F.W. Bell 7030, Instruction Manual

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F.W. BELL Model 7030 Gauss/Tesla Meter Instruction Manual
Section 6 – Flux Density Measurement 6-13
RELATIVE MODE
The relative mode allows a specific flux density value to be subtracted
from all future readings. Thus all future readings will be “relative” to that
value. For instance if the relative value is +100.0 gauss, and the
present flux density is +112.0 gauss, the actual displayed value will be
+12.0 gauss. If the flux density drops to +77.0 gauss, the actual
displayed value will be -23.0. Thus the relative mode allows for the
direct readout of variations around a given field, whether static (dc) or
alternating (ac).
There are two ways to generate a relative value. When the RELATIVE
key on the front panel is pressed, the instrument uses the present flux
density reading from the probe as the relative value. Alternatively, you
may specify a pre-determined value from the RELATIVE menu.
There may be situations when the user may prefer to shield the probe
from all external magnetic fields prior to performing a relative operation.
Provided with the instrument is a “zero flux chamber” which is capable of
shielding against fields as high as 30 mT (300 G or 23.88 kA/m). The
probe is simply inserted into the chamber before the relative operation
begins.
Handle the Hall probe with care. Do not bend the stem or apply
pressure to the probe tip as damage may result.
Relative and ac Mode Operation
In normal operation, ac readings do not indicate a polarity as they
represent the true rms magnitude of the flux density reading. With the
relative mode however, the polarity indicates whether the magnitude of
the measured ac field is greater or less than the relative value. For
example, if the relative value is 100.000 gauss ac and the measured flux
density is 90.000 gauss ac, the displayed reading will be –10.000G.
Note: The relative value in ac mode is always positive, the relative
reading may be positive or negative.
Note: The relative mode is cancelled if the probe is disconnected,
if the instrument is turned off and back on again, or if the
channel is switched between ac and dc modes.