Minute of Meeting on EMI
Taping of Towers
There was a lot of
discussion about whether it was really needed and who would do it that I can't
really capture here. There will have to be further discussion of this at
management meetings. For the moment it is clear that tower A will be done
at SLAC; that it would be best if Plyform could but the foil on the top tray,
and that the foil and tape should really go through the tower thermal vac test to make sure there are no problems with it.
The technical discussion in
the last 20 minutes of the meeting is easier to summarize. Below is a
list of concerns that were expressed and responses that have
been taken or who is going to take action:
There are action items for
NORDBY and HIMEL.
There are resistors on the
cable that will get covered with aluminum tape. They are only protected
with conformal coating. This is not enough to be sure the tape won't
short them out. General agreement with this concern.
We will protect them with kapton tape. Nordby will
add this to the draft procedure.
The ground layer of tape on
the outside of the cable could cause electrical change. Himel checked
with Johnson about this after the meeting he was not at all concerned about
this over such a short distance. Note that after the tape is applied there
will be an electrical test.
Abrading the aluminum could
cause conductive dust which could cause shorts. This shouldn't be done on
the completed tower. Himel will check with NASA to see if the abrasion is
really necessary. If it is, we may be able to vacuum or clean
afterward. The problem the abrasion is supposed to solve is that aluminum
has a nonconductive oxide that can prevent good electrical contact.
Cleaning with acetone is a
problem because it dissolves the solithane and the
adhesive on the tape. Can its use be eliminated from the procedure?
Himel will check with the same NAS person to see if it is absolutely necessary.
Use of Isopropyl alchohol, IPA is not considered to
be a problem
It was suggested that the
tape on the vertical corners be applied in many short pieces instead of one
long piece. Nordby will see what works best on the EM tower.
There was concern that the
aluminum would come off the sidewalls if the tape is pulled off to remove a
wrinkle. Himel stated that he had tried this on a coupon without any
problem. There was still concern that the EM towers aluminum wasn't stuck
on as well. Nordby will check when testing the taping procedure on the EM
tower.
Tape on the top covers
places the CMM touches and will mess up its measurements. Nordby thought
those touch points were only used for rough alignment. He will check to
make sure.
Finally at the tracker
technical meeting on Thursday the 16th the use of electrodag
504 was suggested instead of aluminum foil. Himel looked this up after
the meeting. He found the manufacturer's web site: http://www.achesonindustries.com/electronic_materials/shielddata.asp with other model numbers of
conductive paints (but not 504). They are paints intended for EMI
shielding and most of them are intended to be used on plastics. Some are
intended for metal. Normally a 1 to 2 mil layer is sprayed on.
Spraying conductive paint on a completed tower seems to Himel like it is too
likely to create conductive dust that can get where we don't want it.
He's also dubious about getting a good (and permanent) seal across the cracks
between the sidewalls. If someone wants to pursue this further, please do
so.
------------------------------------------------------------
Tom
Himel
snail mail
SLAC MS 66
email
thimel@slac.stanford.edu
2575 Sand Hill Rd
Phone
(650)926-2004
Fax
(650)926-5124