David,
You might try re-indexing your probes.
Not sure of your upper bore setup, but if it can move up and down, then push
it down onto the RT shim set. Then release the allen screws holding the
indexing flange on the probe and push it up until it makes firm contact with
the upper bore tube. If the probe is not aligned that can cause problems
with Z5. Basically, you are trying to shim a region that is on the edge of
the magnet’s sweet spot instead of being centered.
Jeff
> From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> On Behalf Of daveonofrei_at_msn.com
> Sent: Tuesday, October 10, 2023 8:49 PM
> To: main_at_ammrl.groups.io
> Subject: [AMMRL] Shimming From (almost) scratch on Varian
Thank you to everyone to responded to my last question. I have been trying
to hold off asking too many questions at once, but I have a long standing issue
that I'm really stumped on and could use some advice. I had a Varian AutoX-style
dual broadband probe recently break on my 400 (Protune box broke a tuning rod,
as it seemingly is programmed to do) and I fortunately I had my backup probe
(same type; autoX DB) recently repaired and ready to go. Pulse calibrations were
easy, but this backup probe hasn't been in the magnet for a very long time and
getting good shimming on it has been a huge struggle. I've tried getting gradient
shimming set up and no matter what sample I use to make my shim maps, or how
much manual shimming I do on beforehand I keep ending up with my z5 shim going
to the end of it's range and the resulting gradient shimming doesn't work very
well. I've seen this same issue on my 500 occasionally. Peaks are resolved but
not very well and often there is a shoulder near the very bottom of the peaks
after grad shimming. With my primary probe, I have the shims locked in and I
get beautiful lineshape on routine samples where I can resolve second order
splitting often down to baseline.
I've learned a lot about NMR hardware in the three years I've been managing
this facility but I think I was spoiled in grad school. Most of my graduate
career was spent with a modern Bruker instrument where 3D Topshim got me >95%
of where I needed to be and then it was just manual touch-up from there on
sample to sample. During the shutdowns in 2020 when I had no one using the
instruments, I dabbled with Varian's own 3D gradient shimming on my 500, but
with little success. I'm afraid I'm just not sure where to start in Varian
with a probe for which there is no previously existing set of shims or even
a decent map. Here is one of my attempts at mapping z1-5:
Link
https://drive.google.com/file/d/1-LppePDWZPvqnNufuhFBSzm3dFlGF20q/view?usp=drive_link
The protocols in Varian are not clear to me even with the manuals handy. I
understand in general that the lineshape sample (CDCl3 in Acetone) should be
used for the radial shims (since mostly my chemists use this instrument and
less so the bio folks), and then a more common solvent (CDCl3) for the axial
shims and routine shimming. I've even tried using the autotest sample for mapping.
But no matter what I do I always end up with z5 giving the "out-of-range" warning.
I have tried reading several primers on the subject but it's like I'm just
feeling my way in the dark. Does anyone have a standardized way to shim a probe
from scratch? Also, Is there some other hardware issue that could be causing this
or am I just really, really bad at shimming?
Best,
David O
San Diego State University
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Received on Tue Oct 10 2023 - 18:10:22 MST