Thank you all for your responses regarding the error message I was getting
on my Bruker AVANCE 500. The E84 Excessive Coil Power error message
indicates that the total shim power dissipated into the shim coils has
exceeded a specified limit. While each shim has a maximum current/power
limit, Bruker also sets a limit to the sum of the power over all shim
channels to prevent overheating. When this limit is exceeded, the BSMS
will shut off the shim power for about a second and then turn it back on
again. This causes the “clicking” sound I was hearing and the drop in the
lock signal.
The reason our shim values were so high may have been that a student was
trying to shim X with the spinner on (non-spinning shims do not respond
well while shimming), however, upon looking at the shim file values, we
noticed that several shims were in the +/-30-50K range. We set these shims
to zero, and then ran Topshim 3D (you need a 2H-TX board to use this) using
a sample in H2O/D2O and the shim values were greatly reduced. I put in the
lineshape sample and shimmed that and got a 0.34 Hz linewidth and a
Lorentzian lineshape.
I also tried setting all of the other shims to zero except for Z1-Z4, X, Y,
XZ, YZ, X2-Y2, XZ2 and YZ2 (so that I could still lock the sample) and ran
Topshim 3D again but it didn’t work nearly as well. It didn’t populate
most of the higher order shims at all.
Note: I previously had a Varian 500 and our old lab manager wrote a 72
step shim routine that would shim from zero. It would take several hours
but it worked great and the shim currents were minimized. Unfortunately, I
don’t have the code/programs for his shim routines but Varian does allow
you to write your own.
Hope this helps!
Thanks again,
Mark Swanson
Received on Thu Oct 22 2015 - 11:50:29 MST