Bruker BioSpin NMR Fourier 300, Site Planning Manual

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B127527_00_03
Lab Requirements
that may operate in the vicinity of NMR frequencies of interest.
If you suspect that you have a source of interference located near the proposed
magnet site then you should contact Bruker Biospin for a site survey.
Types of EMF Interference
• DC Interference
• 50/60 Hz Interference
• Radio Frequency (RF) Interference
4.7.1 DC Interference
DC interference generally comes from devices operated on DC, such as elevators,
trains, subways, trams, etc. The locations of both the device and its power supply & lines
relative to the proposed NMR site are essential to the amplitude and orientation of DC
fields and how they may interfere with the NMR system. DC feeder lines are just as
disturbing as a subway, and they do not run necessarily parallel to the track.
4.7.1.1 Measuring DC Fluctuating Fields
DC EMF measurements should be conducted using a fluxgate magnetometer . The
fluxgate sensor is capable of accurately measuring magnetic field changes below 1mG.
The sensor is connected to a magnetometer, and the voltage output from the meter is
then converted into digital form. The magnetic field is recorded and plotted on a
computer display in real time.
4.7.1.2 Reducing DC Interference
The amplitude of the “full external perturbation” (peak-to-peak) is measured with the
fluxgate magnetometer at the proposed magnet location but in the absence of the
magnet. There are two levels of compensation against these external DC field
perturbations:
• First, the magnet screens itself against external perturbations, hence only a fraction
of the full perturbation is left at the magnet center. We call this residual field
perturbation after magnet screening. It’s value is relevant to NMR experiments
without lock and experiments using gradients which require lock hold.
• Second, the advanced digital NMR lock further minimizes the interference after
magnet screening.
4.7.1.3 Guidelines: DC Interference
When determining the effect of fluctuating magnetic fields, two parameters are
important: the size of the fluctuation and the rate of change (gradient).