Several respondents mentioned the field centerpoint and I think you were
leaning in the right direction. I think the story is that all the gradient
pots got changed when we serviced the shim power supply in-house. I started
them all at 500 and tried to shim my way to good lineshape. Failed. Gary
dialed in the last recorded values for Z3X and Z3Y and that is when we
started to make progress. These two gradients, btw, are not driven by DACs
so that is why the computer could not get me out of trouble as it has
before. These two are also reputed to be highly associated with the shimming
center.
Thanks for all your replies. Varian tells me that they can field map without
converting data systems and Resonance Research does field mapping
independent of spectrometer console as well. I can't afford it anyhow and it
looks now like I can get by without it.
I encourage you to write down all relevant shimming settings (pots, DACs) if
you haven't done so in awhile.
Bill
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William C. Stevens, Ph.D. Nuclear Magnetic Resonance Facility
Director Southern Illinois University
Carbondale, IL 62901-4405
wstevens@siu.edu
http://www.siu.edu/departments/shops/bill.html
wstevens@intrnet.net voice: 618-453-6498 fax: -6408
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