We recently had a second Varian cold probe installed
(for our 800 MHz system). Both the new cold probe and the
previously installed cold probe on our 500 MHz system are
on the same emergency power system which has generator
backups. Once a month we have a generator test where the
building generators are spun up and the emergency power
to switched over to them. This results a power droop for
several seconds. The cold probe on our 500 MHz system has
survived this without any errors in the cryobay log for
almost two years (with over 18 generator tests).
However the first generator test after the installation
of our 800 MHz cold probe resulted in an accidental warmup.
The system had T-drift and Low cooling power errors one second
after each other. My understanding is that this combination of
errors will cause an automatic shutdown of the coldprobe and
is a fatal condition. Varian has suggested that this probe
may be warming up faster than expected when the compressor
stops for a few seconds. They are recommending that we
increase the T-drift limit from 10 to 15 or 20 degrees to
suppress this error.
Has anyone else run into this issue? Currently this problem
has happened in 2 out of 3 of the generator tests since the
800 MHz cold probe was installed. I am curious if this problem
is widespread at all and how others are coping with it.
Jack
ps Originally we though the problem might be due to the
Brown-Out feature being disabled on the He compressor in
in the cryobay. However enabling that feature doesn't seem
to eliminate the problem. Also, we never see a cold-pack or
compressor error which makes me think that the compressor
is restarting but that the probe is drifting out of the
temperature limit before the compressor fully recovers
its cooling capacity.
------------------------------------------------------------------------------
Jack W. Howarth, Ph.D. 231 Albert Sabin Way
NMR Facility Director Cincinnati, Ohio 45267-0524
Dept. of Molecular Genetics phone: (513) 558-4420
Univ. of Cincinnati College of Medicine fax: (513) 558-8474
Received on Mon Jul 17 2006 - 15:24:24 MST