Bruker AVANCE, Руководство пользователя

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Environment and Site Survey Measurement
H157655_1_008 55
Above 10 Hz: Maximum 700 nT magnitudes (0 to peak) can be tolerated for interferences
with frequencies above 10 Hz.
Figure 7.10: Specification Framework with the Magnetic Field Represented as 0 to Peak Values
7.3.3.3 Reducing AC EMF Interference
Two Bruker technologies help to suppress the DC field perturbations:
• Modern magnets with EDS
TM
technology (External Disturbance Suppression) efficiently
suppress AC interferences by a factor ~25-10000, depending on the model and
disturbance frequency. Above 1 Hz, one can generally state: the higher the frequency the
better the suppression and the less sensitive NMR is to interferences.
• The advanced digital lock (if present) further suppresses the field fluctuations at the
sample. Depending on various parameters, its efficiency varies considerably.
7.3.4 HF Interference
The NMR instrument is effectively a very sensitive radio frequency receiver. Possible sources
of interference are local radio or television broadcasts, low Earth orbit satellite systems, and
signals emitted by personal paging systems. Of particular concern will be interference at
frequencies at which NMR experiments are carried out. Although the interference effects will
depend greatly on the strength of the transmitter, as a rule of thumb only broadcasting
transmitters located within a radius of approximately 5 kilometers (3 miles) are likely sources
of interference.
HF interference may also occur between two or more spectrometers located in close
proximity and operating at the same nominal 1H resonance frequency.
7.3.4.1 Measuring HF Fluctuating Fields
Radio Frequency Interference measurements should be conducted using a spectrum
analyzer. The analysis should be done for the resonance frequency of each of the nuclei of
interest (proportional to the 1H resonance frequency of the spectrometer). The minimum
frequency sweep is 400 kHz.