View source for Top stringer in a drift chamber for CLAS12 project





==Procedure to drop the wire inside the chamber==

The chamber location is in a clean room, before following the next procedure, the stringer is expected to follow all the clean room instructions that include safety instructions to be in a clean and safe working environment for him (her) and the other co-workers.

Prior to beginning work.  Top stringer should remove covers on pins, chains, and stringing machine.  Give folded bag to bottom stringer.  

The top stringer is going to :

1- locate then Raise up the lift to a height  that helps to see the all the top and top feed through rows that he is going to string. he/she should distinguish their locations and their numbers (The rows are numbered for accuracy). The lift is positioned away from the chamber to avoid any direct contact with the chamber. 

2- Be sure that the stringing machine is in an appropriate location (the bottom stringer helps to relocate if needed), and the wire is stretched around the machine's pulleys. Wire comes off of the spool, passes around and under the right pulley first and then up and around the left pulley.  The wire then is put through the wire guide and then down through the wheels. 

3- Check the crimper's gap using the feeler gauge (gaper). Crimper's jaws should touch the feeler gauge but compress the guage..

4- Clean  hands using alcohol. 

5- Attaching chain to wire.  After snot is removed, hold the chain and the snot in the same hand so you feed the free end of wire gently into the snot.  WHile holding the snot and the wire in the other hand,  then feed the needle of chain gently into the snot.   The wire should not pass completely through the snot.  The chain only needs to fit snug enough so it does not fall out when the wire is dropped through the chamber.

Inserting Chain into top feed through

6- Extend the wire by pressing the button of the machine until the top of the  chain passes through the top feed through with a distance of  1-2" (or shorter if possible) from the inside end of the top feed through. Click the machine button  with the least pressure so limited force is exerted on the stringing machine.. Use a paper clip, if necessary, to push on the snot until the chain has pass completely through.  Avoid  kinging the wire as a result of continuing to push on the wire after the chain has stopped moving through the feed through.

7- Wait until the chain is stable. The amplitude of the chains' swings should be less than the distance between adjacent wires before you attempt to drop the wire.

8- Drop the wire at a continuous velocity until the end of the chain is slightly above the inside bottom feed through (trumpet).  Don't touch the wire as it is falling through.  Watch the wire as it falls for static behavior and crossing other wires.

9- Two ways to feed the wire inside the bottom feed through:

a- Some times the chain will  (for Field and Guard wires) fall directly into the feedthrough by tapping on the stringer feed button.  (preferred method for field and guard but not for sense because of increase probability of wrapping a sense wire around a guard.)

b- Otherwise, gently grasp the wire using two fingers.  Tap the stringing machine button, if necessary, to give you some slack. Then lower or lift the wire until it enters the feedthrough.   If its a guard wire, you may twist the wire move it into position above the feed through.

Feeding the wire continues until the snot is just outside the bottom feed through.  Be careful that the chain does not get stuck in the bottom feed through.   You will notice this because the wire will become slack inside the chamber and light be reflected (flash) off the wire as it moves around laterally inside the chamber.

If the chain is stuck in the bottom feedthrough.  The top stringer should try to lift the wire until the chain is once again just in the entrance to the bottom feed through and drop the wire again.  If this fails ask the bottom stringer to pull the needle through.

If the needle is not far enough to be grabbed by the bottom stringer, the bottom stringer can use a paper clip to guide the needle through.

If the snot is stuck on the trumpet, the top stringer will gently lift up enough for the snot to move into position so it may be dropped through. 


10- Extend the wire to have an additional length of 10-12" beyond the bottom feed through. Counting is used to reach the desired length. Check with the bottom stringer if he/she has enough wire length.

11- Use the tip of the cutters to cut the wire in one stroke leaving 4 inches of wire above the top feed through.  Do not kink, pull, or stretch the wire.  Feed  the crimp onto the wire then seat the crimp pin into the top feedthrough using your hand.  The wire should be held by one hand at all times.  Lift the wire a distance equal to the length of the crimp pin so any possible wire defects caused by stringing are reduced.  Use crimpers to apply pressure on to the top of the crimp pin,  be careful not to bend the crimp pin while checking that the pin is seated.  The pin may need to be pushed into the seated position with this pressure.  Pull the wire up 1/2 the length of the crimp pin to remove a kink that may have occurred on the previous step.  If you are not confident that the pin has been seated, push down on the pin while you are crimping at the right distance.  This distance is determined by resting the open crimper jaw on the top of the feedthrough, lift the jaw up 1 mm, crimp (push if needed while crimping).

If the pin is bent, replace it with new one, check that bottom stringer has enough lead,  and return to step 11.  

Pull gently on the wire to be sure that the crimp is sound and the crimp pin is seated.

12- Cut the wire exactly above the feed through. Put the wire end in the trash and avoid dropping wire ends into the chamber.

After completing the work, use the multimeter to check that there is NO continuity between adjacent wires, neatly place your tools in the bucket, and cover crimp pins and chains.  Cover the machine, the plastic should not some in contact with the hot solenoid of the machine.