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  3746   Wed Oct 20 18:17:35 2010 Suresh, JenneUpdateSUSPRM assembly

We have positioned the guide rod and the wire-stand-off on the optic in the axial direction. 

We have selected six magnets whose magnetic strength is +/-5% of their mean strength (180 Gauss).  The measurement was made as follows:

1) each magnet was placed on its  end, on the top of a beaker held upside down. 

2) The Hall probe was placed directly under the magnet touching the glass from the other side (the inside of the beaker). 

This ensures that the relative position of the magnet and the probe remains fixed during a measurement.  And ensures that their separation is the same for each of the magnets tested. 

With this procedure the variation in the measured B field is less than +/- 10% in the sample of magnets tested.

  3936   Tue Nov 16 23:36:29 2010 Suresh, JenneUpdateSUSAssembly of ETMs

[Jenne, Suresh]


The ETM assembly has moved forward a couple of steps.  We have completed the following:

1) Positioning the guide rod and wire stand-off on both the ETMs (5 and 7)

2) The magnets had to be cleaned with an acetone wash as they had touched the plastic Petri-dish (not cleaned for vacuum).

3) The magnets and the Al dumb-bells have been glued together and left to cure in the gluing fixture.

4) The guide-rod and wire stand-offs have also been glued to the optic and left to cure for 24 hrs.



JD:  As you can see in my nifty status table, we are nearing the end of the suspension story.  


We are going to try (but can't guarantee) to get ETMX to Bob for baking by Friday at lunchtime, that way we can re-suspend it on ~Monday, and place it in the chamber.  Then we could potentially begin Green arm locking next week.  Steve has (hopefully!!) ordered the spring plungers for ETMY.  The receiving and baking of the spring plungers is the only current delay that I can foresee, and that only is relevant for one of the optics. 

We (who is going to be in charge of this?) still need to move the SRM OSEMs & cables & connectors to the ITMY chamber from the BS chamber. 



  4297   Tue Feb 15 06:59:57 2011 Suresh, JenneOmnistructureGeneralX end enclosure left open

[Jenne, Suresh]

 Jenne found the X-end table enclosure had been left open.  She replaced the lid on it.


  4414   Fri Mar 18 16:31:11 2011 Suresh UpdateGreen LockingRe: Y arm plan for today

The reason for using Alberto's laser is that some amount of work has already gone into characterising its phase noise.  Ref elog entry 2788

  3725   Thu Oct 14 23:33:45 2010 SureshUpdateIOO2W NPRO laser output power versus temperature

Steve measured an apparent power drop in the 2W NPRO output from 2.1W to 1.6W(elog entry no 3698) at 2.1A of diode current in the laser (elog entry:  2822).  It was later noticed that the laser temperature was set to about 45 degC while the initial calibration was done at 25 deg C.  

It was felt that the recent power drop may have something to do with the increase in the operating temperature of the laser from 25 to 45 deg C.  Therefore the laser was returned to 25 deg C and the power output was remeasured and found to be 2.1W as it was at the begining(elog entry:3709)

It was also noticed that returning the laser to 25 deg. C resulted in a loss of efficiency in coupling to the PMC.  We suspected that this might be due to multimode operating conditions in the laser at particular operating temperatures.  In order to see if this is indeed the case the laser power output was observed as a function of temperature.  We do notice a characteristic saw-tooth shape which might indicate multimode operation between 39 and 43 deg C.  It is best to verify this by observing the power fluctuations in the transmitted beam of the stabilised reference cavity.




The measurement was made by attenuating the roughly 2W laser beam by a stack of two Neutral Density filfers and then measuring the transmitted light with the PDA36A photodetector.  This was because both the power meters used in the past were found to have linear drifts in excess of 30% and fluctuations at the 10% level. 



Attachment 2: Scan2010.zip
  3730   Fri Oct 15 21:25:23 2010 SureshUpdateIOO2W NPRO laser output power drop question

  The power meter used in the measurements of elog entries 2822, 3698 and 3709 was the Ophir PD300-3W.  This power head has several damaged patches  and a slight movement of the laser spot changes the reading considerably.  To verify I checked the power out with another power meter (the Vector S310) and found that there is no significant variation of the power output with the temperature of the laser.  And the power at 2.1A of diode current is 2W with 10% fluctuation arising from slight repositioning of the laser head.  There are regions of the Ophir PD300 which show the laser power to be about 1.9W.

  3798   Wed Oct 27 16:15:35 2010 SureshUpdateSUSRe-glued magnet to the PRM

Thanh and I re-glued the magnet to the PRM following the procedure outlined by Jenne

The PRM in the gluing fixture has been placed in the little foil house and left to cure for a day.

If all goes well the balancing the PRM will be done tomorrow.



  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).




  3801   Wed Oct 27 21:51:29 2010 SureshUpdatePSLAttenuation of PSL NPRO removed

The laser power was attenuated to 40 mW yesterday for ensuring that the power built up within the MC does not damage the optics. 

This however stopped us from the doubling work and besides also reduced the power available for locking the PMC. 

Therefore, today the laser attenuation was removed and once again 500mW is available at the exit of the PMC .  

However the power sent to the MC has been reduced to 60mW by changing one of the mirrors in the zig-zag to a 33% beam splitter.  Though about 450mW is incident on the beam splitter the reflected beam is only about 55mW since the mirror reflectance is specified for P polarised light incident at 45deg while ours is S-polarised incident at less than 45deg.   The light transmitted through the beam splitter has been blocked by a beam dump.



  3804   Thu Oct 28 03:21:35 2010 SureshUpdateLockingAligned the MC2 transmission photodiode

Yuta and Suresh

The MC2 transmission is seen on the QPD

Once the laser was locked to the cavity, and the PMC was able to follow the laser (ref: elogs by Yuta and Rana today)  we had a steady TEMoo mode in the MC.  This gave us sufficient transmission through MC2 to be easily visible with an IR viewer and we were able to guide the beam on to the QPD.  The beam however seemed to over fill the QPD, a lens (f=180mm) was placed before the beam folding mirror and the spot sized reduced.   The the QPD was found to be not fixed to the table and this was also recitified.  The signal level is still low: total signal is just about 7 DAQ steps amounting to about 5mV.  Tomorrow we plan to work on the alignment of the PSL and MC and thus increase this signal.

