Hi Chris,
Is the helium boil off normal? We had a "soft touch" in our oxford magnet
many years ago that caused the field to drift radically but we caught it
before it quenched. Ours was caused (we think) by heavy construction and
pile-driving outside our building. They also stored a pile of metal
directly above our magnet on the floor above.
Cheers,
Mark
On Fri, May 29, 2015 at 1:17 AM, Christophe Farès <fares_at_kofo.mpg.de> wrote:
> Dear AMMRLers,
>
> I've seen some amazingly fast and helpful crowd-problem-solving on the
> AMMRL network lately, and so I thought I would share my own issue hoping
> for a similar response ;)
>
> We have a relatively newly installed AVIII Nanobay 300MHz system (with an
> older ultrashield magnet) used in open-access for routine 1D NMR. The 2D
> experiments are however plagued with horrible T1-noise streaks and we
> identified some major field instabilities as the most probable source of
> the problem. If we run a 1D 1H continuously without lock, we see erratic
> field jumps of up to +/-30 Hz! Curious however is that this phenomenon does
> not seem to occur completely randomly. For instance: it seems that there
> are periods of 5-8 minutes every 25-35 minutes where they are more intense.
> And nights between approx 11pm and 4am, the interferences are almost
> completely gone. To illustrate what I mean, I've attached a printout of
> the 2d stacks (each column represents 2048 1D 1H measured every 2
> seconds)...
>
> This is not observed on 400, 2x 500 and 600MHz spectrometers sitting only
> a few tens of meters away.
>
> Of course, the night relative calmness and "regular" more intense periods
> made us look into public transport schedules. The closest streetcar stop is
> 400m away, but the schedule correlates quite wellwith this phenomenon (for
> instance, the first one runs at 4:30, intervals are 20-30 minutes).
>
> So my questions are: what could be causing these disturbances and how? And
> of course, what can we do about it?
>
> best regards
>
> Chris
>
> --
> Dr. Christophe Farès
> Head of the NMR Department/Leiter der NMR Abteilung
> Max-Planck-Institut für Kohlenforschung
> Kaiser-Wilhelm-Platz 1
> 45470 Mülheim an der Ruhr, Germany/Deutschland
> Tel: +49-208-306-2130
> E-mail: fares {at} kofo.mpg.de
> Web:
> http://www.kofo.mpg.de/en/research/service-departements/nuclear-magnetic-resonance-spectroscopy
>
>
Received on Fri May 29 2015 - 07:58:13 MST