i'm posting this for dr. david eliezer at cornell medical college.
please send copy of any responses to him
(eliezer@brooklyn.med.cornell.edu)
as he's a new addtion to this list and doesn't yet get stuff
forwarded to him as he should.
thanks,
john chung
the scripps research institute
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Subject: Z0 coil field strength survey
We have discovered (on a new Varian Inova AS600 instrument) that the
field strength
of our Z0 shim coil is about 22000 Hz total (+/- 11000 Hz). This means
that for a
relatively stable magnet, drifting at 2 hz/hour, the Z0 coil will not be
able to maintain
the field, and lock frequency, beyond around 11000 hours {(22000
Hz)/(2Hz/hr)} which is
a little over a year. So, the spectrometer frequency has to be changed
roughly every year.
In my experience, this is rather unusual. Varian insists that this is
perfectly normal, and
has always been so. I am trying to gather information about the
'typical' field strength
of a high field spectrometer Z0 coil. I would be grateful to anyone who
would be willing
to supply this information, in any form (i.e. a number in Hz, or how
ofter do you need
to change the spectrometer frequency on your system), along with the
field drift rate
of the instrument.
I will post a summary of the responses.
Many Thanks,
David Eliezer
Weill Medical College of Cornell University.