llegr Bolocam Web Page: Setting up for Observing

Setting up for Observing

  1. Summary and Planning
  2. Glossary
  3. Orientation and Directions
  4. Mirror Installation
  5. Rotator Installation and Removal
  6. Optics Box Installation and Removal
  7. Optical Alignment
  8. Dewar Installation/Removal
    1. Moving the dewar down to the alidade
    2. Mounting the dewar on the optics box
  9. Cabling Setup
    1. Rotator Electronics Setup and Cabling
    2. Telescope Interface Cabling
    3. Physical Routing of Cables
  10. Electronics Setup
  11. Revision History
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Summary and Planning

At least in the near term, it will be necessary to mount Bolocam from scratch on the day that observing begins -- usually another instrument has been in use at the Cass focus up until the night before run start.  This procedure takes essentially all day, from about 9 am to usually 6 or 7 pm.  Plan your manpower accordingly.  The overall order of the steps for mounting, along with the persons who are usually responsible, are:
  1. Dismount previous Cass focus instrument (day crew)
  2. Mount Bolocam optics box at Cass focus (day crew)
  3. Bring Bolocam and dewar cart down to alidade platform (day crew + instrument team)
  4. Test mount Bolocam to optics box (instrument team)
  5. Start fridge cycle with Bolocam on cart on alidade (instrument team)
  6. Align Bolocam optics (instrument team)
  7. Mount Bolocam and set up all cabling (instrument team)
Items 1. and 2. can be done by the day crew alone, so the instrument team members need not even be at the summit for these steps.  Depending on which instrument was at the Cass focus prior to Bolocam, these steps are usually done by 10 am or 11 am; consult with the day crew on this.

Any necessary preparation of the optics box should be done prior to the instrument switch day.  This includes
Do everything possible before the day of the instrument switch, as you already have plenty to do on that day!

In terms of fridge cycling, what we usually do is to hold off on the fridge cycle until the dewar has been moved down to the alidade and a test mount to the optics box has been done.  The fridge cycle can then occur while the optics box is being aligned and cables are being routed over from the racks on the third floor.  It is necessary to  wait until the end of the cycle to mount the dewar onto the optics box.  One could in theory do the cycle in the morning before bringing the dewar down, but one might reduce the hold time with all the jostling during moving of the dewar.

In terms of cryogen fills, it is best to do a LHe fill while the dewar is still on the 3rd floor, and then do both LN and LHe after the dewar is in its final position on the optics box.  The LHe is needed for the fridge cycle, while adding LN early will just unnecessarily increase the weight of the dewar.

Glossary

Orientation and Directions

Mirror Installation

Rotator Installation and Removal

It is up to you whether you want to install the rotator before or after the optics box has been attached to the telescope.  It tends to unbalance the optics box weight a bit and so makes it harder to lift down to the alidade and install, but getting it on beforehand saves about 30 minutes so is certainly worthwhile.

Here's a picture of the optics box with the rotator installed.

If the homing sensor and limit switch have already been installed, be careful to avoid damaging them!

Installing the rotator is trivial, but takes 3 people due to its weight.  You can get away with 2, but 3 makes it easier. The two lifters can't be 90-pound weaklings.  Remember, lift with your legs, not your back!  Here are the steps:
  1. Make sure the correct rotator plate is in place on the optics box; the Bolocam plate is heftier than the SuZIE plate and has a flat milled region that the rotator mates to.  There is only one way that the plate can fit on the optics box.

  2. Bring the rotator behind the optics box, rotating it so the motor mount points due right.

  3. Check that four surfaces are clean: the mating surface on the rotator plate, the mating flange on the rotator, the curved flange down inside the optics box that the bottom of the rotator will rest on, and the bottom of the rotator.  Clean any other crud off the rotator so it doesn't end up on the optics.

  4. The two people doing the lifting should stand on the right and left sides of the rotator.  The third person (who doesn't need to be particularly strong) should stand behind the rotator.

  5. The two lifters should grab the rotator at the top flange (the one that mates to the dewar), lift the rotator straight up and then over the rotator plate hole.  Think ahead of time about how high the rotator will have to be lifted and set your grip accordingly.

