AMMRL: autoshim on Varian Unity-300

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I'm trying to get an ASM-100 sample changer hooked up to our 
Unity-300 (VNMR 6.1C running on an Ultra 10), and I've started to 
experiment with autoshim methods.  I'm finding that nothing comes 
close to hand shimming, no matter what criteria (L>M, M>M, M>T, T>T, 
T>E, E>E) I try.  The problem is in the final approach to a really 
good shim.  I can move Z1C and Z2C 4 units each away from a perfect 
shim, and it can't find its way back.  Even a monkey could do 
this!  You just change Z1C in steps of 1 and monitor the lock 
signal.  The do the same for Z2!  What is so hard about this?

I'm wondering if the step size is too large.  I can watch the lock 
signal and even with very tight criteria it's jumping around quite a 
bit.  There doesn't seem to be a parameter for step size.  I can't 
see the actual code (it's hard coded in VNMR) so I don't really know 
what it's doing.  Does anyone have experience with this who can offer 
advice?  I would really appreciate it.  If I could just write a shim 
method that does what I do with my hand and my eye, it would be great!

Neil


Neil E. Jacobsen, Ph.D.
NMR Facility Manager
Department of Chemistry
119 Old Chemistry
1306 E. University
University of Arizona
Tucson, AZ 85721
520-621-8146
FAX 520-621-8407

• Next message: Fishbein, Kenneth (NIH/NIA/IRP) [E] "AMMRL: MRI Console Needed, MRI Magnet Trade-in"
• Previous message: JOHNSON, Toni A "AMMRL: Determination of Equlibrium constant of coordinated water using"