A new channel to observe the length variations in the MC.

A long BNC cable was laid from the MC locking electronics next (southwards) to the PSL table to the DAQ cards picking up the signals from the PRM OSEMS.  This is to pick up one of the MC locking signals and collect it on a DAQ channel.  However as there are no spare DAQ channels currently available one of the PRM OSEM (UL and LL) photodiode channels was unplugged and replaced with the signal from the long BNC cable.   For identifying the correct DAQ channel we put in a 2 Vpp 10Hz signal with a function generator into this BNC.  Tow signals can be picked up in this fashion and they are available on PRM_LLSEN_IN1 and PRM_ULSEN_IN1. We plan to use this for improving the alignment of the MC tomorrow. 

The algorithm for this alignment is that if the beam from the PSL is not centered on the MC1 then tilting MC1 would result in a change in the length of the cavity as seen by the light.  Using this as feedback the spot could be precisely centered on the MC1 and then the MC alignment could be completed by moving MC2 and MC3 to reobtain TEM_oo within the cavity.

  3843   Tue Nov 2 00:17:01 2010 SureshConfigurationLockingTemporary changes to the Video Mux

Fiber coupling 1064 nm light at the end of X arm

This is 'work in progress'.  The attempt is to bring a few milliwatts of the 1064 nm light from the NPRO at the end of the South(X) Arm to the PSL table through an single mode optical fiber.  This would enable us to tune the two NPRO's to be less than 15 MHz apart by looking at their beat frequency before doubling.  Because we have a 1GHz bandwidth PD at 1064 nm, while the photodiode for green has a BW of about 30MHz.

A PBS (P-type) cube has been introduced into the beam of the X arm NPRO  (between the lamda/2 plate and the input lens of the doubling crystal).  By rotating the face of the PBS slightly away from normal incidence, I have diverted away 1.5mW of the 1064 light for coupling into the fiber. The beam has shifted slightly because of this and the green beam from the south arm has to be realigned to reach the PSL table.

A single mode fiber (Thorlabs SM980-5.8-125),  which was already laid half way, has been extended all the way to the PSL table. It runs along the  South arm in the cable tray. 

A pair of mirrors have been arranged in a zig-zag to steer the beam into a fiber coupler.  There was some hope that this coupler had been aligned at some point in the past and that attaching a fiber might result in some transmission.  But this is not the case and fiber coupler needs to be readjusted.

In order to see the light transmitted through the fiber, a camera has been set up on the PSL table.  Its output has been routed into the 'Ref Cavity reflected' video signal.  A video cable running from the ETMX to the Video-MUX used to be connected to the input channel 9 of the Video MUX.  This has now been shifted to output channel 25 of the MUX and disconnected from the camera at the ETMX.   The 'Ref Cav Refl.' video signal has been routed to the output channel 25.  The camera looking at the fiber output can now be seen on a local monitor at the end of the X arm and on the video monitor in the control room.

With the fiber disconnected, the 1064 nm beam was steered into the fiber coupler and its transmission maximised by observing  with an IR viewer.  The fiber was then connected and then the transmission at the PSL table was sought.  There was no transmission seen after a searching around this region for a few mins.

The plan is to purchase a Visual fault locator which would enable us to quickly get a rough alignment of the fiber coupler. A local vendor is listed as a distributor for this product from JDSU.  Contact info:

DuVac Electronics (EDGE)
Tel: 626-796-3291
Email: jack@duvac.com
1759 E Colorado Blvd
Pasadena, CA 91106


  3859   Thu Nov 4 03:13:46 2010 SureshUpdateLockingFibre coupling 1064nm light at the south-end table

[Kiwamu, Suresh]

We decided to use the 1064nm beam reflected from the Y1-1037-45-P mirror after the collimation lens following the doubling crystal for coupling into the optical fiber (ref 3843 and 3847 ).

We replaced a beam dump which was blocking this beam with a Y1-1037-45-P mirror and directed the beam into the fiber coupler with another Y1-1037-45-P.  The power in this beam was about 1W.  This has been stepped down to 10mW by introducing a reflective ND filter of OD=2.  The reflected power has been dumped into a blade-stack beam dump.

Steve has ordered the The Visual Fault Locator from Fluke.  It is expected to arrive within a day or two.



  3865   Thu Nov 4 19:00:57 2010 SureshUpdateLockingFibre coupling 1064nm light at the south-end table

The Fluke Visual Fault locator (Visifault) arrived and I used it to couple 1064nm light into the single mode fibre at the south-end-table.

Procedure used:

When the output end of the fiber is plugged into the Visifault the light emerges from at the south end (input side for 1064nm).  This light is collimated with the fiber coupler at that end and serves as a reference for the optical axis along which the 1064 light must be directed.  Once the two beams (red and 1064) are overlapped with the beam steering mirrors, the Visifault was disconnected from the fiber and the  fibre output ( 1064 at the PSL table) is maximized by walking the beam at the input end and adjusting the collimation at the input.

The output of the fiber has been collimated with a fiber coupler.

7.5mW are incident on the input end and 1.3mW have been measured at the output.    This output power is adequate for the observing the beats with PSL NPRO.




  3866   Thu Nov 4 19:26:51 2010 SureshUpdateLockingChanges to the Video MUX reversed

All the temporary changes to the video cables and the video MUX ( 3843 ) have been reversed and the system returned to its original state.

  3882   Mon Nov 8 18:30:33 2010 SureshUpdateIOOMC Trans Mon QPD gain increased by 50x

Increased the transimpedance gain of the MC-Trans-Mon QPD ckt

The gain of this QPD was insufficient to see the light transmitted through the MC2.  The resulting voltage output was about  10 steps of the 16-bit ADC card.  As the input power, which is currently held at about 40mW may be increased to the vicinity of 2W (total output of the NPRO) we would have 500 ADC steps.  But the dynamic range of the ADC is 64k and  increasing the gain of this QPD ckt by a factor of 50 would enable us to utilise this dynamic range effectively.  However as we do not need a response faster than 10Hz from this ckt its response time has been limited by increasing the feedback capacitance value.

