Introduction - AKA Berkut 5 Operating Instructions Manual

INTRODUCTION

What is the hodograph and why is it so important? The received signal is characterized
not only by its amplitude and phase, but it is also a vector quantity. Amplitude and phase
depend on the electro physical parameters of objects such as conductivity, magnetic
permeability, depth, geometry, etc.
In order to accurately describe the nature of the received signal from an object is very
difficult, given the variety of influencing factors. However, it is possible to point out some
general patterns. Earlier, we mentioned that the signal is a vector quantity characterized
by amplitude and phase. If you hold any metal object to the coil it is evident that the
magnitude of this vector will vary. The end of the vector will describe, on a coordinate
plane, some shapes (lines, loops, etc.). These shapes are called Hodographs. The latter
most closely describes the complex interactions of the coil with metal objects.
When analyzing the hodographs remember a few general rules:
• Hodographs of small and medium-sized ferromagnetic objects are in the left quadrant
(i.e. have a negative vector angle);
• Hodographs of objects of non-ferrous metals and large ferromagnetic objects lie in the
right quadrant (positive vector angle);
• The larger the area of the surface of an object the higher the electrical conductivity,
hence the greater the slope of the hodograph to the right;
• Travel times of medium and large ferrous objects, as a rule, have the shape of a loop;
• Hodographs of non-ferrous metal objects are mainly straight;
• A properly ground balanced unit will have a vector along the horizontal axis. Examples
of the hodographs of some objects are shown in Fig. 14. Thus, analyzing the shape and
position of the hodograph, along the coordinate plane, there can be a certain degree of
probability as to the identity of the object type.
Examples some objects are resulted in a Fig. 1:
It should be noted that the hodograph examples given are idealized and do not take into
account the effect ground mineralization.
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Fig. 1