Rana removed the (possibly) offending capacitor from EW2.

* Rana and I isolated the craziness to the final differential output stage.  We tried each of the testpoints after the individual gain / filter stages, and found that the signals were all fine, until after the output stage.

* I started to remove the resistors in the output stage (with the plan to go through the resistors, capacitors, and even the amplifier chip if neccessary), and noticed that 2 of the 1k resistors came off too easily, as if they were just barely connected in the first place.  After replacing only the 4 1k resistors, the craziness seemed to be gone.  I poked and gently bent the board, but the output wouldn't go crazy.  I declared victory.

* I reinstalled the box in its normal spot, and put Gur2 (which had been out by the bench for use as a test signal) back next to the other seismometers.  We are in nominal condition, and should be able to do a huddle test this week.

 

I looked at the time traces of all the seismometer channels, and they all looked good.  I'll put a spectra in in the morning....I'm too impatient to wait around for the low frequency FFTs.

 

Attached are the before and after pictures of the output stage of EW2 / Gur2X.  The "before" is the one with the OUT+ and OUT- words upsidedown.  The "after" picture has them right side up.

  12374   Thu Aug 4 17:29:17 2016 PrafulUpdateGeneralGuralp Cable

The Guralp cable has been pulled and put in the corner to the left of the water cooler:

 

Ben came by today before the cable had been pulled but he said he'll be back tomorrow.

  12387   Tue Aug 9 15:50:30 2016 PrafulUpdateGeneralGuralp Cable

The Guralp cable has been reconnected and powered after having the connector changed out.
 

  12000   Fri Feb 19 15:12:38 2016 KojiSummaryPEMGuralp Health Check

I measured the guralp raw outputs and the TFs using the handheld unit and an FFT analyzer.

[Setup]

The handheld unit was connected to each guralp with the same cable which is confirmed t be functional with the Yend Guralp.

The signal for Z, N, and E directions are obtained from the banana connectors on the handheld unit. Each direction has mass, low gain velocity, and high gain velocity output. The PSDs of the signals were measured with an FFT analyzer. The transfer function from the mass signal to the low/high gain signals were also measured for each direction.

The adjustment screw for the E output of the Xend does not work. I had to tilt the Xend Guralp using the leg screws to bring the E signal to zero.

[Result]

Attachment 1: Raw voltage PSD for all outputs
Attachment 2: Comparison of the low gain vel outputs

- All of the mass output show similar PSDs.
- Low gain velocity outputs shows somewhat similar levels. I still need to check if the output is really the ground velocity or not.
- High gain velocity outputs are either not high gain, broken, or not implemented.

- We need to calibrate the low gain output using signal injection, huddle test, or something else.

Attachment 3: TFs between each mass output and the low or high gain outputs

- TFs between the mass signal and the low vel signals show the similar transfer functions between the channels.
- The high gain outputs show low or no transfer function with regard to the mass signals.
 

  2660   Sun Mar 7 07:01:21 2010 ranaUpdateWienerFilteringGuralp Huddle Test software

We need to do a new huddle test of the Guralps for the Wiener filtering paper. The last test had miserable results.

I tried to use recent data to do this, but it looks like we forgot to turn the Guralp box back on after the power outage or that they're far off center.

So instead I got data from after the previous power outage recovery.

I tried to use our usual Wiener filter method to subtract Guralp1-Z from Guralp2-Z, but that didn't work so well. It was very sensitive to the pre-weighting.

Instead I used the new .m file that Dmass wrote for subtracting the phase noise from his doubling noise MZ. That worked very well. It does all of the subtraction in the frequency domain and so doesn't have to worry about making a stable or causal filter. As you can see, it beats our weighted Wiener filter at all frequencies.

huddlez.png

The attached plot shows the Guralp spectra (red & green), the residual using time-domain Wiener filtering (black) and the Dmass f-domain code (yellow).

As soon as Jenne brings in her beer cooler, we're ready to redo the Huddle Test.

 

  2672   Sat Mar 13 22:16:03 2010 ranaUpdateWienerFilteringGuralp Huddle Test software

I used some recent better data to try for better Z subtraction.

Dmass helped me understand that sqrt(1-Coherence) is a good estimate of the theoretical best noise subtraction residual. This should be added to DTT. For reference the Jan statistic is the inverse of this.

This should get better once Steve centers the Guralps. 

  1800   Tue Jul 28 16:03:14 2009 ClaraUpdatePEMGuralp Seismometer cable pin diagram

I mapped out the corresponding pins on both ends of the Guralp seismometer cable. Here is the diagram:

guralp_pin_diagram.png

The circular 26-pin end of the cable (that plugs into the seismometer) is labeled as above. The other end (the 39-pin end) is not physically numbered, so I just came up with a numbering system. They are both pictured on the non-cable end of the connector. The colored circles indicate the pin pairs.

 

FROM JENNE, 30JULY2009:  the Dsub end is 37 pin, not 39.

