Shimming with UXNMR

Alan Boyd (cheasfb@bonaly.hw.ac.uk)
Mon, 30 Oct 95 09:19:43 BST

Dear Bruker Users,
Following some useful correspondence with Guenter
Schmidt of Bruker, the ambiguity over the parameters for the SET command
in UXNMR shim programs seems now to have been resolved. Here is a
revised instruction manual paragraph which I think describes the command
more clearly:
----------------------------------------------------------------------
SET This command is used when you wish to designate several shim
gradients to be optimised at the same time using the simplex
method.Three parameters are required: firstly, the name of one
of the gradients to be optimised, secondly the starting step
change size for that gradient, and finally the step change
size for that gradient below which convergence is deemed to
have been reached. If any one gradient reaches its convergence
limit before the others it is removed from the simplex and
will not be changed again.

Example:

SET Z1 20 3 # include Z1 and Z2 in the simplex optimisation,
SET Z2 20 3 # starting with a step change of 20 units, and stop
# the simplex when the change in the gradient is 3
# units or less.

----------------------------------------------------------------------

All we need now are some suggestions for shim programs that will do
the work. I found it reasonably easy to write these for our AC200 which
I can get to shim itself up with practically no intervention. However, I
can not trust our DPX400 to do this, and I've had to spend hours
manually adjusting some gradients that the system just could not get
hold of. High order Zs are, as ever, the main problem.

Alan

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
UXNMR - its fundamental design flaws are completely
hidden by its superficial design flaws
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
----------------------------------------------------
Dr A S F Boyd Chemistry Department
NMR Spectroscopist Heriot-Watt University
phone: +44-131-451 3214 Riccarton
fax: +44-131-451 3180 Edinburgh
cheasfb@bonaly.hw.ac.uk EH14 4AS
http://dava.che.hw.ac.uk/ Scotland
----------------------------------------------------