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:
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.
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
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.
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.
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.
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 !
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.
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.
[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.
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.
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 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.
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!
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.
[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.
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.
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.
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.
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
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.
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
[Kiwamu, Suresh, Rana]
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....
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?
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.
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.
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.
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.
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.
C1:IO VIDEO 8ETMYF
C1:IO-VIDEO 6 ITMYF
C1:IO-VIDEO 21 SRMF
C1:IO-VIDEO 25 OMCT
C1:IO-VIDEO 19 REFL
C1:IO-VIDEO 22 AS
C1:IO-VIDEO 18 IMCR
C1:IO-VIDEO 14 PMCT
C1:IO-VIDEO 12 RCT
C1:IO-VIDEO 9 ETMXF
C1:IO-VIDEO 1 MC2T
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.
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?
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.
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.
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.
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.
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.
[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.
[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.
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 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.
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.
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.
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:
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.
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
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
Repositioning the optics on the Y-end table and relocating Alberto's laser ( at this point it will be rechiristened as Y-End-NPRO )
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 ...
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
LP Filter (U5)
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.
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.
The measured power levels of the RF source harmonics are given below:
We are considering inclusion of bandpass filters centered on 11 and 55 MHz to suppress the harmonics and meet the requirements specified in Alberto's thesis (page 88).
As part of the RF system upgrade some of the demod boards in the lab were modfied. The filter U5 (see the circuit schematic) was replaced. These changes are tabulated below.
Next, I and Q phase has to be checked for orthogonality. And noise levels of the cards have to measured.
We found a stray unused heliax cable running from the LSC rack 1Y2 to a point between the cabinets 1X3 and 1X4. This cable will need to be redirected to the AS table in the new scheme. It is labled C1LSC-PD5 The current situation has been updated as seen in the layout below
As seen in the previous measurement the first harmonic of both the 11 MHz and 55 MHz outputs are about 30dB
higher than desired. In an attempt to attenuate these and higher harmonics I introduced SBP-10.7 filters into
the 11MHz outputs and SLP-50 filters into the 55 MHz outputs.
Then I measured the height of the harmonics again and found that they were suppressed as expected. Now harmonic
at 22 MHz is 58dB lower than the 11 MHz fundamental. And the 110 MHz is lower by 55 dB compared to the 55 MHz
fundamental. None of the higher harmonics are seen => they are below 70dB
SLP-50 has an insertion loss(IL) of 4.65 dB and Return Loss(RL) of 3dB. It would be better to use SBP-60
(IL=1.4 dB and RL=23dB)
The filter on the 11 MHz lines is okay. The SBP-10.7 has IL=0.6 dB and RL=23 dB.
RF Amp operating temperature
Earlier measurement reported by Alberto in LIGO-T10004-61-v1 based on the LM34 temperature sensor were lower than that shown by placing a calibrated thermocouple sensor directly on the heat sink by about 5deg C. The difference probably arose because the LM34 was located on a separate free-hanging copper sheet attached to the RF Amp by a single screw, resulting in a gradient across the copper strip. I tried to move the LM34 which was glued down, but broke the leads in the process. I then replaced it with another one mounted much closer to the heat sink and held it down with a copper-strip clamp. There is no glue involved and there is heatsink compound between the flat surface of the LM34 and the heatsink. Picture attached.
The picture also shows the new filters which have been put in place to reduce the harmonics. Note that the SBP-10.7 which was to go on the 11 MHz Demod output is located much farther upsteam due to space constraints.
RF Source box has been mounted in the 1X2 rack.
Heliax cables have been directly attached to the box and anchored on the side of the 1X2 rack. Here is a list of Helix cables which have been connected so far.
RF Distribution box has been mounted in the 1Y2 rack and is ready for use.
The box receives 11 and 55 MHz Demod Signals from the RF source located in the 1X2 rack.
[Joe, Jamie, Suresh]
We have installed the IDE to SCSI adaptor module into the 1X2 rack and have connected the AA filter outputs to it.
We have removed the following cables running between the 1X2 and 1X3 racks.
The long twisted pair ribbon cable which previously carried the ADC signals.
1X2-ASC 6, 1X2-ASC 47, 1X2-ASC 9, 1X2-ASC 8, 1X2-ASC 10, 1X2-ASC 7,
CAB-1X2-LSC 42, CAB 1X2-LSC 56, CAB 1X2-LSC 41, CAB 1X2-LSC 43
1X3-2 ASC 47
We have also removed the following by mistake. We will put them back them on Monday
1X2-LSC 21, 1X2-LSC-20.
We have also removed the ASC QPD cables and moved the QPD cards which were present in the middle Eurocate (#2) to the unused Eurocrate at the bottom position (#3).
The binary input cables at the back of the cards require to be supported so that their weight does not pull them out of the sockets at the back of the crates.
Some of the slots where we plan to plug in Demod boards (the 165 MHz boards) are not currently connected to any binary output on the C1:LSC computer. We need these binary controls for the fitlter modules on the cards.
