Hello Rainer,
We observed something similar quite a while back, i.e. the apparent
magnetic field strength increased. In our case it was actually a bad REF
board (I believe) which contains the clock frequency. Actually, cleaning
the contacts (chemically and moving it in and out) solved the issue. The
quartz oscillator is temperature controlled.
Cheers,
Ulli
On Thu, Apr 11, 2024 at 2:16 PM Platz Hirsch via groups.io wrote:
> Hi,
>
> although retired since about 5 years, there are nice challenges from time
> to time.
>
> The recent one within my former university gave me some questions.
>
> ==========
> Equipment
> ==========
>
> unshielded 360 MHz magnet, discharged to 300 MHz about 10 years ago
> helium level (dipstick measured): about 80%
> AV III console
> Windows workstation running TopSpin 3.2
>
> ==========
> Magnet behaviour
> ==========
>
> Since about one year, the helium level meter always shows the same value.
> To make the story short, with very high probability a lot of air condensed
> within the magnet, maybe due to a broken sealing.
>
> Now the magnet began to drift with about 100 Hz/hour.
>
> Very bad, presumably an ice bridge between one of the joints and a warmer
> part of the cryostate, but, of course, I am not sure.
> But now the unexpected things began ...
>
> ==========
> Drift direction
> ==========
>
> The magnetic field increases! It was possible to get the spectrometer back
> to operation by increasing the base frequency by 100 MHz (from 300.13 to 300.23) using
> cf.
>
> ==========
> TopShim
> ==========
>
> After changing the base frequency the data sets have to be corrected using
> expinstall.
> This works perfect for nearly all data sets stored within
>
> .../exp/stan/nmr/par
>
> with the exception of topshim1d2H.
>
> This data set becomes *deleted*. Tried to manually install a copy from
> par.AVANCE, but running
>
> expinstall again to configure the parameters deletes this data set again.
> Only this one, nothing else.
>
> The data set for topshim1d1h is fine and produces the expected results.
> Didn't test the 3D data set.
>
> ==========
> user defined data sets
> ==========
>
> For ICON-NMR these are stored within
>
> .../exp/stan/nmr/par/user
>
> expinstall doesn't touch these data sets. I tried a dirty trick and moved
> one data set from
>
> .../par/user
>
> to
>
> .../par
>
> but even in this case the user defined data set remains unchanged doing
> expinstall.
>
> I fear, the magnet is lost. Nevertheless I am very interested to
> understand this unexpected drift behaviour.
>
> Greetings
>
> Rainer
>
>
--
Dr. Ulrike Werner-Zwanziger
Adjunct Professor
Department of Chemistry, NMR-3,
Dalhousie University
6245 Castine Way (!!!new address!!!)
PO BOX 15000
Halifax, NS B3H 4R2
e-mail: Ulli.Zwanziger_at_Dal.ca
Tel. 1 902 494 8085
FAX: 1 902 494 1310
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Received on Thu Apr 11 2024 - 10:30:55 MST