The ckt diagram for the QPD ckt is D980325-Rev-C1  .  The particular unit we are dealing with has the Serial No. 110.  The resistors R1, R2, R3, R4 are now 499 kOhm.  As per the guidelines in the ckt diagram, we increased the capacitance values C3,C4,C5,C6 to 2.2 nFThe current cut off frequency for the MC-Trans-Mon is 145 Hz (computed).

Initially, while reassembling the QPD unit, the IDC 16 connector to the ckt board was reversed by mistake and resulted in the OP497 chip over-heating.  Consequently one of the opamps on the chip was damaged and showed monotonously increasing ouput voltage.  Todd Etzel gave us a spare OP497 and I replaced the damaged chip with this new one. The chips are also available from  Newark Stock No. 19M8991 . The connector has been marked to indicate the correct orientation. The ckt was checked by temporarily connecting it in the place of the PRM Optical lever QPD.  It worked fine and has been put back in its place at the MC2 Transmission.  The QPD was wiped with a lens tissue+Methanol  to remove dust and finger prints from its surface.

It may need to be repositioned since the beam would have shifted under the MC realignment procedure.




  3902   Fri Nov 12 00:13:34 2010 SureshUpdateSUSETM assembly started

[Jenne, Suresh]

Selection of ETMs

Of the four ETMs (5,6,7 and 8) that are with us Koji gave us two (nos. 5 and 7) for use in the current assembly.  This decision is based on the Radius of Curvature (RoC) measurements from the manufacturer (Advanced Thin Films).   As per their measurements the four ETMs are divided into two pairs such that each pair has nearly equal RoC. In the current case, RoCs are listed below:


Radii of Curvature of ETMs
ETM # RoC from Coastline Optics (m) RoC from Advanced Thin Films (m)
5 57.6 60.26
6 57.4 54.58
7 57.1 59.48
8 57.9 54.8


The discrepancy between the measurements from these two companies leaves us in some doubt as to the actual radius of curvature.  However we based our current decision on the measurement of Advanced Thin Films. 


Assembly of ETMs

We drag wiped both the ETMs (5 and 7) and placed them in the Small Optic Gluing Fixture.  The optics are positioned with the High Reflectace side facing downwards and with the arrow-mark on the Wire Standoff side (big clamp).  We then used the microscope to position the Guide Rod and the Wire Standoff in the tangential direction on the ETMs (step 4 of the procedure specified in E010171-00-D)

We will continue with the rest of the assembly tomorrow.


  3928   Mon Nov 15 22:24:28 2010 SureshUpdateSUSSelection of Magnets

I have selected a set of 16 magnets which have a B field between 900 to 950 Gauss (5% variation) when measured in the following fashion.

I took a Petri-dish, of the type which we usually use for mixing the glue, and I placed a magnet on its end.  I then brought the tip of the Hall-probe into contact with the Petri-dish from the opposite side and adjusted the location (and orientation) of the probe to maximise the reading on the Gauss meter.

The distribution of magnets observed is listed below


Range of B Field (Gauss) # of Magnets
800-849 2
850-899 6






The set of sixteen has been have been placed inside two test tubes and left on the optical bench (right-side)  in the clean room.



  3953   Fri Nov 19 04:23:12 2010 SureshUpdateSUSCleaned and stuck magnets to dumbbells

To clean the glue off the magnets and dumbbells I soaked them in Acetone for about an hour and then scrubbed the ends clean with a lint free tissue soaked in Acetone. 

I then examined the ends under a microscope and found that while the flat faces were clean some of the grooves were still filled with glue.


Top Bottom


 magnets_after_scrub.jpg magnets_after_scrub.jpg

While examining the magnets I found some small magnetic fibers stuck to the magnets.  Rana had mentioned these before as potential trouble makers which could degrade the high frequency performance of the OSEMs.



To try and get the glue out of the grooves I put the dumbells through an ultrasonic bath for ten mins.  Most of the glue has been removed from the grooves.  Pics below





I proceeded try and recover the lost time by sticking the magnets back to the dumbbells.  Increased the quantity of the glue to a slightly larger amount than usual.  It should definitely squish out a bit now.  We will know tomorrow when we open the gluing fixture.




  3958   Fri Nov 19 18:20:59 2010 SureshUpdateSUSGlue dynamics!

I examined the magnet-dumbbell joints under the microscope to see whether the glue that I applied yesterday was sufficient or in excess.

I think the pictures below speak for themselves !  


Too_much_glue_1.jpg Too_much_glue_2.jpg Too_much_glue_3.jpg


During the gluing process the Al dumbbell stays below and the magnet with a drop of glue on the lower face is placed on it and held in the teflon fixture.  As seen in the pics the glue seems to have run up the surface of the magnet and has not collected in the narrow part of the dumbell.  So it has climbed up along the narrow gaps between the magnet and the teflon fixture by capillary action. The glue stops where the teflon fixture ends, a little before reaching the free end of the magnet, which further indicates the capillary action.



Attachment 2: Too_much_glue_2.jpg
  3991   Mon Nov 29 22:50:07 2010 SureshUpdateSUSETMU05 Side Magnets glued back

[Suresh, Jenne]

ETMU05 : Gluing Side magnets back on to the optic.

The following steps taken in this process:

1) The two magnet+dumbell units which had come loose from the optic needed to be cleaned.  A lint free wipe was placed on the table top and a few cc of acetone was poured on to it.  The free end of the dumbbell was then scrubbed on this wipe till the surface regained its shine.  The dumbell was held at its narrow part with a forceps to avoid any strain on the magnet-dumbbell joint.

2) The optic was then removed from its gluing fixture (by loosening only one of the three retaining screws) and placed in an Al ring. The glue left behind by the side magnets was scrubbed off with a optical tissue wetted with Acetone. 

3) The optic was returned to the gluing fixture.  The position of the optic was checked by inserting the brass portion of the gripper and making sure that the face magnets are centered in it [Jenne doubled checked to be sure we got everything right].

4) The side magnets were glued on and the optic in the fixture has been placed in the foil-house.

If all goes well we will be able to balance the ETMU05 and give it to Bob for baking.


ETMU07 : It is still in the oven and we need to ask Bob to take out. It will be available for installation in the 40m tomorrow.  


  4002   Wed Dec 1 02:39:00 2010 SureshUpdateSUSInstallation of ETMU07 as ETMX

[Kiwamu, Jenne, Koji, Suresh]

The following steps in this process were completed.

