I should add that Oxford Instruments (who makes the ITC unit)
suggested I look at the temperatures in the cryobay logs at the
time of the T-drift/Low-cooling power error during our generator
tests. I can now eliminate the He compressor as being the source
of the problem. The cold probe was running fine at 25K and then
the first change is a drop to 18K followed by a few minutes later
by a warmup of the probe when the fatal combination of T-drift/
Low-cooling power occurs. It would be impossible for the cold
probe to get colder if the compressor had stopped so the only
explanation is that the ITC stopped heating the probe. This is
identical to the other issues we have seen where the heater
current goes to zero and a 19400 or 5013 error occurs. Interestingly
in both of the fatal events during the generator tests we didn't
get either of those error messages logged. The first error message
was the T-drift/Low-cooling power error which shutdown the system.
The problem apparently is either UPS, ITC or software. We plan
on starting with a replacement UPS.
Jack
------------------------------------------------------------------------------
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 Wed Jul 26 2006 - 23:43:19 MST