Strongly Magnetized Markers - Schonstedt Instrument GA-52Cx Instruction Manual

Strongly Magnetized Markers

A strongly magnetized marker at or near the surface may provide location information that is misleading.
The heavy line in Figure 7 represents the variations in tone frequencies when the locator is moved over the
marker. When moving the instrument from A to B, the frequency of the tone increases and then suddenly
decreases at B. From just beyond B the frequency of the tone increases sharply, becomes very high directly
over the marker and decrease just before reaching C. From C to D the pattern is the reverse of that from A
to B. It is obvious that the locator must enter the B-C region. Otherwise the marker might be assumed to be
between A and B, or C and D.
Figure 7. Signal Pattern From a Strongly Magnetized Marker
This phenomenon is explained by the fact that the locator is sensitive to the magnetic field components
parallel to its long axis. At points B and C the field is perpendicular to the locator so no high frequency is
produced at these points.
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