Hello all.
I have a shim problem on our Inova 300 MHz narrow bore that i have never
encountered before and open to any suggestions. I am not sure what
precipitated the problems for what had been a generally well behaved and
well shimmed magnet (we use it exclusively for 5 mm X - H dual probe),
but i have some suspicions that someone may have bumped the magnet or
probe/room temp shims in some non gentle way. There are no signs of damage
to magnet or the probe though.
First symptom of problems is, shimming has become much more
difficult in general (btw, no gradient shims on this system,
unfortunately). However with extensive effort, I can get just about to
resolution specs in spinning mode. However, once real samples are used
rather than the sealed resolution standard, a large change in Z1 is always
necessary (despite correct volume used), usually accompanied by residual
small but annoyting asymmetrical bumps indicating Z3, Z4 problems. Again,
these can be shimmed on a sample by sample basis, but, normally, have never
had this problem once higher order shims were set with our resolution
standard. My instincts tell me, my shims may be in some local minimum,
so that the slightest change in sample, throws things off, but wanted some
feedback if any of you have encountered some similar problems.
Thank you for any help, and your indulgence on this relatively mundane problem.
Herb Schwartz PhD.
Dept of Chemistry and Biological Chemistry
Rensselaer Polytechnic Institute
Troy , NY
Received on Tue Aug 08 2006 - 16:29:48 MST