Many thanks. As always, the collective mind of the magnetic resonance
community is amazing. Most of the comments have to do with vibrations
caused by the centrifuges.
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> From: Robert Honeychuck <rhoneych_at_gmu.edu>
> Date: February 10, 2009 1:27:48 PM EST
> To: ammrl_at_ammrl.org
> Subject: AMMRL: Centrifuges
>
> We're getting an unshielded 400. I found out today that it will be
> downstairs from a high speed centrifuge room, with several
> centrifuges, which I take to mean ultracentrifuges. The NMR room has
> a floor to ceiling height of about 4 m. The 5 gauss line will be at
> the ceiling of the NMR room. The issues as always are 1) the effect
> of the magnet on the ultracentrifuges and 2) the effect of the
> ultracentrifuge motors on the magnet. Any words of wisdom will be
> welcome. Thank you.
>
> Bob Honeychuck
> George Mason U
> Fairfax VA
> rhoneych_at_gmu.edu
Summary:
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Bob, we recently had an issue with metal doors being hung in the lab.
The following excerpts come from the magnet installation and site
preparation handbook
"[relative to the 5 G line] the presence or movement of ferromagnetic
objects over 45 kg such as pushcarts, hand trucks and gas cylinders"
will affect the magnetic field. And at the weaker break point of 2-5
gauss the vendor indicates that the "presence or movement of
ferromagnetic objects over 450 kg such as small delivery trucks,
automobiles pallet movers, forklifts and elevators" will effect the
magnetic field."
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1) None
2) None
Outside 5G there shouldn't be any significant effect in either
direction.
The centrifuge frames will become slightly magnetized in time, but
that will
not affect their operation. The centrifuge operation should not
affect you
at all, unless it is from vibration. If you are buying a new
instrument,
then the mfr. should presurvey and certify the suitability of your
site. I
suppose you could ask them to check for spurious RF signals while the
centrifuges are running, but everything should be well enough shielded
already. The common, absolute limit for placement of equipment near a
magnet is 50G. The 5G line is a 10:1 fudge factor.
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Get a scaled map of where the centrifuges are located. Offset your
axial fringe field between the centrifuges. Make sure you get TMC or
vibration legs. Have a detailed analysis of the frequencies of noise
in the room (site survey), especially when the centrifuges are
running. Bruker engineers did this for me, because I'm near building
facilities (HVAC, electrical services....).
I definitely need my TMC legs, where I'm currently located.
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I would not expect much interference from the magnet on the
centrifuges. The worst would be a bit of eddy currents generated in
the centrifuges. This might prevent them from reaching their maximum
speed.
The main concern for the NMR would be vibrations. If any of the
centrifuges is not perfectly balanced they would generate vibrations
that could be picked up by the NMR.
If the centrifuges are in place already a vibration analysis would
tell you the expected effects.
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I had a similar situation a few years ago. A centerfuge was directly
above the center line of the magnet up one floor.
I had them let me know when it was being used and I couldnt see any
field blips or drift. I think the ceiling height was 14 feet.
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Because of the height of your room, I don't think stray field will be
an issue.
I believe your biggest problem will be the potential for vibrations.
There is a large centrifuge located in one of the labs above one of
our spectrometer rooms.
I only discovered this fact one morning when someone had turned on the
centrifuge and the samples were --- not quite balanced. I felt the
vibrations through the floor while I was sitting at my desk. I
investigated where the vibrations were coming from, and that's when I
found the centrifuge.
When the centrifuge(s) is/are operated properly, I suspect there is
enough vibration damping built in that they shouldn't be a problem.
But when someone is negligent.... ?
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Bob, I had a similar problem here, albeit with a shielded 400 magnet. I
found that vibrations were more of an issue in this instance but fitting
anti-vibration devices to the magnet removed most of the problems.
Eventually the ultracentrifuges were relocated to a distant part of the
building (for a reason not connected to proximity to my NMR magnets).
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Received on Thu Feb 12 2009 - 05:52:05 MST