Sorry that this is a litte after the fact, but wanted to comment:
On Wed, 5 Apr 1995, Andy Rous wrote:
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> 3. The probe can be close to a magnet 'O' ring. Repeated
> vt work can cause these to fail resulting in a quench. I didn't
> know about this. Ouch!!!
True enough, the O-ring is pretty close to the probe, and may be of
concern when doing a lot of VT. We have a Bruker spectrometer here with
an ultra-low loss dewar. (AC300, vintage 1988) which more often than not
has a probe in it sitting at 125 celsius. We have run for weeks at a time at
150 Celsius, with a LOT of ramping from room temp to 150 (i.e. we're a
little harsh).
The shim set gets quite noticably warm, and as yet we have had nothing
nasty happen with regards to quenches or the magnet going soft. Others
that I know of in the polymer NMR community (who warm things up
most of the time) don't have any horror stories of quenches
Don't know about the bottom end of the thermometer...
Cheers,
Tim
P.S. Don't mean to step on your toes Andy, just wanted to possibly
alleviate some fears. Thanks for the summary.
P.P.S. If anyone is thinking of doing high temperature work for extended
periods, I can recommend highly Brukers water cooled probes. Give a shout
if you want more info.
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Z Y' : DR. TIM BREMNER, Inst. for Polymer Research |
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