27
The example below shows a hodograph for two nearby objects. Dimensions of the Hodograph loops
will depend on the ratio of the size of these objects and the distance between them.
SEARCHING FOR METAL OBJECTS WITH LARGE EDDY CURRENT LOOPS.
These types of objects include, for example, large copper/silver coins, and other large planar objects
of non-ferrous metals with a diameter greater than 40 mm. Due to the particular interaction
between the search coil and these types of targets certain difficulties arise. This is due to the very
narrow difference between the vector angle of these targets and those of the ground signal.
This useful component of the vector is the projection of AB to the vertical Y axis. The smaller the
angle difference between the ground signal vector and the vector of the coin the less useful part of
the projection of the signal and the less sensitivity. More important is the fact that the angular
difference becomes even less with the so-called "hot-stone" (see fig. 26).
In these cases, even a minor incorrect setting of the ground balance can lead to a significant loss of
sensitivity to the large copper/silver coins or an undesirable (annoying) response to "hot rocks" if the
algorithm DHR is not used.
Note that when setting the ground balance, such as on loam, the angular difference between the
signal and the signal of large copper/silver coins is about 7-8 degrees. At the same time, the angular
To Next Page
Loading...
