Gautam and Steve,
Our TP3 drypump seal is at 360 mT [0.25A load on small turbo] after one year. We tried to swap in old spare drypump with new tip seal. It was blowing it's fuse, so we could not do it.
Noisy aux drypump turned on and opened to TP3 foreline [ two drypumps are in the foreline now ] The pressure is 48 mT and 0.17A load on small turbo.
We want to measure the pressure gradient in the 40m IFO
Our old MKS cold cathodes are out of order. The existing working gauge at the pumpspool is InstruTech CCM501
The plan is to purchase 3 new gauges for ETMY, BS and MC2 location.
Basic cold cathode or Bayard-Alpert Pirani
Steve & Bob,
Bob removed the head cover from the housing to inspect the condition of the the tip seal. The tip seal was fine but the viton cover seal had a bad hump. This misaligned the tip seal and it did not allow it to rotate.
It was repositioned an carefully tithened. It worked. It's starting current transiant measured 28 A and operational mode 3.5 A
This load is normal with an old pump. See the brand new DIP7 drypump as spare was 25 A at start and 3.1 A in operational mode. It is amazing how much punishment a slow blow ceramic 10A fuse can take [ 0215010.HXP ]
In the future one should measure the current pick up [ transient <100ms ] after the the seal change with Fluke 330 Series Current Clamp
It was swapped in and the foreline pressure dropped to 24 mTorr after 4 hours. It is very good. TP3 rotational drive current 0.15 A at 50K rpm 24C
The main laser went off when PSL doors were opened-closed. It was turned back on and the PSL is locked.
Gautam & Steve,
Our controller is back with Osaka maintenace completed. We swapped it in this morning.
TP-1 Osaka maglev controller [ model TCO10M, ser V3F04J07 ] needs maintenance. Alarm led on indicating that we need Lv2 service.
The turbo and the controller are in good working order.
Our maintenance level 2 service price is $...... It consists of a complete disassembly of the controller for internal cleaning of all ICB’s, replacement of all main board capacitors, replacement of all internal cooling units, ROM battery replacement, re-assembly, and mandatory final testing to make sure it meets our factory specifications. Turnaround time is approximately 3 weeks.
RMA 5686 has been assigned to Caltech’s returning TC010M controller. Attached please find our RMA forms. Complete and return them to us via email, along with your PO, prior to shipping the cont
Osaka Vacuum USA, Inc.
510-770-0100 x 109
our TP-1 TG390MCAB is 9 years old. What is the life expectancy of this turbo?
The Osaka maglev turbopumps are designed with a 100,000 hours(or ~ 10 operating years) life span but as you know most of our end-users are
running their Osaka maglev turbopumps in excess of 10+, 15+ years continuously. The 100,000 hours design value is based upon the AL material being rotated at
the given speed. But the design fudge factor have somehow elongated the practical life span.
We should have the cost of new maglev & controller in next year budget. I put the quote into the wiki.
Chub Osthelder received 40m specific basic safety traning today.
It took at least ten years to rust away.
Physical plan is cleaning our roof and gutters today.
We have no coffee machine.
We are dreaming about it
We still do not have it.
The Contec test board with Dsub37Fs was on the top shelf of E7
I tried to plot a long trend MC Transmitted today. I could not get farther than 2017 Aug 4
The mode cleaner was misaligned probably due to the earthquake (the drop in the MC transmitted value slightly after utc 7:38:52 as seen in the second plot). The plots show PMC transmitted and MC sum signals from 10th june 07:10:08 UTC over a duration of 17 hrs. The PMC was realigned at about 4-4:15 pm today by rana. This can be seen in the first plot.
The vacuum and MC are OK
Jon and I stuck a extender card into the eurocrate at 1X8 earlier today (~5pm PT), to see if the box was getting +24V DC from the Sorensen or not. Upon sticking the card in, the FAIL LEDs on all the VME cards came on. We immediately removed the extender card. Without any intervention from us, after ~1 minute, the FAIL LEDs went off again. Judging by the main volume pressure (Attachment #1) and the Vacuum MEDM screen (Attachment #2), this did not create any issues and the c1vac1 computer is still responsive.
But Steve can perhaps run a check in the AM to confirm that this activity didn't break anything.
Is there a reason why extender cards shouldn't be stuck into eurocrates?
It is posted at the 40m wiki with Gautam' help. Printed copies posted around doors also.
The 40m vacuum envelope has one large single O-ring on the OOC west side. All other doors have double O-ring with annuloses.
There are 3 spacers to protect o-ring. They should not be removed!
The Cryo-pump static seal to VC1 also viton. All gate valves and right angle valve plates have single viton o-ring seal.
Small single viton o-rings on all optical quality viewports.
Helium will permiate through these fast. Leak checking time is limited to 5-10 minutes.
All other seals are copper gaskits. We have 2 manual right angle with METAL-dynamic seal [ VATRING ] as VV1 & RV1
Our 4 ion pumps were closed off for a lomg time. I estmated their pressure to be around ~1 Torr. After talking with Koji we decided not to vent them.
It'd be still useful to wire their position sensors. But make sure we do not actuate the valves.
The cryo pump was regenerated to 1e-4 Torr about 2 years ago. It's pressure can be ~ 2 Torr with charcoal powder. It is a dirty system at room temperature.
Do not actuate VC1 and VC2, and keep its manual valve closed.