  12047   Fri Mar 25 19:17:28 2016 NikhilUpdatePEMGuralp Seismometers

Calibration of Guralp Seismometers

Objective

  • Estimate transfer functions of Guralp A ( near ETMX) and Guralp B ( near ETMY)
  • Calibrate the instruments by estimating Velocity Sensitity Parameter
  • Convert previously measured Voltage Spectrum to Velocity Spectrum

Instruments Used

  • Guralp CMG-40 T Seimometers  : Guralp A (Serial Number: T4Q17)
  • Guralp CMG-40 T Seimometers  : Guralp B (Serial Number: T4157)
  • Guralp Handheld Control Unit (HCU)
  • FFT Spectrum Analyzer: Model SR785: 2 Channel Dynamic Signal Analyzer
  • Oscilloscope: TDS 3014B
  • Function Generator: DS 345

Procedure & Results

Sinusoidal current of known frequency and amplitude was injected to the Seismometer calibration coil using signal generator and handheld control unit & corresponding Magnitude and Phase response were recorded.  For  Guralp B, system response was also estimated with a FFT Spectrum Analyzer. 

 

    

Frequnecy Range: 0.1 Hz to 45 Hz.

Equivalent Input Velocity was derived from the Input Voltage measurements using the relation: v = V/ (2*pi*f*R*K) , V is the peak to peak Calibration Signal voltage, f is the calibration signal frequency, R is the calibration resistor and K is the feedback coil constant.  [See Appendix for R & K values]                                     

Velocity Sensitity at the required frequency is obtained by dividing the Output Response Voltage by the Equivalent Input Velocity.

               

The obtained Velocity Sensitivity is used to convert the recorded Volatge PSD to Velocity PSD as shown below. The obtained results are compared to gloabl high noise model [NHNM] and USGS New Low Noise Model [NLNM,Peterson 1993] which gives the lowest observed vertical seismic noise levels across the seismic frequency band. Plot legend NLNM shows both the high & low levels.

 

                                                                    Guralp A [X Arm] Low Velocity Output                                          

                  

                                                                    Guralp B [Y Arm] Low Velocity Output                                          

            

                                                                            DTT Power Spectrum                                                             

Both the Seismometers were connected to the 40 M Control and Data Acquisition System (CDS) and Power Spectrum was estimated for the Vertical, North/South & East/West Channels using Diagnostic Test Tool (DTT) software.

                                                            

Comments

  •  The transfer function from Guralp A [ETMX] looks similar to that of Guralp B [ETMY] in both magnitude and phase but with a lower gain.                                                                                                                                                                                                  
  • Velocity Sensitivity of Guralp A is comparable to the value provided in the Calibration Data Sheet [~ 400] for all the channels [Vertical, North/South, East/West] after 1 Hz. For Guralp B, Velocity Sensitivity is a factor of 2.5 higher [all channels] than the specification [~ 400] after 1 HZ.Below 1 Hz Sensitivity drops down for both sensors. I am not ruling out a missing common factor in the calculation, but anyway, test shows that Guralp B has ~2.5 times better Velocity Sensitivity than Guralp A.                                                                                                                                                               
  • The Calibrated Seismic Velocity Spectrum for Guralp B is within the Globally Observed High and Low Noise Seismic Spectrum while Guralp A's Spectrum is more noisier above 1 Hz [Anthropogenic Activity normally contributes the most in 1 Hz to 10 Hz frequency band].                                                                                                                                                                                                                                                                          
  • Concurrently acquired Power Spectrum using DTT [Diagnostic Test Tools] shows that Guralp A Spectrum behaves rather strangely. The system response seems to be completely different from the one we obtained locally using signal generator. While Guralp B functionality seems normal. One reason for this erratic beahvior might be faulty cables used for data acquisition from Guralp A. This needs to be verified.                                                                                                                        

Appendix

                                                                            CMG-40T Guralp A Calibration Sheet                                                           

  Velocity Output: V/m/s (Differential) Mass Position Output (Acceleration Output) : V/m/s^2  Feedback Coil Constant : Amp/m/s^2
Vertical 2 x 400 19 0.00397
North/South 2 x 398 23 0.00486
East/West 2 x 401 23 0.00479                 

Calibration Resistor: 51000

                                                                            CMG-40T Guralp B Calibration Sheet                                                           

  Velocity Output: V/m/s (Differential) Mass Position Output (Acceleration Output) : V/m/s^2  Feedback Coil Constant : Amp/m/s^2
Vertical 2 x 401 19 0.00408
North/South 2 x 400 20 0.00421
East/West 2 x 404 22

0.00466

Calibration Resistor: 51000 

  12048   Fri Mar 25 23:54:04 2016 ranaUpdatePEMGuralp Seismometers

Something seems not right. The Guralp response should be flat in velocity from 0.05-30 Hz. Why is there any feature at 1 Hz? Saturation of some kind?

ELOG V3.1.3-