1)  Secured the current ETMX (Old ETMY) with the earth quake stops.

2) Removed the OSEMs and noted the Sl no. of each and its position

3) Placed four clamps to mark the location of the current ETMX tower (Old ETMY's position on the table)

4) Moved the ETMX (Old ETMY) tower to the clean table flow bench.  In the process the tower had to be tilted during removal because it was too tall to pass upright through the vacuum chamber port.  It was scary but nothing went wrong.

5) Koji calculated the location of the new ETMX and told us that it should be placed on the north end of the table.

6) Moved the OSEM cables, counter balancing weights and  the 'chopper' out of the way.  Had to move some of the clamps securing the cables.

7) Moved the ETMU07 tower from the clean room to the ETMX table

8) Positioned the OSEMs as they were placed in the earlier tower and adjusted their position to the middle of the range of their shadow sensors.  The four OSEMs on the face did not give us any trouble and were positioned as required.  But the side OSEM could not be put in place.  The magnet on the left side, which we are constrained to use since the tower is not designed to hold an OSEM on the right side, seems a little too low (by about a mm) and does not interrupt the light beam in the shadow sensor.  The possible causes are

   a) the optic is rotated.  To check this we need to take the tower back to the clean room and check the location of the optic with the traveling microscope.  If indeed it is rotated, this is easy to correct.

   b) the magnet is not located at the correct place on the optic.  This can also be checked on the clean room optical bench but the solution available immediately is to hold the OSEM askew to accommodate the magnet location.  If time permits the magnet position can be corrected.

We have postponed the testing of the ETMU07 tower to 1st of Nov Dec.


  4022   Tue Dec 7 18:37:15 2010 SureshUpdateSUSETMU05 ready for baking

The ETMU05 has been removed from the suspension and put into the little foil house. 

Before removing it I checked the position and pitch of the optic with reference to the table top. 

The height:

     Using the traveling microscope I checked the height of the scribe lines from the table top.  They are at equal heights, centered on 5.5 inches, correct to about a quarter of the width of the scribe line.

The pitch

    The retro-reflection of the He-Ne laser beam is correct to within one diameter of the beam at a distance of about 1.5m.  This is the reflection from the rear, AR coated, surface.  The reflection from the front, HR coated, surface was down by about two diameters.

Jenne has checked with Bob and agreed on a date for baking the optic.



  4092   Thu Dec 23 08:54:32 2010 SureshUpdateelogthe delhi univ syndrome

Sorry folks!  I couldnt get to the elog and didnt know that the elog was crashing every time I tried to access it. 

But have found other means to access it and the elog is safe for now!

  4106   Tue Jan 4 15:12:33 2011 SureshUpdateIOOMC Trans Mon QPD gain decreased by 10

 Decreased the gain of MC-Trans-Mon QPD ckt

The resistors R1, R2, R3, R4 are now 49.9 kOhm. The previous elog on this subject 3882 has the ckt details. 

  4137   Tue Jan 11 17:08:43 2011 SureshConfigurationPSLreplaced the pzt-steering mirror on PSL

[Rana, Jenne, Suresh]

Yesterday, We replaced the existing beam steering mirror and the PZT it was mounted on with a Gooch and Housego mirror (20ppm transmission at < 30deg incidence @1064nm) and a Polaris-K1 Newport steel mount. (JD)

We realigned the G&H mirror to get the MC flashing. 

We then had to reduce the gain in the servo circuit to accommodate the increased optical power going into MC. 

MC locked to PSL once again.


      the old mirror stuck on the PZT has been removed.  The mirror had no markings and has been stored in the 'Unknown Optics' Box along the East Arm.

      The PZT has been stored in the PZT cabinet along with its 2in mirror mount.

  4143   Wed Jan 12 17:22:47 2011 SureshConfigurationLockingMC demod phase adjusted to minimise the I output

[Koji, Suresh]

We wanted to check and make sure that the relative phase of the two inputs ( local oscillator and photodiode signal ) to the demod board is such that the Q output is maximised.   We displayed the I and  Q signals on the oscilloscope in XYmode with I along the X direction.  If Q is maximised (and therefore I is minimised) the oscillocope trace would be perfectly vertical since all the signal would be in Q and none in I. Initially we noted that the trace was slightly rotated to the CCW of the vertical and that a short cable was present in the PD input line.  Removing this rotated the trace CW and made it pretty much vertical.  The screen shot of the oscilloscope is below.


  4147   Wed Jan 12 22:39:16 2011 SureshUpdateIOOPut MC PZT offset onto MC board, instead of on awkward cart


I can not think of any reason that the input impedance of 13kOhm between the pos/neg inputs produces such a big change at the output. In any case, the differential voltage between the pos/neg inputs produces a big output. But the output was just 2V or so. This means that the neg input was actually about zero volt. This ensures the principle of the summing amplifier of this kind.

Because the input impedance of the summing node (the additional resister you put at the negative input) is not infinity, the voltage divider is not perfect and shows 10% reduction of the voltge (i.e. the output will have +4.5V offset instead of +5V). But still it is not enough to explain such a small output like 2.3V.

What I can think of is that the earlier stages somehow have the offset for some reason. Anyway, it is difficult to guess the true reason unless all of the nodes around the last stage are checked with the multimeters.

At least, we can remove the voltage divider and instead put a 10k between -15V and the neg input in order to impose +5V offset at the output. This costs 1.5mA instead of 10mA.


[Larisa and Jenne]

We wanted to get rid of the awkward cart that was sitting behind the 1Y1 rack.  This cart was supplying a +5V offset to the PZT driver, so that we could use the MC length signal to feedback to lock the laser to the MC cavity.  Instead, we put the offset on the last op amp before the servo out on the Mc Servo Board.  Because we wanted +5V, but the board only had +5, +15, -15V as options, and we needed -5 to add just before the op amp (U40 in the schematic), because the op amp is using regular negative feedback, we made a little voltage divider between -15V and GND, to give ourselves -5V.  We used the back side of the voltage test points (where you can check to make sure that you're actually getting DC voltage on the board), and used a 511Ohm and 1.02kOhm resistor as a voltage divider. 

