Geometrics Memory-Mag G-856AX, Руководство по эксплуатации

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Geometrics, Inc
.
G-856AX Operation Manual
29
Field Operation
This section provides information about the G-856AX related to surveying technique and
efficient operation in the field. It is recommended that the user become familiar with
basic magnetometer operation as described in the preceding sections of this manual
before attempting their first survey.
Sensor position and measurement repeatability
Measurement repeatability is important for verifying that the magnetometer is working
correctly and that field conditions are have enough stability to insure that useful data can
be collected. Repeatability is the demonstrated by obtaining the same measurement for
several readings taken consecutively at the same position. The relationship between
sensor position and repeatability is critical if a high degree of precision is required in this
test. Repeatability will also be influenced by conditions at the measurement site.
Conditions that are of particular concern include: high magnetic field gradients, large or
rapid amplitude changes in the diurnal field, the presence of magnetic dust on the sensor
and magnetic objects carried by the operator.

HIGH GRADIENTS: In an area of l sq. meter where the magnetic field varies by
less than 1 nT, you should expect less than 1 nT variation in repeatability. That
is, changes in position by as much as 30 or 40 cm should not produce
measurements that vary by as much as 1 nT. Under these conditions you might
see changes of several tenths of an nT.

RAPID DIURNAL CHANGES: Depending on solar and local thunderstorm
activity, you might observe magnetic field charges even if the sensor is held
perfectly still. A magnetometer like the G-856AX, with precision of 0.1 nT, will
detect such temporal activity.

MAGNETIC DUST: If dust or dirt has accumulated on the sensor it may be
magnetically contaminated if this material is sufficiently magnetic. This material
may noticeably affect the measurement results when the sensor is rotated. We
recommend that the sensor and sensor cable be kept clean and dust free in order to
provide the best survey results.

OPERATOR CONTAMINATION: Steel-toed boots, a key ring, knife, pistol,
GPS receiver or any other magnetic object carried by the survey operator can also
become a source of errors in the magnetic data. In addition, if steel-clad batteries
are installed in the instrument the console itself will almost certainly contribute to
the magnetic field measured at the sensor. All articles carried by the operator
should be considered suspect until they have been checked with the
magnetometer. See the following section for the recommended magnetic
screening procedure.