Gradient Shimming

Gradient shimming usually works well on the 400s, 500, and 600 (there can be a signal-to-noise problem on the VNMRS400, but if you set parameters well, it is good enough).

I have setup standard shimmaps (essentially a map of the probe). The maps are stored in the /vnmr/gshimlib/shimmaps directory.

To accomplish gradient shimming for the first time:
Type in vnmr window: gmapsys

If you are on the 400s: Set nt = 8 for CDCl3, or nt = 2 for any other solvent. For methanol or acetone, set d1 = 5. Then, click on Autoshim on Z button. The gradient shimming should finish in 2-4 iterations; the lock should have increased after the gradient shimming is done. If for some reason the gradient shimming does not succeed, abort acquisition; if this does occur check the lock level, if it is lower than when you started, reset to standard shims, rts('cdcl3') su

If you are on the 500 or 600: Set nt = 4 for CDCl3, or nt = 2 for any other solvent. For methanol or acetone, set d1 = 5. Then, click on Autoshim on Z button.