Then we put a 3.32kOhm resistor in ~"parallel" to R124, which is the usual resistor just before the negative input of the op amp.  Our -5V goes to our new resistor, and should, at the output, give us a +5V offset. 

Sadly, when we measure the actual output we get, it's only +2.3V.  Sadface.

We went ahead and plugged the servo out into the PZT driver anyway, since we had previously seen that the fluctuation when the mode cleaner is locked was much less than a volt, so we won't run into any problems with the PZT driver running into the lower limit (it only goes 0-10V).

Suresh has discovered that the op amp that we're looking at, U40 on the schematic, is an AD829, which has an input impedance of a measely 13kOhm.  So maybe the 3.32kOhm resistors that we are using (because that's what had already been there) are too large.  Perhaps tomorrow I'll switch all 3 resistors (R119, R124, and our new one) to something more like 1kOhm.  But right now, the MC is locked, and I'm super hungry, and it's time for some arm locking action.

I've attached the schematic.  The stuff that we fitzed with was all on page 8.




[Koji, Suresh]

    We looked at the board and found that the resistor R119 (the feed back) is 1.65k instead of the 3.32k that was needed for unity gain.  The gain has been intentionally reduced to 0.5 so that output range would be close to the 0-10V that is required at the input range of the PZT driver which follows.   A note to this effect is already present in the D040180-B, page 8.

    The voltage divider with 1k and 0.5k provides 4.5V (ref Koji's note above) this provides 2.25V at the output due to the gain of 0.5.  To get to the original goal of introducing a 5V offset on the output, we introduced the modification shown in the  'D040180-B with 5V offset.pdf' uploaded below.  Please check page 8, the changes are marked in red.  We checked to make sure that the output is 5V when the input is disconnected. 


The PCB pics at the end are also attached.  The 4.99k resistor is glued onto the PCB with epoxy and placed as close to the opamp possible.

Attachment 1: P1120508.JPG
Attachment 2: P1120509.JPG
  4161   Sun Jan 16 02:20:59 2011 SureshUpdateLockingcomparing the PSL with the X-end-NPRO through the green beat


      We wish to study the coherence of the two NPROs i.e. PSL and the X-end-NPRO by locking both of them to the X-arm and then observing the green beat frequency fluctuations. 

What we did:

   a) locked the PSL to the X-arm as described in 4153

   b) locked the x-end-NPRO to the X-arm with a PDH lock to the reflected green from the ETMX

   c) Obtained the green beat signal with a spectrum analyser as described in 3771


   Please see the attached screen shots from the spectrum analyser.   They are taken with different BW and sweep range settings.  They give a estimate of the width of the green beat signal and the range of the frequency fluctuations of the beat-note.





   a) width of the beat note is less than 6KHz if measured over time scales of a few milli seconds

   b) the frequency fluctuations of the beat note are about 100KHz over time scales longer than 100ms

Next Step:

    We wish to record the beat note frequency as a function of time in order to establish the stability over time scale of a day.



  4166   Wed Jan 19 03:37:30 2011 SureshUpdateLockingcomparing the PSL with the X-end-NPRO through the green beat



 [Kiwamu, Suresh]

Today we attempted to convert the beat-note frequency into an analog voltage using the SR620 frequency counter.

First an observation: the stability of the green beat was seen to be much better than the 100kHz fluctuation seen yesterday. Probably because Kiwamu noticed that one of the MC mirrors had a large variance in its motion and changed the  gain and filter parameters to decrease this.  The PSL was therefore more stable and the green peak fluctuation was less than 10kHz over time scales of a few seconds. 

SR620 D/A output resolution given by the manufacturer is 5mV over the -10 to +10V range and this range corresponding to 300MHz.  We, however saw fluctuations of 100mV on the screen which looked as if they corresponded to the  least significant bit.  This would imply a resolution of 1.5MHz at this range.   Even if the manufacturer's claim was true it would lead to a resolution of 75kHz, far in excess of the required resolution a few hundred Hz.

We therefore require to set up the VCO-PLL to obtain a finer frequency resolution.

In the mean time the green beat drifted beyond the 100MHz detection band of the green-PD.  So we changed the x-end-NPRO temperature by -0.05 to bring it back into the detection band.


We are also considering, Rana and Koji's suggestion of using a set of 14 flip-flops to divide the ~80MHz beat frequency so that it comes down to about 4kHz.  This could then be sampled by the usual 16-bit, 64kSa/s ADC cards and brought into the digital domain where further digital processing would be needed to extract the the required frequency variations  in the 0 to 10kHz band.  Found a nice paper on this object

Attachment 1: Phase_noise_in_digital_frequency_dividers.pdf
Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf
  4187   Sat Jan 22 01:56:04 2011 SureshUpdateGreen LockingExamining the stability of VCO PLL at low frequencies

[Kiwamu, Suresh, Rana]

Our goal:

        We wished to determine the performance of the VCO PLL at low frequencies,. 

The procedure we followed:

        The scheme is to use the Marconi (locked to Rb Clock) as an 80MHz reference and lock to it using the PLL. 

        We set up the VCO PLL as in the diagram shown in the attachment and obtained the spectra shown below.


          We need to figure out the PLL servo gain profile in order to build the Inv PLL filter....








  4225   Sat Jan 29 00:31:05 2011 SureshUpdateGeneralVertex crane upgrade completed

The Vertex crane is smarter and safer now.  This upgrade ensures that the two sections of I-beam (8ft, 4ft) remain firmly latched to form a straight member till the latch is released.

In specific, it ensures that problems such as this one do not occur in the future.


The new safety features are:

When the I-beam sections are latched together, a pneumatic piston ensures that the latch is secure. 

If the latch is not engaged the trolley does not move outward beyond the end of the 8-foot section of the I beam.

If the trolley is out on the 4-foot section of the beam then we cannot disengage the latch.


How does it work?


 Vertex_Crane-2.png Vertex_Crane-4.png


The state of the Limit Switch 1 changes when the trolly goes past it.    The Limit Switch 2 gets pressed when the two sections are latched together.

The pneumatic piston raises or lowers the latch.  The Pneumatic Latch Switch operates a pneumatic valve controlling the state of the piston.



Vertex_Crane-3.png P1280545.JPG

The new controller now has Pneumatic Latch Switch in addition to the usual Start, Stop, Up, Down, In and Out buttons. 