When we eventually begin to use the 15PDs as planned, then we will occupy 30 ADC channels (I & Q outputs). Currently we have just one ADC card installed on the C1:LSC providing 32 ADC channels. Joe found another 16bit 32 channel ADC card in his stash but we need to get a timing+adaptor board for it. In general we are going to need the third Eurocrate.
A platform for the power supply of the RF Distribution box needs to be built and the power supply needs to be moved into the 1X2 rack rather than sit on top of 1X2 rack.
The countersink gives rise to another problem when we mount the N-type-to-SMA bulkhead adaptor. As we are making a circular hole in the plastic strip (instead of a hole with two flat sections) the adaptor is free to turn when we tighten it with a wrench. We currently hold the smooth circular part on the other side with a gripping pliers and while tightening. If that part disappears into the countersink (as seen in the pics) we will not be able to tighten the adaptor sufficiently and consequently we will also not be able to get the heliax connector to be tight.
A better solution would be to use the 1/4-inch plastic L-angle beam which Steve has used on the AS table. In addition to solving this loose connector problem, the beam is also more rigid than the plastic strip.
The first time I noticed that the MC was not locking was after I had finished switching the RF source installation. Before this change the RF modulation frequency (for MC) was 29.485 MHz as read from the Marconi RF Source. We replaced this with a Wenzel crystal source at 29.491 MHz. This may have changed the loop gain.
Today, I changed the MC alignment to optimise the MC lock. Valera pointed out that this is not a desirable solution since it would shift the beam pointing for all components downstream. However, since we are not sure what was the last stable configuration, we decided to stay with the current settings for now and see the trends of several parameters which would tell us if something is drifting and causing the autolocker to fail.
The MC Auto locker is now working okay. However to obtain lock initially we reduced the loop gain by decreasing the VCO gain. We then increased the gain after the autolocker had locked the MC.
REFL55 has been installed on the AP table. REFL11 has been moved to make space for a 50% beam splitter. The reflected beam from this splitter is about 30% of the transmitted beam power. The reflected beam goes to REFL11 in the current configuration. The DC levels are 1.2V on REFL 11 and 3.5V on the REFL55.
I redid some of the cabling on the table because the we need to choose the heliax cables such that they end up close to the demod board location. As per the 1Y2 (LSC) rack layout given here, some of the PD signals have to arrive at the top and others at the bottom of the LSC rack.
Currently the PDs are connected as follows:
REFL11 PD --> Heliax (ASDD133) (arriving at the top of LSC rack) --> REFL11 Demod Board
REFL55 PD --> Heliax (REFL166) (arriving at the top of LSC rack) --> AS55 Demod Board
AS55 PD --> Heliax (AS166) (arriving at the top of the LSC rack) --> not connected.
We are waiting for the Minicircuits parts to modify the rest of the demod boards.
The heliax cables arriving at the LSC rack are not yet fixed properly. I hope to get this done with Steve's help today.
We now have the DC signal from three PDs available in the ADC channels 14,15 and 16. The signals are from REFL55, AS55 and POY photodiodes respectively. As the DC signals on all the other PDs of the same port (REFL, AS and PO) have the same information we do not need to monitor more than one DC PD at each port.
The LSC PD Interface Card, D990543 - Rev B, can take 4 PDs and provides the DC signals of the PDs on the connector P2 (the lower of the two) on the back plane of the chassis. An adaptor card, D010005-00, plugs into the back plane from the rear of the Eurorack and provides the four DC signals on two-pin lemo sockets.
I have connected the three DC signals from the relevant RF PDs (above) to a DC whitening filter, D990694-B-1 which is associated with the channels 9 to 16 of the ADC card.
The cables are in a bit of a mess right now as some of the PD power supply lines are too short to reach up the the Interface card in the top Eurocart. Steve and I plan to redo some of the cabling later today
The SLP-50 filters which were on the 55 MHz lines have been replaced with the SBP-60. Their respective characteristics are given below:
SBP-60 has lower insertion loss and higher return loss.
This may however change the phase of I and Q in the demod boards and they will therefore need to be readjusted. Currently the output power level of 55 MHz demod is at 2dBm, whereas it ought to be at 6dBm. I have not yet corrected that. Once that is completed Kiwamu will adjust the phases.
I shifted the temperature sensor to a new location. See the photograph below. I noticed that the higher temperature is reached on the side where there are two RF Amps. So it would be better to check the temperature of that area and make sure that it remains well below 65 deg. The operating maxium is 65deg C
Here is a picture of the new RF source layout.
And here is a photograph of it
We started to clean up the RF cables (heliax and PD interface cables) at the LSC rack.
We have pulled out all the RF cables from the small hole on the side-board close to floor. Passing the cables through this hole makes some of the cables much too short for good strain relief. So we removed the side panel on the vacuum tube side and are going to pass the cables into the rack from there at about waist height. We now have plenty of cable lengths to tie them off to the rack at several points.
We have traced all the available Heliax cables and have attached blank tags to them. We have allocated some cables to REFL11, REFL55 and AS55. These are therefore back in working order. We have also taken stock of the available PD interface cables. They do not have consistent names on both ends of the cable and we will identify and label the ends tomorrow.
MC is locked. The auto-locker works fine.
Handing over the system for night time interferometer work now. Will continue with the cabling tomorrow.