The latest shift report stated that L21 could only hold 2000 voltages.
This is misleading and an incorrect reading of the situation.
The normal trip we experience occurs when the sense wire draws too much
current and the power supply turns that channel off. This is not what
happened in this case.
The trip that lead to the above problem is due to a current into the
guard wire. The power supply can supply current and regulate the
voltage but it can not absorb current and still regulate voltage. The
guard wire power supply turns itself off and disables that channel. The
sense wire also trips as soon as the guard wire loses voltage. The
normal reset command does not re-enable the guard wire channel so it
stays off. With no voltage on the guard wire the sense wire trips
immediately at any voltage above 2000 V.
The solution is to go to STBY and back to OPER. This resets the guard
wire voltage and re-enables the channel. There is an easier way
through FTP but not using the HVGUI at the moment.
Note this technique of going to STBY and then OPER should only be used
in cases when the channel enable (ie CE status bit) is 0 indicated that
the channel has been disabled. For all other cases press reset on the
HVGUI as normal.
If this type of trip happens repeatedly. Lower the sense wire voltage
while in OPER mode, SAVE that setting, and then do the STBY-OPER cycle.
Lowering the sense wire voltages by 50 V results in a lower efficiency
which we may be able to handle. Lowering it by hundreds of volts means
the whole box and 5 cells in the chamber are off which is a big hole in
the reconstruction. So if you feel you have to do this please call an
expert.
Cheers,
Douglas
26-415 M.I.T.
Tel: +1 (617) 258-7199
77 Massachusetts Avenue Fax: +1 (617)
258-5440
Cambridge, MA 02139, USA E-mail:
hasell@mit.edu
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