  6. The third person should push the bottom of the rotator from behind so it tilts and goes into the rotator plate hole.

  7. As the rotator drops in, it usually hangs up; the third person just needs to provide more tilt.

  8. Once the rotator has dropped into place, it is stable (i.e., the lifters can let go).  Rotate the mating flange so it lines up with the large bolt holes in the rotator plate and screw it in.  Again, make sure the motor mount points due right before you screw in.
Removal is also easy, just reverse the above steps.  Screw the rotator-rotator plate mating bolts back into the rotator plate so they don't get lost.

Attaching the motor and belt:
Attaching the homing tab and sensor, limit switch, and encoder:

Optics Box Installation and Removal

The day crew are really the experts on this; they will drop the optics box onto the alidade, wheel it into position, and then lift it up and bolt it to the telescope frame at its front end.  A couple of useful bits of information or things to watch out for:
Similarly, the day crew will take care of removal of the optics box once the dewar has been dismounted and is out of the way.

Optical Alignment

The general strategy is to make use of the telescope as the reference surface and align relative to it.  You will first level the box, then dead-reckon align the two flats, then laser align the tertiary.  Make sure the front and back plates and right side access panels are off so you can put the level on the mirrors.
  1. Level the optics box

  2. Align the flat mirrors:

  3. Align the Bolocam tertiary.  You have dead reckoned the flat mirrors, so now the idea is to send a laser beam out along the optical axis and look for its spot on the secondary, tweaking the tertiary until the laser is centered on the secondary.

  4. Finally, remove the laser jig from the rotator, remove the batteries from the laser and tape them to the jig, and put the jig away in the 3rd floor lab where the rest of the Bolocam equipment is stored.  Store the digital level with the laser alignment jig.  It's very important to not lose the level or the jigs, they are unique and trying to do the alignment with kludgey replacements is very difficult!

Dewar Installation/Removal

This is the part that usually inspires fear -- getting the dewar down to the alidade platform and onto the optics box.  There are two steps: getting the dewar down to the alidade and situated on its cart there, and then mounting the dewar on the optics box.

Moving the dewar down to the alidade

You will remove the dewar from its cart with the crane, leave it suspended on the crane while you move the cart down to the alidade, and then drop the dewar down to the alidade and reattach it to its cart.   If you have trouble remembering how to deal with the dewar straps and buckles, refer to the Messing with the Innards page.
  1. Put the window cap on the dewar -- you do not want to accidentally puncture the window during any of the following steps!

  2. If you have not already, do a LHe fill.  Do not do a LN fill unless you did not do one the day before.

  3. Remove the electronics box.  This will of course require turning off the power and disconnecting all cabling.  See the Electronics page for instructions on doing this.

  4. Screw the dewar eyebolts into the 4 threaded holes on the top of the dewar (the same holes that accept the support legs).  These eyebolts are usually stored with the dewar screws.

  5. Wheel the dewar over to where one can access it with the crane.  The day crew will rig the dewar to the crane using the eyebolts.  Slowly take up the weight of the dewar with the crane.  When you are confident the rigging is solid, release the dewar straps so that the dewar comes free of the dewar holder and cart.  Leave the dewar hanging from the crane (lower it down close to the floor so it doesn't have far to fall if something happens!).

  6. Disassemble the cart.  Check that the cotter pin that prevents rotation of the dewar holder is in place.  The dewar holder is attached to the cart with two aluminum rods on the back held in place with cotter pins; you will have to remove these rods to free the dewar holder.  You have to take the weight off the rods to get them out, but the holder is very heavy.  Lower it down to a height where one person can get a good grip on it (lifting with the legs, not the back!) and then one other person can pull the cotter pins and rods.  Once the dewar holder is off, pull the cart legs out.  They are held in by spring-loaded pins.  Sometimes you have to tilt the cart back a bit to get the weight off the legs.  Finally, remove the crank (also held in place by a spring-loaded pin).

  7. Take the pieces down to the alidade.  The cart is the hardest part; we usually drop it down over the side directly to the alidade, see the picture.  Remember, it's heavy and wants to catch on the red rail.

  8. Reassemble the cart on a large rectangular dolly on the alidade so that it can be used to lift the dewar onto the optics box.

    The orientation of the dewar on the cart is important, so we provide some pictures of the mounting of the dewar onto the optics box to give you a better idea: picture 1, picture 2, picture 3.  As you can see, the cart must be oriented a certain way to tilt the dewar so that is can be mounted on the rotator, but this orientation is incompatible with moving the cart toward the optics box as the dewar is eased into place because it is transverse to the normal direction of motion of the car.  Hence the dolly -- it allows the cart to move as needed.  Note the orientation of the dolly on the alidade platform, the orientation of the dewar cart on the dolly, and how the cart must be placed to align the dewar with the rotator.  See the picture to see what your end result should be.

