January 20, 2011 FDC meeting
- Production (David)
- Blue Crab status
- ETC schedule
- Electronics (Fernando, Chris, Roger)
- Rigid-flex assemblies
- Foil production status
- Engineering (Bill, David, Lubomir)
- Wire stringing FDC Log Book, page 549
- Movement control
- Full-scale prototype studies
- Latest tests FDC Log Book, page 550 (Lubomir)
Participants: Dave, Chris, Simon, Beni, Fernando, Glenn, and Lubomir.
- Dave: there was a walk trough the clean room yesterday with the vendor. The emergency exit door must be sealed better. Glass on the dark room door must be covered. The move in date is postponed to Jan 31. Dave has prepared conduct of operation documents for the clean room.
- New ETC schedule: the full package testing is postponed and squeezed. Fernando: even with the new schedule we may not have the electronics needed for the tests, so we need to have alternative testing procedure.
- Chris sent the first article signal cables back to the company to fix the cable problem.
- We discussed two issues with the rigid-flex assemblies. The thickness of the board is 18-18.5 mils, while it is specified to be 14+/-3 mils. Assuming before a thickness of 22 mils, Bill found this will cause a problem in a region where the connectors from two neighboring cathodes overlap. Bill will have the final word if this will still be a problem with 18.5 mils. The second issue is if we want to have the flex contacts tinned. It is related to the soldering procedure we want to use: conventional soldering, or using conductive tape. Fernando explained to us that the tinning can be done later during the board stuffing, although the tin layer will have different shape. This will give us time to investigate both options. Therefore, everybody agreed to approve the rigid-flex production as it is, i.e. with bare gold contacts. We discussed again the two soldering options. All they require more tests that we will do in the coming weeks.
- Fernando: thanks to Glenn the PR for the ASICs is now out and we expect all the ASICs by the end of May.
- Working with the new stringing system is so far successful. Wires for one full chamber were strung. The wire positions were measured by Beni (page 549): the resolution is about 10-15 microns which is acceptable. The main issue is the flatness of the frame on the strongback. Right now the frame has a conical shape with the outer diameter sticking up (up to 1-2mm at some places) that makes problematic putting the wires on the pads. Bill proposed to add clamps (like a comb) between the wires too press the frame down to the strongback. These clamps may interfere with the wires during the stringing and so far the proposal is to cover the whole frame during the stringing with a flat sheet. It might be a problem to take it out since there's not enough clearance between the wires and the frame when it is at the lowest position. Another option was investigated by Casey: to tape down the wires close to the pads. He used the height gage to put the tape vertically; it moved by about 25 microns.
- Larry from Cross Computing was at JLab once more at the end of last week. He made few low level programs that were actually used for the position measurements. This automated procedure was checked by visually looking at the laser spot. Apart from a systematic offset (few tens of microns) different for the sense and field wires, the procedure gives consistent results.
Full-scale prototype tests
- Lubomir re-visited the unsolved problem that wires are not in the middle w.r.t. top and bottom cathodes. This time the long wires were scanned along their lengths. One sees (page 550) systematically that the wires are closer to the middle at the beginning of the wire going up at the middle of the chamber by up to 1.5mm. This may indicate that the cathodes are sagging. It could be due to pressure difference, gravitation, or electrostatic forces. The last two effects normally must be small. The holes on the cathode frames must eliminate the differential pressure on the cathode, but it could be that the ground plane sags and couples to the cathodes strongly in the middle. The plan is to investigate the pressure effects by changing the gas flow. The next step would be to turn the chamber upside down, but most likely at this position the chamber will not be operational. Therefore, before doing this any other ideas of what needs to be checked, are welcome.
For the next collaboration meeting (Feb 2-3) Beni and Lubomir will decide about the FDC talks in the tracking session. Simon will talk about the tracking analyses in the off-line session.