11
is much weaker than the signal from a larger target, such as an 18-inch length of 3/4 inch
rebar which can be located at depths up to 8 feet.
Figure 14: Decreasing gain Eliminates Unwanted Signals
Strongly Magnetized Markers
A strongly magnetized marker that is at or near the surface will provide a weaker indication on
both sides of the marker, and that could be mistaken for the marker.
The heavy line in Figure 15 represents the increase and decrease in the audio and bar graph
indications as you move the locator over a marker. Between points A and B, the signals
increase slightly and then decrease. Just beyond B, the signals increase rapidly, peak
directly over the marker and then decrease at point C. From C to D, the signals increase and
decrease again. Therefore, if you do not move the locator completely across the marker, you
might assume that the weaker indication on either side of the marker is its location. The two
weaker indications occur because the locator is extremely sensitive to the magnetic field
components that are parallel to its long axis. At points B and C, the field is perpendicular to
the locator; therefore, no significant audio or bar graph indications are produced at these
points.
Figure 15: Signal Pattern from a Strongly Magnetized Marker