    We usually use one of the dollies that are used for storing instruments up on the third floor.  Orient the dolly on the alidade so that its long axis is transverse to the platform (going left-right).  Put the cart on the dolly and attach the legs.  Position the cart on the dolly so that when the dolly is pushed toward the optics box, the dewar cart will hold the dewar in a position such that it can be aligned with the rotator.  And of course make sure the cart is placed so that the dolly won't tip when the dewar is placed on it!  Clamp the cart into place using 2x4's screwed into the dolly; see picture 1 and picture 2.  It's hard to see in the picture but there are 2x4's along both the legs and the along the main section of the cart; the cart is completely immobilized.

    Finally, reattach the dewar holder to the cart.  This is a bit difficult because of its weight.  Again, use one person to carry the weight of the holder and 1 or 2 others to get the aluminum rods in and insert the cotter pins.  Make sure the holder is oriented as indicated in the picture.

  9. Bring the dewar down and reattach to the cart.  The travel of the crane prevents you from bringing the dewar down into the most convenient place; the dewar usually ends up on the right half of the alidade, so you have to rotate the dewar cart around to mate to it.  See picture 1 and picture 2 to get an idea of where the dewar sits when the crane lowers it to the alidade, though note that 1) we no longer leave the e-box and dewar holder attached to the dewar when moving it; and 2) depending on the length of your dolly, you may have to rotate it 90 degrees to bring the cart close enough to the dewar.  Once you have the dewar close enough to the cart, you can strap it into the dewar holder in the usual manner.  Remember to get the orientation of the dewar holder correct and to use the correct slot in the holder to grab the dewar's middle flange; see the picture.  Make sure to get the azimuthal rotation angle of the dewar correct; the bath exhaust ports should point back toward the cart.  If you do not get close enough, you will not be able to tilt the dewar properly for the fridge cycle.

  10. If you want to do a test fit to the optics box (e.g., to make sure you have mounted the cart onto the dolly correctly), you can do so now; basically, just follow the directions below for attaching the dewar to the optics box, except you don't need to bother with the spacer and you can quit once you get close enough that it is clear the dewar will mate properly.

  11. Reattach the e-box, recable it, and power up; see the Electronics page for instructions on doing this.  In routing the cables, think about how the cart will have to be oriented during the mounting process and route the cables so they will not interfere.  This usually means they should go toward the back of the alidade.

  12. At this point, you should tilt the dewar and start the fridge cycle, and then start doing the optical alignment.

Mounting the dewar on the optics box

This is really not that hard.  You just have to make sure you get the orientation right.  Look at these pictures to get an idea of how it will look: picture 1, picture 2, picture 3.  See also how the dewar looks when finally mounted.

Remember that you have to wait until the fridge cycle is done because the dewar must be rotated such that it is not tilted to the fridge cycle position.

Preparations:
  1. You will need 0.75 inches of lucite electrical isolated/spacer between the dewar and the rotator.  This usually means the specialized 0.25 inch spacer (which has shoulders to clear the rotator encoder gear) and a simple 0.5 inch spacer.  These should be in the 3rd floor Bolocam storage room.

  2. You will also need the special dewar mounting bolts.  These are special long bolts with hex heads and, most importantly, nylon shoulder washers and oversized metal washers.  They should be in a tupperware container with the laser alignment jig and the digital level.  The nylon washers are important for ensuring electrical isolation between the dewar and the optics box, and the shoulder washers prevent the bolt heads from biting into the nylon.  Make sure you understand how they all fit together: each bolt gets two nylon and two oversized washers, with the shafts of the nylon washers pointing toward each other and the oversized metal washers sitting on the large flat part of the nylon washers.

  3. You will also need some freedom to rotate the rotator.  If the belt is not attached, then you are all set.  If it is attached, make sure the motor is off.

