Light rail uses fairly large currents, and you will see transient
effects while a car is operating in the immediate area. If the cars are
using DC power, you'll experience B0 shifts (the lock system may or may not
be able to compensate) and/or changes in homogeneity. AC power will
produce a modulation at the line frequency (some systems operate at
frequencies other than 60 Hz) that will appear as sidebands in spectra;
since the effect is unlikely to be constant during a full phase cycle, they
won't average out. The distance over which effects are noticeable are hard
to predict and depend strongly on the geometry of the installation, but I
would be concerned about any installation closer than a couple of hundred
feet. A few years ago the folks at ETH had exactly this problem, so you
might contact them to get details.
Good luck,
Alan
At 08:13 PM 2/3/99 -0800, you wrote:
>Hello all:
>Our region is planning on running a light rail line near the University.
>Originally, this line was to run about 500 yds away (underground), and I
>wasn't too worried about it. However, the Physics Dept, which is closer
>to the original path has convinced the planners to consider alternate
>routes, some of which appear to be much closer to our instruments. Does
>anyone have experience with installation of light rail lines anywhere near
>NMR instrumentation? It is difficult to estimate the effects from what I
>am being told. On the one hand, I am told that they might be able to
>guarantee that we will see less than 0.5 mG of magnetic "noise", but the
>effect of this would greatly depend on its frequency components. If anyone
>has any insight into these effects I would be greatly appreciative. I will
>of course provide a summary if anyone has anything to say.
>
>
> Tom Pratum
> Dept of Chemistry
> Box 351700
> Univ of Washington
> pratum@u.washington.edu
> http://weber.u.washington.edu/~pratum
>
____________________________________________________________________________
Alan Ronemus, Instrumentation Scientist Alan Ronemus
J. W. Amy Facility for Chemical Instrumentation 1928 Indian Trail Drive
Brown Laboratory, Room 5128 West Lafayette, IN 47906
Chemistry Department - 1393
Purdue University Telephone: (765)463-9231
West Lafayette, IN 47907-1393
Telephone: (765)496-3262
Facsimile: (765)494-9388
World Wide Web: <http://www.chem.purdue.edu/facilities/jafci/alan.html>