Thursday,  March 26  Notes

Present:  A. Byon, R. DeMaat, C. Drennan, J. Elias, S. Hahn, 
	  S. Orr, J. Patrick, JJ. Schmidt, K. Schuh 

Front End CPU Links
     The VME processors in the front-end crates are 6U commercial cards mounted
onto 9U adapter modules to be designed and built by Terry & company.  Although
the decision on which CPU cards are "right" for us hasn't been made yet, we are
assuming the both fast ethernet and a TTY link will be via the standard front
panel connectors for those links.
     For RS232, the newer CPU cards provide a strapable RS232/485 transceiver.
Since this link is only activated to reset/restart a balky processor, it is not
a source of radiated EMI.  In fact, it can be completely quiescent when not in
use.  Thus the potential EMI issues are conducted noise through the shield and
conducted host computer noise on the wires.  The recommendations for this link
are:
1) Use the differential version (not RS232) which we believe is RS485.
2) Hard ground the cable shield at the upstairs switch (or fanout) box and
AC terminate the cable shield and the common mode impedance at the front-end
crate.  (refer to the studies made by S. Chappa for the clock cables)
3) Install the receiver and shield termination network on the 9U adapter card,
and interconnect to the processor with a short jumper from the 9U front panel to
the 6U front panel using standard cable and connectors.
4) Prepare for tests this summer with ARCHTEST.
     For fast ethernet, the CPU card provides a plastic TELCO style connector
with one of the pins being ground.  The jumper cables are deliberately
unshielded for performance reasons, but specialty houses offer shielded
versions.  The configuration will be a star with either local concentrator hubs
at each cluster of crates or one large hub upstairs.  Since these links send
information continuously even if it is just fill patterns to maintain synch, it
is important to find out about EMI problems.  JJ showed that breaking up ground
loops optically is reasonably expensive (>$200) and the packages are too large
to put on the 9U adapter card.  Recommendations at this point are:
1) Investigate further the possible optical solutions including in-house.
2) Measure the EMI from unshielded fast ethernet jumper cables.
3) Prepare for tests this summer with "ARCHTEST".

Relay Rack Power Distribution
     Racks are to be installed in the first and second floor counting rooms
starting some time in April.  For safety, Keith and Stan say each rack must be
grounded and bonded to the closest ground point - in our case its the big
isolation transformers.  We would prefer to see this done through the power cord
rather than through bare wire running along the underfloor and possibly touching
bad stuff.  The fallout from this situation is eternal vigilance against ground
loops at the detector.