  4. Tilt the telescope to ZA = 4 degrees and hit the alidade stop button.

  5. Make sure the dewar window cap is on!
Mounting:
  1. Rotate the dewar so that it is in the correct orientation for mounting.  Rather than the bath exhaust lines pointing at the cart, they should point 90 degrees away, counterclockwise as viewed from the top.  See the mounting picture for clarification.  To do this, you have to loosen the dewar straps 1-2 clicks and then rotate the dewar, taking up some of the weight yourself to reduce the friction.  Loosening the straps is tricky: you have to release the buckle and let the strap slip 1-2 notches on the ratchet and then lock again.  If you loosen too much, the dewar will fall out of the cart!  The bottom strap is noncritical right now (the top strap is the one holding the dewar to the cart), so you can use the bottom strap for practice.  You should have two spotters: one pushing up on the e-box (who will push the dewar back toward the cart if you loosen too much) and one at the back of the cart (to prevent if from sliding away when the other spotter pushes).  Once you have the straps loosened, the e-box spotter and the strap-loosener can push up on the dewar (to take the weight off the straps) and rotate it.  Once the dewar has been rotated, retighten the straps.

  2. Rotate the dewar rotator into the correct position.  There is a label on the rotator that says something like "E-box points this way".  If you cannot find the label, the e-box should be between 90 and 120 degrees counterclockwise (as viewed from the top) away from the rotator belt length takeup loop.  See the picture.  Rotate the rotator so the e-box label points straight down; as indicated in the mounting picture, the e-box itself will be pointing straight down when it is mounted onto the optics box.

  3. Rotate the dewar cart around so that the e-box points toward the back of the alidade, as in the mounting picture.  Make sure any cables are moved so they will not interfere with mounting.

  4. Remove the dewar holder cotter pin so you will be able to rotate the dewar.

  5. Get your lucite spacers in place on top of the rotator.  You may need to use some tape to hold them in place until the snout is inserted into the rotator barrel and can catch them.

  6. Now you will raise the dewar up, tilt it, and slowly ease the dewar into place by alternately pushing toward the optics box, tilting the dewar, and lowering the dewar until it can mate to the rotator.

    When raising the dewar, note that the dewar cart actually lets you go higher than you might think; the holder will run into the top of the cart, and you will feel resistance from the crank, but if you keep cranking, a second mast starts moving and the dewar will go higher.  Of course, don't go so high that the entire cart becomes unstable.

    Another problem you will run into is the worm gear -- in principle, one would like to tilt the dewar 40 degrees (the angle that the rotator is tilted to) raise it up so that the window is above the rotator, push it toward the optics box, and then drop it in.  The dewar will probably run into the worm gear and prevent you from doing this.  So what you must do is tilt more than 40 degrees, push the dewar toward the optics box to get the snout into the rotator a bit, lower the dewar a bit, tilt back toward 40 degrees a bit, push toward the optics box a bit, and so on until the snout is feeding into the rotator.  The picture shows what things look like midway through this process.

    Trust me, it can be done!  You just have to keep pushing, tilting, lowering, etc., etc.

  7. Once you have the dewar snout very close to touching the lucite spacers, get all your screw holes aligned.  It is useful to stick a bolt through the holes in the rotator and spacers and then into the dewar flange.  You may need ot rotate the rotator a little bit to get the alignment.

  8. Continue to ease the dewar in so that its weight comes to rest on the rotator.  Get some bolts in, starting from the top side of the rotator (toward the telescope).  Remember, you must insert the bolts from the bottom so the shafts do not stick out and interfere with the rotator belt, and you must use the nylon spacers and oversized washers!  See the picture.  It is dangerous to stand under the dewar at this point, so stick to the top side bolts for now.  You will find that you have to get a couple bolts in, ease the dewar in a bit more, tighten up the bolts a little bit, ease the dewar in more, etc. until the dewar surface is flush against the lucite spacer.

  9. Continue to add bolts.  You won't be able to get a few bolts near the rotator motor right now, but do as many of the others as you can.  Tighten them up, taking care to adjust the dewar cart height to make this easy.

  10. Once you are happy with the tightness of the bolts and the stability of the dewar, start loosening the dewar straps to release the dewar from the holder.  Start with the bottom one, and then the top one.  Be careful to watch out for any signs that the bolts are not taking up the weight of the dewar.  Once the dewar is completely free from the cart, pull the cart away.

  11. Rotate the dewar counterclockwise to get access to the bolts you missed and install them.  Tighten up all the bolts.  Make sure you are happy with the stability of the dewar.

