BW Fiber Testing
Procedural Corrections - 8/30/2018
The fibers are too dirty. So are the popsicle stick, the alignment jig, and the desk we use to align the fibers. The SiPMs might be dirty too. Now I need to clean everything.
Our alignment should be improved. If a straight edge is held against the end of the popsicle stick, the fibers in positions 16 to 30 should be touching it. If the straight edge is against the end of the part under positions 1 to 15, the fibers should be touching that too.
The straps should not be projecting beyond the end of the bundle. Also, if the clamp sticks out, it could damage the alignment jig.
Procedural Corrections - 9/6/2018
The front strap should be under the front of the clamp, not at the back. I should still be able to prevent it from extending past the end of the popsicle stick.
Wrinkles or ripples in the front strap can block light going to the back half bundle.
The scraps should be aligned better for the normalization tests. Both the full-length fibers and the scraps should be well aligned.
Mounting Fibers on the Popsicle Stick
The Kapton straps go through little slots at the bottom of the alignment jig. When tightening them I should pull them a little toward the rear of the alignment jig so that they won't come out from under the clamps. I don't want to pull them too much that way, though, because they might tear.
I may be asked to remove the collars from the fibers in the dark box so we can test them for crosstalk. To do this, I should use two collars to hold the fibers in place. One will be temporary and put on in the most convenient way as soon as I tighten the Kapton strips. The temporary collar will be in an inconvenient position for removing once the fibers are in the dark box, so I need to turn the fibers over and put on a permanent collar. After the permanent collar is on, I can remove the temporary collar before putting the fibers in the dark box.
One method of aligning the fibers that I used is to get them through the Kapton straps and pull them fairly tight but still let the fibers move. There should be a collar near the popsicle stick and one near the middle of the bundle. Then you can take fibers one by one between the collars and push them into alignment. If it appears that the bottom 15 fibers (the ones that come to the front) are aligned adequately but the top 15 (the ones set back) are not yet aligned, you can put a strip of paper between the top 15 and the bottom 15 so that you will be able to take just the top 15 and push them forward. When checking the alignment, the collar should be tight so the fibers will not slip. If they need to be adjusted, the collar must be loosened. Once they are aligned correctly, the collar should remain tight.
I think it is good practice to put a piece of paper on the bottom of the dark box to protect the polished ends of the fibers from being scratched.
9/28/2018: I have to remove the box that helped to hold the fibers on the desk where I align them. This is the box that was taped to the table so that the fibers would be close to the same curvature they have in the dark box. The edge of the cardboard box that would contact the fibers was 19.75" behind the back end of the alignment jig.
Putting Fibers in Dark Box
SUM1 to SUM3 go to board 1, the bottom preamp board. SUM4 to SUM6 go to board 2, the top preamp board.
The curtain should not be closed until the fibers are all aligned in the chimneys and the preamp boards are in place. Closing the curtain before putting the fibers through the chimneys means they bend too much on the way in as they are put through the positioning wire above the preamp boards.
Instead of closing the curtain, use the positioning wire that is somewhere along the ramp that slopes down toward the mirror to keep the fibers from falling over.
Making Kapton Straps
The washers need to be washed with ethanol to remove oil before putting them in the strap. After washing them with ethanol we need to remove our gloves so they will not stick to the Kapton during strap assembly.
The Kapton tape needs to be unrolled slowly enough that it will not curl up like a ribbon on a gift package. To make the straps, tape a piece of Kapton tape to the table – Scotch tape is all right for this purpose. The Kapton should be stretched out flat and straight. It should remain in that position until the top piece is completely laid down.
Put the washer on the bottom piece of Kapton close to one end but far enough from the Scotch tape to cut off the part under the Scotch tape and still have some extra length of Kapton beyond the washer.
Add the top piece of Kapton over the washer and the bottom Kapton. It needs to be stretched to the same tightness as the bottom piece so that the strap will come out straight rather than curved. The top piece should align as nearly as possible with the bottom piece, and there should not be air bubbles in the strap.
Use your fingernails to compress the Kapton around the washer, but avoid nicking the strap at the edge because that can start a tear.
When the top piece is on extending all the way to the Scotch tape at both ends, cut off the Scotch tape while shortening the strap as little as possible.
Use a razor blade to make a hole in the strap coinciding with the hole in the washer. Be careful not to damage the strap elsewhere with the blade.
Preamp-Backplane Connection Problems
Sometimes a preamp does not connect completely to the backplane. Symptoms of this problem include unusually low data values from particular SiPMs that do not follow a bell curve. The loose connection has sometimes affected SiPM 23. This problem appeared in runs 1898-1906.
The cause of the loose connection is that the backplane is flexible. It may bend too much when the preamps are inserted.
To solve this problem, it is necessary to make sure the ethernet cable is unplugged from the control board first. Unplugging the cable prevents short circuits when you press on the backplane to complete the connection.
The preamps should be inserted and the screws tightened on the parts that hold them. Then go to the back of the dark box and press gently on the the double row of pins on the backplane with your thumbs. Giving a little push can help the pins connect to the preamp.
Popsicle stick Storage
For storage, the clamps on the popsicle stick should be loose enough not to compress the sponge gasket and make it ineffective over time.