Geometrics, Inc. G-824A Magnetometer Manual
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milli-volt as it delivers both heater and lamp oscillator power to the sensor. Anything
that increases the cross-talk between the power and signal circuits or introduces noise
into the power circuit can degrade the sensor output signal and affect system
performance.
4.1 Sensor orientation
Although the G-824A measures the total intensity of the earth’s magnetic field, magnetic
fields in general are vector fields. The total field is the sum of the three components as
projected onto the earth’s field vector which is roughly vertical at the poles and
horizontal at the magnetic equator. At any point the field is defined by its magnitude and
direction. Unless the sensor is very near highly magnetic objects, the local magnetic field
will be almost entirely due to the earth’s magnetic field. In order for the G-824A to
accurately measure the local magnetic field magnitude, it must be properly oriented
relative to the local magnetic field direction.
The sensor head must be oriented so that the local field flux vector impinges at an angle
of from 15º to 75º to the cylindrical axis of the sensor, for all platform attitudes
encountered during survey. Alignments that produce a field/axis angle less than 15º
place the magnetic field within the sensor’s "polar dead zone". Similarly, alignments that
produce a field/axis angle greater than 75º place the magnetic field within the sensor’s
Figure 5 Magnetic field intensity at the Earth's surface.
Epoch 2000, 1000 nT contour interval.
