Dear Bruker Users: You can minimize this problem by passing
N2 gas from top of the magnet and coming out of the shim
stack base plate during Low VT work.
Dr. K. P. Sarathy
> --- Jane Strouse <strousej_at_chem.ucla.edu> wrote:
> > Date: Thu, 11 Apr 2002 09:22:14 -0700
> > To: ammrl_at_chemnmr.colorado.edu
> > From: Jane Strouse <strousej_at_chem.ucla.edu>
> > Subject: Another shimming weirdness
> >
> > Dear AMMRL'ers,
> >
> > I have had exactly the experience that Ben
> describes below. We do a
> > lot of VT work and I have fixed these connections more
> times than I would
> > like to remember. I agree 100% with Ben that Bruker
> should consider making
> > these connections a lot more robust.
> >
> > Jane Strouse
> >
> >
> >
> > >Date: Thu, 11 Apr 2002 09:05:16 -0400
> > >From: Ben Bangerter <ben.bangerter_at_yale.edu>
> > >X-Mailer: Mozilla 4.76 [en] (Win98; U)
> > >X-Accept-Language: en
> > >To: Karen Ann Smith <karenann_at_unm.edu>
> > >CC: ammrl <ammrl_at_chemnmr.colorado.edu>
> > >Subject: Re: Another shimming weirdness
> > >
> > >Karen Ann,
> > >
> > >Is it possible you have a bad connection to one of the
> shims, perhaps at the
> > >base of the shim coil asssembly? If this were the
> case, when you have the
> > >bad lineshape, one of the shims would have no effect.
> I think you have
> > >Brukers, right? From my experience with Bruker shim
> stacks, the soldered
> > >connections where the wires of the shim coils are
> attached to the PC board
> > >where the wires to the shim cable attach, at the base
> of the shim stack, are
> > >prone to fail. I have seen this a couple of times. I
> believe the culprit
> > >is electrolytic corrosion that occurs when there is
> water condensed in this
> > >area during low temperature operation, when the shim
> assembly is cooled
> > >below the dew point. A small amount of mechanical
> disturbance can break or
> > >open the connection, and when a connection is remade
> it can "weld" slightly
> > >due to the current density at the point of contact.
> The first time I
> > >experienced this, it was maddening until we removed
> the shim stack,
> > >disassembled the base, and examined the connections.
> Lots of corrosion
> > >products were evident, and an open connection.
> > >
> > >If this is the cause of the problem you are
> experiencing, it is easily
> > >fixed. You would need to remove the shim assembly to
> the bench, disassemble
> > >the base to examine the connections, clean off any
> corrosion products, and
> > >repair any break. I have long thought Bruker ought to
> passivate these
> > >connections because of the potential corrosion
> problem, perhaps with a
> > >coating of lacquer of some sort.
> > >
> > >Of course these comments may be way off the mark in
> this case; if so,
> > >"never mind!"
> > >
> > >Ben
> > >
> > >*****************
> > >
> > >Karen Ann Smith wrote:
> > >
> > > > AMMRLers,
> > > >
> > > > I have been seeing a pretty weird problem on my
> 500. Sometimes when I
> > > > swap probes, the shim goes to (really bad). As in
> linewidths of (many)
> > > > 10s of Hz. But only sometimes.
> > > >
> > > > The most recent example is that last week the 5 m
> probe was in and
> > > > shimmed pretty well. Swapped it for the 2.5 on
> friday and all was
> > > > well. Swapped the 5 back in on Monday and again,
> all was well. I did a
> > > > little shimming on Monday and saved the file.
> Tues. I swapped the 2.5
> > > > back in. The lineshape was terrible, the field had
> to be changed to get
> > > > the system to lock, and the o1 necessary to put
> water on resonance was
> > > > off by about 1100 Hz. Today I put the 5 back in,
> read in Monday's shims-
> > > > and the field was fine, but the shims... not so
> good.
> > > >
> > > > Last month, this happened about every probe swap.
> I looked up the bore
> > > > and didn't see anything. I cleaned the bore
> anyway, and the problem
> > > > seemed to go away - until yesterday. When this
> first started, I blamed
> > > > the surrounding- esp. as it seemed that the nearby
> (touching 5 gauss
> > > > lines) 250 also seemed to be changing. Now, I
> don't think so. I can't
> > > > find any changes in the nearby labs- and the shims
> are fine as long as a
> > > > probe is left in the magnet. I am sure the probes
> are aligned the same
> > > > every time- I have marks on the probe and magnet.
> > > >
> > > > Last month, z4 was the big changer. Today, z4 was
> not too bad, but
> > > > lower x,y,z all needed some adjustment.
> > > >
> > > > Ideas, thoughts, suggestions??? Please note that
> not-swapping probes is
> > > > not an option.
> > > >
> > > > kas
> > > >
> > > > --
> > > > Karen Ann Smith karenann_at_unm.edu
> > > > Director, NMR Facility Adj. Asst. Prof.
> > > > Dept. of Chemistry Clark Hall
> > > > University of New Mexico Albuquerque, NM 87131
> > > > 505.277.4031 url:
> http://www.unm.edu/~karenann
> > > > Out of this world screensaver:
> http://setiathome.ssl.berkeley.edu/
> > > > "There is nothing a good day of cycling won't
> cure."
> >
> > Dr. Jane Strouse
> > Department of Chemistry & Biochemistry
> > UCLA
> > Los Angeles, CA 90095-1569
> > (310)-825-9841 - voice
> > (310)-825-0393 - FAX
> > strousej_at_chem.ucla.edu
> >
> >
>
>
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Dr. K. P. Sarathy
Department of Chemistry
Texas A&M University
College Station TX 77842-3012
Tel: 979 458 0705
Fax: 979 845 4719
Received on Thu Apr 11 2002 - 15:42:25 MST