Ака Berkut-5 VERSION 5.01 [6/43] Introduction

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:

Fig. 1

It should be noted that the hodograph examples given are idealized and do not take into

account the effect ground mineralization.