Each of the Up, Down, In and Out buttons have two operational states:  Half pressed (low speed) and Full pressed (High Speed).  Their functions remain the same as before.


The new Pneumatic Switch:

When this switch is 'Engaged' and the 4 ft section is swung in-line with the 8 ft section, the two sections get latched together.

To unlatch them we have to throw the switch into the 'Disengage' state.  This makes the piston push the latch open and a spring rotates the 4 ft section about its pivot.

Limit Switch 2 is not pressed (I-beams not aligned straight) ==> Limit Switch 1 will prevent the trolley from out going beyond the 8 ft section.

While Limit Switch 2 is pressed we cannot disengage the latch.



   The pneumatic piston requires 80psi of pressure to operate.  However we have only 40psi in the lab and the piston seems to operate quite well at this pressure as well.  I believe a request has been made to get an 80psi line laid just for this application.


Attachment 1: Vertex_Crane-2.png
Attachment 2: Vertex_Crane-4.png
  4243   Thu Feb 3 04:43:58 2011 SureshUpdateElectronicsAdded two new DAQ channels

[Suresh, Joe]

We added the following two new DAQ channels into the c1:GCV model.  The daq:analog input channels are on card ADC0 and correspond to channels 3 and 4 on the card.

c1:GCV-EXT_REF_OUT_DAQ   Sampling rate=2kHz  acquiring a 1Hz sine wave from the SRS Function Generator DS345.  This is using the Rb 10MHz signal as an external frequency reference.

c1:GCV-PLL_OUT_DAQ    Sa.rate=2kHz acquiring the demodulated signal from the PLL servo.

This work is connected to the study of VCO PLL loop noise at frequencies below 0.1Hz.    We are trying to measure phase noise in the VCO PLL servo at low frequencies as this noise would result in arm length fluctuations in the green-locking scheme.




  4248   Fri Feb 4 11:10:27 2011 SureshUpdateGreen LockingVCO PLL Frequency noise

This measurement pertains to the BL2002 VCO PLL unit.


Our goal is to measure the frequency fluctuations introduced by the VCO. 


First the VCO calibration was checked.  It is -1.75 MHz per volt.  The calibration data is below:





Next we measured the Transfer function between points A and B  in the diagram below using the Stanford Research System's SR785.  This measurement was done with loop opened just after the 1.9MHz LPF and with the loop closed.



The TF[open] / TF [closed ] gave the total gain in the loop.  As shown below:


Green curve is the Transfer Function with the loop open and the red with that of the loop closed.

Gain Shown below is the quotient TF[open]/TF[closed]




 c) As can be seen from the graph above the loop gain is >>1 over 0.1 to 300Hz.  And hence the frequency noise of the VCO is just the product of the voltage noise and the VCO calibration factor over this range,

d) the noise power at the point B was measured and multiplied by the VCO calibration  factor to yield dF(rms)/rtHz:


The green line with dots are the data

The blue line is the rms frequency fluctuation.

This corresponds to a arm length fluctuation of about 20pm.



  4266   Wed Feb 9 23:48:12 2011 SureshConfigurationCamerasVideo Cable work: New Labels

[Larisa, Aidan,Steve,Suresh]

   Today was the first session for implementing the new video cabling plan laid out in the document " CCD_Cable_Upgrade_Plan_Jan11_2011.pdf"  by Joon Ho attached to his elog entry 4139.  We started to check and label all the existing cables according to the new naming scheme. 

So far we have labeled the following cables. Each has been checked by connecting it to a monitor near the Video Mux and a camera at the other end.













Next we need to continue and finish the labeling of existing cables.  We then choose a specific set of cables which need to be laid together and proceed to lay them after attaching suitable lables to them.



  4272   Fri Feb 11 00:20:58 2011 SureshUpdateElectronicsREFL11: Photodiode requires replacement


This is with reference to Kevin and Jenne's elogs  # 3890, 4034 and 4048

While the electronics are working okay, there is no DC signal from the photodiode. 

Since the solderings and tracks on the PCB were fine I took a close look at the exposed front face of the photodiode.


As we can see, one of the thin wires on the top surface of the photodiode is broken.  We can see some wipe marks closer to the lower left edge..

Something seems to have brushed across the exposed face of the photodiode and dislodged the wire.



The new photodiode still has its protective can intact.   Do we need to remove the can and expose the photodiode before istallation?


  4275   Sat Feb 12 08:08:05 2011 SureshUpdateElectronicsREFL11 Photodiode replaced

A new photodiode ( Perkin and Elmer Model no. C30642GH Sl No.1526) has been installed in the place of the old photodiode.  The datasheet of this model is attached. 

The 68pF capacitor which was present in parallel with the photodiode has been removed.  Here is a picture of the PCB ( in all its gory detail!) and the photodiode after replacement.

  P2120565.JPG   P2120571.JPG


I also checked to see if we have a DC output from the new PD.  With 375mW of 1064nm light incident we have 15mV of output.  Which matches well with the typical Reponsivity of 0.8V/A reported in the datasheet and our REFL11 ckt .  The schematic of the ckt is also attached here for easy reference.  The various factors are

V_dc = 0.375 mW x 0.8 V/A x 10 Ohm x 5 = 15mV

The last factor is the gain of the last stage on the DC route.

When I reassembled the box I noticed that there is problem with the SMA connectors popping out of the box.  The holes seem misplaced so I enlarged the holes to remove this concern.



Attachment 1: C30642_datasheet-1.pdf
C30642_datasheet-1.pdf C30642_datasheet-1.pdf C30642_datasheet-1.pdf C30642_datasheet-1.pdf C30642_datasheet-1.pdf
Attachment 2: 40mUpgradeREFL11schematic.pdf
  4279   Sun Feb 13 16:20:53 2011 SureshUpdateElectronicsREFL11 Photodiode replaced

It is 0.375 mW as in the calculation.  The total diode output is just 1mW and it is divided with a 50/50 beam splitter...  There are a couple of lenses along the way which may account for the ~12% loss. 

I used a handheld multimeter to measure the output.  


  4284   Mon Feb 14 07:37:13 2011 SureshUpdateElectronicsRF Generation Box: capacitors across power lines


There were several parts in this box which did not have shunting capacitors across their input power lines.  Only the four RF amps (ZHL-2) had them.