  12. Tilt the telescope to ZA = 4 degrees and measure the optics box tilt angle in both left-right and front-back directions by placing the digital level on the plate with the large circular hole.  The left-right tilt should be 0 degrees and the front-back tilt should be 4 degrees.  Compare the front-back tilt to that measured earlier after tightening the turnbuckles and leveling the optics box without the dewar attached.

Cabling Setup

This section discusses 3 items: cabling of the rotator, cabling of the telescope interface, and physical routing of all cables.

Rotator Electronics Setup and Cabling

You should have already attached the motor, belt, adjusted the pulley, and installed the homing sensor and tab, limit switch, and encoder; see Rotator Installation for instructions.  You will now attach all the electronics for driving the rotator, measuring its position, and communicating with allegro.  If not already mounted to the optics box, all the parts mentioned below should have been found in an obvious storage place, either in the 3rd floor Bolocam storage room or near allegro.  Refer to these two pictures (double-click to get larger versions):

   

Telescope Interface Cabling

There are multiple BNC cables that connect between the telescope computer, allegro, and the DAS.  A schematic of the cable connections is provided here.  Some explanation is necessary:
The meaning of the signals is not important now; see the discussion on the Data Acquisition, Rotator Control, Data Handling page for details.

These BNC cables should already be in place and connected at the telescope computer and allegro.  They will be labeled by their signal names at each end.  If any are missing, you will have to run new ones.  If they are in place and not connected, go ahead and connect them to the channels at each point as the diagram indicates.  The connections at the DAS rack are given on the Electronics page.

The digital I/O box at allegro connects to allegro via a simple DB37/DB37 cable to a unique port on the back of allegro.  Make sure the digital I/O box power switch is on (it draws power from allegro). 

The best way to test the connections is simple to do fake observation and see if everything works.  If you find possible problems, you can tee in DMMs on the various BNCs at the digital I/O box and also monitor the signals going to the DAS via the DAS.  All the signals are TTL logic levels; logic 0 is between 0V and 0.5V and logic 1 is around 3V I think.

If you find deeper problems (the signals are not being asserted by the telescope or the digital I/O box as they should, the signals make it to the DAS rack but the optoisolator board fails to transmit them to the multiplexer), you will probably have to call an expert.  If you are feeling brave, schematics of the digital I/O box and the optoisolator board can found in the Bolocam big black binder or on the Bolocam internal web page.

Physical Routing of Cables

All these cables have to be run around in ways that keep them out of the way and allow dewar and telescope motion.

The most painful to deal with are all the cables that go between the e-box and the lockin/DAS and fridge racks.  This consists of the e-box power cable, the fridge and aux thermometry cables, the GRT readout cable, the bias spider cable, and the 6 monster preamp-to-lockin cables.  The usual way we do this is to route the cables from the dewar up to the hex plate, over to the elevation bearing by the side cab, on top of the side cab, and to the racks.  It is simplest if you first route the bundle consisting of the 6 monster cables and the bias spider.  Cable ties should be used to tie these cables to the various eyeholes along the way.  At the dewar, the cables should be cable-tied to the through holes in the middle flange so that their weight is not resting on their connectors to the e-box.  Enough slack between the hex plate and the dewar must be provided to allow rotation of the dewar.  Some pictures serve to illustrate:
Take up the slack in the monster cables on top of the side cab.  Once these guys have been run, you can run the GRT cable, the e-box power cable, and the fridge and aux thermometry cables on top of them.

The BNC cables carrying the TTL signals are routed primarily on cable trays.  The cables come out from the blue and silver boxes in the AOS rack and run to the cable tray above the rack.  The cables going to allegro will branch off into a different tray running to the control room, staying in cable trays until they drop down to the floor near allegro.  The cables going up to the DAS run through a hole in the AOS lab wall (the same hole used for cables going to the sidecab) and then run up between the AOS lab wall and the sidecab up to the 3rd floor.

As mentioned above, the chopper encoder cable runs out from the hole in the sidecab wall up to the 3rd floor.

Finally, once you are all cabled up, watch the cables as you run the telescope from ZA = 4 degrees to ZA = 65 degrees (or so) to make sure nothing will get damaged during normal observing.

Electronics Setup

There's not much to this once you are cabled up; for your first night pointing study, you just want to make sure you have a vaguely reasonable bias and can see astronomical signals.  Do the following:

Revision History
Questions or comments?  Contact the Bolocam support person.