Hello All -
We recently purchased a Varian MR-400, and the engineers brought it up
to field back in November. Since Varian officially "certified" the
installation complete in January, we've been noticing what, to our
minds, is a fairly significant drift for the 400 MHz magnet - about 12
DAC units/hr - which works out to about 4 Hz/hr. Varian says this is
within spec - their limit is 8 Hz/hr.
That said, we're having to reset the "lockfreq" parameter from an HDO
standard about once every few months to keep all solvent systems
accessible - a procedure we didn't have to repeat at all over several
years on our other magnets. We've also had other reps express their
surprise at the magnitude of the drift - even if it is within spec.
What is your collective experience out there for drift on the MR-400?
Have you experienced similar drifts in this magnet? Even within the
Varian spec, what would you consider an "acceptable" amount of drift
to be?
We're a smaller, primarily undergraduate institution, so our
experience is limited to only about 3 high field magnets - our Inova/
Oxford 500 (which still runs like a champ), a now decommissioned
Varian R2D2 300, and now this new Varian/Magnex 400 - so we're totally
aware that this just may be a bit of paranoia on our part - that said,
we've never had a magnet drift quite this significantly before.
Your help is appreciated -- I will summarize responses and repost them
to the list.
David Sibley
Furman University, Greenville, SC
david.sibley_at_furman.edu
Received on Thu Jul 17 2008 - 04:14:46 MST