I soldered two capacitors (100 microF electrolytic and 150pF dipped mica) across the power supply lines of each of the following units:  11MHz oscillator, 29.5 MHz oscillator,  Wenzel 5x frequency multiplier and the 12x RF amplifier (ZHL-1HAD).

It was quite difficult to reach the power inputs of these units as some of them were very close to the inner walls of the box.  To access them I undid the front panel and found that there were several very taut RF cables which prevented me from moving the front panel even a little.

I had to undo some of the RF cables and swap them around till I found a solution in which all of them had some slack.  At the end I checked to make sure that the wiring is in accordance with the schematic present here.


  4285   Mon Feb 14 07:58:43 2011 SureshUpdateCDSToday's CDS problems


  I am concentrating on the RF system just now and will be attending to the RF PDs one by one.  Also plan to work on some of the simpler CDS problems when I overlap with Joe.  Will be available for helping out with the beam alignment.



  4296   Tue Feb 15 06:15:07 2011 SureshUpdateASCno signal from IP_ANG_Seg1

[Valery, kiwamu, Jenne, Suresh]

    I first interchanged the two QPD's on the Y end table to see if the problem QPD related.  Exchanging the units did not make any difference.  The problem therefore had to be in the cables or the circuit boards in 1X4

    We traced the signals pertaining to the IP_ANG QPD ( "Initial Pointing Beam") using  Jay's wiring diagram (pages 2 and 5 of 7).  We noted that while the signals were available on all Segments till the Monitors (Lemo) on 1X4-2-2A card, two of the lines did not reach the output of the cross connect 1X4-B8.  We checked card to make sure that the signals were indeed reaching the back plane of the 1X4-2 chassis using a D990612 extension board.  The card was found to be okay.  We therefore suspected that the cable (CAB_1X4_?) going from the card to the cross connect 1X4-B8 was faulty.  Indeed visual inspection showed that the crimping of the connector was poor and weight of the cable had put further strain on the crimping.  

   I changed the 64-pin connector on the 1X3-2-2A side of the cable. 

When I connected everything back together the problems persisted. Namely the lines P1-1A  (Segment 1 high) and P1-2C (Segment 2 Low) were floating They were not reaching points 2T and 3T respectively on the output of the cross connect.

   I therefore replaced 1X4-B8 with a similar unit which I found in one of the shelves along the East (Y) arm. 

I then checked with the StripTool to make sure that all the quadrants are showing similar response to a flashlight on the QPD.   All Segments are working fine now. Currently the IR Initial Pointing beam reaches the QPD but is not centered on it. 

I did not attempt to center it since the beam appeared to be clipped and may anyway require repositioning.

JD: We need to meditate on where this beam could be getting clipped.  Suresh and I checked that it's not on the viewport on the beam's way out of the ETMY chamber by seeing that the beam is far away from the edges of the viewport, and also far away from the edges of the black beamtube between the viewport and the table.  Suresh mentioned that the clipping nature of the IP_ANG beam sometimes goes away.  I don't know if this is the same clipping that Kiwamu might be seeing with the main beam, or if this is separate clipping just with the IP beam, after it's been picked off.  I suspect it's the same as what Kiwamu is seeing....maybe when we move PZT1, we clip on one of the MMT mirrors or PZT2??  If this is true, it's a total pain since we might have to vent if we can't steer around it.



  4314   Thu Feb 17 13:20:06 2011 SureshUpdateVIDEOSome more labels

[Larisa, Kiwamu, Steve and Suresh]


  We continued the labeling of video cables. All exiting cables which are going to be used used in the new scheme have been labeled.

We also labeled the cables running from the video mux to the TV monitors in the computer room. Some of these will be removed or reallocated.

We will continue next Wednesday (after the meeting) and will lay cables that are most urgently required. 


  4315   Thu Feb 17 14:17:27 2011 SureshUpdateElectronicsRF Distribution box and REFL11


The Distribution box is several steps nearer to completion.


1) Soldered capacitors and DC power lines for four units of the distribution box.

2) mounted all the components in their respective places.

3) Tomorrow we prepare the RF cables and that is the last step of the mechanical assembly. 

4) we plan to test both the generator and distributon parts together.






[Kevin, Suresh]

Kevin took a transfer function of the newly assembled PD and noticed that the frequency has shifted to 14.99  freom 11. MHz.

We needed to find the current RLC combination.  So we  removed the ferrite core from L5 rendiring it to its aircore value of  0.96/muH. We then used this to find the Capacitance of the PD (117pF)

We  used this value to compute the inductance required to achieve 11.065MHz  which turned out to be 1.75microH.

This was not reachable with the current L5 which is of the type  143-20J12L (nominal H=1.4 micro Henry).

We therefore changed the inductor to SLOT 10 -3-03. It is a ferrite core, shielded inductor with a plasitc sleeve. Its nomial valie is 1.75 microH

We then tested the DC output to see if here is a response to light. There was nonel. l

The problem was traced to the new inductor.  Surprisingly the inductor coil had lost contact with the pins.

I then replacd the inductor and checked again.  The elecronics seems to work okay..   but there is a very small signal 0.8mV for 500microW. 

There seems to be still something wrong with the PD or its electronics.



  4330   Sat Feb 19 05:25:20 2011 SureshUpdateElectronicsRF: Distribution box

Most of the RF cables required for the box are done.   There are two remaining and we will attend to these tonight. 

We expect to have finished the mechanical assembly by Sunday and start a quality test on Monday.



  4336   Tue Feb 22 00:41:34 2011 SureshUpdateElectronicsRF Distribution box: assembly completed

The mechanical assembly of RF distribution box is 99% complete.  Some of the components may be bolted to the teflon base plate if needed. 

All RF cables and DC voltage supply lines have been installed and tested.  I removed the terminal block which was acting as a distribution box for the common zero voltage line.  Instead I have used the threaded holes in the body of each voltage regulator.   This allows us to keep the supply lines twisted right up to the regulator and keeps the wiring neater.  The three regulator bodies have been wired together to provide a common zero potential point. 

I did a preliminary test to see if everything is functioning. All units are functioning well.  The output power levels may need to be adjusted by changing the attenuators. 

The 2x frequency multiplier outputs are not neat sine waves.  They seem to produce some harmonics, unlike the rest of the components.

