Hi Wendy,
Your problem reminds me of a problem we had many, many years ago. We had an
NMR for which the shims would suddenly go bad, as in 20% spinning sidebands.
This would happen intermittently and seemingly out of the blue for no apparent
reason. Readjusting the shims (even by the instrument manufacturer engineers
since the instrument was still under warranty) would resolve the problem for
a period of time but sooner or later the jump to bad shims would happen.
Looked at every possible cause you could imagine... But one day when I was
tuning and matching the probe by physically getting down on the floor and
adjusting the tuning knobs I noticed the shim stack could move. Turns out the
problem was simply a loose holding screw, tightened it, adjusted the shims,
and that was the problem solved. So if you are lucky, whilst you might be
getting driven crazy by the problem as I am sure you are, it could be something
very simple.
Regards,
K. Klika
________________________________________
> From: main_at_ammrl.groups.io on behalf of CHARLES G FRY via groups.io
> Sent: 16 August 2024 00:13:42
> To: main_at_ammrl.groups.io
> Subject: Re: [AMMRL] Off axis shims bad after 24 hours on 40-year-old Oxford magnet #Bruker #Hardware
Wendy,
More data helps. Other possibilities suggest themselves. One possibility
is your shim power supply being unstable. Stable last night but back to
fluctuating this morning. Intermitant contacts to RT shims are another
possibility. Large metal objects are not being moved within 10-20 ft of
the magnet (including floor above or below)? Shim stack is loose and
moving a bit? Etc.
Quenches are one way events. Once they happen a power supply has to be
attached to reenergize the main coil or cryoshims coil. There is usually
a period before the quench when increased drift is observed.
Charlie
On Aug 15, 2024, at 4:54 PM, Spin-Doc wrote:
Hi,
Could you possibly specify “lineshape deterioration” a bit
more precisely? I mean, are we talking about a change from 1 Hz linewidth
at half-height to something like 5-10 Hz (not great, but can easily be
induced by e.g. changes in the sample like bubble formation, product fallout
or solvent evaporation) or 200-2000 Hz (making up numbers, but that’s
what a failing cryoshim can easily lead to)?
A failing cryoshim is also one-way only, so lineshape is and stays bad
afterwards and an only rarely be compensated by RT shimming. Your case doesn’t
sound like a cryoshim effect to me…
Best regards
Bert
-> Sent via mobile <-
Spin-Doc
Magnetic resonance equipment, service, training & more
Dr. rer. nat. Bert Heise
Owner, applications scientist
Kiefernweg 13
58239 Schwerte
Germany
Web: http://www.spin-doc.net
Mail: bert.heise_at_spin-doc.net
Phone: +49-171-5135315
Representing MestreLab, Stelar & Barthel HF
Am 15.08.2024 um 22:24 schrieb Wendy Breyer <web216_at_lehigh.edu>:
Hi,
Is it possible to have a cryoshim fail intermittently? I made a full drift
measurement over 13 hours last night as outlined by Charlie Fry and saw very
little drift AND very little change in peak shape... but, on the same sample
on other days, I've seen peak shape degrade over a few hours ("lock" was on
though so I don't know if center position drift happened during those data
collections). In fact, a student used the spectrometer this morning after me
and saw large degradation in peak shape over the course of his 1.5 hour experiment.
Thanks for all your help!
Wendy
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