IF someone feels we should vent them for some reason, let us know here in the elog before Monday morning.
Wiring of the power, Ethernet, and indicator lights for the vacuum Acromag chassis is complete. Even though this crate will only use +24V DC, I wired the +/-15V connector and indicator lights as well to conform to the LIGO standard. There was no wiring diagram available, so I had to reverse-engineer the wiring from the partially complete c1susaux crate. Attached is a diagram for future use. The crate is ready to begin software developing on Monday.
Gautam, Aaron, Chub and Steve,
Vent 80 is nearly complete; the instrument is almost to atmosphere. All four ion pump gate valves have been disconnected, though the position sensors are still connected,and all annulus valves are open. The controllers of TP1 and TP3 have been disconnected from AC power. VC1 and VC2 have been disconnected and must remained closed. Currently, the RGA is being vented through the needle valve and the RGA had been shut off at the beginning of the vent preparations. VM1 and VM3 could not be actuated. The condition status is still listed as Unidentified because of the disconnected valves.
The vent 81 is completed.
4 ion pumps and cryo pump are at ~ 1-4 Torr (estimated as we have no gauges there), all other parts of the vacuum envelope are at atm. P2 & P3 gauges are out of order.
V1 and VM1 are in a locked state. We suspect this is because of some interlock logic.
TP1 and TP3 controllers are turned off.
Valve conditions as shown: ready to be opened or closed or moved or rewired. To re-iterate: VC1, VC2, and the Ion Pump valves shouldn't be re-connected during the vac upgrade.
Thanks for all of your help.
Gautam, Aaron, Chub & Steve,
ETMY heavy door replaced by light one.
We did the following: measured 950 particles/cf min of 0.5 micron at SP table, wiped crane and it's cable, wiped chamber,
placed heavy door on clean merostate covered stand, dry wiped o-rings and isopropanol wiped Aluminum light cover
Chub & Steve,
We swapped in our replacement of Varian V70D "bear-can" turbo as factory clean.
The new Agilent TwisTorr 84 FS turbo pump [ model x3502-64002, sn IT17346059 ] with intake screen, fan, vent valve. The controller [ model 3508-64001, sn IT1737C383 ] and a larger drypump IDP-7, [ model x3807-64010, sn MY17170019 ] was installed.
Next things to do:
Exceptions: cryo pump and 4 ion pumps
Vac Status: The vac rack power was recycled yesterday and power to controller TP1,2 and 3 restored. atm3
VME is OFF. Power to all other instrument are ON. 23.9Vdc 0.2A
ETMY sus tower with locked optic in HEPA tent at east end is standing by for action.
The N2 pressure reading (C1:VAC-N2PRES) is now up-to-date after rebooting c1vac1.
The vaccum system is "Vacuum normal". We now have a space pressure transducer.
Our vacuum valves are manipulated with 60~75 PSI of nitrogen. All the valves are configured to be closed in the case of low N2 supply pressure.
In order to avoid this safety shutdown accidentally triggered, we have two N2 cylinders to sustain the vacuum valves. When one cylinder goes to low
the mechanical valve switches over to the other cylinder.
We have the monitor channel for this (combined) cylinder pressure. One shoulbe be able to see periodical pressure variation when the auto cylinder
switch is operating. However, the nirogen pressure reading got stuck at 66 PSI on Dec.16, 2014 (See attached 60-day plot of N2 supply pressure).
What we did
This morning we tracked down the cause of the trouble. We first closed the valves on EPICS and started to vary the N2 pressure.
Our first guess was the pressure transducer (Omega #236PC100GW) that was already 15 yrs old. We even has a sensor spare for replacement.
But it turned out that the direct voltage reading (to be 1mV/PSI) is changing correctly. The second guess was Omega Controller-Monitor
#DPiS32-C24 that is reading the voltage from the tranceducer. The display on this small black unit was changing corresponding to the
So our thought was
1) RS232C of the monitor unit is not working correctly
2) c1vac1 is not communicating with the monitor unit.
We wondered what could cause c1vac1 not communicating with the monitor unit, but we were afraid that some function got stuck
during either the nodus upgrade or chiara rebooting (or something else). So we decided to reboot c1vac1
In order to avoid any glitch in the main vacuum pressure, Steve disconnected some of the controller connectors for the closed valves.
We did this treatment before and it was successful.
Then c1vac1 was rebooted just by telnet and type reboot in the terminal.
Once the target is back in action, we noticed that the monitor value started to move.
Steve reverted the cables to the valves and operated the valves to recover "Vacuum Normal" state. Everything is now nicely settled.
1)Power to the seismometers were turned down,
2)Guralp2 was moved to North side of POX table
3)Guralp2 was aligned in N-s Direction and leveled before connecting
4)Power to seismometers was turned on once Guralp2 was connected
An exercise of optimally subtracting one seismometer signal by another using weiner filters was done. Results have been summarized document attached.
I used MC_L signal from the Mode Cleaner as the desired signal with GUR2_X as witness signals. I observed good subtraction where coherence is high. But there was noise added in other frequency bands. I am not sure how to avoid that.
Please find attached documents that contains relevant plots.
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.
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.
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.
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).
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.
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.
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)
1759 E Colorado Blvd
Pasadena, CA 91106
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.
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.
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.
All the temporary changes to the video cables and the video MUX ( 3843 ) have been reversed and the system returned to its original state.
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 nF. The 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.
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.