crackling shim coils

Bill Stevens (wstevens@siu.edu)
Tue, 19 Dec 1995 13:13:49 -0600

I have recently zeroed my shim DACs and reshimmed from the shim power supply
on my VXR-500. There are two gradients, Z3X and Z3Y, that are obviously
functional but are not controlled by DACs, only by power supply potentiometers.

When I move the pots for these shims, I can hear crackling noises emanate
from the magnet which I assume means that either the coils are arcing or it
is somehow caused by dirty pots.

I am having trouble getting my non-spinning lineshape narrow enough and
wonder if the above might be related. (Spinning is 3.3 Hz/5.5 Hz)

Anyone else heard shim coils crackle? Any hints on getting those 1st order
spinning sidebands down (and hence, I presume, my non-spinning lineshape)?
I've had good luck at this before, but neither I nor the computer can find
the errant gradient.

I wish everyone happy holidays.

Bill

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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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