Geometrics, Inc. G-824A Magnetometer Manual
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4.2 Environmental Considerations
Optically pumped magnetometers are more sensitive to magnetic field variation than are
proton (Overhauser) and fluxgate types. To realize the full performance of the cesium-
vapor technology, special precautions must be taken during planning and execution of the
installation.
Vibration
The G-824A is usually installed in aircraft and this environment presents particular
challenges. Intense vibration of system circuitry can induce microphonic noise and
shorten the life of system components. For performance and safety considerations the
sensor, sensor driver, and system cabling are normally hard mounted to the aircraft or are
hard mounted in components that are themselves firmly attached to the aircraft in
structures such as stinger and wingtip pods. Some attachments points may be prone to
intense vibration and we recommend the use of good quality shock mounts that are
designed to isolate the G-824A components from as much of the intense vibration as
possible. Special care should be taken in securing or routing the cable so that it does not
encounter hard or sharp objects that could damage the cable. Those components used to
mount the G-824A sensor or any or any objects near this sensor should be non-magnetic
in order to minimize the system heading error.
Electronic/electromagnetic
Sources of performance problems may arise in two areas: external electromagnetic noise
and errors introduced from platform motion. Electrostatic and electromagnetic signals
from aircraft systems, including other sensor instrumentation, can significantly lower the
signal to noise ratio of the magnetometer. An example is the "hash" created by sparking
brushes in certain aircraft generators. This can be seen as a rapidly changing field value
causing excessive scatter in the readings. The permanent, induced and eddy-current
magnetic fields of the airplane can cause significant errors that are dependent on attitude,
acceleration and heading in the earth's magnetic field. The use of a device such as the
RMS Instruments’ Automatic Aeromagnetic Digital Compensator, Geometrics software
program MagComp or fixed passive aero-magnetic compensation techniques will help
reduce these types of errors (See Geometrics technical report TR-15). Variations in
electrical currents in aircraft systems will also cause shifts, bias or increased heading
error in the readings. Consult with Geometrics about the compensation and noise
reduction processes before installation if you are unfamiliar with the procedures used to
minimize noise and platform errors.
G-824A DC power and RS 232 Data pass through a common, non-magnetic,
multiconductor cable. The ground wires of this cable should not be connected to
aircraft/ship ground at any place other than the aircraft battery or the G-824A Junction
Box. We recommend keeping the DC voltage applied to the Sensor Electronics between
24 and 33volts DC for proper operation.