I will post the measured power output at each point tomorrow.  The RF power meter could not be found in the 40m lab.  We suspect that it has found its way back to the PSL lab.


  4342   Wed Feb 23 08:53:58 2011 SureshUpdateElectronicsRF Distribution box: Output power levels

We wish to have roughly 2 dBm of output power on each line coming out of the RF distribution box.  So I adjusted the attenuators inside the box to get this.

I also looked at why the 2x output looked so distorted and found that the input power was around 17 dBm whereas the maximum allowed (as per the datasheet of Minicircuits MK-2) is 15dBm.  So I increased the attentuation on its input line to 5dBm (up by 2dBm)  The input power levels are around 14.6dBm now  and the distortion has come down considerably.  However the net output on the 2x lines is now down to 0.7dBm.  We will have to amplify this if we need more power.

The schematic and the power output are now like this:


  4377   Fri Mar 4 09:47:46 2011 SureshUpdateElectronicsHarmonic distortion calculations for RF distribution box

Fast work indeed! It would be nice if we could have the following details filled in as well
a) A short title and caption for the table, saying what we are measuring
b) the units in which this physical quantity is being measured.

It is good to keep in mind that people from other parts of the group, who are not directly involved in this work, may also read this elog.

  4416   Fri Mar 18 17:55:58 2011 SureshConfigurationGreen LockingWork Plan for Y-end Aux laser installation

A rough time-table and the various tasks are given below:

Note:  700mW NPRO sitting on AP table (Model No: 126-1064-700, Sl No. 415)  = Alberto's laser



Y-arm Aux laser installation

Temperature dependence of frequency of Alberto's laser:

 a) Shifting Alberto's Laser (AL) to the PSL table and setting up a beat frequency measurement between AL and PSL

 b) Determining the frequency vs Temperature curve for the AL

Mar 21st to 25th Bryan and Suresh
2 Re-positioning the Input beam onto the IP-ANG-PD and realigning the X-arm Mar 21st to 25th Kiwamu and his 'team'  :-)

Repositioning the optics on the Y-end  table and relocating Alberto's laser ( at this point it will be rechiristened as Y-End-NPRO )

Mar 27th - 28th
Bryan and Suresh
4 Maximising the doubling effiiciency and obtaining the PD and QPD signals into the CDS Mar 29th - Apr 1st "
5 Aligning the Y-end green to pass through the Y-arm and locking the green to the Y arm Apr 3 - 8th "
6 Aligning the IR beam to the Y- arm and locking the Y arm to the IR Apr 10 - 15 "


  4436   Thu Mar 24 01:16:19 2011 SureshSummaryGreen LockingY-END green equipment is all available
There was a 2" mirror mount among the spares on the PSL table.  It has a window LW-3-2050 UV mounted in it.  I
have moved it to the Y-end table.  We seem to have run out of 2" mirror mounts ...
  4459   Wed Mar 30 02:55:02 2011 SureshConfigurationElectronicsRF System : Status and Plans

I have prepared several diagrams outlining the current state of the RF System.

These are uploaded into the svn40m here  and will be kept uptodate as we complete various parts of the task.  These plans have taken into account

the new priorities of the LSC (set out by Koji here )

We (Koji, Kiwamu and I) took stock of the RF cables which we have inherited from the earlier RF system and have made new plans for them.

I took stock of the filters purchased for the modifying the demod boards.  We have pretty much everything we need so I will start modifying the boards right away.   The following table summarises the modifications


PD freq # of PDs

LP Filter (U5)

  Demod board

Qty available Inline HP filter Qty available
11 MHz 5 SCLF-10.75 7 - -
22 MHz 1 SCLF-21.4 3 - -
33 MHz 2 SCLF-36 3 SHP-25 1
55 MHz 3 SCLF-65 4 SHP-50 2
110 MHz 1 SCLF-135 3 SHP-100 1
165MHz 3 SCLF-190 1 SHP-150 1

We seem to have a spare SHP-175.  I was wondering where that is supposed to go. 

This is the status and tentative schedule for completing the various tasks.  I have put the dates based on priority and state of the hardware.


The RF Cable layout plans are drawn on top of a Lab Layout.  The various subsystems are drawn (not to scale) on separate layers.  The graffle files are located here  .  I thought they might come in handy for others as well.



  4474   Thu Mar 31 08:31:44 2011 SureshUpdateVIDEOCable laying...continued

The video work has crossed a milestone.    

Kiwamu and Steve have shifted the three quads from the control room to the Video MUX rack (1Y1) and have wired them to the MUX.

The monitors in the control room have been repositioned and renumbered.  They are now connected directly to the MUX. 

Please see the new cable list for the input and output channels on the MUX.

As of today, all cables according the new plan are in place.  Their status   indicated on the wiki page above is not verified .  Please ignore that column for now, we will be updating that soon.

I shifted the MC1F/MC3F camera and the MC2F cameras onto the new cables.  Also connected the monitors at the BS chamber and end of the X arm to their respective cables.  I have removed the RG58B BNC (black) cables running from MC2 to BS and from ETMXF to the top of the Flow Bench. 

Some of the old video cables are still in place but are not used.   We might consider removing them to clear up the clutter. 

Some of the video cables in use are orange and if the lab's  cable color code is to be enforced these will have to be replaced with blue ones..

Some of the cables in use running from the MUX to the monitor in the control room are the white 50 Ohm variety.  There are also black RG59 Cables running the same way ( we have surplus cables in that path)  and we have to use those instead of the white ones. 

There are a number of tasks remaining:

a)  The inputs from the various existing cameras have to be verified. 

b) There are quite a few cameras which are yet to be installed.

c) The Outputs may not not be connected to their monitors.  That the monitors may still be connected to an old cable which is not connected to the MUX.  The new cable should be lying around close by.  So if you see a blank monitor please connect it to its new cable. 

d) The status column on the wiki page has to be updated.

e) Some of the currently in place may need to be replaced and some need to be removed.  We need to discuss our priorities and come up with a plan for that.

After checking everything we can certify that the video cabling system is complete.

I would like Joon Ho to take care of this verification+documenting process and declaring that the job is complete. 


Steve attached these two pictures.

Attachment 1: P1070489.JPG
Attachment 2: P1070494.JPG
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