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GSM19 Series Magnetometers - Version 7
GEM Systems, Inc. Advanced Magnetometers
For more technical information, visit www.gemsys.ca
3. EARTH’S MAGNETIC FIELD
The nominal distribution of the Earth’s magnetic field is shown in Figure A1 in Appendix A and the
separation of equatorial and polar regions is shown in Figure A2. In polar regions the inclination of
the magnetic field vector is approximately vertical, whereas in equatorial regions it is horizontal.
In general, the sensor axis must be approximately at right angles to the magnetic field to obtain the
best signal. For this purpose, the sensor must be kept oriented in a magnetic East-West direction in
equatorial regions.
NOTE:
Omnidirectional sensors (i.e. do not need to be oriented) can be purchased as an
option from GEM Systems.
Initially, the tuning of the instrument should agree with the nominal or expected value of the
magnetic field for the particular region (see Figure A1 in Appendix A). You can set this tuning
automatically or use the
tune initialize
feature provided for this purpose. After each reading the
instrument tunes itself automatically.
If large changes in magnetic field are encountered between successive readings, you see a warning
and you may have to repeat the reading to obtain an accurate result.
Local ferromagnetic objects (such as screws, pocketknives, wristwatches, tools etc.) may impair the
quality of measurement or, in drastic cases, obscure the proton precession signal by creating
excessive gradients.
NOTE:
For best results, you should keep ferromagnetic objects away from the sensor.
In normal applications, the magnetometer console does not produce appreciable effects on
measurements provided that the sensor is installed on the staff and kept at least at arm’s length from
the operator and the console.