Ака Signum 7272M MFT version 1.00 [25/34] Using the hodograph for identification

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Селективный металлодетектор «Сигнум MFT» 7272М. Руководство по эксплуатации.

As we gain experience the company reserves the right, without notice, to change the value

of the factory settings.

A very useful practice is to switch between user modes to access changes in menu

options. A good example of this is changing “Backlight” settings. To do this there are a pair

of identical search programs (1 and 2, 3 and 4) the only difference is the value of the

backlight (one pair of programs is on, the other is off). Further, if you need to change the

current state of the backlight, no need to go to the menu and look for the desired setting.

You can just toggle the search program.

USING THE HODOGRAPH

FOR IDENTIFICATION

We have previously mentioned about using the

hodograph for identifying targets. But what is the

hodograph and what it is for? 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. To accurately describe the Fig. 14

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 should be 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. It should be noted that the hodograph examples given are

idealized and do not take into account the effect ground mineralization.